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4 Answers

Approval to deviate from desired track due to weather

Asked by: 3562 views Airspace

Can anyone advise me of what the procedure is for airline pilots on deviating from their desired track ( hazard avoidance ) due to weather. ( lets say a developed CB )?  Would approval need to be requested and if so how many nautcal miles off track can the aircraft deviate until approval is needed?

Thanks everyone and happy flying. 

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4 Answers

  1. Jim Foley on May 02, 2012

    “St. Louis approach, American 1, request”
    “American 1, St. Louis approach, go ahead.”
    “American 1 needs to deviate 3-0 degrees to the right for weather avaidence”
    American 1, approved, 3-0 degrees right to heading of XXX for weather”
    Or something like that.  It’s just like any other radio conversation.  Sometimes, depending on the situation, the deviation might cut off part of their STAR or DP, and shorten what the need to to, in which case they might approve them to head direct to a fix that is farther down the sequence.  It’s really just a case-by-case situation, all dependant on type/speed of aircraft, other traffic, where they are, ect…

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  2. John D. Collins on May 02, 2012

    Any pilot can request a deviation due to weather or other reason.  There are no defined maximum limits.  I asked for a deviation to the north of a bad frontal system while flying between Dallas and Charlotte and it was granted. The deviation was over a hundred miles and lasted for at least three quarters of my flight. ATC is very receptive to such requests. I have never been denied, although it might be possible due to traffic.  Usually there are other options, such as turning around, changing altitude, or diverting to a nearby or other airport.  If push came to shove, the pilot in command is ultimately responsible for the safety of the flight and could declare an emergency if needed.

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  3. Matthew Waugh on May 02, 2012

    So as mentioned – you just ask. It’s a negotiation, you might ask to go right, ATC might say you can go left, but in the end you can’t fly through a thunderstorm, so you gotta go round.
    You need approval for ANY deviation – now sure, in theory, there are tolerances within the navigation systems, so you COULD deviate within those limitation without approval IF you knew how accurate you were within the tolerances anyway. But you probably don’t know any of that, so deviating without permission has it’s risks.

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  4. Patrick Flannigan on May 02, 2012

    Everybody is right on here. But do remember that as PIC, you are the final authority as to the safety of flight, not ATC. If you need to deviate, make a request early as it sometimes takes a moment for ATC to get approval.
    But do not allow ATC to fly you into anything dangerous, like a thunderstorm. Be courteous, but make it clear that you need that deviation. And if it comes down to the wire, just turn and let ATC know you’re doing it. Nobody but the C-130 Hurricane Chasers have any business inside a T-Storm.

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