What happened
On April 25, 1999, a DR 400/180 S Regent, registered in Switzerland, departed Sion, Switzerland, for a flight to Friedrichsh．afen, Germany, to attend an aviation exhibition. The aircraft was carrying four occupants: a flight instructor, a flight student, another student, and one passenger. All four individuals were Swiss nationals.
The flight proceeded via several waypoints, including Martigny, Meiringen, and Konstanz. Upon entering the Friedrichshafen control zone, the pilot was instructed by air traffic control to fly the right-hand contra-approach very close to runway 24 to maintain traffic flow during the AERO 99 trade fair. To avoid overshooting the approach line, the pilot had to execute a 180-degree turn. Shortly after confirming the instruction to enter the right-hand base leg, the aircraft entered a steep right bank and struck an orchard at low altitude. The impact caused the deaths of all four occupants.
The investigation
The BFU investigation examined the aircraft, the flight logs, and the engine. The aircraft was found to have been slightly overweight at departure, and its landing mass exceeded the maximum allowable limit by approximately 7 kg. While the engine showed no mechanical defects, witnesses reported seeing the aircraft in a steep bank, with one noting a sputtering engine sound. The investigation also reviewed the fuel levels; although the main tank was empty upon impact, calculations suggested sufficient fuel should have been available for the landing if properly managed.
Findings
- The pilot executed a steep bank angle during the turn into the final approach.
- The pilot failed to maintain the required airspeed, leading to an aerodynamic stall.
- Air traffic control instructions required a tight maneuver that significantly increased the stall speed depending on the bank angle.
- A potential engine disturbance during the maneuver could not be entirely ruled out, though no mechanical failure was found.
- The aircraft was operating slightly above its maximum landing weight.