Digital flight data recorders for transport category airplanes

This regulation requires turbine-powered transport category airplanes operated under Part 121 (scheduled airlines) to have digital flight data recorders (DFDRs) that can store and retrieve operational data. The rule lists 91 specific parameters that must be recorded, ranging from basic flight data (altitude, airspeed, heading) to detailed information about control inputs, engine performance, autopilot status, and system warnings.

Many parameters include the phrase "when an information source is installed," meaning you only need to record them if your airplane already has the necessary sensors or systems—you don't have to install new equipment just to record that parameter.

This data proves invaluable for accident investigation, maintenance troubleshooting, and flight operations analysis. The comprehensive recording requirements help investigators understand exactly what happened during incidents, making air travel safer through detailed post-flight analysis.

*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.*