ACCIDENT PILATUS PC-6

AT GELBRESSEE ON 19 OCTOBER 2013

Rf. AAIU-2013-21 Issue date: 22 July 2015 Status: Final

Safety Investigation Report

Air Accident Investigation Unit (Belgium) City Atrium

Rue du Progrs 56 1210 Bruxelles

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TABLE OF CONTENT

TABLE OF CONTENT ........................................................................................................... 3

FOREWORD ......................................................................................................................... 5

SYMBOLS AND ABBREVIATIONS ...................................................................................... 6

TERMINOLOGY USED IN THIS REPORT ............................................................................ 9

SYNOPSIS ........................................................................................................................ 10

1 FACTUAL INFORMATION. ............................................................................ 12

1.1 HISTORY OF FLIGHT. .......................................................................................... 12 1.2 INJURIES TO PERSONS. ...................................................................................... 14 1.3 DAMAGE TO AIRCRAFT. ...................................................................................... 14 1.4 OTHER DAMAGE. ............................................................................................... 14 1.5 PERSONNEL INFORMATION. ................................................................................ 14 1.6 AIRCRAFT INFORMATION. ................................................................................... 16 1.7 METEOROLOGICAL CONDITIONS. ........................................................................ 30 1.8 AIDS TO NAVIGATION. ........................................................................................ 32 1.9 COMMUNICATION. ............................................................................................. 35 1.10 AERODROME INFORMATION. .............................................................................. 37 1.11 FLIGHT RECORDERS. ......................................................................................... 39 1.12 WRECKAGE AND IMPACT INFORMATION. .............................................................. 42

1.12.1 On-site examination of the wreckage ................................................. 42 1.12.2 Detailed examination of the wreckage ................................................ 48

1.13 MEDICAL AND PATHOLOGICAL INFORMATION ....................................................... 63 1.14 FIRE ................................................................................................................. 64 1.15 SURVIVAL ASPECTS ........................................................................................... 64 1.16 TESTS AND RESEARCH. ..................................................................................... 67

1.16.1 The horizontal stabilizer trim actuator ................................................. 67 1.16.2 Aircraft performance ........................................................................... 67 1.16.3 Barrel roll in flight simulator Marchetti 260 .......................................... 68

1.17 ORGANIZATIONAL AND MANAGEMENT INFORMATION. ........................................... 69 1.17.1 Operation of the aeroplane................................................................. 69 1.17.2 Operation authorization for a permanent site of parachuting activities 70 1.17.3 Special ratings for pilot performing parachute dropping flights ........... 72 1.17.4 Insurance company requirements ...................................................... 72 1.17.5 Paraclub Namur organization ............................................................. 72

1.18 ADDITIONAL INFORMATION. ................................................................................ 73 1.18.1 About the management of a horizontal stabilizer trim runaway ........... 73 1.18.2 About parachuting aeroplanes accidents, period 1987-2014 ............. 73 1.18.3 Pilatus PC-6 accidents showing similarities ........................................ 75

1.19 USEFUL OR EFFECTIVE INVESTIGATION TECHNIQUES ........................................... 76

2 ANALYSIS. ..................................................................................................... 77

2.1 INFORMATION FROM WITNESSES ........................................................................ 77 2.2 WRECKAGE EXAMINATION .................................................................................. 78 2.3 COMMUNICATIONS ............................................................................................ 79 2.4 THE SEQUENCE OF THE DIFFERENT STRUCTURAL FAILURES ................................. 80 2.5 RECONSTRUCTION OF THE LAST PHASE OF THE FLIGHT ........................................ 81

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2.6 POSSIBLE MANOEUVRES .................................................................................... 86 2.6.1 Possible medical incapacitation ........................................................... 86 2.6.2 In-flight collision avoidance .................................................................. 87 2.6.3 Bird Strike ............................................................................................ 87 2.6.4 Wake vortex ......................................................................................... 88 2.6.5 Wind turbine turbulences ..................................................................... 88 2.6.6 Meteorological turbulence. ................................................................... 88 2.6.7 Intentional Manoeuvers ........................................................................ 88 2.6.8 V-n Diagram analysis ........................................................................... 93 2.6.9 Conclusion of possible manoeuvres analysis ....................................... 94

2.7 OPERATOR AND PARACHUTE CLUB ORGANIZATION .............................................. 94 2.8 WEIGHT AND BALANCE ...................................................................................... 95 2.9 USE OF RESTRAINT SYSTEMS ............................................................................. 96 2.10 USE OF OXYGEN SYSTEM ................................................................................... 98 2.11 PILOTS SEAT AND PILOTS BACK PROTECTION ..................................................... 99 2.12 MAINTENANCE MANUAL ................................................................................... 100 2.13 FLIGHT DATA RECORDING ................................................................................ 101

3 CONCLUSIONS. ........................................................................................... 103

3.1 FINDINGS. ....................................................................................................... 103 3.2 CAUSES. ........................................................................................................ 106

4 SAFETY RECOMMENDATIONS .................................................................. 107

4.1 SAFETY ISSUE: THE WEAKNESS OF LEGAL FRAMEWORK AND EFFECTIVE OVERSIGHT. .................................................................................................... 107

4.2 SAFETY ISSUE: THE LACK OF MANDATORY REQUIREMENT TO INSTALL DEVICES RECORDING FLIGHT DATA ON BOARD AEROPLANE USED FOR PARACHUTING. ................................................................................................ 108

4.3 SAFETY ISSUE: THE WEAKNESS OF FRAMEWORK REGARDING THE TECHNICAL REQUIREMENT OF RESTRAINT SYSTEMS FOR PARACHUTISTS ON BOARD AIRCRAFT. ...................................................................................................... 108

4.4 SAFETY ISSUE: INSUFFICIENT BACK PROTECTION FOR THE PILOT. ....................... 109 4.5 SAFETY ISSUE: NO EASY DETERMINATION OF THE WEIGHT AND BALANCE OF

THE AEROPLANE DUE TO THE PASSENGERS NOT SITTING IN PREDETERMINED POSITIONS. ..................................................................................................... 110

4.6 SAFETY ISSUE: GRANTING OVERLAPPING AUTHORISATIONS BY THE BCAA. ......... 110 4.7 SAFETY ISSUE: POSSIBLE ERRONEOUS INTERPRETATION OF THE

MAINTENANCE MANUAL. ................................................................................... 111 4.8 SAFETY ISSUE: LACK OF ORGANIZATIONAL STRUCTURE BETWEEN THE

OPERATOR AND THE PARACHUTE CLUB. ............................................................ 112

5 APPENDICES ............................................................................................... 113

APPENDIX 1: EXTRACT OF BCAA DELIVERED AERIAL WORK AUTHORIZATION .................... 113 APPENDIX 2: EXTRACT OF BCAA DELIVERED AUTHORIZATION FOR THE OPERATION

OF A PERMANENT SITE FOR PARACHUTE JUMPS. ............................................... 115 APPENDIX 3: EXTRACTS OF PART SPO REGULATION REGARDING THE PARACHUTE

OPERATION AND SEATS, SEAT SAFETY BELTS AND RESTRAINT SYSTEMS .............. 118 APPENDIX 4: SPECIAL CONDITION DOCUMENT USE OF AEROPLANE FOR

PARACHUTING ACTIVITIES. ............................................................................... 120 APPENDIX 5: ROYAL MILITARY ACADEMY FRACTOGRAPHICAL ANALYSIS ........................... 123 APPENDIX 6: HORIZONTAL STABILIZER TRIM ANALYSIS ..................................................... 127

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FOREWORD This report is a technical document that reflects the views of the investigation team on the circumstances that led to the accident. In accordance with Annex 13 of the Convention on International Civil Aviation and EU Regulation 996/2010, it is not the purpose of aircraft accident investigation to apportion blame or liability. The sole objective of the investigation and the Final Report is the determination of the causes, and to define recommendations in order to prevent future accidents and incidents. In particular, Article 17-3 of the EU regulation EU 996/2010 stipulates that the safety recommendations made in this report do not constitute any suspicion of guilt or responsibility in the accident. The investigation was conducted by Luc Blendeman, Henri Metillon and Sam Laureys. The report was compiled by Henri Metillon and was published under the authority of the Chief Investigator. Notes: 1. About altitude and Flight Level: The vertical position of aircraft during climb is

expressed in terms of altitude (with feet as unit) until reaching the transition altitude (which is 4500 ft in Brussels FIR) above which the vertical position is expressed in terms of flight levels. To indicate altitudes, the local barometric pressure at sea level (QNH) is used as altimeter setting. To indicate flight levels, the Standard Atmosphere pressure of 1013,25 hPa is used as altimeter setting.

