FAR Ninety-One One Seventeen, the Speed Limits, and Why Two Hundred and Fifty Knots Below Ten Thousand Is the Rule Almost Nobody Explains to a Student Pilot

SUMMARY: FAR 91.117 caps you at 250 knots below 10,000 feet MSL and 200 knots near busy airspace - here’s why it matters.

FAR 91.117 sets four aircraft speed limits, and the one every pilot should know is the ceiling of 250 knots indicated airspeed below 10,000 feet MSL. Two more limits drop you to 200 knots near busy airspace - under a Class B shelf and within the immediate area of a Class C or Class D airport - and a fourth provision allows faster flight only when an aircraft’s minimum safe speed is higher than the limit. In a typical trainer you’ll never reach these numbers, but they become real the moment you step into a faster airplane.

What Does FAR 91.117 Actually Say?

The rule lives in Title 14 of the Code of Federal Regulations, Part 91, Section 117 - pilots just call it 91.117. Its title is simply “Aircraft speed.”

Inside that plain heading are four separate speed limits, and each one exists for a specific reason. Here’s what each one covers.

How Fast Can You Fly Below 10,000 Feet?

Below 10,000 feet MSL, you may not fly faster than 250 knots indicated airspeed. Note the reference: that’s mean sea level, not height above the ground.

Why 10,000 feet? The number isn’t random. Below 10,000 feet is where the airplanes live - where training happens, and where a pilot in a Champ with no electrical system and no radio has every legal right to be enjoying a Sunday afternoon. It’s crowded down low.

The deeper reason is closure rate. Speed steals your time to react. When two airplanes are on a collision course, the closure rate is both of their speeds added together.

Picture a jet doing 400 knots meeting a trainer doing 100 knots. That’s 500 knots of closure - roughly 850 feet every second coming at you. By the time your eye catches the speck, recognizes it as an airplane, and your brain says “turn,” you’ve eaten up several seconds, and at that closure rate several seconds is all the distance you had.

Slowing that jet to 250 knots doesn’t fix the problem, but it buys time. This is a see-and-avoid rule wearing a speed limit’s clothing.

Why Does the Limit Drop to 200 Knots Under Class B?

When you’re below the floor of Class B airspace, or flying through a published VFR corridor that cuts through a Class B, your limit drops to 200 knots.

Class B is the upside-down wedding cake around the biggest, busiest airports - Los Angeles, Atlanta, Chicago. The airspace steps down in shelves as you get closer to the field. Right below the bottom of each shelf is a thin layer where light airplanes squeeze through underneath the airliners.

That layer is a pressure cooker: jets descending into the Class B above you, and a crowd of general aviation traffic threading the needle below, all trying to stay under the shelf so they don’t bust the airspace without a clearance. It’s one of the most congested slices of sky in the country.

Same logic as before - more traffic, less speed, more time to see the other airplane. Notice that this 200-knot limit is lower than the 250-knot limit. When the airspace gets tighter and busier, the number comes down.

What’s the Speed Limit Near Class C and Class D Airports?

In the airspace around Class C and Class D airports - at and below 2,500 feet above the surface and within 4 nautical miles of the primary airport - your speed limit is 200 knots.

Class C and Class D are your medium and smaller towered fields, including the Class D where your flight school probably lives. That 4-mile, 2,500-foot bubble is exactly where the traffic pattern is - where airplanes are slowing to land, speeding up to depart, and converging on the same runway.

In a trainer you’re doing 70 or 80 knots on downwind, nowhere near 200. But the moment you’re flying something faster, this is the rule that says don’t come screaming into the pattern hot. Bleed off the speed and fit into the flow. The pattern only works if everyone is flying roughly the same speeds.

MSL vs. AGL: The Detail Examiners Love

Here’s a subtlety the examiner might dig into. There’s a difference between the first limit and the other two.

The 250-knot rule below 10,000 feet is measured above sea level (MSL). The 200-knot rules - under the Class B shelf and around Class C and Class D - are measured above the surface (AGL). The Class C/D bubble is 2,500 feet AGL.

Sea level for one, ground level for the others. That’s the kind of detail that separates a pilot who memorized a number from one who actually understands the regulation - and understanding is what the examiner is looking for.

A Real-World Scenario: Busting 91.117 in a Cirrus

Say you’ve moved up into a Cirrus SR22. It cruises around 180 knots true, and in a descent with the nose down and throttle up, it will easily march past 200.

You’re coming home from a cross-country, descending out of the flight levels, set up to fly right under a Class B shelf near a big city on the way to your home Class D field. Down through 10,000 feet you go, indicated airspeed sitting at 220 knots because you’re using the descent to make up time.

Stop there - you just busted 91.117. Below 10,000 feet you’re capped at 250, so that part is fine. But the second you slide under that Class B shelf, your limit dropped to 200. Then within 4 miles of your Class D, at and below 2,500 feet AGL, it’s 200 again. You needed to plan that speed reduction miles out.

A clean, slick airplane doesn’t slow down when you want it to. Pull the power back and it keeps trucking, trading speed reluctantly. The real lesson isn’t the number - it’s that you have to think ahead of the airplane and plan your slowdown before the airspace boundary is already sliding under the nose.

The Minimum Safe Speed Exception

There is one relief valve in the regulation. If an aircraft’s minimum safe speed for a particular operation is greater than the limit, the pilot may fly at that minimum safe speed instead.

In plain English: some aircraft - certain jets and certain military aircraft in certain configurations - physically cannot fly as slow as 200 or 250 knots and still be safe. If slowing that much would put them too close to a stall or make the airplane hard to control, they’re permitted to fly faster. Safety of the machine wins over the number.

This is not a loophole for light-aircraft pilots. A Skyhawk’s minimum safe speed is about 60 knots, so the exception simply doesn’t apply. For the vast majority of pilots in the vast majority of airplanes, the limit is the limit.

Can ATC Clear You to Exceed the Speed Limit?

No. A controller can ask you to slow down - they do it constantly to sequence traffic - but no controller can authorize you to exceed the 91.117 speed limits.

There’s no such thing as “cleared to exceed 250.” If a controller ever assigned a speed that would put you over the limit, the regulation still wins, and the correct response is “unable.” The FAA wrote this as a hard limit, and the tower can’t lift it.

Key Takeaways

• Below 10,000 feet MSL, the maximum speed is 250 knots indicated airspeed.
• Below a Class B shelf or in a VFR corridor through Class B, the limit is 200 knots.
• Within 4 nautical miles and at or below 2,500 feet AGL of a Class C or Class D airport, the limit is 200 knots.
• The first limit is measured in MSL; the two 200-knot limits are measured in AGL - a favorite examiner detail.
• The minimum safe speed exception exists but almost never applies to light trainers, and ATC cannot authorize you to exceed any of these limits.