N7849

On June 29, 2024, about 1840 eastern daylight time, a Grumman G-164A, N7849, was substantially damaged when it was involved in an accident near Toccoa, Georgia. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight.

According to the pilot, he departed Toccoa Airport-RG Letourneau Field (TOC), Toccoa, Georgia, for Walnut Ridge Regional Airport (ARG), Walnut Ridge, Arkansas. During takeoff, he noticed the engine rpm did not reach 100% but he continued the flight. Shortly after takeoff, the engine appeared to surge and the pilot decided to return to the departure airport. As he approached the airport, the engine surging worsened. During touchdown, he pulled the throttle back to beta; however, the engine started to increase in power. He tried to shut down the engine, but it continued to increase in power. He applied heavy braking to slow the airplane down; the left brake then locked, and the airplane departed the left side of the runway. The right main landing gear separated and the wings were substantially damaged.

Postaccident examination of the engine revealed that the engine’s main shaft, torsion shaft, first-stage compressor impeller shroud, first-stage impeller, first-stage diffuser, second-stage compressor housing, and second-stage compressor impeller, displayed rotational scoring and damage that was

consistent with an engine that was rotating and operating at the time of impact. The aft turbine bearing support assembly was submitted to the manufacturer’s failure analysis group for further analysis. According to the manufacturer’s report, the separation of one strut and cracking of the inner and outer portions of the other struts resulted from overload. No evidence of fatigue was observed on the fractured struts. The strut base material was verified by energy-dispersive Xray and microstructural analysis to be the specified IN713C nickel alloy in the cast condition. No material anomalies were observed, and no pre-existing condition was found that would have prevented normal operation.

The manufacturer issued Pilot Advisory Letter (PAL) PA331-09 in August 2013, addressing the issue of engine oscillations. The PAL read in part:

When performing a takeoff, pilots normally advance the power lever(s) to a takeoff value as specified in the POH/AFM and as indicated on the torque (or equivalent) gauge. If a takeoff is attempted with the Engine Speed Control(s) in any position other than full forward, resulting in the engine not achieving 100-101% RPM, the engine(s) may very well achieve the desired indicated torque; however, the engine(s) will actually develop a reduced level of horsepower. A reduced level of horsepower will result in the degradation of aircraft performance.

The letter also notes that, “One and possibly two adverse effects can result if a takeoff is attempted with the Engine Speed Control(s) in any position other than full forward. They are reduced power output from the engine(s) and the possibility of accompanying engine oscillations…The primary driving function for these oscillations is that the fuel control’s Main Metering Valve (MMV) set point has intersected the acceleration schedule.”

Review of the accident airplane’s maintenance logbook revealed that the engine was installed on November 15, 2023. At the time of the accident, it had accumulated 22 hours of operation.