Accident Summary
On November 9, 2021, at approximately 1605 eastern standard time, a Piper PA-28-151, registration N40831, sustained substantial damage in an accident near Sarasota, Florida. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight with a student pilot on board, who was not injured.
The student pilot was returning to his home airport after a roundtrip cross-country flight. While turning from the left downwind leg to the left base leg for runway 14 at Bradenton International Airport (SRQ), with 10° of flap extension, he noticed that the throttle lever was stuck at the 2,000 rpm position. He then turned onto final approach with 25° of flaps and realized the descent rate was too great to reach the runway. He fully retracted the flaps to reduce drag and attempted to loosen the throttle friction lock, but neither action had any effect. To avoid houses at the approach end of the runway, the pilot turned right and ditched in an adjacent bay. The student pilot egressed, and the airplane subsequently sank.
Examination Findings
The wreckage was recovered from the bay and examined by a Federal Aviation Administration inspector, who noted substantial damage to the right wing. The inspector also observed that the throttle cable was jammed inside its housing. The throttle cable was forwarded to the National Transportation Safety Board Materials Laboratory in Washington, DC, for metallurgical examination.
The examination revealed that the Teflon liner, which supports the inner cable and prevents metal-to-metal contact with the helical coil of the cable housing, was worn. Six of the seven wires of the inner cable had separated due to metal-to-metal contact wear. The seventh (single central) wire lacked the capacity to resist compressive and torsional loading, leading to collapse and torsional unfurling of the cable.
Maintenance History
The airplane was manufactured in 1973 and had accrued about 14,000 hours of operation at the time of the accident. There were no life-limited components on this make and model, and no published schedule to replace them. Review of the maintenance manual for the 100-hour (500-hour, and 1,000-hour) inspections revealed a checklist item (item 37) in the engine group section related to the throttle cable, which stated, “Inspect throttle, carburetor heat, and mixture controls for security, travel, and operating condition.” Review of maintenance records dating back 2 years before the accident did not reveal any problems with the throttle.