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## ETD question

• Posts: 5

### SteveS created the topic: ETD question

Hi all,
Stumbled upon this question and thought I'd get some clarification in here.

Q: An aircraft is scheduled to depart aerodrome XX at 1200 UTC for aerodrome YY, which requires an alternate. Flight time to the destination YY is 1hr and 15mins and the flight time to the alternate ZZ is 40mins. If the aerodrome forecast for ZZ expires at 1500 UTC, the latest time the aircraft can depart XX is:

A. 1205 UTC
B. 1255 UTC
C. 1305 UTC
D. 1405 UTC

Answer is A. The answers quote an AIP reference of ENR 1.10 1.2.5 which is: '......a pilot must ensure forecasts are valid for a period of not less than 30mins before and 60mins after the planned ETA....'

If someone could kindly show working and explain why the answer is A it would be greatly appreciated.

• Posts: 2261

### bobtait replied the topic: ETD question

This question is not one of ours. However the answer (a) is obviously not correct. All you have to do is subtract the total flight time plus 60 minutes from the expiry time of the TAF.

Bob

• Posts: 6

### Kerrylee replied the topic: ETD question

To get Answer A it seems to work out latest time can leave working backwards as follows:

Forecast expiry 1500 - 60min buffer = 1400 UTC
1400 - 1hr 55min total flight time (1hr 15min + 40min alternate)