Definition
The section of the U.S. federal aviation regulations that prescribes how landing distance is determined and certified for transport-category airplanes. It defines the standard conditions, configuration, approach speed, and procedures used to calculate the distance from a height of 50 feet above the landing surface to a full stop on a dry, level, smooth, hard-surfaced runway.
Plain English
It is the rule that tells manufacturers exactly how to measure and publish the landing distance for large airplanes, so every airplane's published landing distance is calculated the same way under the same conditions.
Context Anchor
Seen in jet landing performance discussions, especially when explaining where certified landing-distance numbers come from.
Derivation
14 CFR means Title 14 of the Code of Federal Regulations, which contains the aviation rules. Part 25 covers airworthiness standards for transport-category airplanes. Section 25.125 is the specific paragraph within Part 25 that deals with landing performance.
Why Pilots Care
Pilots use the certified landing distances that come from this regulation to decide whether a runway is long enough for their airplane under the day's conditions.
Analogy
The citation works like an address. “14 CFR” is the rulebook, “part 25” is the chapter, and “section 25.125” is the exact rule being pointed to.
Intuition Check
Do not read “part” as an airplane component here. In this citation, “part” means a major division of federal regulations, and “section” means the specific rule within that division.
Example Sentence 1
The landing distance chart in the AFM was developed using the procedures defined in 14 CFR part 25, section 25.125.
Example Sentence 2
During preflight planning the crew verified that the available runway exceeded the distance required by 14 CFR part 25, section 25.125 for the reported conditions.