What happened
On March 21, 2008, an AVRO 146 RJ85 was prepared for a passenger flight from Frankfurt to Florence. During the boarding process, weather conditions deteriorated significantly, involving thunderstorms, graupel, and heavy rain. During a pre-departure inspection, the crew identified contamination and ice on the lower edge of the co-pilot's window. However, because the de-icing station was closed and a de-icing procedure was no longer possible at the parking position, the crew decided to taxi without de-icing after observing that the wingtips appeared clear and the slush on the ground was melting.
Shortly after taxiing, the tower informed the crew that a follow-me driver had observed accumulation on the aircraft's wings. A communication breakdown occurred in the cockpit: the pilot misunderstood the message, believing the agent was asking if they had detected contamination themselves, rather than reporting that contamination had been seen. The pilot concluded that no contamination was present and proceeded with the takeoff.
At 12:46, the aircraft departed Frankfurt. During the climb through flight level 110, the aircraft experienced longitudinal changes and fluctuations in vertical speed while the autopilot was engaged. The aircraft was unable to maintain the target climb speed of 280 knots. The continuous oscillations caused nausea in approximately 50% of the passengers. The pilot eventually switched to manual flight, noting high control forces. Due to the unstable flight conditions, the crew declared an emergency and diverted to Stuttgart, where they landed safely.
The investigation
The BFU examined the flight data recorder (FDR) and cockpit voice recorder (CVR). The FDR analysis confirmed the observed fluctuations in vertical acceleration and the autopilot's inability to maintain stable flight parameters. A post-flight inspection of the aircraft revealed traces of de-icing fluid on the horizontal stabilizer rudder, but also evidence of melting ice on the surface. No significant residues of de-icing fluid were found on the wings or other surfaces.
Findings
- Inadequate assessment of wing contamination due to a misunderstanding of a communication from the tower.
- Presence of ice/contamination on the horizontal stabilizer, as evidenced by post-flight inspections.
- Communication failure between the pilot and co-pilot regarding the specific nature of the ramp agent's report.
- Flight instability characterized by longitudinal oscillations and vertical speed fluctuations during the climb phase.