Engine out · the terrain below the cruise
Build a net drift-down path and find where the aircraft can stabilise.
Where will the aircraft go after an engine fails?
If remaining maximum continuous thrust cannot support level flight, the aircraft must decelerate/reconfigure as prescribed and descend toward an engine-out stabilising altitude. The selected drift-down speed is the approved schedule that balances drag, descent and terrain clearance; it is not automatically maximum-range cruise or the fastest available speed.
The existing level may be unsustainable
If remaining maximum continuous thrust cannot support level flight, the aircraft must decelerate/reconfigure as prescribed and descend toward an engine-out stabilising altitude. The selected drift-down speed is the approved schedule that balances drag, descent and terrain clearance; it is not automatically maximum-range cruise or the fastest available speed.
Deceleration initially releases kinetic energy and can delay height loss, but it also consumes distance and time. A steady-state descent line cannot represent that transient without the prescribed method. Greater mass, higher temperature, icing, bleed use, failed-engine drag, wind and turns can lower the net terrain clearance or stabilising level.
Choose the correct regulatory route
Class-A CAT OEI net en-route path data apply the CS-25 gross-to-net decrements: 1.1, 1.4 and 1.6 percentage points for two, three and four engines. CAT.POL.A.215 permits the specified positive-net-gradient route at 1,000 ft above terrain/obstacles, or the drift-down route clearing relevant terrain/obstacles by at least 2,000 ft while continuing to a suitable aerodrome, subject to all conditions.
The ordinary lateral accountability is 9.3 km (5 NM) each side of track, increased to 18.5 km (10 NM) where at least RNAV 5 navigation accuracy cannot be met. The net path must also have a positive gradient at 1,500 ft above the aerodrome at which landing after engine failure is assumed. Account for expected winds and temperatures, fuel burn, and a critical failure point. Landing mass and approach requirements at the diversion aerodrome still matter. Fuel jettison, where available, is only used under the authorised assumptions/procedure.
Can you make the performance decision?
Four original questions. Work from the stated conditions and review the reasoning.