Introduction
On 30 May 2015, a Piper PA-28RT-201T aircraft, registration HB-PLC, operated by MaximAir AG, was involved in an accident during landing at Grenchen/SO regional airport (LSZG). The flight was a training flight conducted under visual flight rules (VFR). The crew consisted of a flight instructor, a pilot, and a passenger with no flying experience.
Flight History
The aircraft departed runway 25 at 14:34 local time. After four uneventful circuits, during the fifth approach, the landing gear did not fully extend. While the nose and right main landing gear indicators showed green, the left main landing gear indicator did not. The flight instructor ordered a go-around. The crew replaced the indicator lightbulb to rule out a defective bulb, but the issue persisted. After another go-around, the crew informed the aerodrome controller and climbed to approximately 5500 ft QNH near Lake Biel for troubleshooting.
Troubleshooting
The crew followed the emergency checklist for manual landing gear extension. They set the gear selector to DOWN, pulled the landing gear circuit breaker, and activated the emergency gear extender. Despite multiple attempts, only the front and right landing gear indicators showed green. The crew noted that the red gear unsafe light extinguished in both retracted and extended positions, leading them to suspect a faulty down lock switch. They returned to Grenchen for a low pass to allow the aerodrome controller a visual inspection. The controller estimated the left main landing gear was extended to approximately 70 degrees. A mechanic contacted the crew by radio and confirmed the gear was not locked. The crew performed elevated-g and yaw manoeuvres, and a descent at 75 kt, but could not fully extend the left gear. A second low pass over the grass runway confirmed the gear still not fully extended.
Landing and Accident
The crew prepared for landing on runway 25. They briefed the passenger on emergency procedures, including a brace position. At 16:23, they reported for approach. The flight instructor was at the controls. During landing with partially extended landing gear, the left main landing gear collapsed. The aircraft exited the runway at low speed and came to a stop in the adjacent meadow. The aircraft sustained minor damage. There were no injuries to the two crew members or the passenger.
Causes
According to the Swiss Transportation Safety Investigation Board (STSB), the accident was due to a landing with partially extended landing gear. The left main landing gear could not be fully extended through either normal extension or the alternate free-fall procedure due to the combined effects of increased mechanical resistance causing jamming of a landing gear leg, and a cable break on the main landing gear that caused the hydraulic pump to stop before the affected main landing gear was locked.