Cessna 170 N4476B accident near Missoula, Montana

Probable cause

The pilot receiving instruction's failure to maintain directional control during the takeoff roll, which resulted in a runway excursion and ground-loop, and the flight instructor’s failure to adequately monitor the pilot.

NTSB analysis

The pilot, who was receiving instruction for his tailwheel endorsement, reported that, during the takeoff roll, the airplane began to veer left. He applied corrective control inputs, and the flight instructor called for him to abort the takeoff, but the airplane ground looped and departed the runway. The airplane sustained substantial damage to the right wing and aileron. The instructor reported that the event happened too fast for him to correct the diversion and that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR20CA053 for the full record.