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Refer to figure.
Prior to an oceanic crossing the flight crew review their one engine inoperative level-off heights at key points along their route. With the conditions listed below, what is the maximum one engine inoperative net level-off height?

Expected Gross Mass: 66 000 kg
Temperature: ISA+15°C
Long Range Cruise speed (LRC)
Engine anti-ice: ON

  • A
    17 800 ft
  • B
    19 000 ft
  • C
    20 200 ft
  • D
    20 600 ft

Refer to figure.
If an engine fails in the cruise, the remaining engine(s) are set to maximum continuous thrust, in an attempt to maintain height. At cruise altitudes, the attempt to maintain height usually fails, because of inadequate thrust on the remaining engine(s) and the aircraft will descend down to a height at which it is able to stabilise. This is called "driftdown".

This is a quite straightforward graph, which helps to find the maximum one-engine inoperative net level-off height for different temperature conditions and configurations:

1. Enter with the expected gross mass 66 000 kg and draw a vertical line upwards, until intersecting the ISA+15ºC dotted curve (dotted curves are for LRC, while bold lines for Green Dot speeds.
2. Continue horizontally to the left and read the net level-off height FL 190.
3. Correct for Engine Anti-Ice-ON at ISA+15ºC: 19 000 ft - 1 200 ft = 17 800 ft.

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