What happened
On September 30, 1965, a Piaggio P-149E, registration HB-EER, was involved in a ground taxi incident at Zurich-Kloten Airport. The aircraft, operated by Swissair, was being used for flight training purposes. Following a series of landing exercises at Altenrhein, the pilot returned to Zurich and landed at 12:24.
While taxiing toward the Jet Hangar, the pilot attempted to maneuver the aircraft into a parking position by driving onto the grass to perform a 180-degree turn before returning to the paved surface. Due to the resistance of the tall grass, the aircraft was moving at a low speed. During the transition from the grass back onto the hardstand, the nose gear collapsed, resulting in a broken nose gear strut and a destroyed propeller.
The investigation
Investigators examined the site of the incident, specifically focusing on the edge of the concrete apron. They identified a drainage channel approximately 50 cm wide and 10 cm deep along the edge of the concrete. The investigation revealed that the ground level where the grass met the concrete edge had subsided irregularly, creating a vertical difference of approximately 8 cm. This unevenness was partially obscured by grass that was roughly 15 cm high.
The aircraft, which had only 10 hours of total flight time, showed no signs of pre-existing cracks or mechanical defects in the landing gear assembly. The investigation also confirmed that the aircraft's weight and center of gravity were well within permissible limits, with only two occupants and minimal baggage on board.
Findings
While the aircraft was moving at a very low speed, the investigation concluded that the impact with the 8 cm vertical step was sufficient to cause the structural failure. The investigation noted that the specific weight distribution—with two passengers seated in the forward seats—likely increased the load on the nose gear, reducing its ability to withstand horizontal shocks. Additionally, the necessity of using brakes to execute a tight turn may have contributed to the increased stress on the nose gear assembly during the transition.