Fuel valves

This regulation sets three design requirements for fuel valves on aircraft operated under Part 121 (air carriers).

First, fuel valves must meet the materials and workmanship standards in § 121.257. Second, they must have positive stops or clear indexing in both "on" and "off" positions—meaning pilots can definitively feel or see when the valve is fully open or fully closed, preventing ambiguous intermediate positions that could cause fuel flow problems.

Third, the valves must be mounted so that operational forces (from turning the valve) and flight loads (from acceleration, turbulence, or maneuvers) don't stress the fuel lines connected to them. This prevents potential fuel line damage or leaks.

These requirements ensure fuel valves are reliable, clearly positioned, and structurally sound—critical for maintaining proper fuel flow and preventing fuel system failures during flight operations. This is primarily a certification standard that aircraft manufacturers must meet, though operators should understand these design features.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*