Aircraft Speed Limits Explained: FAR 91.117, Class B Restrictions, and Speed Assignments

Aircraft speed limits are some of the most consistently tested regulations on the written exam and one of the most operationally important rules for safe flight in busy airspace. The 250-knot rule below 10,000 feet, the 200-knot rules around Class C/D airports, the special handling under Class B — these aren't arbitrary numbers. They exist because aircraft operating at vastly different speeds in the same airspace create unsafe closure rates and difficult ATC sequencing. Understanding the speed rules thoroughly helps you stay legal, helps ATC manage traffic, and helps everyone get where they're going safely.

This post covers FAR 91.117 in practical depth: the four major speed restrictions, the minimum safe airspeed exception, helicopter rules, ATC speed assignments, and how to respond when you can't comply with an assigned speed.

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Why Speed Limits Exist

Aircraft span an enormous performance range. A typical Cessna 172 cruises at 110 knots. A regional jet on approach might be doing 220 knots. An airliner descending could be at 280 knots or more.

When aircraft of these different speeds share the same airspace:

Closure rates become extreme:

• 280 knot jet + 110 knot Cessna head-on = 390 knot closure rate

• Time from sighting an aircraft at 5 NM to passing it: about 47 seconds

• Time to make a decision and maneuver: not much

Sequencing becomes impossible:

• ATC managing traffic streams needs predictable speeds

• Aircraft at 250 knots can't follow aircraft at 110 knots without significant adjustment

• Vertical separation becomes the primary tool, limiting traffic flow

Wake turbulence becomes more dangerous:

• Following at higher speeds reduces escape time

The FAA speed limits in 14 CFR 91.117 directly address these issues by mandating predictable speeds in critical areas.

The Four Speed Limits

Speed Limit 1: 250 Knots Below 10,000 Feet MSL

The cornerstone rule: no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots.

Where it applies:

• All airspace below 10,000 feet MSL

• Except Class A airspace (which is above 18,000 feet)

• Except Class B airspace (different rules apply)

• Except as authorized by ATC

Why 10,000 MSL:

• High-altitude traffic at FL250+ operates above this threshold

• Below 10,000 MSL is where significant traffic mixing occurs

• This altitude protects most of the airspace where speed differentials matter

For pilots:

• Most GA aircraft can't reach 250 knots anyway

• Turbine aircraft (jets, turboprops) must reduce to 250 KIAS below 10,000 MSL

• This causes a "speed brake" effect for arriving jet traffic

• Pilots must remember this transition when descending through 10,000

Common ATC announcements:

• "Descend and maintain 11,000, slow to 250 knots before reaching 10,000"

• "Maintain 250 knots until 5-mile final"

• "Cleared for visual approach, slow to 230 knots"

Speed Limit 2: 200 Knots Within 4 NM of Class C/D Primary Airport

The second major rule: 200 knots maximum within 4 nautical miles of the primary airport in Class C or Class D airspace, at or below 2,500 feet AGL.

Where it applies:

• Within 4 NM of the primary Class C or Class D airport

• At or below 2,500 feet AGL

• Around the airport, not in the surrounding airspace

Why this rule:

• Aircraft are typically in the traffic pattern in this area

• Smaller, slower aircraft are operating at the same altitudes

• Sequencing requires controlled speeds

• Safety margin in the immediate airport vicinity

The geometry:

• 4 NM radius around the runway

• 2,500 feet AGL ceiling

• A cylindrical airspace where speeds are restricted

Common scenarios:

• Arriving Class C aircraft on visual approach

• Departing Class C/D aircraft climbing through 2,500 AGL

• Pattern traffic at the primary airport

• Aircraft transiting through Class C/D for landing

Outside Class C/D primary area:

• Outside the 4 NM radius or above 2,500 AGL: standard 250 knot limit applies

• This creates a "step-up" effect for arriving aircraft

Speed Limit 3: 200 Knots Under Class B Airspace

When operating in the airspace underlying a Class B (the outer shelves) or in a VFR corridor through a Class B, the limit is 200 knots indicated airspeed.

Where it applies:

• Airspace below the lateral limits of Class B (the "shelves")

• VFR corridors through Class B (where they exist)

• The mode C veil around major airports (in some cases)

Why this rule:

• The airspace under Class B has high traffic density

• Often used by aircraft operating in and out of satellite airports

• Vertical proximity to Class B airline traffic

• VFR aircraft transitioning the area need predictable speeds

Class B airspace itself:

• Above the lateral boundary of Class B (inside the airspace) — no specific speed limit beyond 250 knots below 10,000 MSL

• ATC may assign different speeds

• IFR traffic flows requires predictable speeds

The practical pattern:

A typical Class B airport has shelves at different altitudes:

• Inner ring: 10,000 MSL down to surface

• Outer shelves: lower altitudes, sometimes shelving outward

• Underneath the outer shelves: 200-knot limit applies

Common situations:

