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8 Answers

ATC instructions! Which instruction is the first ?

Asked by: 1789 views
Commercial Pilot, General Aviation, Private Pilot, Student Pilot

Hi folks,

I have 2 questions :


1- when you instructed by Atc : " decsent and maintain 3000, turn ritgh heading 270, QNH 1012 " . What is the sequence to do this instruction ? Decending first ? Or turn first ? Or change the QNH then decsnd ? " 

2- whats rhe diffence between requestion " a flight following " to a certain destination and requesting " Radar vectoring " ? 


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8 Answers

  1. Robert Jankowski on Aug 14, 2016

    1) All three at once, it would make the most sense to adjust the altimeter setting and then start a descending turn to the new heading and altitude.

    2) Flight following is the pilot doing their ‘own navigation’ whereas requesting radar vectoring is asking the ATC facility for a heading to the fix/destination.

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  2. John D Collins on Aug 14, 2016

    You are expected to do all as simultaneously as practical, but usually turning is the easiest to initiate. While turning, I would start the descent, as it takes more time to set your power and pitch to establish the descent. Finally, I would adjust the altimeter setting as it does not affect the initial action requested by ATC and is just an adjustment you want to have made if needed before you reach your new altitude.

    I would use the same sequence if I was using the autopilot. First set the heading bug and engage heading mode. Then set your new selected altitude, set your new AS or your VS bug and engage the altitude change, and adjust your power to descent power. Verify that your descending turn is initiated and then adjust your altimeter setting.

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  3. eversamh on Aug 15, 2016

    Thanks Robert and John for the answer, but I belibe changing the QNH should be first, I fly between 2 cities ( 125 nm ) usually the ATC gives the low altitude for this route 5,000 to 7000 msl and the departure airport is 1870 msl and the arrival ones is 2100 msl, but the QNH is really vary between the 2 airports, for example in the departure one usually 1012/3 in the arrival always below 900 . I belive changing the altimeter would come first because of the low near altitude and the variation in QNH. What do you advise ? Or what is the best practices you know as CFIs ?

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  4. Best Answer

    Russ Roslewski on Aug 15, 2016

    I highly doubt your QNH values are routinely less than 900, as that would be in an extremely strong hurricane.

    Regardless, I’m not sure why setting your QNH (or starting a turn, or starting a descent) takes long enough that it becomes a factor whichever order you do them.

    The most logical to me would be start the turn first, then start the descent, then work on setting QNH. You probably have at least a couple minutes of descent before worrying about leveling out, but how long does it take to set QNH? A few seconds? Shouldn’t really matter at all the sequence of events, as long as you get them all done promptly.

    Determining the best order is really splitting hairs.

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  5. eversamh on Aug 16, 2016

    @Russ Correction below 1000 . And thanks for answering both questions .
    @John thanks too for your very clear answer .

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  6. Mark Kolber on Aug 18, 2016

    I agree with John’s answer and it is what I do as well. Turn, descend, take care of the altimeter setting. Seem to be the most reasonable combination.

    But just a thought: The question makes it sound like there is a great rush to do these three things. That something terrible will happen if the are done in the “wrong” order. That’s also the net thrust of eversamh’s comment. Sure, it would be a big deal if you were being asked to descend to 3,000 from 3,200 at the same time as you receive the new QNH different enough to make a 1,000 difference, but how typical is that?

    It won’t. And it’s not. Unless the instruction includes “expedite” or “immediate” there is plenty of time for all three at a reasonable pace, in any order you want.

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  7. Heather McNevin on Aug 18, 2016

    There may be a time where the controller wants something done before something else. In that instance it would be something like “Turn left heading 270 then climb and maintain 7,000” if I want you on that heading prior to the altitude change. Often, with ATC phraseology, the devil is in the details. Always pay attention to the instructions. Usually if I issue a heading and an altitude with an altimeter setting, I expect all will begin relatively quickly and happen simultaneously.
    One note of caution, as a controller, my weather (including altimeter settings) update only once every 75 minutes. As a pilot, I prefer local altimeter settings I get from AWOS or such prior to an approach rather than rely on what might be around an hour old.

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  8. eversamh on Aug 22, 2016

    @Mark you read my mind actually thank you for the answer , thanks Heather too .

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