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Copyright Avfacts 1999. All rights reserved. Rwy Perf 1/page 1.

You will need to refer to CAO 20.7.1b whilst reading these texts. This CAO is allowed in the CASA ATPL examination as this is an open book exam. You do NOT need to memorise the gradient numbers ! Depending on the number of engines the aircraft has fitted, there is different minimum performance climb criteria that must be met. Most of these revolve around the one engine inoperative scenario. Obviously a twin engine will lose half it's power when one of the engines fail, a three engined aircraft will lose 1/3 rd of its power, and a four engine aircraft such as the Airbus A340 will lose only 1/4 of its power. There are two definitions of climb gradient which you must know - they are: Gross climb gradient, which is the minimum climb performance that must be satisfied during

certification trials when flown by the test pilots. As stated earlier the test pilots are aware that one engine inoperative performance tests are to be carried out, and are ready for the occurrence. Additionally, the aircraft and their engines are new and will develop more thrust than ones that has been in service for several thousand hours. All gradients are to be without ground effect.

Net climb gradients are the gross gradients with an standard deduction for pilot operating technique of line pilots instead of test pilots, and reduction in engine thrust performance with age (refer tables 1 to 4).

Number of engines Gross Gradient % Reduction applied % Net gradient %

Two Positive Nil Positive Three 0.3 Nil 0.3

Four 0.5 Nil 0.5

Climb Segments (refer CAO 20.7.1b paras 7.1 to 7.5) These are split into 4 different zones according to aircraft configuration and height above the takeoff surface. The segments are: From 35 ft AGL to the point at which the landing gear is fully retracted. Flap in the takeoff position, and

takeoff power on operating engine(s). Critical engine windmilling unless NTS* is fitted. Speed at least V2.

From landing gear retraction to at least 400 ft above the takeoff surface. Flap in takeoff position, takeoff

power on the operating engine(s). Propeller windmilling unless a NTS* system is fitted. The aircraft may fly level to accelerate from V2 to final takeoff climb speed, providing terrain clearance is

not a problem. Flaps can be retracted on schedule to achieve clean aircraft. The aircraft must have some climb ability available in the segment with flaps down in case terrain is a problem.

From the point at which zero flaps final takeoff climb speed is attained in the en-route configuration on to

the destination or alternate. Power at maximum continuous setting. Propeller feathered. Flaps retracted. Gear retracted. This is the EN-ROUTE zone.

Table 1. First segment (VLOF to gear retraction).

* NTS is a negative torque sensing system that automatically feathers the propeller after engine fails.

Module 1 - Runway Performance Minimum Climb Gradients

Pic

ture

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of p

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Two 2.4 0.8 1.6

Three 2.7 0.9 1.8

Four 3.0 1.0 2.0

Table 2. Second segment (Gear retraction complete to at least 400 ft agl).

Table 3. Third segment (End of second segment to final climb speed).

4th (En-route)

400 ft minimum

35 ft

Gear retraction

RWY Perf fig 15. Climb segments.


Two 1.2 0.8 0.4

Three 1.4 0.9 0.5

Four 1.5 1.0 0.5

Table 4. Final segment (En-route).

If the aircraft is certificated in the commuter category, the gross gradient in the second segment need only be 2%.

1st

2nd 3rd

Flap retraction

Takeoff surface

Copyright Avfacts 1999. All rights reserved.


Two 1.2 0.8 0.4

Three 1.4 0.9 0.5

Four 1.5 1.0 0.5

Final takeoff climb speed

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Rwy Perf 1/page 2.

