Engine instruments

This regulation lists the engine instruments required for Part 121 air carrier operations. The Administrator may approve different instrumentation for turbine-powered aircraft if it provides equivalent safety.

Required instruments include:

• Carburetor air temperature for each engine
• Cylinder head temperature for air-cooled engines
• Fuel pressure indicator and flowmeter/mixture indicator (unless automatic altitude mixture control is installed)
• Fuel quantity indicators for each tank in use
• Manifold pressure indicator
• Oil pressure, quantity (when transfer/reserve systems are used), and temperature indicators
• Tachometer for each engine
• Fuel pressure warning device (individual or master system with isolation capability)

For reversible propellers, a reverse pitch indicator must activate somewhere between normal low pitch and full reverse, but cannot indicate at or above the normal low pitch position. The indicator must respond directly to blade angle.

These instruments ensure pilots can monitor critical engine parameters during commercial 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.*