What happened
On May 2, 1986, the pilot of a Robin DR 400/180S (registration HB-KAT) departed Geneva for a short trip to Annemasse, France, accompanied by his parents. The group returned to Geneva in the late afternoon as a thunderstorm was passing through the area, bringing gusty winds and reduced visibility.
Upon approaching Geneva-Cointrin Airport around 17:45 local time, the pilot contacted the control tower. At that moment, he was positioned behind a DC-9 airliner that was on final approach to runway 23. The air traffic controller confirmed the pilot had the DC-9 in sight and authorized him to turn onto the final approach segment immediately behind the larger aircraft.
Witnesses observed the small Robin flying at an unusually low altitude, significantly closer to the DC-9 than standard separation procedures would typically allow for light aircraft approaching Geneva. As the Robin entered the wake turbulence generated by the DC-9, it pitched up sharply and rolled over in a half-barrel roll before impacting the ground vertically approximately 1,400 meters from the runway threshold.
The impact destroyed the aircraft and killed all three occupants instantly. The plane had landed on grass adjacent to the runway, causing minor damage to the field and spilling fuel, though no fire ensued.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) conducted a thorough inquiry into the accident. Key elements examined included:
- Flight Path Analysis: Eyewitnesses and reconstruction tests confirmed that HB-KAT was flying at a similar altitude to the DC-9, well below the normal glide path for light aircraft at Geneva, which typically aim to land further down the runway to avoid occupying the concrete strip too long.
- Meteorological Conditions: A thunderstorm was active, with wind gusts reaching 27 knots. The controller had warned the DC-9 crew of wind shear at 800 feet on final.
- Pilot Status: The pilot held a valid private license and had approximately 485 hours of flight experience, including 250 hours on the Robin type. An autopsy revealed an alcohol content between 0.10% and 0.20%, though the report noted this was not necessarily the primary cause.
- Aircraft Condition: The Robin was airworthy, with weight and balance within limits. Post-impact examination showed flaps were extended and the engine was producing low power at impact.
The investigation ruled out mechanical failure or a single wind gust as the primary cause. Instead, it focused on the proximity to the larger aircraft and the resulting aerodynamic interference.
Findings
The accident was caused by:
- Loss of control in final approach due to wake turbulence from the preceding DC-9, which the pilot followed too closely.
Contributing factors included:
- Inappropriate flight tactics, specifically deviating from the standard low-level avoidance profile for light aircraft at Geneva.
- Pressure to land quickly, possibly influenced by discomfort caused by turbulence for the elderly passengers and the approaching storm.
- Potential misinterpretation of ATC instructions or situational awareness regarding wake vortex dissipation times.
The SUST concluded that the Robin penetrated the DC-9's wake vortices while at a critical phase of flight (low altitude, low speed), leading to an uncontrollable roll. The proximity was exacerbated by the pilot's decision to follow the airliner directly rather than maintaining a higher approach path typical for smaller aircraft at this airport.
Safety action
The report highlighted the dangers of wake turbulence for light aircraft following larger jets, particularly in non-radar environments where standard separation minima may not account for vortex persistence. It underscored the importance of pilots adhering to recommended approach profiles that keep them above or well clear of the flight path of preceding heavy or medium aircraft. No specific new regulatory actions were detailed in this summary beyond the implicit reinforcement of wake turbulence avoidance procedures.