Mooney M20F N9613M accident near Marion, Montana

Probable cause

The pilot’s improper rotation during takeoff from a high-altitude airport and his failure to abort the takeoff, which resulted in an impact with trees and terrain. Contributing to the accident was the pilot’s improper management of the turbocharger, which reduced the engine’s maximum performance during the ground run.

NTSB analysis

The pilot was departing at the time of the accident. At the beginning of the short field takeoff, he held the brakes as he advanced the throttle to 2,650 rpm. He then released the brakes and began the takeoff roll. The airplane was about 1,600 ft down the runway when the pilot attempted to rotate, but the airplane did not accelerate as the pilot had anticipated after he rotated about midfield. A witness observed the airplane in a nose-high attitude about this time.

As it was too late to abort the takeoff, he turned left to avoid a tree-lined hill at the end of the runway and obstacles to the right of the runway. He also engaged the power boost (turbocharger) at this time, which yielded little improvement in the airplane’s performance. The airplane was unable to gain sufficient altitude to clear trees so the pilot leveled the wings prior to the impact.

According to the pilot, the airplane had been underpowered during previous takeoffs and exhibited sudden slight drops in rpm; however, postaccident examination of the engine did not reveal any anomalies that could have precluded normal operation. The pilot stated that the engine appeared to function normally on the day of the accident but suggested that the propeller governor may have contributed to a performance deficiency as it had not been serviced for the past 30 years (or since the last major engine overhaul 30 years ago).

A functional test and disassembly of the governor revealed low performance output and excessive leakage due to pitting of the pilot valve. However, the loss in pressure output is not likely to have affected the propeller’s pitch attitude during the takeoff attempt.

Performance computations were consistent with the pilot’s and demonstrated that a successful rotation and transition into a climb for a midfield takeoff was attainable. A witness observed the airplane in a nose-high attitude after rotation. While the airspeed at which the pilot rotated is unknown, the airplane’s nose-high attitude suggests the airplane was not accelerating, thus inhibiting its transition out of ground effect. The investigation also found that the pilot did not properly engage the power boost (turbocharger) at the beginning of the takeoff as required by the flight manual. As the power boost is recommended at high elevation airports, like the pilot’s departure airport, the additional manifold pressure and engine power is likely to have increased the engine’s overall performance.

The evidence suggests that the accident was due to the pilot’s improper rotation during takeoff, which resulted in a runway overrun and an impact with terrain. Contributing to the accident was the pilot’s improper management of the turbocharger during a takeoff from a high-altitude airport, which reduced the engine’s maximum performance during the ground run. The airplane also had sufficient distance to stop had the pilot selected an earlier point to abort the takeoff.

Text from the NTSB. Open the NTSB docket for WPR21LA249 for the full record.