2. About the time: For the purpose of this report, time will be indicated in UTC, unless otherwise specified.

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SYMBOLS AND ABBREVIATIONS Minute Degree C Degrees centigrade AAD Automatic Activation Device of a rescue parachute AAIU(Be) Air Accident Investigation Unit (Belgium) ACC Area Control Center (En-route air traffic control) AccRep Accredited Representative of a State Investigation Unit ACTT Aircraft Total Time AD Aerodrome AFIS Aerodrome Flight Information Service AFM Airplane Flight manual AFMS Airplane Flight manual Supplement AGL Above Ground Level AMM Aircraft Maintenance Manual Amp Ampere AMSL Above Mean Sea Level APP Approach Control Service ARC Airworthiness Review Certificate ASD Air Safety Directorate (Belgian Defence) ATC(O) Air Traffic Control (Officer) ATIS Automatic Terminal Information Service ATPL Airline Transport Pilot Licence ATS Air Traffic Services BCAA Belgian Civil Aviation Authority BCMG Becoming (used in weather reports) BEA Bureau dEnqutes et dAnalyse (French authority responsible for

safety investigations into accidents or incidents in civil aviation) CAMO Continuing Airworthiness Management Organisation CAS Calibrated airspeed CAVOK Ceiling and Visibility OK CERPS Centre Ecole Rgional de Parachutisme Sportif de Namur CIAIAC Comisin de Investigacin de Accidentes e Incidentes de Aviacin

Civil (Spanish investigation authority for accident and incidents in civil aviation)

CG Centre of Gravity CPL Commercial Pilot Licence CS Certification specification E east EASA European Aviation Safety Agency EBBE Beauvechain Air Base EBBR Brussels Airport EBCI Charleroi - Brussels South Airport EBNM Airfield of Namur/Suarle EBLG Lige airport EBMO Airfield of Moorsele

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EU European Union EUROCAE European Organisation for Civil Aviation Equipment FAA Federal Aviation Administration (USA) FARs Federal Aviation Regulations (in the United States) FDR Flight Data Recorder FH Flight hour(s) FIR Flight Information Region FL Flight Level FOCA Federal Office of Civil Aviation (Switzerland) fps Feet per second ft Foot (Feet) ft/m Feet per minute FTD Flight Training Device FTL Flight Time Limitation hPa Hectopascal(s) g Acceleration due to Earths gravity GDF-05 BCAA Circular Descentes en ParachuteValschermspringen ICAO International Civil Aviation Organisation IMC Instrument Meteorological Conditions IPC Illustrated Parts Catalog KIAS Knots Indicated Airspeed kgf Kilogram-force (equal to the force exerted by one kilogram of mass

on the earth surface) km Kilometre(s) kt Knot(s) KTAS Knots True Airspeed lbs Pounds LH Left hand LOC-I Loss of Control In-flight m Metre(s) MAC Mean Aerodynamic Chord METAR Meteorological Aerodrome Report MHz Megahertz MSN Manufactures serial Number MTOW Maximum Take-off Weight N North n load factor NM Nautical mile(s) NOSIG No significant change (used in weather reports) NTSB National Transportation Safety Board (US) O/H Overhaul PIC Pilot in Command POH Pilots Operating Handbook PN Part Number PPL Private Pilot Licence QFE Pressure setting to indicate height above the airfield runway QFU Magnetic bearing of the runway

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QNH Pressure setting to indicate elevation above mean sea level RH Right hand RPM Revolutions per Minute RWY Runway S.A. Socite Anonyme (Belgian equivalent of a public limited company) SAIB Swiss Accident Investigation Board SCF-NP System/Component Failure or malfunction (Non-Powerplant) SEP Single Engine Piston rating SET Single Engine Turbine rating SHP Shaft Horse Power SN Serial Number SPO Specialised Operations STOL Short Take-Off and Landing TMA Terminal Control Area TSB Transport Safety Board of Canada ULM Ultra-Lger Motoris (microlight aircraft) US United States US CARs Civil Aviation Regulations (former US legal requirements preceding

the current Title 14 of the Code of Federal Regulations aka FARs) US gal US (United States) Gallon UTC Universal Time Coordinated V As a unit: Volt. As a quantity: Velocity or speed VA Design manoeuvring Speed VC Design cruise speed VD Design diving speed VFE Maximum flap extended speed VFR Visual Flight Rules VNE Never-exceed speed VS Stall speed VMC Visual Meteorological Conditions

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TERMINOLOGY USED IN THIS REPORT Safety factor: an event or condition that increases safety risk. In other words, it is something that, if it occurred in the future, would increase the likelihood of an occurrence, and/or the severity of the adverse consequences associated with an occurrence. Contributing safety factor: a safety factor that, had it not occurred or existed at the time of an occurrence, then either: (a) the occurrence would probably not have occurred; or (b) the adverse consequences associated with the occurrence would probably not have occurred or have been as serious, or (c) another contributing safety factor would probably not have occurred or existed. Other safety factor: a safety factor identified during an occurrence investigation which did not meet the definition of contributing safety factor but was still considered to be important to communicate in an investigation report in the interests of improved transport safety. Safety issue: a safety factor that (a) can reasonably be regarded as having the potential to adversely affect the safety of future operations, and (b) is a characteristic of an organisation or a system, rather than a characteristic of a specific individual, or characteristic of an operational environment at a specific point in time. Safety action: the steps taken or proposed to be taken by a person, organisation or agency on its own initiative in response to a safety issue. Safety recommendation: A proposal of the accident investigation authority in response to a safety issue and based on information derived from the investigation, made with the intention of preventing accidents or incidents. When AAIU(Be) issues a safety recommendation to a person, organization, agency or Regulatory Authority, the person, organization, agency or Regulatory Authority concerned must provide a written response within 90 days. That response must indicate whether the recommendation is accepted, or must state any reasons for not accepting part or all of the recommendation, and must detail any proposed safety action to bring the recommendation into effect. Safety message: An awareness which brings under attention the existence of a safety factor and the lessons learned. AAIU(Be) can disseminate a safety message to a community (of pilots, instructors, examiners, ATC officers), an organization or an industry sector for it to consider a safety factor and take action where it believes it appropriate. There is no requirement for a formal response to a safety message, although AAIU(Be) will publish any response it receives.

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SYNOPSIS Date and time of the accident: 19 October 2013 at 13:35 Aircraft: Pilatus PC-6/B2-H4, MSN 710 Accident location: 50310.5 N - 4571.0 E Terrain elevation: around 200 m In a field in Gelbresse, Namur, Belgium Aircraft owner: Namur Air Promotion S.A. Type of flight: Aerial Work - Parachute dropping Persons on board: 11 Abstract: The aeroplane was used for the dropping of parachutists from the parachute club of Namur1. It was the 15th flight of the day. The aeroplane took off from the Namur/Suarle (EBNM) airfield at around 13:25 with 10 parachutists on board. After 10 minutes of flight, when the aeroplane reached FL50, a witness noticed the aeroplane in a level flight, at a lower altitude than normal. He returned to his occupation. Shortly after he heard the sound he believed to be a propeller angle change and turned to look for the aeroplane. The witness indicated that he saw the aeroplane diving followed by a steep climb (major pitch up, above 45), followed by the breaking of the wing. Subsequently, the aeroplane went into a spin. Another witness standing closer to the aircraft reported seeing the aeroplane flying in level flight with the wings going up and down several times and hearing, at the same time an engine and propeller sound variation before seeing the aeroplane disappearing from his view. The aeroplane crashed in a field in the territory of Gelbresse, killing all occupants. The aeroplane caught fire. A big part of the left wing and elements thereof were found at 2 km from the main wreckage. Occurrence type: Loss of control-inflight (LOC-I) followed by system/component failure (non-powerplant SCF-NP).

1 Paraclub Namur but officially called Centre Ecole Rgional de Parachutisme Sportif de

Namur (CERPS)

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Cause(s): The cause of the accident is a structural failure of the left wing due to a significant negative g aerodynamic overload, leading to an uncontrollable aeroplane and subsequent crash. The most probable cause of the wing failure is the result of a manoeuvre intended by the pilot, not properly conducted and ending with an involuntary negative g manoeuvre, exceeding the operating limitations of the aeroplane. Contributing safety factors: The weakness of the monitoring of the aeroplane operations by the operator. The lack of organizational structure between the operator and the parachute

club. Other safety factors identified during the investigation: The performance of aerobatic2 manoeuvres with an aircraft not certified to

perform such manoeuvres. The performance of aerobatic manoeuvres by a pilot not adequately qualified

and/or trained to perform such manoeuvres. Transportation of unrestrained passengers, not sitting in seats during higher-

risk phases of the flight. The weakness of legal framework and effective oversight. The lack of mandatory requirement to install devices recording flight data on

board aeroplane used for parachuting. Insufficient back protection for the pilot. Lack of guidance for W&B calculations of aeroplane used for parachuting. Granting overlapping authorisations by the BCAA. Possible erroneous interpretation of the maintenance manual. Violations and/or safety occurrences not reported as required by the Circular

GDF-04, preventing the BCAA from taking appropriate action. Peer pressure of parachutists sometimes encouraging pilots to perform

manoeuvres not approved for normal category aeroplanes. Flying at high altitude without oxygen breathing system although required by

regulation.

