Beech V35B N777PH accident near Alva, Oklahoma

Probable cause

The flight instructor's and pilot's failure to recognize that a high descent rate had developed on short final, likely due to their distraction by an open engine cowling, and the unexpected strong pitch-down force during flap extension due to the installation in the airplane of a Short Takeoff and Landing system.

NTSB analysis

The private pilot had recently purchased the Bonanza airplane, which he and an experienced flight instructor were using to conduct his first training flight in a Bonanza. During a visual approach, the engine's left cowling opened. According to the pilot, who initially survived the accident, the flight instructor assumed control of the airplane. Based on video from home surveillance cameras, the descent rate for the approach increased to about 1,000 ft per minute about 100 ft above ground level. About 7 seconds later, the airplane impacted trees and a power line located 1/2 mile from the runway threshold.

The airplane was one of three Bonanza airplanes modified with a Robertson Short Takeoff and Landing (STOL) system. The flight characteristics for this modification included a strong pitch-down force while extending the flap from 15° to 30° position, which is greater than in Bonanzas without this STOL system. The investigation could not determine if the pilot or flight instructor was aware of this unique flight characteristic, which was not described in the STOL certification information.

The pilot had compiled a list of airplane discrepancies, which included "cowling latch - pilot's side rear spring." It is likely a latch for the left engine cowling opened in flight because it was not properly secured during the preflight. The flight instructor and pilot were likely distracted by the open engine cowling and did not expect the strong pitch-down force during flap extension, which resulted in a high descent rate on short final.

Text from the NTSB. Open the NTSB docket for CEN18FA023 for the full record.