NTSB Factual Report

On August 15, 2018, about 1145 central daylight time, an Aero Commander S2R, N5521X, was substantially damaged during a runway excursion on takeoff from runway 9 at the Rolling Hills Airport (3MN4), Westbrook, Minnesota. The operator stated that the airplane did not climb as expected after takeoff and it encountered a corn field off the end of the runway. The pilot was not injured. The airplane was registered to and operated by Olsem Aerial Application Service as a Title 14 Code of Federal Regulations Part 137 flight. Day visual meteorological conditions prevailed. The local flight was not operated on a flight plan. The flight was originating at the time of the accident.

The pilot informed a Federal Aviation Administration (FAA) inspector that he had experienced a loss of engine power at rotation during takeoff. The pilot reported that there were two small rises along the turf runway. The airplane normally became airborne at the second rise. The accident takeoff proceeded normally past the first rise. However, as the airplane approached the second rise, the tail of the airplane dropped to the ground. The pilot perceived a loss of engine power and began to drop the application load immediately afterward. The operator stated that the airplane was fueled before the accident flight and was within the maximum gross weight limitation at the time of the accident.

The airstrip was oriented east-west and the accident takeoff was preformed toward the east. A soybean field was located immediately off the end of the runway, followed by a two-lane roadway, and a corn field. The soybean field exhibited evidence of the application load being dropped as the airplane passed over but appeared to be otherwise undisturbed. The airplane continued across the intervening two-lane roadway and traveled about 300 ft into the corn field, leveling the existing 8-foot corn crop, before nosing over and coming to rest. A postaccident examination conducted by FAA inspectors did not reveal any anomalies consistent with a loss of engine power or a failure or malfunction of the flight control system.

The airplane was equipped with an engine monitor unit which was recovered from the wreckage and downloaded. A review of the data indicated that the accident takeoff was the fifth of the day. The data revealed a momentary exceedance of the interstage turbine temperature (ITT) on the initial engine start of the day consistent with a hot start event. Otherwise, the engine parameters appeared to be within normal operating limits during the previous flights. The engine was not shutdown between flights.

The data revealed that, at the beginning of the accident takeoff, the engine speed increased smoothly from an idle speed of about 64% to 99% over a period of 5 seconds, and it remained at or above 97% for the remainder of the takeoff run. The fuel flow and oil pressure increased in conjunction with the engine speed. The engine torque increased in conjunction with the engine speed and subsequently stabilized at 100% about 35 seconds later. Each of the noted parameters stabilized within normal operating limitations during the takeoff run and were consistent with the engine operating normally at full takeoff power. About 50 seconds after the takeoff began, the engine speed and torque parameters decayed abruptly. The engine speed decreased from 98.3% to zero over a 4-second time interval. The engine torque increased momentarily to 106% before decreasing to zero over the following 3-second interval. The abrupt decrease in engine speed and torque was consistent with the encounter with the corn field.