getting to grips with aircraft performance 如何掌握飞机性能 1(42)

Green dot
Engine failure Drift down ceiling (MCT)
Green dot Drift down ceiling
Engine failure
(MCT)

Figure D1: Drift Down Procedure (Climb and Descent)
Green dot speed, indicated by a green circle on the primary flight display (PFD), represents the best lift-to-drag ratio speed, where aerodynamic efficiency is maximum. As a consequence, the drift down strategy is the procedure enabling the highest possible altitude to be achieved versus the distance covered.
2.1.2. Gross and Net Drift Down Flight Paths
JAR 25.123 Subpart B  FAR 25.123 Subpart B
2.1.2.1. Gross Drift Down Flight Paths
The Gross Drift Down Flight Path is the flight path actually flown by the aircraft after engine failure (Figure D2). Regulations require that operators be provided the with drift down performance information, as stated below:
“JAR/FAR 25.123
(a) For the en-route configuration, the [gross drift down] flight path must be determined at each weight, altitude, and ambient temperature […]. The variations of the weight along the flight path, accounting for the progressive consumption of fuel […] by the operating engines, may be included in the computation. The flight paths must be determined at any selected speed, with:
.  
The most unfavourable centre of gravity

.  
The critical engine inoperative”

2.1.2.2.  Net Drift Down Flight Path
The Net Drift Down Flight Path represents the Gross flight path minus a mandatory reduction (Figure D2).
1 Drift down ceiling = maximum altitude that can be flown at green dot speed (level off)
“JAR/FAR 25.123
(b)
The one-engine-inoperative net flight path data must represent the actual climb performance diminished by a gradient of climb of

.  
1.1% for two-engined aeroplanes

.  
1.6% for four-engined aeroplanes.”

(c)
The two-engine-inoperative net flight path must represent the actual climb performance diminished by a gradient of climb of

.  0.5% for four-engined aeroplanes.”
Net Gradient = Gross Gradient – Gradient Penalty
Gradient penalty
Two-engine aircraft Four-engine aircraft
Net flight path (one engine out) 1.1%
1.6%
Net flight path (two engines out) -
0.5% Table D1: Gradient Penalties Between Gross and Net Drift Down Flight Paths
Green dot 
Gross flight path  Drift down ceiling  Engine failure (MCT)  Gross Flight Path 
Green dot  Net flight path 
Drift down ceiling 
Net Flight Path 
Engine failure (MCT) 

Figure D2: Gross and Net Drift Down Flight Paths (Climb and Descent)
2.1.3. Takeoff Alternate Airport
JAR-OPS 1.295 Subpart D  FAR 121.617 Subpart U
If an engine failure occurs during the takeoff phase, the preferred option is generally to turn back and land at the departure airport. When the landing requirements are not met, for meteorological or performance reasons, it is necessary to plan a takeoff alternate airport, which shall be located within:
　
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