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CNAV Passed - Question

  • Aaron
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Aaron created the topic: CNAV Passed - Question

G'day guys,

I passed Nav today which leaves me 2 more exams to do (Air Law and Performance).

I had a question in the exam today that went something like this:
"You arrive overhead your destination aerodrome at 2105UTC, but due to low cloud in the circuit area, you are unable to land and are required to hold. Your safe endurance (excluding reserves) is 110 minutes. Your flight time to your alternate aerodrome is 40 minutes and you require 30 minutes holding. What time can you leave your destination aerodrome for your alternate?"

Now what I did was add the 40 minutes flight time to the 30 minutes holding, to give you 70 minutes. Therefore 110-70 = 40 minutes. So, 2105+40 = 2145UTC

I'm not sure if I did it correctly, but I would like some piece of mind :)

Cheers,
Aaron
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Richard replied the topic: CNAV Passed - Question

Hi Aaron,
That sounds good to me but only assuming they didn't give you any other information on holding and cruise fuel flows. With only a safe endurance value, you would have to work it out the way you described.
In real life, you would not be holding at cruise power setting but rather at something closer to max endurance. In that case, if it was really coming down to the wire, you could work out how *much* fuel you needed to get to your alternate (at cruise) and also hold there (with hold power) for 30 minutes, subtract that from your current flight fuel available to get an amount you could burn in the hold and then work out how long that will last using hold power. You would find it to be significantly longer than simply calculating on cruise power settings.
Cheers,
Rich
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  • Aaron
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Aaron replied the topic: CNAV Passed - Question

G'day Rich,

From what I remember, the safe endurance was all I was given. So no cruise fuel flows etc

That gives me some piece of mind

Cheers
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