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Refer to figures or CAP 758 Figures 2.3 and 2.19.
Determine VNE at the engine critical altitude, if the helicopter's All-Up-Mass with doors-off configuration is 2 000 lb, flying in ISA conditions.

  • A
    84 KIAS
  • B
    95 KIAS
  • C
    84 KTAS
  • D
    95 KTAS

Refer to figures.
1. From Figure 2.19, we get that the Engine Critical Pressure Altitude is at 4 200 ft. It is where the power available starts to reduce, so the rate of climb for a constant mass decreases.

2. From Figure 2.3, we get the VNE for a density altitude for two masses with the doors on and doors off. The doors being off will increase parasite drag, but more importantly will cause disturbed airflow which reduces the VNE:

  • In ISA conditions, the pressure altitude is equal to the density altitude.
  • Enter from the left side with the density altitude 4 200 ft and move horizontally to the right.
  • For AUM 2 000 lb, intersect the "GROSS MASS > 1 700 lb" line and continue vertically down to read the VNE: 84 KIAS.

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