• VFR aircraft transitioning underneath Class B

• Departing a non-Class B airport adjacent to Class B

• Arriving at a satellite airport near a Class B

Speed Limit 4: ATC Speed Assignments

In addition to the regulatory speed limits, ATC can assign specific speeds to manage traffic:

Common ATC speed assignments:

• "Maintain 280 knots until 10 miles out"

• "Slow to 210 knots for sequencing"

• "Maintain assigned heading, 250 knots"

• "Reduce to maximum forward speed for sequencing"

Why ATC assigns speeds:

• Maintain in-trail spacing between arriving aircraft

• Sequence traffic for approach

• Manage approach gaps

• Coordinate with departures

• Manage holding patterns

Pilot compliance:

• Pilots must comply with ATC speed assignments unless safety is at risk

• "Unable" responses are legitimate when:

  • Aircraft cannot reach the assigned speed

  • Aircraft is at minimum safe speed and cannot slow more

  • Aircraft is above maximum operating speed and cannot speed up

  • Configuration changes would be required at the wrong time

Example "unable" responses:

• "Unable 280 knots, maintaining 240 knots maximum"

• "Unable 180 knots due to minimum safe speed"

• "Unable to comply, will require slowing to 210"

The Minimum Safe Airspeed Exception

FAR 91.117 includes an important exception: aircraft with a minimum safe airspeed above the published limit may legally fly at that minimum safe speed.

Where this applies:

• High-performance jets with high approach speeds

• Aircraft with high landing weights

• Aircraft in specific configurations

• Specific operational scenarios

Example: A jet on approach

A heavy 737 on final approach may have:

• Maximum approach speed: 145 KIAS

• Minimum approach speed: 140 KIAS (Vref + 5)

• This is below the 200 knot Class C/D limit, so no exception needed

But during descent or maneuvering:

• Aircraft at 220 KIAS minimum to avoid stall warnings

• 200 knot limit within 4 NM of Class C/D would not be possible

• Legal exception applies — aircraft may fly at minimum safe speed

Communication to ATC:

• "Unable 200 knots, requesting maximum forward speed for sequencing"

• "Unable due to minimum safe airspeed of 240 knots"

The pilot's responsibility:

• The minimum safe airspeed is determined by the aircraft and conditions

• Pilot must inform ATC when unable to comply with assigned speeds

• ATC will accommodate by adjusting traffic flow

Speed Limit Interactions With Airspace Classes

The speed limits interact with airspace in specific ways:

Class B Airspace:

• Within Class B: ATC manages speeds, generally 250 knots below 10,000

• Below Class B: 200 knots in the "shelves" and VFR corridors

• Above Class B: Class A above 18,000, 250 knots below

Class C Airspace:

• Within 4 NM of primary at/below 2,500 AGL: 200 knots

• Outside Class C: 250 knots below 10,000

Class D Airspace:

• Within 4 NM of primary at/below 2,500 AGL: 200 knots

• Outside Class D: Standard airspace rules apply

Class E Airspace:

• Standard airspace rules apply

• 250 knots below 10,000

Class G Airspace:

• Standard airspace rules apply

• 250 knots below 10,000

Class A Airspace:

• Above 18,000 MSL, generally no specific speed limits

• Subject to ATC instructions

Common Operational Scenarios

Scenario 1: Descent to a Class C airport

You're descending through 10,000 MSL into a Class C airport for landing.

• At 10,000 MSL: 250 knot limit becomes active

• At 4 NM and 2,500 AGL or below from the airport: 200 knot limit

• Approach speeds (typically 100-130 KIAS for typical GA): no specific limit beyond 200

Practical descent:

• Descend at 250 KIAS through 10,000

• Reduce to 200 within 4 NM of airport

• Continue slowing to approach speed for final

Scenario 2: Departure under Class B

You're departing a satellite airport that's underneath the Class B shelves.

• Initially in the airspace underlying Class B: 200 knot limit applies

• After climbing through the Class B floor: above the shelf, different rules

• Continuing to climb out of Class B vicinity: 250 knot limit below 10,000

Practical considerations:

• Manage climb power and pitch to avoid exceeding 200 in the airspace underneath

• Watch for the floor altitude of the overlying Class B

• Standard 250 knot limit applies once clear

Scenario 3: VFR transition through Class B

You're flying VFR through a Class B VFR corridor.

• VFR corridor: 200 knot limit

• Outside VFR corridor (still under Class B): 200 knot limit (under the shelves)

• Outside Class B entirely: 250 knot limit (below 10,000)

Scenario 4: Cruising at 12,000 MSL

You're cruising at 12,000 MSL on a cross-country.

