Engine Power Lost: NTSB Reconstructs the Final Minutes of Piper N4187Q

A magneto impulse-coupling failure caused a cascading engine failure, while outdated runway information shaped the pilot’s emergency options.

On November 27, 2023, Piper PA-32R-301T N4187Q was flying IFR from Scott Municipal Airport in Tennessee to H. L. Sonny Callahan Airport in Fairhope, Alabama. Near Gadsden, the aircraft began descending without an ATC instruction. Seconds later the pilot reported that engine RPM had fallen and declared an emergency. The NTSB ultimately traced the loss of power to a failed magneto impulse coupling and a cascading chain of damage through the engine’s accessory gear train. But the emergency also became an airport-information problem.

Accident Facts

The Emergency Begins

At 17:43:03, the airplane began descending while about four nautical miles north-northeast of GAD. Thirty-two seconds later the pilot told Birmingham ATC that he had lost engine RPM and was declaring an emergency. The controller immediately supplied airport options. The first options were not necessarily the closest in actual distance, and the pilot soon recognized that GAD was near his position.

The Gadsden Problem

The pilot asked about GAD twice. Each time, ATC relied on the available runway information: Runway 6/24 was closed and Runway 18/36 was unlit, with construction work also reported. Based on that information, the controller told the pilot that landing there would not be feasible. The investigation later found that the actual airport condition was different: construction personnel had left, one runway was free of equipment and both runways had operable pilot-controlled lighting.

The Diversion to 20A

At 17:44:58, the pilot asked for a heading to the “closest one.” ATC vectored him toward Robbins Field, about 15 nautical miles away at that point. The airplane remained on a westerly track until 17:45:43, then turned left toward a south-southwesterly track at about 3,150 ft. By 17:46:04 the pilot reported 3,000 ft. Twenty-six seconds later he said he did not have an airport in sight.

The Final Minute

The last ADS-B target appeared at 17:46:34 at about 2,300 ft. The controller later reported radar contact lost at 17:47:32 and asked whether the pilot had a nearby highway in sight. The final recorded transmission came at 17:48:02, when the pilot reported a terrain warning at about 1,100 ft. Security-camera footage captured the impact sequence at approximately 17:48:10.

What Failed Inside the Engine

The NTSB traced the power loss to the left magneto’s impulse coupling. Both pawl retaining rivets showed heavy wear; one experienced fatigue fracture, followed by failure of the second rivet, the left gear retainer assembly and multiple accessory-gear teeth. The resulting damage affected the engine accessory section and caused the loss of engine power.

Could Maintenance Have Prevented It?

The magneto manufacturer called for a 500-hour inspection of the impulse coupling under a non-mandatory service bulletin. The airplane had undergone the inspection in April 2022, and investigators could not determine whether the wear or fatigue existed at that time. The report therefore did not conclude that the inspection was improperly performed or that the failure should definitely have been detected.

The Airport Information Changed the Emergency

The investigation found that GAD’s runway situation at the time was more usable than the information available to the pilot suggested. Because GAD was non-towered and airport personnel had left, ATC had limited ability to obtain current runway details beyond the NOTAM information. The NTSB concluded that the lack of current information likely influenced the pilot’s decision to continue toward 20A.

The Aircraft Stayed Controllable

Wreckage evidence showed no preimpact failure of the primary flight controls. The airplane struck trees in a wings-level, slightly nose-low attitude. That matters because the accident was not a final loss of control after engine failure. The pilot was still flying the airplane, but the combination of reduced power, distance, altitude and terrain left too little margin to reach the intended airport.

Conclusion

N4187Q’s final minutes show how a mechanical failure can become a navigation and information problem. The engine failure was physically explained, but the emergency landing options were shaped by the runway information available to the pilot. The aircraft remained controllable until terrain became unavoidable, and the final report connects the mechanical failure and the information gap without treating either as the whole story.

Sources & Reconstruction Note

• https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193432/pdf