FAR 91.603 — Aural Speed Warning

FAR 91.603 is a short but important equipment rule for transport category airplanes operating in air commerce. It requires the airplane to be equipped with an aural speed warning device that complies with § 25.1303(c)(1) (the airworthiness standard for that device).

In plain terms:

• The rule applies only to transport category airplanes (think airliners and large jets certificated under Part 25), not to small piston singles or most general aviation aircraft.
• The airplane must be equipped with the warning device — it isn't optional gear.
• The device must meet the design standard in § 25.1303(c)(1), which is the certification rule for aural overspeed warnings.

Why it matters operationally: at jet speeds, exceeding VMO/MMO can cause structural damage or loss of control. An audible warning gives the crew an immediate, attention-getting cue to reduce speed before the aircraft is damaged or upset, even when pilots are heads-down or distracted.