2 Aerobatic flight means manoeuvres intentionally performed by an aircraft involving an abrupt change in its attitude, an abnormal attitude, or an abnormal variation in speed, not necessary for normal flight or for instruction for licenses or ratings other than aerobatic rating.

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1 FACTUAL INFORMATION.

1.1 History of flight. On 19 October 2013, the Pilatus Porter was being used for parachute drops. The day started normally with the first take-off at 07:21. Each flight transported 9 or 10 passengers. Except for the first two, all the flights of that day were conducted by the same pilot.

Flight # Time of take-off Time of drop Pilot # of passengers 1 07:21 07:39 P1 9 2 07:49 08:03 P1 10 3 08:12 08:32 P2 9 4 08:39 08:55 P2 10 5 09:02 09:18 P2 10 6 09:24 09:42 P2 10

Refuelling and lunch 7 10:24 10:40 P2 9 8 10:47 11:04 P2 9 9 11:11 11:26 P2 9

10 11:32 11:48 P2 10 11 11:54 12:13 P2 9 12 12:21 12:40 P2 10 13 12:48 13:01 P2 10 14 13:07 13:20 P2 10 15 13:25 P2 10

The aircrafts last landing in EBNM was at 13:20 to board the next group of 10 parachutists. After the take-off, the aircraft appeared again on the radar at 13:28 at an altitude of 1200 ft. At 13:28:52, the EBCI Air Traffic Control Officer (ATCO) instructed the aircraft to remain at 2000 ft AMSL to allow for crossing traffic, a B737 landing at EBCI, and to proceed further to the east. After the crossing, the Pilatus was authorized to climb to 5000 ft. At 13:33:32, when the aeroplane was flying at 4400 ft, the pilot was authorized to turn back to the drop zone and turned towards its target, the EBNM airfield. Shortly after, a witness observed the aeroplane making a wide turn to the left. This witness monitored the aeroplane for about 40 seconds. He indicated the engine was making an abnormal noise which he compared with the explosions made by the exhaust of a rally car when decelerating. Finally, the witness heard a loud explosion ending by the dive of the aeroplane. He believed that the sound of an explosion was caused by the engine turbine disintegration.

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Figure 1: last flight approximate flight path

Another witness driving on the E42 highway saw the aeroplane performing what he perceived as being some aerobatic manoeuvers. The aeroplane was diving and was spinning. A moment later, he saw the wing break-up, including the separation and falling of smaller parts. A sailplane pilot was standing in his garden not far from the crash site. He first heard the sound of the Pilatus which he described as being typical, smooth and constant. He looked at the aeroplane and noticed it was flying at a lower altitude than usual. He stopped observing after a few seconds. 30 to 40 seconds later, he heard an abnormal noise change which he thought was a propeller pitch change or an engine power change. He looked for the aeroplane in the sky and saw the aeroplane diving with an angle of more than 45 immediately followed by a sharp pull-out angle of over 70, followed by the upwards breaking of a wing. The aeroplane went down as in a stall. The witness still heard the sound of propeller angle moving after the wing separation. Another witness standing approximately at an horizontal distance of 600 m from the aeroplane described having heard a sound change. He looked at the aeroplane and saw the aeroplane flying horizontally, making several significant left and right roll movements of the wings before it disappearing from his view. The aeroplane crashed on a field in the territory of Gelbresse, killing all occupants. The aeroplane caught fire shortly after the impact. A big part of the left wing, elements thereof and the right sliding door of the cabin were found at 2 km from the main wreckage.

Of the aircrafts occupants, 4 parachutists were ejected from the aircraft just prior to impact.

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1.2 Injuries to persons.

Injuries Pilot Passengers Others Total Fatal 1 10 0 11 Serious 0 0 0 0 Minor 0 0 0 0 None 0 0 0 0 Total 1 10 0 11

1.3 Damage to aircraft.

The aeroplane was entirely destroyed.

1.4 Other damage.

Minor damage to grass area and ground contamination by Jet A1 fuel and engine oil occurred.

1.5 Personnel information.

Pilot Sex: Male Age: 35 years old Nationality: Belgian Licences: PPL licence first issued on 06 June 2001

CPL licence first issued on 23 March 2006. ATPL licence first issued on 23 November 2011, last issued on 19 July 2013 in accordance with EASA Air Crew Regulations, Part-FCL.

Rating: SEP (land), valid until 31 March 2014 Pilatus PC-6, valid until 30 September 2015 Cessna SET, valid until 31 July 2015 Avro RJ/Bae146, valid until 30 April 2014 Last endorsement in the pilot log book to perform parachute dropping flights on 21 September 2013, valid until 30 November 2015

Medical: Medical certificate: Class 1&2, issued 12 November 2012, valid (Class 1) until 23 November 2013.

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General experience: Total experience: 2919 FH, from which 775 FH as PIC. Among others, a practical test for aerobatics flights was passed on 19 May 2005 in order to obtain a CPL licence. However, there is no indication of any authorization granted for the performance of aerobatics flights.

Pilatus PC-6 experience: Qualification on PC-6 completed on 1 November 2011. The pilots log book shows an accumulation of 332 FH on PC-6 since 17 March 2012, including 782 landings. The dropping flights on PC-6 show: An average duration of 25 minutes and 30 seconds. The lowest time duration is 18 minutes. The longest total flight time in a single day is 12:30 FH The highest number of landings in a single day is 34 for 12:30 FH.

The last flight as airline pilot, flying a BAe146 aeroplane, was performed on 17 October 2013 at 22:00 ending on 18 October 2013 at 01:10. Previous 24h flight activities: The pilot flew that day 13 flights with the Pilatus. Total flight time around 4:20 FH (20 min average). Previous week flight activities: 08:22 FH (BAe146) PC-6 flights over the last 6 months: Date (2013) Hours Min Total min Landings 5 April 1 4 64 3 6 April 3 15 195 6 7 April 8 43 523 19 14 April 7 45 465 20 21 April 5 45 345 13 4 May 6 56 416 17 (Estimated) 18 May 9 12 552 22 (Estimated) 14 June 0 26 26 1 15 June 4 0 240 8 16 June 7 14 434 18 29 June 10 32 632 25 4 July 10 15 615 23 6 July 0 45 45 1 6 July 10 30 630 25 21 July 8 42 522 20 15 August 7 10 430 17 17 August 11 10 670 28 18 August 0 45 45 1 21 September 0 25 25 1

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21 September 1 12 72 3 21 September 0 40 40 2 21 September 0 40 40 2 22 September 6 22 382 15 19 October 4 20 280 12

Pilot history at EBNM airfield: The pilot had been called to order twice in December 2012 and in July 2013 by the EBNM airfield authority for repeated violations of approved aerodrome procedures and the performance of manoeuvres deemed inappropriate. These occurrences were not reported to the BCAA.

1.6 Aircraft information. General information The Pilatus PC-6 is a single-engine high wing Short Take-Off and Landing (STOL) utility aircraft with conventional fixed landing gear, designed by Pilatus Aircraft of Switzerland. First flown in 1959, the PC-6 has been built in both piston engine and turboprop powered versions. The accident aeroplane was powered by a P&WC PT6A-27 free turbine engine. Certification The Pilatus PC-6s first version had been certified by the Federal Office for Civil Aviation (FOCA) of Switzerland in December 1959, under the Type Certificate reference F 56-10. The aircraft complies with the US Civil Air Regulations, Part 3 (US CAR3) as a normal category aeroplane. PC-6 is not approved for aerobatics manoeuvres. The model PC-6/B2-H4 variant had been approved on 20 November 1985. General characteristics Crew: one pilot Capacity: up to ten passengers Length: 10.90 m Wingspan: 15.87 m Height (Static): 3.20 m Wing area: 30.15 m Empty weight: 1387 kg MTOW: 2800 kg Max zero fuel weight: 2400 kg Centre of Gravity envelope: Up to 1450 kg = 11% to 38% MAC (3.209 m to 3.722 m from the reference line). At 2800 kg = 32% to 38% MAC (3.608 m to 3.722 m from the reference line). Straight line between variation points. Powerplant: P&W Canada PT6A-27 turboprop, 550 SHP Never exceed speed (VNE): 280 km/h (151 kt)

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Max Structural cruising (VC): 220 km/h (119 kt) Max Manoeuvring (VA): 220 km/h (119 kt) Max flaps extended (VFE): 176 km/h (95 kt) Stall speed (VS): 96 km/h (52 kt) (flaps down, power off, at

MTOW) Manoeuvring load factors: + 3.58 - 1.43 Service ceiling: 25000 ft

Figure 2: Pilatus PC-6 B2H4

Airframe: Manufacturer: Pilatus Type: PC-6/B2-H4 (Upgraded from an original PC-

6/B1H2 type in 1985) Serial number: 710 Built year: 1969 State of Registry: Belgium Certificate of Registry: N 5269, delivered by BCAA on 5 March 2003 Certificate of Airworthiness: EASA Form 25, delivered by BCAA on 15

February 2007 Airworthiness Review Cert.: Renewal on 28 March 2013 at 15803:13 FH.

