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Performance Question
Sunny11
Topic Author
Sunny11 created the topic: Performance Question
Hi,
I need help working this question.
A certain multi engine aeroplane has a max single engine service ceiling of 7000ft density height. The altitude you would expect it to be able to maintain on a day when the QNH is 1001 hpa and the ISA deviation is +20 ?
ISA + 20 does not mean that the temperature is 20°. It means that the temperature is 20° hotter than the temperature you would expect in ISA at that height. Every one degree of deviation from ISA, causes a density change equivalent to a height change of 120 feet. So ISA+20 would mean that the density height is 2400 feet greater than the pressure height.
If it is ISA +20, it means that 20 x 120 [2400] was added to the pressure height to get the density height.
So the pressure height must have been 7000 - 2400 = 4600 feet.
The QNH of 1001 means that 12 x 30 [360] was added to the altitude to get the pressure height.
So the altitude must have 4600 - 360 = 4240 feet.
