The scheduled passenger flight with a Fokker 70 from Vienna (Austria) to Munich (Germany) had departed Vienna at 07:27lt for the short flight.
Shortly before 08.00lt, the crew received clearance to descend from Flight Level 280 to Flight Level 100. During the descend the ice detection system activated alerting the crew that icing conditions existed, as per procedure wing and engine anti-ice systems were activated.
The incident aircraft (© Jan Gessmann)
The ice alert activated when the aeroplane entered the clouds. After levelling off at Flight Level 100 ice was building upon the windscreen edges. The righthand engine started to vibrate increasingly 6 minutes after the aircraft levelled off at FL100. During further descend the vibration of the righthand engine started to increase during the descend, so much that the VIB HIGH ENG2 message was shown to the crew. After completing the relevant checklist the engine was not shut down, in absence of other failure messages. At 08.08lt the EPR (Engine Pressure Ratio - measurement of engine thrust) for the lefthand dropped to 1,0, meaning the engine effectively no longer produced thrust, Heavy vibrations were felt by the crew together with rattling noises, with no vibration indicated to the crew. Because of the problems with the engines, the crew declares an emergency and requested an immediate landing. ATC cleared them for an immediate descent to 5000 feet, followed by further descent to 3500 feet. The aircraft was configured as per procedure during the descent and approach to runway 26L at Munich. After levelling off at approximately 3500 feet the crew observed that the engines were not responding to thrust lever movement, the EPR for both engines remained around 1.00, while the engine speeds and temperature of both engines increased. After being transferred to the tower controller the landing clearance was received. shortly afterwards the tower controller informed the crew they were 500 feet below the glideslope, at about the same time also the Ground Proximity Warning System alerted the crew of the low altitude. It became apparent to the crew they would not reach the runway and informed ATC they would be landing ~4 miles (~7 km) short of the runway. 13 seconds prior to touchdown the gear was selected down, too late to be fully down and locked at the time of the off runway touch down. With the gear partly extended the aircraft touched down 2,5 miles from the threshold and slid to a stop 220 meters from the touchdown zone of the runway. There was no post-touchdown fire and all passengers and crew left the aircraft via the passenger door.
The field with the path the aircraft followed (© BFU)
Soon after an investigation was launched by the German Aviation Accident investigation Authority (BFU), after an investigation that lasted nearly 2 years the following cause was determined;
Prolonged flight at low power settings in moderate icing caused ice build-up on the fan of both engines.
Vibrations caused by the ice buildup caused the ice impact panels to break free from their bonding (glue)
The loose ice impact panels got trapped in front of the Outlet Guide Vanes of the fan, causing a severe obstruction in the airflow, reducing the amount of thrust produced by the engines.
No warnings were presented to the crew to indicate the loss of thrust, resulting in the landing short of the runway.
The Ice Impact Panels blocking the airflow in the left engine. The fan blades in the foreground and the Outlet Guide Vanes behind the brown-grey Ice Impact Panels (© BFU)
The full investigation report (in German) is available by clicking here. A good summary can be found here; https://aviation-safety.net/database/record.php?id=20040105-0