ARC was valid until 25 March 2014.

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Total Time: 16159:20 FH Time since overhaul: 4427:55 FH (Performed 08/2002 to 02/2003) Time since last partial O/H: 765 FH (Performed 11/2011 to 03/2012) Total number of landings: 34903 Last 100 hour Insp/Maint: Performed 18 September 2013 at 16112:58 FH Fuel capacity: The aeroplane was equipped with large fuel

tanks. Total usable fuel capacity was 170 US GAL (644 litres)

Engine: Manufacturer: Pratt and Whitney Canada Type: PT6A-27 Serial number: PC-E41246 Engine hours: Total Time: 15273:50 FH Time since overhaul: 764:57 FH Propeller: Manufacturer: Hartzell (FAA STC SA377CH) Type: HC-D4N-3P Serial number: FY2365 Propeller hours: Total Time: 4427:55 FH Time since overhaul: 1161:20 FH This type of propeller is a 4-blade, hydraulically operated constant speed model with feathering and reverse pitch capability. Oil pressure from the propeller governor is used to move the blades to the low pitch (blade angle) direction. A feathering spring and blade counterweight forces are used to move the blades to the high pitch/feather direction in the absence of governor oil pressure. The propeller incorporates a Beta mechanism allowing reverse thrust. The propeller is equipped with an aluminium hub with aluminium blades. The rotation of the propeller is clockwise as viewed from the rear of the aeroplane. Propeller control - Beta propeller pitch in flight The Pilatus Porter is approved to use beta pitch in flight. Beta pitch is a concept whereby the propeller is set at a low positive pitch angle to provide a braking effect for steep controlled descents. When engaged, the propeller acts like a giant air brake. Beta mode is provided at airspeed below 100 KIAS with the power lever near or at the detent. Para dropping equipment The aeroplane incorporated amongst others the Optional Equipment for parachutists operations as detailed in AFM supplement 1824 (Referred to in FOCA data Sheet F 56-10 part 2.96-21 Optional Equipment). The modification encompasses the installation of a longitudinal bench, a stool, an external foot step and several guards.

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AFM supplement 1824 indicates that the jumpers seat belts must be installed if required by the operating regulations. In Belgium, the installation of belts has been required by BCAA since 2003, based on a Safety Recommendation following another fatal crash involving the same parachutist club and the same type of aeroplane in June 2002. Namur Air Promotion S.A. purchased the aeroplane in 2003 without safety belts for the occupants sitting on the bench and on the floor. The owner installed locally manufactured restraints that were tested and accepted by BCAA. The restraints (Single lap belts) were equivalent to Pilatus PN 112.50.06.824. At the same time, BCAA requested the installation of a placard on the dash board indicating that the pilot is responsible for verifying that all the occupants are properly attached before take-off.

Figure 3: location of the restraint system

Pilots seat and pilots back protection

Figure 4: picture of the pilots seat in the aeroplane involved in the accident

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As shown on the picture above, there is no separation between the cabin and the cockpit and the low pilot seats back does not provide any protection to the pilots upper body and head. Oxygen equipment This aeroplane was not equipped with a breathing system for pilot or occupants. Pilots operating handbook The aircrafts original Airplane Flight Manual (AFM) was not retrieved in the wreckage or found elsewhere. The applicable AFM covering the PC-6/B2-H4 is identified as being Report N107220 dated 10 December 1985 (Revision 5 dated February 2013). A supplement N1824 to the AFM refers to parachuting operations. For skydiving operations, the maximum number of occupants is 10, excluding the pilot. This supplement incorporates a change, made on request by the BCAA, showing that the following placard must be installed on the dash board:

Figure 5: Placard to be installed on dash board

The AFM of the accident aeroplane was verified and updated by the Continuing Airworthiness Management Organisation (CAMO) during the last airworthiness review of the aeroplane on 28 March 2013. After updating by the CAMO, this AFM (revision 4 dated January 2003) incorporated all the applicable temporary revisions and supplements and was in compliance with the Status List Documentation PC-6 dated 01 February 2013. Flight controls The aeroplane is equipped with a conventional flight control system for the ailerons, elevators and rudder. Control rods and cables are used to operate the controls. The primary flight controls feature a pilot and a co-pilot control column for the control of the ailerons and elevator and pedals for the rudder. Each aileron assembly has two sections joined together at the centre. A counterweight consisting of a long heavy tube is fixed at the lower surface of each outboard aileron. This means that the outboard aileron section is significantly heavier than the inboard one. Balance tabs are installed on the ailerons and the elevator to reduce the loads required to operate these controls in flight.

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An in-flight adjustable trim tab is installed on the rudder control system. A variable incidence horizontal stabilizer is used for the pitch trim control. The co-pilot control column is removable and was removed for this aeroplane. Each wing features a flap assembly, extending from the wing root up to middle of the wing span and consisting of two sections joined together at the centre. There is no interaction between the aileron and the flaps. The flaps of the crashed aeroplane were manually controlled by a hand crank located on the ceiling of the cockpit. Horizontal stabilizer trim system description The stabilizer is hinged to both sides of the fuselage at the main spar location, which is at approx. 25% MAC, allowing the trailing edge to move up and down under the action of the pitch trim actuator. The actuator is located in the tail section of the fuselage, below the stabilizer and remains stationary as long as it is not electrically activated. When the pilot operates the actuator trim switch, the trailing edge of the stabilizer is moved vertically (up/down) allowing a modification of the stabilizers angle of attack.

Figure 6: drawing of horizontal stabilizer and elevator

A retracted position of the actuator will tend to put the aircraft in a nose down position (=horizontal stabilizer trailing edge down) while an extended position of the actuator will tend to put the aircraft in a nose up position (=horizontal stabilizer trailing edge up).

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The movable tube of the trim actuator is attached by a rod end bearing to the rear lower side of the stabilizer while the stationary end of the actuator is attached to the fuselage frame by a fork fitting and a spherical bearing. In the electrically fully retracted position, the rod end bearing extends 46 mm from the actuator casing. The full stroke of the actuator is 85.8 mm.

Figure 7: Drawing of the trim actuator, the stabilizer trailing edge and the elevator bellcrank.

Figure 8: lateral view of the actuator. Figure 9: installation of the trim actuator

As can be seen in the figures above, the pitch trim system of the PC-6 B2H4 is fully electrically driven, while the rudder trim system is manually driven. The horizontal stabilizer electric system incorporates a dual motor operated linear actuator (One motor for the main and another motor for the alternate system).

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A three-position spring loaded trim switch is installed at each control column grip. The system also incorporates two relays, one to feed the electrical motor towards nose up and the other towards the nose down position. The purpose of the trim switch is to electrically ground either the up or the down relay of the main trim motor. When activated, the relay provides a positive 28 volt supply to the corresponding winding of the linear actuator motor.

Figure 10 : picture of a similar stabilizer trim switch

It has to be noted that it takes about 9 seconds for the actuator to move, by the main system, from a neutral position to the nose up or nose down (electrical) stops.

The 28 volt feed of the stabilizer main electrical system is provided through an interrupt switch and a 10 amp circuit breaker. In case of undesired pitch trim operation, the interrupt switch located on the instrument panel shall, when positioned in the interrupt position, deactivate both the main and the alternate systems.

Figure 11: stabilizer trim alternate switch on the left and interrupt switch on the right

The alternate system can be operated after having manually pulled out the circuit breaker of the main system and repositioned the interrupt switch in the normal position. This procedure is described in the Airplane Flight Manual and is enclosed in annex 6 to this report.

