Accident Overview
On April 30, 2022, about 1000 central daylight time, a Beech B-99 airplane, registration N699CZ, was substantially damaged during an accident at General Mitchell International Airport (MKE), Milwaukee, Wisconsin. The sole occupant, the pilot, was not injured. The aircraft was operating as a Title 14 Code of Federal Regulations Part 135 cargo flight.
The flight originated from Baraboo/Wisconsin Dells Regional Airport (DLL), Baraboo, Wisconsin, with MKE as its intended destination. As the airplane approached MKE, air traffic control cleared the pilot for a visual approach to runway 19R. The pilot reported that the landing was “smooth given the weather conditions” and used normal braking to exit the runway.
Post-Landing Events
After entering the ramp area, the green right landing gear position light extinguished and the red gear handle light illuminated. The pilot observed that the “Landing Gear Control” circuit breaker had tripped. Following parking for refueling, he contacted company maintenance control and was advised not to reposition the aircraft after refueling. The pilot waited approximately 20 minutes for weather to clear before preparing to exit the airplane. At that time, the right main landing gear collapsed, causing the right wing to impact the ground. The resulting damage to the right wing was substantial.
Component Failure
Post-accident examination revealed that the right landing gear drag leg support fitting, part number 50-120201-1, had broken. Further examination by the operator determined that the same part on the left landing gear was also fractured.
Metallurgical analysis of the separated fracture surface on the right drag leg support fitting showed 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 had not completely separated. Exposure of that crack revealed a fatigue crack in approximately the same area as the first, with overload signatures outside the fatigue area.
Maintenance History
The maintenance manual for the airplane specified that the part was to be cleaned and visually inspected at least every 7,500 cycles or every 5 years, whichever occurred first. If a crack was detected by visual inspection, it was to be confirmed by dye penetrant inspection; any cracks found required part replacement. Maintenance records showed that the part had accumulated 762 cycles since the last inspection, which occurred 23 months prior to the accident.
The operator reported that the accident airplane was maintained under an Approved Aircraft Inspection Program (AAIP) and had accumulated 35,012.9 total flight hours and 43,054 total cycles at the time of the accident. The most recent inspection of the drag leg support fitting was performed on May 11, 2020.
Fleet-Wide Findings
The operator examined all drag leg support fittings on its fleet of nine Beech B-99 airplanes (excluding the accident aircraft). Of the 18 fittings examined, 14 were found to be cracked. Among those 14 cracked fittings, 11 required dye penetrant inspection for detection; the cracks were not visible by visual inspection alone.
This accident bore similarities to a previous event on October 14, 2020 (NTSB report number ERA21LA021), involving another Beech B-99 operated by the same company. In that incident, the right main landing gear collapsed while the airplane was taxiing from the runway after landing, and the drag leg support fitting was also found to have fatigue cracking in the same area.