Incident Overview
On March 18, 2007, at 19:33 UTC, an ATR 42-300 aircraft registered F-GVZY, operated by Airlinair, experienced a significant safety incident during a scheduled passenger flight between Lyon and Montpellier. The aircraft was carrying three crew members and thirty passengers. The event involved severe icing of the airframe and engines while in cruise, resulting in no physical damage to the aircraft or injuries to those on board.
Flight Progression and Icing Conditions
The flight departed Lyon at 19:10 UTC under light rain with a ground temperature of 11 °C. The crew entered cloud cover at approximately 3,000 feet and initiated anti-icing procedures as they climbed through freezing levels. Upon reaching the planned cruise level of FL 150, the indicated airspeed was significantly lower than expected, dropping to 185 knots. The crew observed unstable cloud layers with snowfall and an outside temperature of -13 °C.
Believing that climbing would reduce icing severity due to colder temperatures, the crew requested clearance to climb to FL 190. However, while climbing to FL 170, they observed rapid accumulation of uniform white ice on the wings, engine intakes, and cockpit windows. The indicated airspeed dropped further to between 160 and 170 knots, a deficit of 38 knots compared to theoretical values. Recognizing the severity of the icing, the crew abandoned the climb and requested descent to FL 130.
Engine Failure and Recovery
During the descent, as the aircraft passed FL 135 at an indicated speed of 200 knots, the left engine stopped. The investigation suggests this was caused by a large amount of snow detaching from the intake due to warming during the descent. The crew disconnected the autopilot, managed the descent manually, and successfully restarted the engine twelve seconds after the stoppage. An emergency message was transmitted to air traffic control in Marseille. The aircraft landed safely at Montpellier with residual ice still present on certain parts of the airframe.
Investigation Findings
A borescope examination of the left engine revealed no mechanical defects. The incident highlighted limitations in meteorological forecasting, as the crew had interpreted pre-flight weather charts to indicate only moderate icing. In reality, the atmospheric conditions produced severe icing at altitudes where it was not explicitly predicted. The report notes that qualitative assessment by crews can sometimes underestimate icing intensity, particularly when anti-icing systems are active.