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Pitch trim actuator history The pitch trim actuator identification is Electromec EM483-3 PN: 978.73.18.103 SN: 173. It was newly installed on 10 April 2009. Chapter 04 of the Aircraft Maintenance Manual AMM n01975 rev.17 pertaining to the Airworthiness Limitations prescribes that this actuator has to be overhauled every 3500 hours. The installed actuator time in service was within the manufacturers limits. The next replacement was scheduled at 17645 hours ACTT. Variation in load factor with airspeed for manoeuvres (V-n Diagram).

Figure 12: V-n diagram showing Speed versus Load factor

The flight operating strength of an aeroplane is presented on a graph called a V-n diagram with the calibrated airspeed3 (velocity, "V") in the X-axis and the load factor ("n" or "g") in the Y-axis. Each aeroplane model has a unique V-n diagram defined by the certification criteria and the aeroplane design and valid for a given weight. Certain points on the V-n diagram define key operating airspeeds, which are intended to enable pilots to avoid structural damage to the aeroplane due to excessive flight loads. The diagram (also called structural envelope) describes the allowable combination of airspeeds and load factors for safe operation.

3 Calibrated airspeed (CAS) is the indicated airspeed corrected for instrument errors and position error. It describes the dynamic pressure acting on aircraft surfaces regardless of the existing conditions of temperature, pressure altitude or wind.

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Any manoeuvre, gust, or combination thereof outside the structural envelope can cause structural damage or even failure and can effectively shorten the service life of the aircraft. The diagram shows various boundaries. The upper horizontal line is the positive limit load factor. For the Pilatus PC-6 B2H4 this upper limit is 3.58 as determined in compliance with US CAR3. The lower horizontal line is the negative limit load factor which, according to the certification specifications, is -0.4 times the positive load factor (in this case: -1.43).

The aircraft is designed to withstand loads equal to the aeroplanes MTOW (2800 kg) multiplied by the limit load factors, provided in the V-n diagram of the aeroplane. Applying a load above these factors may cause permanent deformations to the aeroplanes structure. Applying a load above the ultimate load factor (which is 50% beyond the limit load factor) may cause the failure of the primary structure. The vertical boundary at the right side of the diagram is the maximum speed limit VD. Above this speed, deformation and failure of the structure may also occur. The maximum allowed airspeed is set at 90% of the speed limit (safety margin). This speed is called VNE, or the velocity to never exceed. The white region on the left of the diagram is edged by the so-called stall lines. They represent the minimum speed to be flown at a given load factor and maximum lift coefficient. Flying at lower airspeeds will cause the aircraft to stall and/or start to descend. It can be observed that the curves above and below the X-axis of the V-n diagram are not equal. This is due to the asymmetric airfoil of the PC-6 wing. The speeds where the curves intersect the limit load factor lines are called the manoeuvring speeds and for the sake of this report indicated as VA (in positive load) and VA- (in negative load). These speeds are important because when flying at speeds below the manoeuvring speed, the aircraft will always stall before exceeding the aeroplanes limit factors. When flying at higher speeds (yellow zone in the diagram), abrupt control inputs or flying in turbulent conditions should be avoided to prevent exceeding the limit factors. It has been calculated that the PC-6 will stay within the envelope and withstand gust conditions of +30 and -30 fps in a normal un-accelerated flight (the load factor equals +1). It can be observed that the yellow zone starts at a lower speed when submitted to negative loads (94 kt versus 119 kt) which means that the limit load will be reached earlier. When extrapolating the negative stall line, the speed at which the negative ultimate load factor is reached can be determined around 115 kt.

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Weight and Balance The aeroplane was last weighed on 28 March 2013 in the following configuration: With full engine oil, unusable fuel and the specific equipment for parachutist dropping installed. A Weight & Balance computation was seldom performed before flight. A pilot flying regularly with this aeroplane and also the president of the parachute club confirmed that it had been determined that the PC-6 loading would not exceed the Centre of Gravity (CG) envelope. This determination was based on different Weight and Balance computations made together with the instructor during all pilots conversion training sessions on PC-6. During the investigation, the weight and balance of the aeroplane was computed, based on the aeroplane data and the actual weight and position of the occupants, (as far as it could be determined) using the following data and/or assumptions: The weight of all the occupants was known. The position in the cabin of most of them was known. The average weight of the full equipment and clothing of each parachutist

was estimated to be 6 kg. A conservative assumption was chosen regarding the places number 6,

7, 8 and 10, for which the actual occupancy was unknown, by placing the heavier persons forwards and the lighter backwards.

The approximate fuel quantity was based on the number of rotations performed since the last refuelling and a mean fuel consumption of 12.5 US GAL per rotation.

The distance from the reference line was estimated based on the expected position of the occupants

Figure 13: sketch showing several distances to reference line

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Figure 14: sketch of the fuselage showing the parachutists' assumed position

Item Arm (m)

from ref line Mass (kg) Moment (kgm)

Aircraft empty weight (*) 3.354 1387.3 4653.004 Pilot In Command 3 91 273 P 5 (Back to front co-pilot seat) 3 93 279 P 1 3.5 66 231 P 3 4 81 324 P 2 4.7 92 432.4 P 4 5.45 96 523.2 P 9 5.5 81 445.5 P 10 in indefinite position 3.6 96 345.6 P 8 in indefinite position 4 82 328 P 7 in indefinite position 4.7 83 390.1 P 6 in indefinite position 5.1 70 357 Estimated fuel (50 USG) 3.95 161 635.95 TOTAL 3.718 2479.3 9217.754

(*) Small co-pilots seat in cockpit, RH seat aft of the cabin, para bench, cabin floor and static line attachment are included in the aircraft empty weight

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The above computation shows that the CG was very close to, or possibly even beyond, the aft limit of the CG envelope of the aeroplane (Aft limit is 3.722 m from the reference line). Furthermore, the weight of the aeroplane was within limits (MTOW is 2800 kg). The AFM supplement N1824 states in section II that the pilot in command must pay special attention to the aeroplanes loading. However, no guidance is provided on how to determine the arm between the reference line and the different parachutists, as they are actually installed on the benches and on the floor and their respective position is difficult to be precisely determined.

Figure 15: extract of POHS N1824

Aircraft history The Pilatus Porter MSN 710 was built in 1969 as a PC-6/B1H2 model and was first operated as a crop duster aeroplane by Ciba-Pilatus and subsequently used by the Red Cross organization in Angola. In 1989, it was purchased by a Belgian parachute club. The aeroplane was by that time already upgraded to the PC-6/B2H4 model. On 12 March 2000, it suffered an accident during a take-off from Moorsele (EBMO) airfield. The aeroplane suffered significant damage. As a consequence of this accident, the aeroplane had been repaired and overhauled in 2002 by Pilatus Flugzeugwerke and was thereafter bought by Namur Air Promotion SA in 2003. During the repairs a new 4-blade propeller of the Hartzell HC-D4N-3P type with SN: FY2365 was installed in accordance with FAA STC SA377CH. The aeroplane was operated by Namur Air Promotion SA from that time onwards for the purpose of parachute drops in Temploux, Namur (EBNM). It had flown around 4420 FH since the time it was purchased by its last owner until the date of the accident.

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Maintenance The aircraft was maintained by an EASA Part M subpart F approved maintenance organization. This organization was also duly approved as a Continuing Airworthiness Management Organisation (CAMO) and as such was in charge of both the maintenance and the airworthiness management of the aeroplane. Records show that the maintenance was regularly performed in accordance with a BCAA approved Aircraft Maintenance Program dated 25 May 2013. The last periodical maintenance (100 h) had been performed on 20 September 2013 at 16112:58 FH (Airframe Total Time). The discrepancy report related to this last maintenance lists a few minor outstanding items awaiting either the owners work order or the delivery of ordered parts. One of these items concerns the replacement of the temporary repaired LH wing outboard aileron section and another concern a possible fuel contamination for which the aeroplanes owner had been advised to check his fuel supply. The remaining items were deemed insignificant in relation to this investigation. In accordance to common practice, the inspection schedule of the Pilatus Maintenance Manual Chapter 5 entitled 100 Hours / Annual Inspection Airframe was used to perform the scheduled maintenance. The maintenance records were examined. These documents showed an anomaly; a task was not signed up and the mention NA was entered at the item 49 (see hereunder) even though this item is partially applicable. The personnel of the maintenance organization was interviewed and it was determined that the functional test (following Ref. 27-40-00) mentioned in the item 49 had been adequately and completely performed as a part of the item 47 Electrical system Examine.

Figure 16: extract of the 100h inspection schedule showing the maintenance

to be performed on both mechanical and electrical system

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1.7 Meteorological conditions.

