What happened
On the morning of July 16, 2008, a pilot operating a Yak-9 U-M—a homebuilt replica of a 1940s Russian fighter—attempted to fly from Aachen-Merlenbrück to Niederrhein Airport. The flight departed at 07:25, outside the airfield's published operating hours. During the flight, the pilot encountered difficulties with the right landing gear failing to retract fully. Due to these mechanical issues and deteriorating weather conditions, the pilot decided to abort the mission and return to Aachen-Merzbrück.
At approximately 07:55, the pilot landed on runway 26. During the landing roll, the pilot noted a failure of the right brake. The aircraft veered in a slight leftward curve, traveling 129 meters beyond the end of the runway. As the aircraft crossed a small depression near the edge of an unpaved farm track, the right landing gear collapsed. The aircraft came to rest on its belly, with the propeller, the underside of the fuselage, and the right wing—which had its flaps extended—striking the ground. There were no injuries to the pilot, though the aircraft sustained heavy damage.
The investigation
The BFU examined the aircraft and the circumstances of the landing. Technical inspection of the aircraft revealed that a castle nut was missing from the bolt of the right landing gear's retraction mechanism. While this nut was intended to hold the drive mechanism bolt in place, investigators determined that the absence of the nut was not a contributing factor to the collapse, as the bolt itself remained in position.
Investigators also reviewed the pilot's recent flight history. It was noted that four days prior to the accident, the pilot had attempted to land at Aachen but was unable to stop within the runway limits, necessitating a go-around. Additionally, on the same day as that previous incident, the pilot had performed a safety landing following high coolant temperatures, which resulted in overrunning the end of runway 26 by approximately 60 meters.