If you were told to "maintain 250 knots" below Class B airspace, what would you do?

Report: Flying Under New York Class B Airspace

There are a lot of rules and restrictions when it comes to flying around busy airspace. This experienced, ATP-rated, corporate jet captain filed a NASA ASRS report for mistakenly breaking a regulation and questioning ATC's rationale. What would you do?

Speed Restrictions In/Around Class B Airspace

There isn't a specific speed restriction for operating in Class B airspace. If you're below 10,000 feet, you need to meet the standard speed restriction of 250 knots. However, if you're in Class B at 10,000' MSL or higher, you can fly faster than 250 knots (though ATC usually restricts aircraft speed for traffic flow and separation).

Most Class B airspace ends at 10,000' MSL, so this isn't much of a factor. However, some Class B airspace extends higher, like Denver's Class B, which extends up to 12,000' MSL.

But what happens if you're under a Class B shelf, and not in Class B airspace itself?

According to 91.117(c), "no person may operate an aircraft in the airspace underlying a Class B airspace area designated for an airport or in a VFR corridor designated through such a Class B airspace area, at an indicated airspeed of more than 200 knots (230 mph)."

This is done to help separate aircraft operating within Class B from those operating outside of Class B. Some aircraft flying below Class B may not be in contact with ATC, and the speed restriction of 200 knots provides ATC an added buffer to get traffic out of the way, should an airspace deviation occur.

Does An ATC Instruction Change The Regulation?

In the example above, ATC issued speed instructions exceeding the regulatory requirement of 91.117(c). Because of this, many pilots have debated if a cleared instruction makes the excess speed legal.

In 91.117(b), the speed restriction around Class C and D is prefaced with "unless otherwise authorized or required by ATC." This phrase is not used regarding speeds under the shelf of Class B airspace.

Based on this, the answer is "no". You cannot fly faster than 200 knots under a Class B airspace shelf. Just like pilots, controllers make mistakes, and this controller likely forgot the regulation.

What Can You Do?

If this happens to you, the most conservative thing you can do is say "unable." If you're asked why, remind ATC that you're below Class B airspace and the speed limit is 200 knots.

Controllers aren't out to catch you, and they make mistakes too.

That being said, know the regulations and always back yourself up by filing a NASA ASRS report if you make a mistake. And if you have questions about speed restrictions, you can always brush up with our National Airspace online course.

Has anything like this ever happened to you? Tell us in the comments below.