Beech B-99 N699CZ accident near Milwaukee, Wisconsin

Probable cause

A right main landing gear collapse due to fatigue failure of the landing gear drag leg support fitting.

NTSB analysis

The pilot reported no difficulties during the flight or landing. While taxing the airplane after landing, the green right landing gear position indicator light extinguished, and the red gear handle light illuminated. The pilot glanced over to the circuit breaker panel and noted that the landing gear control circuit breaker had tripped. After parking the airplane for refueling, he notified his company maintenance control group about the issue and was advised to not reposition the airplane after refueling. The pilot waited about 20 minutes for weather to clear before exiting the airplane. As the pilot prepared to exit, the right main landing gear collapsed and the airplane’s right wing impacted the ground, resulting in substantial damage.

Metallurgical examination of the separated fracture surface on the right landing gear drag leg support fitting revealed an area of fatigue in a machined radius adjacent to the center lug of the drag leg support. The remainder of the fracture exhibited features consistent with overload failure. An additional crack was found in the machined radius on the opposite side of the center lug. This portion of the part had not completely separated. Exposure of the crack revealed the existence of a fatigue crack in about the same area as the first crack, with overload signatures outside of the fatigue area.

The airplane maintenance manual indicated that the subject part was to be cleaned and visually inspected at least every 7,500 cycles or every 5 years, whichever occurred first. Maintenance records indicated that the part had accumulated 762 cycles since the most recent inspection 23 months before the accident.

After the accident, the operator examined the drag leg support fittings on their fleet of 9 other airplanes of the same model. Of the 18 fittings examined, 14 were found to be cracked. Of the 14 cracked fittings, 11 could only be detected using dye penetrant inspection, and could not be detected solely by visual inspection.

Text from the NTSB. Open the NTSB docket for CEN22LA188 for the full record.