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www.brunel.ac.uk/about/acad/sed/sedres/cem/bfsl

School of Engineering and Design

1M

Loss of Control of Light Aircraft:Loss of Control of Light Aircraft:Balancing Cost and Safety in Flight Balancing Cost and Safety in Flight

TestTest

Mike BromfieldMike BromfieldGuy GrattonGuy Gratton

SETP/SFTE 4th European Flight Test Safety Workshop London 28~29, September 2010



2



3G

What’s the question?• GASCo 28 year review of GA fatal accidents

– 35-50% stall/spin– Significant type variations

• Why type variations– C150 rate >> C152 rate (~17:1)– PA28 “Hershey Bar” wing ~population mean, tapered

wing no fatalities

• Understand the reasons– For flying training– For design



4M

Spot the difference…?

Cessna 150L

Cessna 152

0.71 fatals/ 100,000 hrs0.71 fatals/ 100,000 hrs

0.04 fatals/ 100,000 hrs0.04 fatals/ 100,000 hrs



Events

0 2 4 6 8 10

Task: Baulked Ldg

Pilot: Instructor

Pilot: 2 POB

Enviroment: Wind 30 kts+

Aircraft: Cessna 152

Aircraft: Cessna 150 L/M

10 events: C150/C152 stall/spin

fatalities

5M



Methods & EquipmentFlight Test basics

Go-Pro Cockpit mounted camera

Appareo GAU1000A Flight Data Recorder

Garmin 296

6M

J31-Calibration



Flight Test Programme Build-up

•8 aircraft•17 test sorties + 3 checkouts + 1 decline•25hrs 35mins flight test

7M



Flight Test using Rental Aircraft

• Aircraft Variables (ageing?)– maintenance, performance, W&CG

• Organisation– Different priorities

• Flight test .v. Flight School– Aft CG stalling at 3000ft anybody?

• Local environment– Area & procedures, controlled airspace, ATC, Wx

8G



-7.00-6.00-5.00-4.00-3.00-2.00-1.000.001.002.003.004.005.006.007.00

40 50 60 70 80 90 100 110 120

Sti

ck

Fo

rce

Pu

ll (d

aN

) >

>>

Speed KCAS >>>

Polynomial Curve Fit for Apparent LSS - Cruise

F150L G-GBLR CRF150M G-BCRT CRC152 G-BOFL CRStall BoundaryPull Force to Stall Boundary

BTP/Sortie: 2008-06-02/03/04A/C= Cessna F150L,F150M,C152CG = Mid-CGVtrim = 84~88 KCAS

Stick Force to Change AirspeedCessna 150L,M & 152 with Flaps a) UP b) DOWN

(L30)

9M

Flaps UP

0

3

6

9

Start Climb

Mid ClimbEnd Climb

HQR Climb & Point Track

G-BCUH F150M

G-BFLU F152

Desirable: +/- 2 MIAS/KIAS Adequate: +/-5 MIAS/KIAS

BTP/Sortie: 2008-06-12A/C= Cessna F150M G-BCUHDate: 05/03/10Gross Wt.= 1599 lbsCG = 35.03" AoD (25.87%MAC/58.76% CG/Mid -CG)Vtrim = 69 KCAS (81 MIAS)

BTP/Sortie: 2008-06-10A/C= Cessna F152 G-BFLUDate: 12/12/09Gross Wt.= 1655 lbsCG = 33.8" AoD (23.78%MAC/50.71% CG/Mid -CG)Vtrim = 69 KCAS

-7.00

-6.00

-5.00

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

40 50 60 70 80 90 100 110 120

Sti

ck

Fo

rce

Pu

ll (

da

N)

>>

>

Speed KCAS >>>

Polynomial Curve Fit for Apparent LSS - Landing (30)

F150L L30F150M L30C152 L30Stall BoundaryPull Force to Stall Boundary

BTP/Sortie: 2008-06-02/03/04A/C= Cessna F150L,F150M,C152CG = Mid-CGVtrim = 66~68 KCAS

Flaps DOWN

Desirable Pull Force to Stall (PFtS – 10 lbf/4.4475daN)

Desirable Pull Force to Stall (PFtS – 10 lbf/4.4475daN)



10M

Radio Calls >> Increased Workload??

Climbing Flight: Cessna 150M



Flight Test Results• Variability between aircraft, C150 consistently lower pitch forces

– Mean gradient factors ~2-3– C150 sometimes neutral (e.g. L40)

• Stick force dependent on:- – (1) Flaps, (2) Power, (3) Trim, (4) Weight, (5) CG

• Low stick force >> poor airspeed management

• Stall warning– C150 non-compliant with (current) part 23 in certain configs.– Simultaneous stall warning + aerodynamic stall

11M



Simulation Experiments- Scenario-based Testing

Simulator• PC7 Fixed-base research simulator

– Controllable force feedback– 150 x 40 deg. Visuals

Scenarios• 20 pilots x 5 scenarios x 3 stick force gradients

– Circuits, EFATO, Climb-out, Go-around, Base to Finals Turn

Data /Analysis– Workload (Heart Rate, NASA TLX)– Flight dynamics + RT/intercom

12M



13M

Typical simulator test results:Typical simulator test results: margin of safety & effect of stick margin of safety & effect of stick

forcesforces



Example: Pilot 24 Go-around, Full Pwr / Full Flap

Key:Stick Force Gradients

HighMediumLow

Pilot 24 (high hrs):• ATPL• 12,000+ hrs PIC• Age 60~64• Avge 350+ hrs per yr

Non-dimensionalised AoA .v. Elevator

Pilot 23 (medium hrs):• PPL (no IMC) • 1200+ hrs PIC• Age 65~69• Avge 33+ hrs per yr

