Refer to figure or CAP 758 Figure 3.17.
Given the following information, calculate the height loss, if the TETH commenced a driftdown procedure, after having suffered an engine failure:
Engine failure pressure altitude: 11 000 ft
Mass at the start of driftdown: 7 250 kg
Refer to figure.
If the helicopter, after an engine failure, cannot maintain its altitude with the remaining engine(s) at Maximum Continuous Power (MCP) setting, then a "drift down" procedure is commenced. The altitude at which a driftdown may commence varries. It may be a high or a lower cruising altitude, depending each time on the margin between its power required and power available, which is determined by its mass and the ambient conditions.
To determine the height loss after an engine failure of the TETH, proceed as follows:
- Enter with Engine failure pressure altitude 11 000 ft and move horizontally until crossing the Mass at the start of driftdown 7 250 kg line (1).
- Continue parallel with the 7 250 kg line until the reference line (2).
- Move horizontally to the left until exactly below the intersection with the Mass at the start of driftdown 7 250 kg line (3).
- Extend the line beyond (3) to the left, until the Pressure Altitude vertical scale and read the stabilising Pressure Altitude: 9 100 ft.
- The differene between the Engine failure pressure altitude 11 000 ft and the Stabilising pressure altitude 9 100 ft is the Height Loss: 1 900 ft.
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