Definition
A specific paragraph within Title 14 of the Code of Federal Regulations (14 CFR), Part 23, that establishes one of the conditions under which the minimum control speed (VMC) for a multiengine airplane must be determined during certification. Subsection (b)(4) requires that VMC be established with the airplane banked not more than 5 degrees toward the operating engine.
Plain English
It is the rule the FAA used when measuring the slowest speed at which a twin-engine airplane can still be controlled with one engine out. The rule says the airplane is allowed to be tilted no more than 5 degrees toward the working engine when that speed is measured.
Context Anchor
Seen in multiengine training when explaining how the published VMC speed is derived and what test conditions the manufacturer used.
Derivation
Section comes from a word meaning “to cut.” In rules and manuals, a section is a numbered cut-out part of a larger document. The citation 23.149(b)(4) narrows the reader to Part 23, section 149, paragraph (b), item (4).
Why Pilots Care
It guarantees that published V_MC values reflect a consistent, repeatable test condition used for aircraft certification and safe operations.
Grounding Statement
Picture the test condition: after one engine fails, the airplane is in the air with the wheels up, and the pilot must still be able to keep it under control at the stated speed.
Intuition Check
Do not read “section” here as part of the airplane. Here it means a numbered part of the federal aviation rules, and “(b)(4)” points to one exact subparagraph.
Example Sentence 1
The instructor explained that VMC was established under section 23.149(b)(4) with up to 5 degrees of bank toward the operating engine, which is why a wings-level engine-out demonstration will result in loss of control at a higher airspeed than the red line.
Example Sentence 2
During recurrent training the instructor pointed out that section 23.149(b)(4) requires the propeller to be in its minimum-drag position for the V_MC demonstration.