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As a pilot of a small single engine plane, what do we do if ATC instructs us to expedite our climb/descent and doing so would be impossible or unsafe (i.e. we're already at the maximum safe rate of climb/descent)?

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You report unable, and ATC will come up with a different plan.

To provide some context: If I ask you to expedite a vertical manoeuvre, it is probably because you are on crossing tracks with another aircraft, and I want you to pass them either above or below. This could be to meet certain level restrictions, or simply because I want to provide you with continuous climb/descend as a service. At your current rate, you will probably pass them, bot not quite with the 1000 ft vertical separation I need. Because you are so close to fitting into my plan, asking you to expedite is the easiest - it requires the least effort from me, and I won't have to vector you around, giving you a longer than needed flight path.

If you respond with unable, I have other options to choose from, depending on the situation. Typically I would either instruct you to level off or turn. If you are descending through FL160 and I wanted you to go below someone at FL130, I would simply instruct you to level off at FL140, and then descend you further when you are clear, which would only take a few minutes. I could use the phrase "Stop descend FL140, expect further descend in 3 minutes", in which case you could adjust your vertical rate so that you reach FL140 about 3 minutes in the future, resulting in a smooth descend. Alternatively, a turn of 20-30 degrees is often enough to establish lateral separation, which then allows you to descend unrestricted. 3 or 4 minutes later, when you have passed the other traffic, you will be turned back on your track.

The key thing here is communication. As an air traffic controller, when I instruct you to do something, don't think that I don't have backup plans. We are taught to always evaluate situations thoroughly, and come up with 2-3 different solutions to every problem or situation we face. I will start by presenting the easiest solution to you, but if that doesn't work for you, please don't be afraid of informing me - I will then simply choose another solution, and adjust my plan accordingly. And remember, air traffic control is a service. We are here to make your life easier - not the other way around. You can help us doing so by communicating clearly and in due time.

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I'm going to play devils advocate here and give a different perspective.

Do not say "unable", just say "N12345 Expediting". Saying unable is telling the controller that you possibly cannot descend, but in reality you are already descending in an expeditious fashion.

If the controller comes back and says "N12345 can you increase your rate of descent", then reply "unable".

From an airmanship perspective lets say you are approaching VNE in your descent but not descending fast enough (conflicting traffic or wake turbulence for example). The first thing you should do is pull the power all the way back and point the nose down. Descending with power on is probably not your best descent rate. If you are unfamiliar with how to get your aircraft low quickly, go up with an instructor and ask to practice emergency descents. I find them quite fun actually, and it has other uses (like diving through a hole in the clouds to remain VFR).

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  • $\begingroup$ Shame protocol doesn't allow for something like "N12345 I'm expediting as fast as I can" to break the ice. $\endgroup$ – Steve Jessop Jul 22 '16 at 1:42
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    $\begingroup$ If you're already as "expedited" as you can get then letting the controller know that can be helpful (even something as informal as "N12345 expediting - can't give you much better than this though") $\endgroup$ – voretaq7 Jul 22 '16 at 18:11
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I'll echo everyone else and say 'unable', but I'm not even sure that's really necessary. I believe the standard definition of expedite has to be limited to the possible. If you are already at maximum safe, then you are already expediting. It should be just as valid to say 'roger' and keep flying your plane safely. I don't think he's saying 'be unsafe'; I think he's saying do it without delay.

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    $\begingroup$ When a controller says "expedite" they typically mean "go faster than you are now". If you hear a controller say "N12345 Please Expedite your descent" and you are already descending as fast as you can, you should reply "unable" and possibly clarify that you are descending as quickly as possible. $\endgroup$ – Ron Beyer Jul 21 '16 at 4:04
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    $\begingroup$ The official meaning is in the Pilot/Controller Glossary which states: "EXPEDITE− Used by ATC when prompt compliance is required to avoid the development of an imminent situation. Expedite climb/descent normally indicates to a pilot that the approximate best rate of climb/descent should be used without requiring an exceptional change in aircraft handling characteristics." $\endgroup$ – Ron Beyer Jul 21 '16 at 4:50
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    $\begingroup$ As a controller, when I instruct a pilot to expedite climb/descent, I expect them to increase their vertical rate. If they are not able to do so, I certainly expect to be told. Not saying you are unable to increase your rate further if that is the case would be extremely counter productive, and frankly bad airmanship - even if you can read the rules in a way that means you don't necessarily have to do it. $\endgroup$ – J. Hougaard Jul 21 '16 at 11:48
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    $\begingroup$ It may not be necessary, but for the sake of clarity, understanding and safety for all in the sky, it sure would be a Good Idea™ $\endgroup$ – FreeMan Jul 21 '16 at 12:21
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    $\begingroup$ There's a reason why "I'm giving it all she's got, captain" is a Star Trek catchphrase. It provides useful information about the situation instead of just pretending a request to "expedite" is meaningless and waiting for the controller to figure it out. $\endgroup$ – Zach Lipton Jul 21 '16 at 20:08

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