• Above 10,000 MSL: No general speed limit

• ATC may still assign speeds

• Stay below Vno in turbulence

• Standard turbulence rules apply

The "Unable" Conversation With ATC

Knowing how to respond when you can't comply with a speed assignment is critical:

When to use "unable":

• Aircraft cannot achieve the assigned speed

• Below minimum safe speed

• Above maximum operating speed

• Configuration would require unsafe operations

• Performance limitations

Standard phraseology:

When you can't comply with a slow-down:

• "Unable [requested speed], minimum safe airspeed is [actual]"

• "Unable, requesting [alternative speed]"

When you can't comply with a speed-up:

• "Unable [requested speed], maximum speed is [actual]"

• "Unable due to performance limitations"

Example exchange:

• ATC: "Cessna 123, slow to 130 knots for sequencing."

• Pilot: "Unable 130, slowest safe speed is 95 knots. Cessna 123."

• ATC: "Cessna 123, advise when you can slow to 95 knots."

• Pilot: "Slowing to 95 knots now, Cessna 123."

Important: Don't pretend.

If you can't safely comply, say so clearly. Trying to comply with an unsafe speed (slowing below safe minimum, exceeding maximum) creates accidents. ATC understands and accommodates.

Special Considerations

Wake Turbulence and Speed:

The 250-knot limit doesn't change wake turbulence requirements. ATC will adjust spacing for wake turbulence regardless of speed.

Mountainous Terrain:

Some mountain airports have specific speed considerations due to:

• High-altitude operations

• Density altitude affecting speed

• Terrain limitations

• Pattern speeds may be higher than standard

Night Operations:

Same speed limits apply at night. Some pilots fly slower at night for better visual reference, but this is personal choice, not regulatory.

Multi-Engine Operations:

Multi-engine aircraft have specific Vmc, Vyse, and other speed considerations:

• Single-engine speed assignments may exceed Vmc

• Pilot must consider all relevant speeds

• "Unable" responses appropriate when conflicting

Common Misconceptions

• "The speed limit only applies in controlled airspace."

• Wrong — the 250 knot limit applies below 10,000 MSL regardless of class (except above Class B).

• "I can exceed 250 knots if ATC clears me."

• Wrong — ATC doesn't have authority to waive the regulatory speed limit. ATC assigned speeds are typically below 250 knots, not above.

• "I can go any speed in Class A."

• Above 10,000 feet (technically 18,000 in Class A), no specific limit applies, but ATC speed assignments apply. Above approximately 31,000 feet, Mach number becomes the limit.

• "The 200-knot rule under Class B only applies to VFR aircraft."

• Wrong — it applies to all aircraft (IFR and VFR) in the airspace underlying Class B and in VFR corridors.

• "I have to comply with all ATC speed assignments."

• Not if it's unsafe. "Unable" is a legitimate response when you can't safely comply.

On the Written Test and Checkride

Aircraft speed limits appear consistently on tests. The most commonly tested topics:

• 250 knot rule below 10,000 MSL

• 200 knots within 4 NM of Class C/D primary airport at or below 2,500 AGL

• 200 knots under Class B airspace

• Minimum safe airspeed exception

• ATC speed assignment authority

• How to respond when unable to comply

Quick Reference

FAR 91.117 Speed Limits:

Location	Maximum Speed
Below 10,000 MSL	250 KIAS
Within 4 NM of Class C/D primary at/below 2,500 AGL	200 KIAS
Underlying Class B airspace	200 KIAS
VFR corridor through Class B	200 KIAS

Key Concepts:

• All limits are indicated airspeed (KIAS), not true airspeed

• Above 10,000 MSL: No general limit (except ATC instructions)

• Class A (above 18,000 MSL): No general limit

• Class B (within): No specific limit beyond 250 below 10,000

Exceptions:

• Minimum safe airspeed (if higher than limit)

• ATC waivers (rare, specific situations)

• Some emergency situations

ATC Speed Assignments:

• Comply when possible

• "Unable" when not safe to comply

• State actual minimum or maximum capability

• Standard phraseology

Standard Phraseology:

• "Unable [speed], minimum safe airspeed is [actual]"

• "Unable [speed], maximum speed is [actual]"

• "Requesting [alternative speed]"

• "Maximum forward speed for sequencing"

Why Speed Limits Exist:

• Reduce closure rates between aircraft

• Improve ATC sequencing

• Protect slower aircraft from faster traffic

• Standardize traffic flow

• Reduce wake turbulence risk

Pilot Responsibilities:

• Know the applicable speed limits for current airspace

• Comply with ATC speed assignments when safe

• Use "unable" honestly when needed

• Consider minimum safe airspeed for your aircraft

• Adjust speed for traffic and conditions

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Author: Nathan Hodell

CFI, CFII, MEI, ATP, Creator and CEO

Nathan is an aviation enthusiast with thousands of hours of flying and dual instruction over the past 15+ years. Through his aviation career he has been able to earn his ATP, fly as an airline pilot, own/operate flight schools, and create and host wifiCFI.