getting to grips with aircraft performance 如何掌握飞机性能 1(43)

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Two hour flight time at a one-engine-inoperative cruising speed in still air for four engine aircraft.

When it is not possible to return, the flight must be pursued to the takeoff alternate airport, and the en route configuration1 achieved after a maximum of 10 minutes from the brake release point. As a result, the drift down climb phase starts at the end of the takeoff flight path. To reach the takeoff alternate airport, the obstacle clearance must be ensured, in accordance with the following paragraph:
2.2. En route Obstacle Clearance – One Engine Inoperative
2.2.1. Lateral Clearance
Obstacle clearance must be ensured throughout the route, in case of an engine failure. The problem is to clearly identify which obstacles must be cleared. Regulations indicate which obstacles must be taken into account:

“JAR-OPS 1.500
(c)
The net flight path must permit the aeroplane to continue flight from the cruising altitude to an aerodrome where landing can be made […] clearing […] all terrain and obstructions along the route within 9.3 km (5 nm) on either side of the intended track”

(d)
[…] an operator must increase the widths margins […] to 18.5 km (10 nm) if the navigational accuracy does not meet the 95% containment level2.” (Figure D3).

Note that the FAR regulation is quite similar, except that it requires a lateral margin of 5 statute miles on each side of the intended track. Moreover, it stipulates that a “different procedure” approval is needed, when the aircraft is further from the nearest approved radio navigation fix than from the critical obstruction it has to pass over.
To carry out a detailed route study (engine failure case), a topographic map shall be used and the highest obstacles inside the required corridor width determined.
Another, less time consuming, but less accurate method, consists of using the
1 En route configuration = clean configuration, green dot speed, Maximum Continuous Thrust 2 The 95% containment level is generally achieved if the aircraft navigational system has been updated within two hours, or if the aircraft is equipped with GPS primary.

published Minimum Flight Altitudes which already account for a margin of 2,000 feet on the obstacles (refer to the “Minimum flight altitude” section of this chapter).
2.2.2. Vertical Clearance
Vertical clearance shall always be understood as a margin between the net flight path and the obstructions. The en route net flight path shall be determined from the Aircraft Flight Manual, and must take into account the meteorological conditions (wind and temperature) prevailing in the area of operations. Moreover, if icing conditions can be expected at the diversion level, the effect of the anti-ice system must be considered on the net flight path.
　
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