getting to grips with aircraft performance 如何掌握飞机性能 1(44)

Any route study should be conducted by checking one of the following two vertical clearance conditions. When Condition 1 cannot be met, or when it appears to be too penalizing in terms of weight, a detailed study must then be carried out based on Condition 2.
2.2.2.1. Condition 1 : 1,000 feet clearance margin
“JAR-OPS 1.500
(b) The gradient of the net flight path must be positive at at least 1,000 ft above all terrain and obstructions along the route.” (Figure D4)

A-Methodology, in case of an Engine Failure in Climb
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Determine the location of the start of the en route flight path in the worst conditions.

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From a topographic map select, in the regulatory corridor, all the constraining obstacles that must be cleared during the climb phase. Plot these obstacles on a graph, with their distance from the start of the en route flight path (horizontal axis) and their height (vertical axis).

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From the AFM, determine the climb net flight path for a conservative weight (for instance, use the maximum certified takeoff weight), and for conservative meteorological conditions. Plot it on the previous graph.

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Conclusion:

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If the net flight path clears each obstacle with a margin of at least 1,000 feet, the route study is finished and obstacle clearance is ensured at any moment during climb.

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If the net flight path doesn’t clear at least one of the obstacles by 1,000 feet, reduce the takeoff weight and recalculate the net flight path until the previous condition is checked. If it is not possible, establish a new diversion procedure1.

B- Methodology in case of an Engine Failure at Cruise Level
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From a topographic map, determine the highest obstacle in the regulatory corridor and add 1,000 feet to obtain a height H1.

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From the AFM, determine the net drift down ceiling (H2) at a conservative weight. For instance, choose the heaviest possible aircraft weight at the entrance of the constraining area.

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Conclusion:

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 If H2 is higher than H1, the route study is completed and the obstacle clearance is ensured at any moment.

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 If H2 is lower than H1, then a more detailed study based on Condition 2 shall be conducted, or a weight limitation at takeoff established, or a new route found.

2.2.2.2. Condition 2 : 2,000 feet clearance margin
Condition 2 concerns the case of an engine failure during the cruise phase. When Condition 1 is not met, or when it is too limiting in terms of weight, a drift down procedure should be worked out, as detailed below:

“JAR-OPS 1.500
(c) The net flight path must permit the aeroplane to continue flight from cruising altitude to an aerodrome where a landing can be made, […] clearing vertically, by at least 2,000 ft all terrain and obstructions along the route within [the prescribed corridor].” (Figure D5).
　
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