Germany's BFU reported in their monthly Bulletin that the aircraft was climbing through FL130 about 15 minutes into the flight when cabin crew reported smoke and an electrical smell of burning plastics in the cabin. The flight crew began to work the relevant checklist, when an "explosion" occurred in the right hand engine followed by a fire indication for the right hand engine. The crew shut the right hand engine down and activated the first fire suppression system, which extinguished the fire indication. The crew declared emergency and returned to Munich on one engine. During the return cabin crew again reported smoke in the cabin prompting the commander to decide an evacuation would be carried out after landing. Cabin crew began to brief the passengers for the evacuation. During the last stages of the approach the flight crew observed the rudder pedals could no longer be moved despite combined efforts of both flight crew. A yawing moment to the left during the flare thus could not be compensated, the aircraft touched down on runway 26L in some left angle to the runway center line, continued straight and departed the runway about 1290 meters/4230 feet past the runway threshold, collided with the most western antenna of the RVR system and its switchbox, the nose gear subsequently collapsed. The aircraft came to a stand still after rolling over soft ground for about 300 meters. The left engine could not be shut down the normal way and was therefore shut down using the fire handle, the evacuation of the aircraft was initiated. Five passengers received minor injuries.
The aircraft was piloted by the captain (42, ATPL, 7,804 hours total, 5,559 hours on type) and the first officer (35, ATPL, 4,477 hours total, 1,677 hours on type). The aircraft had accumulated 18,521 hours total in 18,712 cycles.
The BFU reported that upon arrival of the investigators both propellers were found in their feathered positions, the left hand propeller could be turned by hand, the right hand propeller could not be moved. The lower part of the right engine's cowling was covered with oil, the upper part of the right engine's cowling showed burn marks. When the cowling was opened traces of fire and a number of fractured pipes in the aft area of the engine were discovered.
In the cockpit both oxygen masks had been used, the throttles could not be moved.
The right hand engine was sent for laboratory examination.
After the aircraft was moved into a hangar the rudder system was examined, it was determined the pedals could only be moved in a restricted range. The Travel Limited Unit (TLU) was found in the "high speed" mode limiting the rudder travel. After the limiter had been mechanically disconnected the pedals could be freely moved and the rudder followed accordingly to its mechanical stops.
After the battery was connected the TLU was electrically tested, it was found the TLU fault indication was illuminated. There was no "low speed" indication, the bus tie connector switch was found in the open position. When the TLU was manually selected to low speed, the TLU fault indication extinguished and the green low speed indication illuminated about 25 seconds later, the TLU mechanics was moved removing the rudder travel limits. When the TLU was selected to high speed, the mechanism moved to engage the travel limits and the TLU fault indication illuminated 25 seconds after the switch was engaged.
The electrical busses were subsequently powered by a ground power unit, the TLU selected to automatic. With the bus tie still disengaged, the TLU was in high speed mode, the FLT CTL indication was missing, the low speed indication was missing, the TLU fault indication was illuminated. When the bus tie connector was closed the TLU moved to the low speed mode, the low speed indication illuminated and the TLU fault indication extinguished.
The investigation is continuing.
On Aug 5th 2020 the BFU released their final factual report in German and subsequently also in English.
The final report terminates the investigation with the factual narrative only, no conclusions or analysis was released.
The report changes the number of minor injuries to 6 (in the bulletin of 2012 5 minor injuries had been reported), the injuries occurred as result of the evacuation.
The right hand engine suffered the fracture of a turbine blade of the 2nd stage due to stress overload. An inclusion of aluminium, chrome and titan most likely was the point of origin of the fracture. The fracture caused secondary fractures at supply tubes of bearings 6 and 7 resulting in an oil leak, which contaminated the cabin air and caused a fire in the right hand engine. The fire was extinguished with the activation of the fire suppression system.