Appendix G Figure G-2. Plot to Determine VMCA
Fna - lbs.
3000 2950 2900 2850 2800 2750 2700 2650 2600
80.5 KEAS 2820 lbs 60 80 100 120 140 160 Ve - kts.
G.1.6 If the force limited VMCA value is high enough to adversely impact the takeoff speed schedule, it can be reduced to an acceptable value by derating takeoff power or thrust.
For example, if the standard day rudder force (FRs) was 140 lbs on an amendment 25-42 airplane, the maximum allowable asymmetric takeoff thrust would be:
G-4
05/04/18
AC 25-7D Appendix G G.1.7 Using the same maximum asymmetric thrust available versus airspeed as before:
Figure G-3. Plot to Determine VMCA for an Amendment 25-42 Airplane
3000 Fna - lbs.
2950 2900 2850 2800 2750 2700 2650 2600 172 KEAS 2686 lbs 60 80 100 120 140 160 180 200 Ve - kts.
G.1.8 Because of the shallow thrust lapse rate with airspeed, the force limited VMCA for these conditions would be 172 knots, which is obviously unacceptable. To reduce this value back to 80 knots (or any other speed), takeoff thrust should be derated to a level that provides a maximum asymmetric thrust value of Fna MCAmax at the desired V (80 knots in this example). The amount of derate required can be determined from the following plot:
G-5
Appendix G Figure G-4. Plot to Determine VMCA for Derate Thrust
3000 Fna - lbs 2900 2800 2700 2600 2500 2400 Maximum Thrust Derated Thrust (5%) 80 KEAS 2686 lbs 50 100 150 200 Ve - kts G.1.9 For a given weight and bank angle, rudder pedal force is determined solely by asymmetric thrust; consequently, takeoff thrust should be limited to a value that results in a pedal force no greater than 150 lbs (180 lbs prior to amendment 25-42).
G-6
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