General Forecast Winds Valid 19 October 2013 from 06:00 to 18:00 at EBBR SURFACE 205 DEG 05-10KT (COAST 10-15KT) BECMG SW/10-15KT AT 1000FT 210 DEG 20-25KT BECMG 230 DEG 25-30KT AT 2000FT 220 DEG 20-25KT BECMG 230 DEG 30-35KT AT 3000FT 230 DEG 20-25KT BECMG 240 DEG 35-40KT AT 4000FT 230 DEG 20-25KT BECMG 240 DEG 35-40KT AT 5000FT 230 DEG 25KT BECMG 240 DEG 35-40KT Airports Observation reports EBCI METARs 19/10/2013 (11:50 13:50 ) METAR EBCI 191150Z 18011KT 9999 FEW008 16/13 Q1009 NOSIG= METAR EBCI 191220Z 18010KT 140V210 CAVOK 16/14 Q1009 NOSIG= METAR EBCI 191250Z 19012KT CAVOK 16/13 Q1009 NOSIG= METAR EBCI 191320Z 19010KT CAVOK 17/13 Q1009 NOSIG= METAR EBCI 191350Z 18008KT 9999 FEW018 17/14 Q1009 NOSIG= EBLG METARs 19/10/2013 (11:50 13:50 ) METAR EBLG 191150Z 20011KT CAVOK 17/13 Q1009 NOSIG= METAR EBLG 191220Z 19011KT CAVOK 18/13 Q1009 NOSIG= METAR EBLG 191250Z 19010KT CAVOK 18/13 Q1009 NOSIG= METAR EBLG 191320Z 19013KT CAVOK 18/13 Q1009 NOSIG= METAR EBLG 191350Z 18011KT CAVOK 18/13 Q1009 NOSIG=

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Observation data (EBCI)

Weather radar

Figure 17: weather radar image at 13:20

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Meteorological conditions summary The crash site was located between EBCI and EBLG airports. As an interpolation of the EBCI and EBLG METARs, the wind speed on the ground at the crash site was around 10 kt coming from 180/190. The data of the general forecasted wind at altitude were extrapolated based on the comparison between the wind values mentioned on the EBCI and EBLG METARS at 13:20 and 13:50 . Based on this, it can be assumed the wind at FL50 was approximately 25 kt coming from 210. Observation reports from EBCI and EBLG show the ceiling and visibility were excellent for VFR flights. A few clouds were reported in the EBCI METAR at 13:50 (CAVOK - no cloud below 5000 feet above aerodrome level) and no gust. Additionally, no witnesses standing in the vicinity of the crash site reported any abnormal meteorological conditions.

1.8 Aids to navigation.

The EBNM airfield being located below the EBCI TMA One (located between FL55 and 2500 ft AMSL), all aircraft taking off from the EBNM airfield and operating above 2500 ft are subject to the EBCI Air Traffic Control. When climbing to the transition altitude (4500 ft AMSL), aircraft are transferred from Charleroi APP (call sign Charleroi Approach) to Brussels ACC (call sign Brussels Control). However, a special procedure has been agreed upon between the various air traffic control services involved together with the pilots of the parachute dropping flights. Each parachute dropping aircraft transferred from Charleroi APP to Brussels ACC must stay in contact with Charleroi APP on the second frequency of the radio. The reason for this procedure is to ensure that both ATC units concerned (Brussels ACC and Charleroi APP) are consulted for the authorization of the parachutists drop for their respective airspaces. When the aeroplane reaches the altitude for the parachute dropping, it contacts Brussels ACC to get an authorization for the zone FL245-FL55. The aeroplane is further required to contact Charleroi APP to get a similar authorization for the zone FL55-2500 ft AMSL.

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The flight path of the aeroplane could be reconstructed based on radar data. The Pilatus appeared on the radar screens around 13:28:10 passing 1300 ft. Shortly after, at 13:28:55 the pilot contacted Charleroi Approach and requested to climb to FL135. The controller instructed the pilot to fly eastwards at low altitude because of inbound traffic approaching EBNM, passing at 4400 ft at 3 NM to the south of the Pilatus. The position of the Pilatus was 1 NM southwest of EBNM.

Figure 18: extract of low air chart showing the approximate flight path

At 13:30:35, the aeroplane was over Bois de Neverle - Mode C indicating 1800 ft. At 13:30:50, when crossing the road N904, still on an easterly heading, the pilot was instructed to climb to FL50. When the aeroplane crossed the highway E411 in the vicinity of Champion (Time: 13.32.32), the pilot asked Charleroi, any chance for left turn to the target? (the target = the dropping area), but this was refused by the controller. At 13:33:30, the aeroplane was cleared by the EBCI controller to resume own navigation to the target. The EBCI controller also instructed the pilot to contact Brussels Control on 128.2 (radio frequency in MHz) to climb higher and also to report back to EBCI before the drop. At 13:33:42, the aeroplane was flying at 4500 ft close to the crossing of roads N992 and N80 (= Top right-hand corner of the EBCI-TMA3B). The pilot read back the last instructions from the controller and the aeroplane initiated a left turn and climbed to FL51 (5000 ft). The pilot did not contact Brussels Control on 128.2.

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Figure 19: last 2 minutes flight path

Figure 20: last minute flight path

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As seen on the preceding graphs, the aeroplane performed a left turn of approximately 120 from 13:33:36 to 13:34:16 while climbing from 4500 ft to FL 51 (5000 ft). Afterwards, the radar data show the aeroplane in a straight and level flight for 12 seconds (13:34:16 to 13:34:28). At 13:34:30, the radar track shows a sudden change of direction. The aeroplane reverses course to the right. Between 13:34:28 and 13:34:32, no altitude is recorded and from that time, the radar shows: 3 last echoes of the secondary radar (with altitude data) originating from

the transponder of the aeroplane at 13:34:36, 13:34:40 and 13:34:44. Few primary radar echoes northeast of the flight path (not represented on

the graphs) without altitude data, obviously originating from parts separating from the aeroplane.

1.9 Communication.

A normal radio communication was established for the take-off with Namur Radio Aerodrome Flight Information Service (AFIS). Conversations held on this frequency are not recorded, nor is it required. After the take-off the pilot contacted Charleroi APP prior to entering the EBCI TMA Sector 1 (2500 ft AMSL FL55). All the communications established between the aeroplane, Charleroi APP and finally Brussels ACC are recorded. Last flight (N15) communication transcript:

Time Charleroi APP Brussels ACC Pilatus Flight altitude

13:28:52 Charleroi, (call sign) on 2000, request one three five

(call sign), track to the east, call you back shortly for further climb

Roger, (call sign) 13:30:50 (call sign), climb to

flight level five zero 1800 ft

Ok, (call sign) 13:32:32 Charleroi, (call sign),

request left turn back to the target

3300 ft

(call sign), continue to the east, call you back shortly to resume

Ok, (call sign) 13:33:30 (call sign), cleared to

resume navigation over the target

4200 ft

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Right, navigation over the target, (call sign)

13:33:38 (call sign), for higher Brussels Control, one two eight decimal two. Report before the drop

13:33:42 (call sign) 4500 ft 13:34:27 Radio emission:

silence

13:34:30 Radio emission: silence 4 seconds

13:34:39 Radio emission: silence 4 seconds

13:34:45 "Aah" The pilot switched the radio frequency to Brussels ACC at or after 13:33:42 but did not check in with Brussels ACC. He continued climbing up to FL51 (5000 ft), ending in a straight level flight for more than 10 seconds. Between 13:34:27 & 13:34:45, several transmissions with only background noise (like gusty wind) were transmitted on the Brussels ACC frequency. During the last transmission, what seems to be a short cry was heard. Flight N14 communication transcript: During the previous flight (N14), it took only 24 seconds for the pilot to contact Brussels ACC after having received the instruction from EBCI APP to get the authorization for climbing higher than FL50. The airplane was flying at 3000 ft at the time.

Time Charleroi Tower Brussels (128.2) Pilatus 13:07:23 Charleroi Tower, (call

sign), one three five (call sign), Climb to

flight level five zero

13:08:45

(call sign), for higher Brussels Control, one two eight two, report before the drop

One two eight two, report before the drop, (call sign)

13:09:09 Brussels Control, (call sign), passing 3000 ft request one three five

(call sign)climb to flight level one three five

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1.10 Aerodrome information.

