What happened
On July 25, 1997, a Cessna 210N, registration N-271WD, departed Grenchen airport for a business flight to Parma, Italy. The aircraft was carrying the pilot and three passengers. During the flight, the aircraft was operating under instrument flight rules (IFR) through clouds and low visibility.
At approximately 09:06, the aircraft began to descend from its assigned altitude of FL150. Radar tracking showed the plane steadily losing altitude until it disappeared from the radar screen at FL118. Witnesses subsequently observed the aircraft in a vertical, spinning dive out of the clouds, striking a slope in the Cuolm-Cavorgia region. The impact resulted in four fatalities, and the aircraft was destroyed.
The investigation
The investigation examined the aircraft's flight path, the weather conditions, and the air traffic control (ATC) monitoring. Investigators noted that the aircraft was slightly overweight, exceeding its maximum takeoff weight by approximately 1.55%. The aircraft was not equipped with an anti-icing system.
Investigators also reviewed the actions of the Zurich Radar North controller. It was established that the aircraft went without radio contact for over 15 minutes. Furthermore, the aircraft flew below its assigned altitude for nearly three minutes without any intervention or altitude correction attempt from the controller.
Findings
- The primary cause of the accident was likely the loss of control due to heavy ice accumulation on the airframe while flying in instrument meteorological conditions (IMC).
- The aircraft lacked an de-icing system, making it vulnerable to the icing conditions present at the time.
- A technical failure, such as an autopilot malfunction or a failure in the vacuum pump affecting the artificial horizon, could not be entirely ruled out.
- The air traffic controller did not intervene when the aircraft deviated from its assigned altitude, an action that might have alerted the pilot to the developing situation.
Safety action
Following the investigation, a recommendation was made to expedite the installation of a Minimum Safe Warning (MSAW) system within the Eurocontrol Eatchip area to better detect and alert controllers to altitude deviations.