Downer Bellanca 14-19-2 N7658B accident near Prosser, Washington

Probable cause

An inadequately welded elevator attachment lug, which caused the elevator to partially detach from its bellcrank, resulting in flutter and structural damage.

NTSB analysis

During cruise flight the airplane lost pitch authority after a flutter event partially disabled its elevator and resulted in structural damage to the horizontal and both outboard vertical stabilizers. Although the airplane had limited pitch authority following the event, the pilot was able to successfully land the airplane in a field.

The airplane was the subject of an airworthiness directive (AD) concerning play in the pitch trim system, which required inspection of the pitch trim tab for play at 100-hour intervals. The play in the pitch trim system had the potential to cause such a flutter event if not complied with. However, the airplane had just come out of its annual inspection and the pilot also examined the airplane in accordance with the AD just before flight. Additionally, no evidence of such play was observed during a postaccident examination. The pitch trim system had failed, but it appeared to be because of overload damage, likely sustained from the high oscillatory forces induced during the flutter event.

Examination of the elevator revealed that the upper lug that connected the elevator pitch control tube to the elevator bellcrank had failed. The weld joints in that area exhibited a lack of fusion and penetration, creating gaps between the filler with the control arm surfaces and the lug. These gaps allowed fatigue cracks to initiate and propagate. Once the cracks had grown large enough, the remaining intact weld material fractured from overstress, leading to the separation of the lug from the control tube.

The lug failure resulted in a partial disconnection of the control surface, which likely started the flutter event. This ultimately led to the failure of the pitch trim control arm, which would have exacerbated the flutter.

Corrosion and primer identified at the lug fracture area indicated the surfaces had not been properly prepared before welding. Although the lower lug had not failed, it also exhibited similar evidence of gaps caused by a lack of fusion and penetration.

It could not be determined if the lugs were welded at the time of the airplane’s manufacturer, more than 66 years before the accident, or during a subsequent repair.

Text from the NTSB. Open the NTSB docket for WPR22LA136 for the full record.