EBNM Namur Suarle airfield

The crash occurred at a distance of about 12,5 kilometres east-northeast of the EBNM airfield. EBNM Namur airfield is located 7 km west-northwest of Namur. Geographical coordinates are 502917 N 44608 E and elevation is 594 ft (181 m). The airfield is equipped with two grass 24/06 bi-directional runways. The dimensions of runway 06L/24R (gliders) is 630 m x 50 m while 06R/24L (used for motorized aircraft) has the following dimensions 695 m x 31 m. Both runway with orientation 24 has a right hand circuit. However, a special opposite circuit (LH for runway 24 and RH for runway 06) is applicable for the parachute dropping aeroplanes based at the airfield. Prior permission is required (PPR) from the operator for the use of the airfield. A mix of aircraft (aeroplanes, helicopters and gliders) are operating from the airfield and parachuting activities in VMC are authorized. Overflight of the airfield must be avoided during parachuting activities. Aerodrome Flight Information Service (AFIS) is provided on 118.000 MHz and radio equipment is mandatory in each aircraft. The technical and operational conditions applicable to airfield without ATC are prescribed by BCAA Circular GDF-04. An extract of Circular GDF-04 about the responsibilities of the airfields commander when observing violations:

6.4 Verantwoordelijkheden van de vliegveldoverste 6.4.2 De vliegveldoverste of zijn plaatsvervanger: a) b) is gehouden elke inbreuk op de luchtvaartwetgeving en -reglementering dat voorkomt op het vliegveld op te tekenen en zonder uitstel mee te delen aan het DGLV

6.4 Responsabilits du commandant darodrome 6.4.2 Le commandant d'arodrome ou son supplant: a) b) est tenu de consigner et de communiquer sans dlai la DGTA toute infraction la lgislation et la rglementation aronautique

Translation : 6.4. Responsibilities of the airfield commander 6.4.2. The airfield commander or his replacement: a) ... b) records and communicates as soon as possible to BCAA every violation of the aeronautical regulation and legislation etc.

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Brussels South Charleroi Airport Brussels South Charleroi Airport (EBCI) is located 23 km west of EBNM Namur airfield. Consequently, several Terminal Manoeuvring Areas (TMAs) are overlying EBNM airfield, located in class G airspace.

Consequently, a large part of the flight path of the aeroplane was performed under the control of the EBCI Airport ATC. Amongst others, the following Air Traffic Services (ATS) communication facilities are available at Charleroi Airport: Charleroi TWR (121.300 MHz) and Charleroi APP (133.125MHz). The crash occurred 35 km east of EBCI close to the intersection of EBCI TMA ONE, TMA TWO A and TMA THREE B (FL55/3500 ft AMSL).

Figure 21: relative position of EBCI, EBNM and the crash site

Airspace view above EBNM The following drawing shows the build-up of the different controlled and uncontrolled areas above Namur airfield.

Namur area One is a circle of 2 NM radius centered on 502917 N 44626 E and extending from the ground up to FL135. This area designates the zone where parachuting activities are organized.

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Figure 22 : airspace above EBNM (not on scale)

1.11 Flight recorders.

The aeroplane was not equipped with a flight recorder, nor was it a requirement. Action cameras were carried by some parachutists. The cameras were examined by the Police Laboratory, but no record of the last flight was found, which is not abnormal as they would normally only be used during the jump. All reserve parachutes were equipped with an Automatic Activation Device (AAD). The AAD devices sample the ambient air pressure to compute the altitude and vertical speed 8 times per second. The AAD is switched on by the parachutist upon climbing aboard the aeroplane to allow the system to measure the ambient pressure on the ground, being the ground altitude of the future drop zone.

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Figure 23 : Reserve parachute automatic activation device (AAD)

Taking into account that the QNH was 1009 hPa and the elevation of the Namur airfield is around 600 ft, the QFE (atmospheric pressure at the airfield) was 889 hPa4 when the AAD of the parachutists measured the atmospheric pressure of the airfield. This explains why the height difference measured by the AAD and the aeroplane encoder (set to 1013 hPa) was around 720 ft (30*(1013-889) =720 ft). During take-off, the AAD will go to an active status and is ready to help the parachutist in a critical situation. In the meantime, it also starts to measure the ambient pressure 8 times per second. The AAD arms itself automatically when a rapid pressure increase is observed, corresponding to a 35m/s fall speed. This activation fall speed is close to a parachutists free fall speed of about 50m/s. The AAD will instantaneously activate the reserve parachute to deploy when both the following conditions are satisfied: The free fall speed is reached and maintained. The altitude drops below the pre-set activation altitude, corresponding to

an approximate height of 300 m AGL. The electronic system of the AAD also feature an internal memory that will log the past data in memory from 7 seconds before the arming point (actually, 7 seconds before the 35m/s fall speed is reached) and stops recording 10 seconds after reaching the ground altitude. The data of all seven AADs could be recovered with the support of the manufacturer (Vigil a Belgian brand). It was determined that all AAD detected a fall speed of over 35 m/s and armed simultaneously while the parachutists were still on board.

4 Below 10000 ft, the pressure lapse rate is about 1 hPa per 30 feet => 600ft/30ft=20 hPa

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Figure 24: last 27 seconds of one AADs record

The above AAD recording shows the last 27 seconds prior to the impact. The Y-axis shows the height above the EBNM airfield ground level while the X-axis represents the time in seconds. Elevation of EBNM airfield is 594 ft (181 m) meaning that the first data of altitude (left ordinate) on the graphs are around 5000 ft (1520 m) AMSL. Elevation of the crash site was quite similar to the EBNM elevation meaning that the last seconds of horizontal flight were performed at 1330 meters above ground level.

Figure 25: AAD record from 7 seconds before the detection of the 35m/s freefall speed

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1.12 Wreckage and impact information.

1.12.1 On-site examination of the wreckage The aeroplane crashed in a ploughed field located north of the village of Gelbresse. The propeller, the engine and the front section of the fuselage impacted first the ground with the aeroplane attitude almost vertical. The approximate direction of impact was west.

Figure 26: general view of the accident site

The propeller, the engine and the nose section of the fuselage were virtually buried in the ground and had disappeared under the other remains of the aeroplane. Witnesses reported that the wreckage caught fire just a few tens of seconds after impact, destroying most of the front and central section of the fuselage. The inner quarter section of the left wing separated from the fuselage at impact and was lying on the ground about 12 meters left of the fuselage. The inboard section of the flap was still attached to this part of the wing. The structural fuel tank built inside this section of the wing was fully open at its outboard rib. The outer three-quarters of the left wing was not found in the vicinity of the main wreckage.

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The right wing structure was still attached to the fuselage and the wing strut. The wing showed obvious impact damage on the leading edge, and the inner part was destroyed by fire. The horizontal stabilizer was lying on the ground in an upside down position the upper surface being in contact with the ground and the leading edge pointing approximately in direction of the front side of the fuselage. The right side of the stabilizer was partially covered and hidden by the tail section of the fuselage. The elevator was still attached to the stabilizer. The tail section of the fuselage was found lying on its left side, meaning that the remains of the vertical fin were in a horizontal position.

Figure 27: aerial view of the wreckage

The left wing integral fuel tank broke open when the wing failed and it suffered additional damage during final impact, but it didnt burn. The right wing integral tank as well as the collector tank located inside the fuselage broke open at the final impact and were largely destroyed by the post impact fire. Most of the instruments were severely damaged, beyond possible use.

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Figure 28: pattern of the in-flight separated parts

A search to locate the severed parts was initiated by the police. The parts were numbered (W01, W02 ) in the order they were found. The table below shows the distance between the main wreckage and the different parts starting with the closest and ending with the parts found the furthest from the main wreckage. Reference

Description Distance (meters)

W03 LH wing outboard aileron 900 W02 LH wing main spar upper cap 980 W01 Rudder counterweight 1020 W04 RH cargo sliding door 1190 W10 RH vertical stabilizer skin and antenna 1420 W05 LH wing (outer 3/4 section) 1460 W09 Fragment of LH wing tip 1600 W07 LH wing trailing edge fragment at rib 12 1700 W06 LH wing outboard flap 2100

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Figure 29: LH wing outboard aileron

Figure 30: Part of LH wing main spar upper cap

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Figure 31: Rudder counterweight.

Figure 32: RH sliding door.

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Figure 33: RH skin and RH antenna of vertical stabilizer

Figure 34: Outer three-quarters of the LH wing (View of the lower surface).

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Figure 35: Fragment of LH wing tip Figure 36: Small stringer

Figure 37: LH Wing trailing edge fragment at rib 12

Figure 38: LH wing outboard flap

1.12.2 Detailed examination of the wreckage The wreckage was transported to the facility of the Belgian Defence Air Safety Directorate (ASD), at EBBE for further examination. A first detailed examination was performed on 24 October 2013 with the support of an Accredited Representative (AccRep) of the Swiss Accident Investigation Board (SAIB) and two safety investigators from Pilatus. Experts from the Belgian Defence Air Component and from the Belgian CAA also helped the AAIU(Be) investigators to carefully examine the wreckage.

