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Conclusion: 

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. 

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 

From a topographic map, determine the highest obstacle in the regulatory corridor and add 1,000 feet to obtain a height H1. 

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. 

Conclusion: 

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

 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). 

At any point of a critical area on the route, it must always be possible to escape while ensuring, during descent, the relevant obstacle clearance margin of 2,000 feet on the net flight path. The following three escape procedures are available: Turn back, Divert, or Continue. 

1 This study mainly concerns the case of a diversion to a takeoff alternate airport 

Methodology in case of an Engine Failure at Cruise Level 

Identify the critical points on the route: A critical point is a point at which, if an engine failure occurs and if the aircraft initiates a drift down, the net flight path clears the most penalizing obstacle by the minimum margin of 2,000 feet. The aircraft weight at each critical point is assumed to be the highest possible weight that can be expected at that point in the most penalizing meteorological conditions. A critical point can be : 

A no-return point (A): Point after which it is not possible to turn back, otherwise the 2,000 feet obstacle clearance margin on the net flight path would not be met. 

A continuing point (B): Point after which it is possible to continue on the route because the 2,000 feet obstacle clearance margin on the net flight path is ensured. 

Select, in the regulatory corridor, all the constraining obstacles that must be cleared during the drift down and plot these obstacles on a graph, with the distance as the horizontal axis and the height as the vertical axis. 

From the AFM, determine the returning net flight path1 and the continuing net flight path, taking into account the most adverse wind conditions. For that purpose, use a conservative initial weight (for instance, choose the heaviest possible aircraft weight at the entrance of the constraining area). Plot the net paths on the previous graph so that the most penalizing obstacles are just cleared with the minimum margin of 2,000 feet. 

Conclusion: 

If the no-return point (A) is obtained after the continuing point (B) (Figure D6), the procedure should be as follows, unless another procedure is found to be more appropriate (closer diversion airport, safer escape procedure…). If the engine failure occurs: 

Before B: Return . After A: Continue . Between A and B: Either return or continue 

1 The returning net flight path takes into account the altitude and time lost for turn back. 

If the no-return point (A) is obtained before the continuing point (B) (Figure D7), the procedure should be as follows, unless another procedure is found to be more appropriate. If the engine failure occurs: 

. Before A: Return 

. After B: Continue 

. Between A and B: Establish an escape procedure, ensuring the relevant obstacle clearance margin. If it is not possible, consider a weight reduction at takeoff. If the weight reduction is too penalizing, consider another route.