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For example, a slower aircraft operating on the North Atlantic Track System would have an operational impact on surrounding/overtaking aircraft as well as potentially increasing ATC workload to ensure separation.

So, are there any formally encoded minimum aircraft speed/performance requirements based on operational environment?

(Maximum speeds are covered in this question and the topic of why aircraft aren't designed to operate at slower airspeeds is covered in this question.)

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I have never heard of any procedures or airways that require a minimum airspeed. Having a minimum climb gradient is quite common, typically on departure procedures to ensure terrain clearance.

It generally works out in such a way that aircraft with similar performance tend to cruise at the same levels. Most passenger jets cruising around 30,000-40,000 feet all happen to have a cruise speed of somewhere in the mach .75-.85 range. Slower turboprops often cruise at about 25,000 feet, and below that various GA planes. Granted, there can be quite a speed difference for those planes cruising at about 25,000 feet and below (for example, an ATR 72 has a cruising speed of 275 KTAS, a Dash 8 Q400 is about 370 KTAS - they both commonly cruise at 25,000 feet). However, these levels are typically less crowded, so it is not so much of a problem. For the really crowded, higher levels, most aircraft have very similar performance.

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The way it works is you file your flight plan for the NAT with a proposed Mach #, but when you get your Oceanic Clearance they will assign Mach #s for each segment of the NAT and that's what you have to fly unless cleared for a different speed. The adherence to assigned Mach #s are the only assurance of separation once out of radar coverage.

Perusing the NAT Operations Manual I couldn't find anything that gives a minimum Mach #, but if you were unable or didn't want to maintain the Mach # assigned, you would probably be given the option of flying down below RVSM airspace, or taking an off-NAT routing like the northerly "Blue Spruce" route (which airplanes use when they have to stop in Iceland for fuel because they don't have the range for the NATs).

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  • $\begingroup$ That's not actually a minimum speed limit, though. It's just an ATC instruction, just like ATC will often instruct aircraft to reduce speed during vectors for approach. $\endgroup$
    – 60levelchange
    Commented Sep 2, 2019 at 11:51

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