:: Flying Way :: - “DRIFT DOWN”

INTRODUCTION
As the airplane climbs to a higher altitude; a higher
thrust is required to maintain that altitude.
When an engine failure occurs during cruise at high
altitudes, the thrust available becomes suddenly less
than the thrust required to maintain that altitude.
As a result, the airplane must descent to a lower
altitude, where the available thrust is equal to the
required thrust to allow the airplane to level off.
GROSS LEVEL OFF ALTITUDE
It is the actual altitude flown by the aircraft after the
engine failure. It is calculated based on: weight,
altitude, ambient temperature, unfavorable CG, critical
engine, and continuous thrust rating (FAR25.123).
NET LEVEL OFF ALTITUDE
It is the gross level altitude degraded by 1.1%, which is
used by regulations for flight planning and terrain
clearance.
ROUTE STUDY:
For any new route, a engine failure study must be made
in order to ensure its safe operations or define the
critical points in case of engine failures during cruise.
Within five statue miles of the intended track:

Condition 1
The net level altitude for the most conservative weight
is higher than the highest obstacle enroute +1000 ft.
not then condition 2 takes place.
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Condition 2
Identify the critical points on the route where
level altitude for the most conservative weight
clear all obstacles enroute by a minimum of 2000 ft.
critical points can be:
a) no return point:
passing this point, the turn
clear the obstacles by 2000 ft.
b) continuing point:
passing this point, the continuation
possible to clear all obstacles by 2000 ft.
In case the no return point is located
continuing point, the area bet
be used to return or to continue the flight

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But in case the no return point is located before the
continuing point, a diversion route or procedure must
be established, less weight is considered, or

route is to be considered

”

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F.O HASHIM HASHIM