ERA24FA157 · Piper Aircraft Inc PA-44-180

The flight instructor and the pilot receiving instruction were practicing a simulated engine-out instrument approach with the left engine operating and the right engine at a reduced power setting. The approach terminated in a missed approach/go-around. According to the pilot receiving instruction, when he added power to go around, the airplane did not respond with the engine power commanded. He turned the airplane to the missed approach heading provided by air traffic control (ATC), and the flight instructor took control of the airplane, declared an emergency, and told ATC they were “single engine.” The flight instructor continued to turn the airplane to the right in an attempt to return to the runway; however, the airplane continued to lose altitude, stalled, and impacted the ground on airport property. Although the pilot receiving instruction perceived that there was no thrust on either engine, data recovered from the airplane’s Avidyne multifunction display (MFD) and primary flight display (PFD) revealed that the left engine was producing full power and the right engine was producing partial power from the time the go-around was initiated to the time of impact. Examination of the right engine revealed that the interlocking teeth of the serrated mating surfaces between the carburetor’s throttle arm and throttle control lever were not securely mated, such that the throttle control lever was loose and could be fully rotated without moving the throttle arm. The teeth on the throttle control lever side were rounded and worn down, consistent with the damage having occurred over a period of time. As such, when the right engine’s throttle was advanced to go around, the worn mating surface of throttle control lever likely did not engage with the mating surface on the carburetor throttle arm (to actuate the valve assembly in the carburetor), which prevented the right engine from obtaining full power. The right engine had undergone an annual inspection the day before the accident, as required by 14 Code of Federal Regulations (CFR) Part 91.409. Per the regulation, such inspections must be performed in accordance with 14 CFR Part 43 and the aircraft approved for return to service by an authorized certificated mechanic. Part 43, Appendix D, paragraph (d)(6) explicitly mandates the inspection of the engine controls for “defects, improper travel, and improper safetying.” The mechanic who endorsed the engine logbook for the inspection said that he thought he checked the security of the throttle arm during his inspection. He also said he understood that a loose and damaged throttle control component could result in a partial loss of engine power and that he was unsure how he missed it in his inspection. Therefore, due to the fact that the throttle control lever was loose and its serrated mating surface exhibited pre-existing damage, it is likely that the mechanic failed to properly check the security of the throttle control lever to the throttle arm when he inspected the engine. The flight instructor was teaching single-engine emergency procedures; however, her actions were inconsistent with her being prepared to handle the partial loss of engine power on one engine after the initiation of the go-around. Per the pilot receiving instruction, the emergency checklist was never used, and the airplane was not configured to maintain flight. As a result, during the flight instructor’s attempted continuation of the go-around, the airplane’s airspeed decayed, and it stalled at a critically low altitude from which it was not possible to recover before ground impact.

Verbatim NTSB analysis and probable cause from the NTSB dataset