Cessna 421C N66NC accident near Longmont, Colorado

Probable cause

The loss of performance for reasons that could not be determined.

NTSB analysis

The pilot reported that he performed the “before starting engine” and “starting engine” checklists and everything was normal before taking off in the twin-engine airplane. He performed an engine runup and then started his takeoff roll. The pilot reported that about halfway down the runway the airplane was not accelerating as fast as it should. He attempted to rotate the airplane; however, “the airplane mushed off the runway.” The airplane settled back onto the runway, then exited the departure end of the runway, where it sustained substantial damage to the wings and fuselage.

The airplane engine monitor data indicated the airplane’s engines were operating consistent with each other at takeoff power at the time of the accident.

Density altitude at the time of the accident was 7,170 ft and according to performance charts, there was adequate runway for takeoff. The reason for the loss of performance could not be determined.

Text from the NTSB. Open the NTSB docket for CEN21LA315 for the full record.