The first time you level off in a descent and consciously hold the speed back to 250 knots, you are obeying one of the most universal rules in the air. The speed limits at lower levels are simple to state but easy to muddle, especially where a tighter limit bites near busy airspace, so it is worth getting the layers straight.
This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.
Why low-level speed is capped
Below 10,000 feet is where the traffic mixes: fast aircraft, slow aircraft, and aircraft operating visually under VFR, all sharing the same air, where see-and-avoid has to work. Slowing everyone down gives more time to see, decide and avoid, and reduces the energy in any collision. That is the reasoning behind the basic limit, and it is why the rule lives at 10,000 feet, the level above which the traffic thins and oxygen requirements begin to limit who is there.
The 250-knot rule
The basic limit is the same on both sides of the Atlantic in substance, if not in wording:
- The FAA, in 14 CFR 91.117, prohibits more than 250 knots indicated below 10,000 feet MSL.
- EASA, in SERA.6001 of the Standardised European Rules of the Air, sets the same 250 knots indicated below 3 050 m (10,000 ft) AMSL. The scheme it uses, a speed limitation attached to each airspace class, comes from ICAO Annex 11, Appendix 4, which is where the airspace-class table lives.
Both are written in indicated airspeed, so the figure you hold is the one on the airspeed indicator, regardless of the groundspeed the wind gives you.
Two details in the European wording are worth pinning down, because both are routinely misremembered.
The first is the datum. SERA.6001 says 10,000 ft AMSL, an altitude flown on QNH, not FL100, which is a flight level flown on the standard 1013.25 hPa setting. On a low-pressure day the two are a long way apart. Take a QNH of 983 hPa, about 30 hPa below the standard 1013 hPa: at roughly 27 ft per hPa that is about 810 ft of difference, so an altimeter set to 1013 over-reads by that much and FL100 is only about 9,190 ft AMSL, some 800 ft below the level the rule actually names. A crew that files the limit in memory as "FL100" is therefore reading it several hundred feet low on exactly the days when it is most wrong. Read it as an altitude, because that is what it says. (The transition altitude is what decides which of the two you are actually flying on.)
The second is where the limit applies at all. SERA.6001 hangs the 250-knot cap on the airspace class, and it does not apply in Class A or Class B. Nor, and this is the part that surprises people, does it apply to an IFR flight in Class C: SERA.6001 imposes the 250-knot cap in Class C for VFR flights only, leaving an IFR flight there with no SERA speed limit, only whatever ATC assigns. So the exempt set under SERA is Class A, Class B, and IFR in Class C; in Class C VFR, and in Classes D, E, F and G, the 250-knot cap below 10,000 ft AMSL bites as written.
The tighter 200-knot limits
The FAA rule then adds slower limits for the busiest low-level airspace:
- 200 knots indicated at or below 2500 feet above the surface within 4 nautical miles of the primary airport of Class C or Class D airspace;
- 200 knots indicated in the airspace beneath a Class B shelf or in a published VFR corridor through Class B.
There is one relief valve: if the minimum safe speed for the aircraft's configuration is higher than a limit, the aircraft may be flown at that minimum safe speed, and the crew should let ATC know.
A worked example
You are descending a fast aircraft toward a Class C airport. Passing 10,000 feet you bring the speed back to 250 knots indicated to satisfy the basic limit. Continuing down toward the field, you join the pattern below 2500 feet above the surface and inside 4 nautical miles of the primary airport, so now the 200-knot limit applies, and you slow again. None of this depends on the wind: a 40-knot tailwind might give you a groundspeed well above 250 knots while your indicated speed sits right on the limit, which is exactly what the rule intends.
Now fly the same descent in European airspace, VFR into a Class D field. The first step is nearly identical in effect, but written differently: passing 10,000 ft AMSL on QNH, not FL100, you come back to 250 knots indicated under SERA.6001, and any further restriction comes from the airspace and from ATC rather than from a second published figure. Had you been IFR into a Class C airport instead, SERA would have imposed no speed limit on you at all, and your speed would have been whatever ATC assigned.
Common pitfalls
- Indicated, not ground. A tailwind cannot bust the limit; the rule is on the airspeed indicator, not the GPS groundspeed.
- Reading SERA's limit as FL100. It is 10,000 ft AMSL, an altitude on QNH. On a low-QNH day FL100 is several hundred feet below it, and the two are not interchangeable.
- Assuming SERA's limit applies everywhere below 10,000 ft. It does not apply in Class A or Class B, and in Class C it applies to VFR flights only, so an IFR flight in Class C has no SERA speed limit.
- The 200-knot pockets are easy to forget. Under the FAA rules, near Class C and D airports and under Class B, the limit drops; plan the second speed reduction, not just the first.
- Minimum safe speed is the only relief. If your clean configuration needs more than the limit, you may use the minimum safe speed and tell ATC; it is not a general exemption.
In Pilot EFB
Pilot EFB is a study and planning companion for the airspace you will cross and the rules that go with it, alongside your weather, NOTAMs and flight time in one offline-first place. It does not monitor your speed or replace the regulations and your charts, so fly the published limits from your official source of record. Pilot EFB is not a certified Electronic Flight Bag, so treat it as a study and planning aid and brief from your official source of record.