Event
On January 28, 2000, an ATR 42-300 operated a scheduled passenger flight from Berlin-Tegel to Bremen under instrument flight rules. The aircraft, with three crew and 42 passengers, departed at 15:47 local time. During the initial climb, the crew detected icing via the ice evidence probe and observed ice accumulation on the leading edges and propeller spinners. Both anti-icing and de-icing equipment were active and functioning normally. The climb-out speed was initially set at 160 kt with a rate of 800-1,000 ft/min; after noting icing, the crew increased speed by 10 kt.
At flight level (FL) 60, the crew noted freezing rain and ice buildup. The climb rate gradually decreased despite both engines operating at maximum climb power. By FL 80, ice accumulation was so severe that the aircraft could no longer climb. The crew assessed that they had entered a zone of severe icing and requested an immediate descent from air traffic control. Descents were cleared to FL 60, then 4,000 ft, and subsequently to 3,500 ft (QNH), but icing persisted. The crew continued descending to 2,000 ft (QNH), where the aircraft exited clouds into visual meteorological conditions with positive temperatures, stopping further ice accretion. After 5-10 minutes at 2,000 ft, the ice shed from the airframe. The crew then proceeded to Bremen, climbing to FL 100 and landing without further issues at 16:45.
Aircraft Information
The ATR 42-300 is a twin-engine turboprop transport aircraft certified under FAR/JAR 25 for day and night operations. It is equipped with a pneumatic de-icing system on critical surfaces (wing and horizontal stabilizer leading edges, engine inlets) and electrical anti-icing on propellers, windshields, sensors, and control horns. The aircraft is approved for flight in icing conditions per FAR/JAR 25 Appendix C. The Airplane Flight Manual (AFM) includes a warning that the aircraft is not approved for operation in severe icing conditions; it provides visual cues for identifying severe icing and prohibits autopilot use when such cues are present.
Weather
Prior to departure, the crew received a weather briefing indicating light to moderate icing and moderate turbulence along the route. The Automatic Terminal Information Service (ATIS) at Berlin-Tegel also noted possible light to moderate icing up to FL 80. AIRMETs active at the time warned of moderate icing between the surface and FL 60. A meteorological assessment by the German Weather Service (DWD) indicated that the flight path lay in a frontal zone with stratocumulus clouds, freezing temperatures near the surface, and temperatures decreasing to -8°C to -10°C at 8,000 ft. Conditions were conducive to moderate to severe icing in the clouds encountered.
Crew Actions
The pilot in command (PIC), who was the flying pilot, had approximately 3,000 total flight hours (3.5 years on the ATR 42-300). The first officer had about 1,000 hours. The crew reported no trim anomalies. Upon identifying severe icing, the crew immediately requested descent from air traffic control. They did not declare an emergency at any point. After descending to 2,000 ft and confirming ice-free conditions using AFM criteria (ice evidence probe, propeller spinners), they decided to continue the flight to Bremen.
Investigation
The investigation confirmed that the aircraft was properly equipped and the crew followed procedures. The AFM's visual cues for severe icing (rapid ice accumulation on side windows and front windshield, possibly accompanied by water droplets) were present. The total air temperature at FL 80 was -10°C, consistent with severe icing conditions. No technical malfunctions were noted; the incident was attributed to an encounter with severe icing that exceeded the aircraft's certification limits.