14M

Elevator

Alpha



15

Conclusions Type training - C150 and C152 are different

Design factors - Certification standards are too subjective, consider use of Human Factors tools

Aircraft design, loading & configuration influence airspeed management & stall avoidance via pilot cues

Low stick force gradients can result in:-– Poor airspeed management cues & stall avoidance

cues– More mentally demanding tasks– Increasing workload– Decreasing safety margins

………which all makes loss of control due to distraction or pilot inattention more likely



Lessons Learned• Independence

– Manage FTI, check maintenance– Always check W&CG reports

• Workup– Essential but spread across sites and aircraft– Use learning curve

• Efficiency– Critical test points– Concentrate flying periods

• But always review data between sorties

• Best practice– Qualified pilot opinion– Redundancy in data collection

16G



Any Questions?Any Questions?

17M/G

Acknowledgements:-Acknowledgements:- Dr Mark YoungDr Mark Young Thomas Gerald Gray Thomas Gerald Gray

Charitable TrustCharitable Trust GASCo, UK-CAAGASCo, UK-CAA Cranfield & Sheffield Cranfield & Sheffield

UniversitiesUniversities



18

Type of Accident (UK) - 1980 to 2006 (GASCo)

Medical/Suicide3%

Airframe Failure4%

Collision with Grnd Object

5%

Mid-air Collision6%

Forced Landing12%

CFIT12%

Low Flying/Aeros16%

Loss of Control IMC8%

Loss of Control VMC25%

Undetermined5%

Low Approach4%

Fixed Wing <5,700kg (non-microlight) fatal

accident causal factors: 1980 to 2006 (UK)



PilotAircraft

Dynamics

ConditionError

(ConditionCues)

ControlOutputs

Gust/Turbulence

ActualCondition

TrackingPoint

(Optimal)

ControlSystem

ControlInputs

Boundary(Unsafe

Condition)Actual

Condition

SafetyMargin

(Safety Cues)

+ -

+

-

+

+

Planned Margin

19

BFSL Safety Model

Aircraft

Environ.

Pilot



Cessna 152

CG Moves aft =Lower stick forces =

More severe stall & spin

20



HQR - Climb & Point Track C152, F150M

0

3

6

9

Start Climb

Mid ClimbEnd Climb

HQR Climb & Point Track

G-BCUH F150M

G-BFLU F152

Desirable: +/- 2 MIAS/KIAS Adequate: +/-5 MIAS/KIAS

BTP/Sortie: 2008-06-12A/C= Cessna F150M G-BCUHDate: 05/03/10Gross Wt.= 1599 lbsCG = 35.03" AoD (25.87%MAC/58.76% CG/Mid -CG)Vtrim = 69 KCAS (81 MIAS)

BTP/Sortie: 2008-06-10A/C= Cessna F152 G -BFLUDate: 12/12/09Gross Wt.= 1655 lbsCG = 33.8" AoD (23.78%MAC/50.71% CG/Mid -CG)Vtrim = 69 KCAS

21



Sim. Experiment 3:Workload Results

22

‘High’ Stick Force :- - Lower Mental Workload- Higher Physical Workload

0

5

10

15

20

25

30

***Practice Circuit***BRS Rwy 27

CircuitBRS Rwy 27

Approach & FULL Flap Landing @65 kts, Rwy 27

2nm700' AGL

(with Go-around)

Base to Finals Turn w/landing

BRS Rwy 27 R/HMid-base750' AGL

Total Workload - All Stick Force Gradients

Total Workload - High

Total Workload - Medium

Total Workoad - Low

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0


CircuitBRS Rwy 27


2nm700' AGL

(with Go-around)



Mental Demand - All Stick Force Gradients

Mental Demand - High

Mental Demand - Medium

Mental Demand - Low

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0


CircuitBRS Rwy 27


2nm700' AGL

(with Go-around)



Physical Demand - All Stick Force Gradient

Physical Demand - High

Physical Demand - Medium

Physical Demand - Low



Example: Pilot 24Climb-out, Full Pwr / Zero Flap

Key:Stick Force Gradients

HighMediumLow

Pilot 24 (high hrs):• ATPL• 12,000+ hrs PIC• Age 60~64• Avge 350+ hrs per yr

Non-dimensionalised AoA .v. elevator

Pilot 23 (medium hrs):• PPL (no IMC) • 1200+ hrs PIC• Age 65~69• Avge 33+ hrs per yr

23



24

Example: Handling assessment in climb-out

1.3 VStall

1.2 VStall

1.1 VStall

Point Tracking

(Maintain)

Boundary Avoidance

(Avoid)

VVStallStall

13 (Sat.)

Speed

Time

46 (Unsat.)

79 (Unaccept.)

10+ Control lost10+ Control lost

Cooper-Harper for boundary avoidance – can be automated

Workload

‘Top-down’

‘Bottom-up’@crossover switch from ‘top-down’

(point tracking) to ‘bottom-up’

(boundary avoidance)



25M

Conclusions – Causes of LoC

• Stall Boundary crossing (not point tracking)– Handling characteristics & workload

• Type training– A C150 is not a C152

• Design factors– Certification standards are too subjective– Consider Human Factors tools

• Further work needed– Historical certification standards for stalling– Apparent LSS results and models (FCMC in longstab calcs)

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