What happened
On May 8, 1976, at approximately 15:28, two Cessna 150 aircraft, registration HB-CSU and HB-CWL, collided at an altitude of roughly 750 meters near Birrfeld airfield. The aircraft were flying in the same corridor used for both arrival and departure routes. The impact was nearly frontal, causing both aircraft to become uncontrollable. The HB-CSU entered a spiral dive, while the HB-CWL suffered significant structural damage, including the loss of a wing section, before crashing. All four fatalities occurred during the accident, as both pilots and both passengers perished in the subsequent crashes.
The investigation
The investigation examined the flight paths, radio communications, and environmental conditions at the time of the accident. The pilot of HB-CS and the ground staff at Birrfeld confirmed that the pilot of HB-CSU had requested permission for a western arrival, which was granted by an unidentified person on the ground. The investigation also reviewed the physical wreckage, noting that the propeller of HB-CSU had struck the upper wing surface of HB-CWL, leading to the separation of structural components. Witnesses observed the aircraft flying at the same altitude and noted the rapid, vertical descent of both planes following the impact.
Findings
- The primary cause of the accident was inadequate airspace monitoring by the pilots.
- Contributing factors included insufficient separation between the western arrival and departure routes at the airfield.
- The pilot of HB-CWL was flying directly into the sun, which caused significant glare and obscured the visibility of the oncoming aircraft.
- The pilot of HB-CWL was known to be highly myopic, and it could not be determined if corrective lenses were being worn at the time of the collision.
- The visibility from the cockpit of the Cessna 150 is inherently limited, making the detection of aircraft on similar headings difficult without active scanning.