What happened
On May 18, 1970, a Zlin 526F, registration HB-UPN, was performing aerobatic maneuvers near the Lommis airfield in Switzerland. The pilot, accompanied by a passenger, was conducting a flight intended to capture film footage of various maneuvers. During the execution of a maneuver—likely a looping or Immelmann turn—the aircraft reached a point of instability due to insufficient airspeed. This caused the aircraft to transition into a normal right-hand spin. As the descent progressed, the spin became increasingly flat, eventually reaching a longitudinal pitch of approximately 10 to 30 degrees. At 17:17 local time, the aircraft struck a meadow roughly 500 meters south of the airfield. The impact resulted in the death of the passenger and serious injuries to the pilot, while the aircraft was destroyed.
The investigation
Investigators reconstructed the flight sequence by analyzing Super 8 film footage captured by the passenger during the accident. This footage confirmed that the aircraft entered a right-hand spin and remained in a flat, rotating state until impact. The investigation examined the pilot's training, the aircraft's maintenance history, and the flight conditions. It was noted that while the pilot held a valid aerobatic rating, he had not completed the specific minimum training required for performing aerobatics with passengers. Additionally, the planned aerobatic program for the day had not been filed with the airfield manager, and the pilot had deviated from the previously established flight plan. The investigation found no evidence of mechanical failure or technical defects in the Zlin 526F.
Findings
- The primary cause of the accident was an unintentional normal spin initiated during an aerobatic maneuver.
- The aircraft transitioned into a flat spin that the pilot was unable to recover from.
- The aircraft's airspeed was insufficient at the apex of the maneuver, leading to the loss of stability.
- The pilot's limited aerobatic experience may have contributed to the inability to execute effective recovery techniques.
- The passenger was likely unaware of the imminent danger, as he continued to film the sequence until the moment of impact.