“A new student pilot was flying a flight school aircraft with a CFI (certified flight instructor),” says this submitting mechanic. “During the student’s first stall practice the warning horn failed to operate through full stall, and the CFI halted the maneuver. Troubleshooting by maintenance personnel confirmed the warning horn assembly (P/N 0713348-1) was defective. The (failed) unit was replaced with a new (assembly), and a maintenance operational check and test flight were completed. This part had 311.7 hours TSN (time since new) and was a replacement for the original, factory installed part...(which failed after 651.0 hours).

“A second 172 aircraft (of three) had the identical problem...at 491.5 hours. In this case the part was replaced twice because the first new part failed during (its) test flight. Aircraft number three has 417.6 hours TSN and has been recently checked: it is okay at this time. (The) probable cause (for these failures) has not been determined.

(I) suggest at least a one time check of all new aircraft be conducted and reported to determine the scope of the problem and to raise awareness of a possible unknown safety problem.”

Part Total Time: 311.7 hours.