Oil system drains

This regulation requires aircraft operating under Part 121 (commercial air carriers) to have oil system drains that meet specific design standards. These drains must be accessible to maintenance personnel and include a positive locking mechanism—either manual or automatic—that securely keeps them closed during flight operations.

The key requirement is that these drains allow the entire oil system to be safely drained when needed. This matters for routine maintenance, oil changes, and inspections where complete drainage is necessary to service the engine properly or check for contamination.

The positive locking feature prevents accidental opening during flight, which could lead to catastrophic oil loss and engine failure. By requiring accessible drains, the regulation ensures maintenance crews can perform oil system servicing efficiently and safely on the ground, while the locking mechanism provides critical safety assurance that drains won't open inadvertently during operations.

*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.*