Commuter vs Normal Category Aircraft - refer CAO 20.7.1b para 7.2.1 (a) Aircraft certificated as commuter category have some different performance requirements to those under the normal category. Exercise care when reading ATPL exam questions to identify the aircraft category. Aircraft certificated as commuter type, need only must achive a gross gradient of 2.0% in second segment. The usual deductions apply to find the net climb - refer CAO 20.7.1b, para 7.5. Although 400 ft above the takeoff surface is the minimum height for the start of the acceleration segment, many airlines specify a greater height in their standard operating procedures within the AFM. Not all aircraft need to fly level to accelerate to flap retraction speeds. Todays jet and turboprop aircraft are if anything a little over-powered, NOT under-powered as was sometimes the case in earlier models. All this talk of guarantee climb gradients assumes you have selected the correct maximum takeoff weight in the first place, and NOT taken off overweight. En-route Climb Performance (refer CAO 20.7.1b) Three and four engine aircraft are assessed as having one or two engines inoperative, whereas twin engine aircraft are only assessed as having the most critical of the two engines inoperative. Gross climb gradient found taking into account weight, altitudes, and expected temperatures (WAT). For the one engine inoperative case the gross climb is reduced by 0.8% for twin engine aircraft, 0.9% for three engine aircraft, and 1.0% for four engine aircraft to find the net climb gradient. For the two engine inoperative case the gross gradients found are reduced by 0.3% for three engine aircraft and 0.4% for four engine aircraft. En-route Obstacle Clearance Requirements (refer CAO 20.7.1b, para 12.4) If the departure airport is continuously below alternate minima, a suitable alternate must be nominated, as this will effectively rule out a circuit and landing at departure in the event of an engine failure after V1. Operationally then, an engine failure after V1 will effectively mean flight to the airport nominated as the engine failure alternate, and it is highly desirable to be able to clear the terrain en-route to there. If VMC, the flight must clear all obstacles within 5 nm either side of track by at least 1, 000 ft. If IMC, such greater lateral distance determined by the accuracy of the navigation aids used. At the pressure altitude (ie: flight level) needed to maintain 1, 000 ft clearance of en-route obstacles, the flight path must have a positive slope with one engine inoperative for twins, and two engines inoperative for 3 and four engine aircraft. Driftdown (refer CAO 20.7.1b, para 12.5) If the aircraft performance is such that it cannot comply with para 12.4 (ie: no positive flight path slope available), a driftdown procedure can be used. The aircraft may descend to its engine failure cruise flight level, provided a 2, 000 ft clearance of obstacles is possible. Arrival at destination or alternate airport (refer CAO 20.7.1b, para 12.6) It must be possible that at the GW on arrival with one engine inoperative, (or two engines in the case of 3 and 4 engine aircraft) a missed approach is possible from 1500 ft above the airport elevation. The CAO describes the flight path must have a positive slope. Calculating ROC required to meet gradients The simple way to calculate the rate of climb that is required to achieve the gradient required is to multiply the groundspeed by the net gradient percentage. Eg: Twin engine aircraft second segment rate of climb (RoC) required. Given groundspeed of 120 kt. RoC required is 120 kt x 1.6% = 192 ft/min. Eg: Four engine aircraft first segment rate of climb required. Given groundspeed 150 kt. RoC required is 0.5% x 150 kt = 75 ft/min.


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Rwy Perf 1/page 3.

Obstacle Clearance After Takeoff

Abridged article by Neville Probert (CASA) from Flight Safety Australia.

If an engine failure is detected after reaching V1, the takeoff is continued because the runway length remaining is insufficient to allow the aircraft to be brought to a stop on the runway. In this situation the aircraft could be at risk of colliding with obstacles or terrain beyond the end of the runway. In Australia, there are two classes of aircraft that are required to be capable of clearing obstacles following the failure of an engine during takeoff. Modern aircraft with a maximum takeoff weight (MTOW) in excess of 5, 700 kg (refer subsection 12 of

CAO 20.7.1b) Aircraft whose takeoff weight exceeds 3, 500 kg, but is not greater than 5, 700 kg, and which are being

operated in regular public transport (RPT) operations ... refer CAO 20.7.1b sub-paragraph 4.1.1. To determine the obstacle-limited takeoff weight from a particular runway, you need to obtain the data relating to obstacles beyond the end of that runway. There are several sources of this type of information, the most readily available in Australia being the Runway Distances Supplement in the En-Route Supplement Australia (ERSA). Obstacle clear gradients The Runway Distances Supplement does not present detailed information about the height and position of any obstacles. Instead it shows the gradient of the Obstacle Clear Surface. An obstacle clear surface is an imaginary plane which is laid into the takeoff area beyond the end of the runway until it first contacts an obstacle (refer Fig 1). The gradient of this obstacle clear surface is published in the Runway Distances Supplement (RDS). For example, below is part of the RDS information for Albury in

Rwy TORA TODA ASDA LDA

07 1900 m (6334 ft) 1990 m (6529) 2.42% 1900 m (6234 ft) 1900 m (6234 ft)

25 1900 m (6334 ft) 1990 m (6529 ft) 1900 m (6334 ft) 1900 m (6334 ft)

With no wind, the runway limited takeoff weights would be the same for both runways. In this situation, a takeoff on runway 07 would be preferable because it provides a greater obstacle limited takeoff weight than does runway 25, simply because of the lower obstacle clear gradient on runway 07. The Flight Manuals contain information about the weights at which the aircraft, with one engine inoperative, can achieve in a range of climb gradients.