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A few days later, the engine and the propeller were thoroughly examined with the support of safety Investigators from Pratt and Whitney Canada and Hartzell Propeller Inc. The safety investigators from Pilatus, Pratt and Whitney Canada and Hartzell Propeller were acting as advisors of the AccRep of respectively the Swiss Accident Investigation Board (SAIB), the Transport Safety Board of Canada (TSB) and the National Transportation Safety Board (NTSB) of the United States. The BEA of France also delegated a safety investigator who participated among other in the investigation on an accident of Pilatus PC-6 in France involving a structural failure. Fuselage and right wing structure. The fuselage front and central structure was almost totally destroyed by impact and the subsequent fire. Only the rear section, from the bulkhead 6 (the cabin rear wall) to the tail remained almost intact. The right wing was significantly crushed at impact along its entire length. A part of the skin had been separated from the wing and came to rest 15 meters in front of the main wreckage. The first, inner, quarter of the wing incorporating the structural fuel tank had almost disappeared under the effect of the post-crash fire. Both half inboard and outboard flaps and ailerons were still attached to the wing remains. The right wing strut was slightly bent and showed burning damage. However it was still complete and attached to the remains of both the fuselage and the wing. Right ailerons The inner and outer ailerons of the right wing were found at their normal position, at the trailing edge of the wing. They were severely damaged by the final impact with the ground. Right wing flaps: The inner and outer flap remains were retrieved at the trailing edge of the wing. All damage was consistent with the final impact and the post-crash fire.

Left wing structure The wing was reconstructed and showed that the wing main spar was broken in several places. The skin and some ribs were cut to gain access to the remains of the main spar.

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Figure 39: LH wing reconstruction

The wing main spar reconstruction could determine that the part found at 980 meters from the main wreckage was a section of the LH wing main spar upper cap installed between ribs N5 and 8.

Figure 40: LH wing main spar upper cap installed between ribs N5 and 8.

This section of the upper spar cap was bent and twisted. The curve shown by the spar cap indicates the wing was bent downwards. The twist showed a downward movement of the leading edge and an upward movement of the trailing edge. This was evidence for the fact that the wing had been submitted to negative g-forces causing an extraordinary downward aimed mechanical load with respect to an aeroplane in normal flight attitude. In summary: The main spar upper caps failed in 3 places: at the wing attachment, at

wing rib No.5 and at rib No.8. The main spar lower caps also failed at 3 locations which are not the same

as those of the upper caps. The wing skin had been torn differently with respect to the spar cap

failures, at approximately the junction of the inner and the outer flap. Most broken lower and upper spar caps remained attached to their

respective skin sections and ribs with the exception of the upper main spar caps between ribs 5 and 8 (Figure 40).

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Figure 41: sketch of LH wing main spar failures and wing strut failures.

Visual examination of all main spar cap fractures could not find any obvious sign of fatigue crack. All fracture areas were isolated and sent for a thorough fractographical analysis at the Belgian Royal Military Academy laboratory. The laboratory examination concluded that no sign of metal fatigue, corrosion, brittle behaviour or other material pathology could be identified (The document showing the results of the laboratory examination are enclosed at the end of this report). Left Wing Strut

Figure 42 : LH wing strut failures.

The left wing strut was broken into 3 sections, the damage being approximately located at mid-point of the struts length. One 1,25 meter section of the strut remained attached to the wing while another 1,50 meter section remained attached to the fuselage. A small central section was retrieved near the main wreckage remains.

Thorough visual examination of the wing strut showed it first distorted into a Z-like shape under a heavy buckling load before breaking. The small piece of strut that formed into a Z-shape showed some traces of blue colour indicating the strut contacted the wing lower surface.

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Examination of the wings lower surface in the vicinity of the strut-to-wing attachment revealed that the strut and the wing fittings were undamaged. However, a collision had occurred between the nut and the wing lower surface caused by an elastic deformation of its fittings.

Figure 43: Sketch of the wing to wing strut connection.

As with the visual examination of the wing main spar fractures, no obvious signs of fatigue crack could be found on the strut and, in order to establish factual information, it was decided to submit all interesting fragments to a fractographic examination, along with the left wing parts. The laboratory examination concluded that no sign of metal fatigue, corrosion, brittle behaviour or other material pathology could be identified (A summary and the conclusions of the fractographic examination are enclosed at the end of this report). Left wing tip The wing tip was reconstructed, and showed its lower surface was free of longitudinal scratches. There was no trace of a previous contact with the ground. Left wing ailerons The inner aileron of the left wing was found still attached to the wing and revealed that both the skin at the outer corner of the trailing edge and the balance tab were missing.

The outer aileron, retrieved at 900 meters from the main wreckage, was largely intact; no skin was missing and the counterweight and the balance tab were still attached at the aileron5. Traces of friction were visible on the counterweight tube including the red painted end of the counterweight. These friction traces matched red paint traces found on the fuselage dorsal fin. Traces of rivets torn out were visible at both lateral ends of the ribs. An old skin repair correctly withstood a structural deformation of the aileron. The axis of the structural deformation of the aileron was determined to be aligned with a similar deformation of the lower skin of the wing.

5 An old skin repair properly withstood a structural deformation of the aileron.

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Figure 44: LH wing outer aileron showing common deformation with the wing inner surface.

Left wing flaps: The inboard flap remained attached to the inner quarter of the wing up to the final ground impact. By contrast, the outboard flap found 2km away, separated from the wing in flight. Examination could determine that the separation of the flap was caused by the separation of the wing at the junction of the inner and the outer flap.

Wing flap position The position of both flap actuators was measured and showed different lengths. This apparent inconsistency was not relevant because of the traction produced on the flap control chain when the wing separated from the aeroplane.

Flight controls: The primary flight control installations consisted of an assembly of control cables, bellcranks, pulleys and connecting rods. Most flight control cables were broken, some of them showing local corrosion consecutive to fire damage. All cable ends were found still attached to their bellcranks or other attachments. Some cables had been cut by the rescue services to gain access to the victims or to facilitate the wreckage transportation.

Friction traces

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Examination of all ruptured areas of the cables showed obvious signs of tensile overload failures, and no trace of abnormal wear; - individual strands were found unwinded, showing the sudden release of

kinetic energy during impact (see Figure 46) - the fracture surfaces of the broken strands were of the cup-and-cone-type

with necking - cables were heavily deformed, also showing the sudden release of kinetic

energy during impact. (see Figure 45 and Figure 47) The same is true for all the failed components, such as connecting rods, of the different flight controls loops.

Figure 45: Remains of the elevator cables

Figure 46: Failed ends of an elevator cable

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Figure 47: Aileron control cables inside the LH wing

The lower bellcrank of the aileron control system inside the fuselage was broken close to the LH aileron cable attachment and at the rod connecting both control sticks together. These damages had been determined to be caused by overload, likely at the final impact.

Figure 48: Aileron bellcrank located inside the fuselage

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Vertical stabilizer

Figure 49 : The structure of the vertical stabilizer

was largely disintegrated.

The vertical stabilizer structure was largely disintegrated showing the main spar still attached to the upper aft section of the fuselage and some fragments of the skins. The vertical stabilizer was equipped with antennas installed symmetrically on both upper sides.

The right side antenna and a significant part of the right structure were found in a cultivated field at 1420 meters from the main wreckage. The metallic leading edge of this antenna was missing. The left top side of the structure, including the left antenna, was found at the crash site.

Figure 50 : leading edge of the vertical stabilizer, showing RH antenna leading edge metallic protection missing

The missing antenna leading edge was found lodged into the left wing lower surface skin.

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Figure 51: View of RH antenna leading edge, retrieved inserted in left wing lower surface skin.

Rudder The rudder was found on the main wreckage site, a few meters behind the fuselage tail section. The top side of the rudder is largely disintegrated and the rudder counterweight is missing. This counterweight was found at a distance of 1020 meters from the main wreckage. The leading edge of the rudder was torn open.

Figure 52: Rudder showing the top end largely disintegrated.

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Horizontal stabilizer

Figure 53: Horizontal stabilizer upside down Figure 54: Horizontal stabilizer in normal

flight position.

The horizontal stabilizer was found resting upside down on the ground with its left side partially covered by the aft section of the fuselage. Both leading edges showed impact damage. Left leading edge damage, contaminated by soil, was the result of the final ground collision while the right leading edge, less damaged, showed evidence of a possible impact by another aircraft structure. Except the severed and broken articulation plates, the central section of the stabilizer suffered less damage compared to the damage at both leading edges. Figure 55 shows the central section of the stabilizer in a normal flight position (upper surface upward). Examination of the rivets and holes of both articulation plates showed they failed by overload. The rivets of the both articulation plates were sheared. The RH articulation plate is slightly deformed.

Figure 55: Horizontal stabilizer forward centre section

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By contrast, the LH articulation plate i