Grumman G-164A N7849 accident near Toccoa, Georgia

Probable cause

The pilot’s failure to set the engine speed control fully forward during takeoff, resulting in an engine surge and subsequent loss of control during landing.

NTSB analysis

The pilot of the turbo propeller-powered agricultural airplane reported that, during takeoff for a cross-county flight, 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 surging worsened and, after touchdown, the engine power started to increase. He tried to shut down the engine, but the power continued to increase. He applied heavy braking to slow the airplane; the left brake then locked, and the airplane departed the runway and the airplane’s wings were substantially damaged.

Postaccident examination of the engine revealed damage indicative of an engine that was rotating and operating at the time of impact; no pre-existing condition was found that would have prevented normal engine operation or control. The engine manufacturer issued a Pilot Advisory Letter more than 10 years before the accident addressing the issue of engine oscillations. The letter noted:

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 added 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.”

Since the previous 22 hours of flying did not demonstrate this type of engine behavior, postaccident examination of the engine found no issues that would have prevented normal operation, and the pilot reported both not achieving 100% speed as well as engine oscillations during and after takeoff, the pilot likely did not advance the engine speed control fully forward during takeoff.

Text from the NTSB. Open the NTSB docket for ERA24LA286 for the full record.