This shows that runway 25 is 1990 m in length, and beyond the runway there is 90 metres of clearway. The obstacle gradient from the end of the clearway on Rwy 07 is 2.42%. Note that the obstacle clear gradient from the end of the other runway is 3.09%. Clearly there is an obstacle beyond the end of runway 25 that is of greater significance than those beyond the end of runway 07.

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Rwy Perf 1/page 4. Copyright Avfacts 1999. All rights reserved.

By entering suitable Flight Manual Charts with airport elevation, temperature, runway wind component, and obstacle clear gradient, it is possible to find the obstacle-limited takeoff weight (i.e. the climb limit weight). This is the highest weight that the aircraft, with 1 engine inoperative, can be assured to fly parallel to the obstacle clear surface and therefore be assured of avoiding obstacles and terrain. STODA (Supplementary Takeoff Obstacle Distance Available) STODs are assessed at the following standard gradients: 1.6%, 1.9%, 2.2%, 2.5%, 3.3%, 5.0%. STODA data is only produced/published for runways longer than 800 metres (refer to ERSA INTRO page 16). In the case of Albury, NSW, the RDS presents the following information about STODAs:

RWY 07 1190 m (1.6%) 1560 m (1.9%) 1800 m (2.2%)

RWY 25 997 m (2.5%)

The obstacle clear gradient associated with the full length of runway 07 (ie: 1800 m) is 2.42%, but an obstacle clear gradient of 2.2% is available with a reduction in TODA from 1990 metres to 1800 metres. Similarly, obstacle clear gradients of 1.9% and 1.6% are available with takeoff distances of 1560 m and 1190 metres respectively. This information gives an operator or pilot using runway 07 four options (the TODA and the three STODAs) for determining the most advantageous matching of runway limited takeoff weight and obstacle limited takeoff weight. Paragraph 12.3 of CAO 20.7.1b requires only that the pilot in command take account of one of the obstacle clear gradient published in the RDS. Namely twin engine aircraft planning to account for only 1.6% gradient, and 3 engine aircraft for only the 1.9% gradients where published. Some runways will NOT have published figures that relate to your aircraft, so no obstacle clearance limit (STOD) exists, and full runway length can be considered available for takeoff in this case. These gradients are NOT guaranteed to provide clearance throughout the climb to minimum sector altitude (MSA), or circuit height. Curved departures (refer CAO 20.7.1b, para 12.1) Should the terrain off the end of the runway be limiting to a straight departure after takeoff, a curved departure may be planned assuming terrain is not limiting there also. If a curved departure is planned of a dry runway, the aircraft must be 50ft above all obstacles before the turn commences, the turn can be left or right with a bank angle not in excess of 15 degrees. All obstacles within the specified flight path safety zone either side if the aircrafts curved flight path must be cleared by 50 ft. Remember this is 50 ft above the net flight path, and it is a greater height than the straight departure largely because one wing is low in the turn. If an engine failure is recognised at or after V1 (wet) during take-off from a wet or contaminated runway, the net flight path may clear obstacles by less than 35 feet, or, during a turn, by less than 50 feet. Obstacles further than 3000 metres It is vital to recognise that the obstacle clear gradients published in the RDS are based on obstacles and terrain within a finite distance from the runway. For some runway, the published gradient is based on obstacles within 3000 metres of the end of the runway. There may be significant obstacles or terrain beyond 3000 metres that present a greater obstacle clear gradient than the one published. For all other runways the published gradients only include obstacles and terrain within 7500 m, or 15000 m of the runway end (refer ERSA INTRO page 16). For more comprehensive obstacle data you should refer to other sources of information. In the event of an engine failure followed by continued takeoff (ie: failure occurring at or after V1), you should account for the large climb performance degradation, and extra ground miles covered to MSA, or circuit height. A curved departure may be required to allow a reasonable takeoff weight to be achieved, and guarantee that all obstacles can be cleared.

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Now attempt the appropriate performance assignment.

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Rwy Perf 1/page 5.

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