Investigation Summary
The flight departed Milan with a 53-minute delay due to poor weather. While climbing through Flight Level 147, the aircraft was in Indicated Airspeed (IAS) hold mode set to 133 knots. This relatively low speed, combined with severe icing, led to a stall. The aircraft began a series of violent rolls, specifically 41 degrees right, 100 degrees left, 105 degrees right, and finally 135 degrees left. During the attempt to recover, the elevator trim moved to a nose-down position three times, which investigators termed 'anomalous trim changes.' This prevented the pilots from pulling the nose up, leading to a high-speed impact with the mountain slopes at approximately 700 meters above sea level.
Final Conclusions
The primary cause was the formation of ice on the wings which, combined with the low airspeed maintained by the autopilot's IAS hold mode, led to an aerodynamic stall and loss of control. Contributing factors included the crew's failure to recognize the severity of the icing and the subsequent anomalous pitch trim behavior that hindered recovery. The accident was a precursor to similar ATR icing events, most notably American Eagle Flight 4184 in 1994.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
IAS Hold Mode
An autopilot mode that maintains a constant airspeed by adjusting the aircraft's pitch; in this case, it allowed the climb rate to decay as ice increased drag.
Pitch Trim
The system experienced three anomalous nose-down movements during the upset, which prevented the crew from recovering from the dive.
Anti-icing System
Though active, the system was unable to cope with the severity of the icing or the aerodynamic consequences of the ice buildup at low speeds.
Interesting Facts
- 01The aircraft was nearly brand new, having been delivered to ATI only five months prior in May 1987.
- 02The aircraft was named 'Citta di Verona' and carried manufacturer serial number (MSN) 046.
- 03The flight was carrying 34 passengers and 3 crew members; all perished in the impact.
- 04The aircraft reached extreme bank angles during the upset, including 135 degrees to the left and 105 degrees to the right.
- 05German racing driver Axel Felder was among the passengers killed in the crash.
- 06The accident led to a manslaughter trial for the ATR designer and ATI executives, though all were eventually acquitted in 1995.
Safety Actions & Advisories
ATR Icing Procedures
The accident contributed to a better understanding of ATR 42/72 sensitivity to icing, eventually leading to revised operating procedures regarding minimum speeds in icing conditions.
Known Controversies & Unanswered Questions
Manslaughter Convictions and Acquittals
Reference ↗A judicial investigation initially led to the manslaughter conviction of ATR designer Jean Rech and three ATI executives. These sentences were controversial and were eventually annulled by the Supreme Court in 1995, resulting in full acquittals.