Definition
A specific provision in Title 14 of the Code of Federal Regulations, Part 23 (Airworthiness Standards: Normal Category Airplanes), which sets controllability requirements for multiengine airplanes following the failure of the critical engine. It is the regulatory basis for the minimum control speed (VMC) standard that manufacturers must demonstrate during certification of light multiengine airplanes.
Plain English
It's the rule that tells airplane makers how a small twin-engine airplane must still be controllable after one engine quits. This rule is what defines the published VMC speed for the airplane.
Context Anchor
Seen in the Airplane Flying Handbook when the text connects multiengine performance terms to the certification rules the airplane was built and approved under.
Derivation
The word “section” comes from a root meaning “to cut.” In regulations, a section is one cut-out part of a larger rule. The numbers and letters narrow the reference: 23 is the airplane certification part, 2120 is the climb-requirements section, and (b)(1) is the exact paragraph inside that section.
Why Pilots Care
It sets the minimum performance standard that determines whether a particular multiengine airplane is approved for operations from a given runway length when an engine failure occurs during the takeoff roll or initial climb.
Intuition Check
Do not read “section” here as a physical part of the airplane. It means a numbered part of the federal aviation rules.
Example Sentence 1
The airplane's published VMC of 80 knots was established under section 23.2120(b)(1) during certification testing.
Example Sentence 2
During the multiengine transition course the instructor explained how section 23.2120(b)(1) directly influences the accelerate-stop and accelerate-go distances published in the Pilot's Operating Handbook.