The German Rail Accident Investigation Agency ('''', EUB) opened investigation number 04/2016 into the crash. The German police opened a separate investigation. Police confirmed that nine of the eleven deaths were local men from the districts of Rosenheim and Traunstein, aged 24–59. The cause of this crash was unclear. By the evening of 9 February 2016, Federal Transport Minister
Alexander Dobrindt reported that two of the trains' three
train event recorders had been recovered. The third was still located in one of the wedged train carriages. On 12 February it was announced that the third event recorder had been recovered. Police said that the recorder was damaged, but attempts would be made to extract the data. Data from the other two recorders had thus far provided no indication of
human error on the part of the train crew. In a press conference on 16 February 2016, the local prosecutor (
Staatsanwalt) identified "human error" by a
train dispatcher at the signalling centre in Bad Aibling as the cause of the crash. German investigators said they found no evidence of mechanical failure or technical defects that would have caused the crash. The dispatcher, Michael P., was also charged with
gefährlicher Eingriff in den Bahnverkehr (dangerous interference with railways), which is punishable with up to ten years' imprisonment. Many
German railway main signals are equipped with an additional subsidiary signal called "Zs 1" (shown as three white dots in a triangle shape). This subsidiary signal replaces a written order authorising a train driver to pass the signal while it is showing a stop aspect. The train dispatcher can activate it from the signal box. There are no safety controls in the signal box, other than special operating rules, for the dispatcher to activate a Zs 1 signal. When a Zs 1 subsidiary signal is shown to the train driver, they must press and hold the PZB button "Befehl" ("Order") in the cab while moving the train over an active
2000-Hz emergency stop inductor located at the main signal. A warning tone sounds in the cab to acknowledge to the driver that they are pressing the Written Order button. If in a station the Zs 1 signal is the last signal, after the complete train has passed the stop signal and any following
points (at a speed not exceeding ), the driver may continue with normal speed. The Zs 1 subsidiary signal is supposed to be used only in circumstances when a route for a train cannot be set. There are sections in the rulebook on how and when it may be activated safely, but according to the local prosecutor, these rules were not adhered to. In April 2016 it was revealed that the dispatcher had been playing a game on his mobile phone at the time. After realising he had made an error, allowing both trains to proceed, he dialled an incorrect number when trying to issue an emergency call. No technical fault existed with either of the trains or the signalling system. With these new findings the prosecutors reversed their initial assumption of
Augenblicksversagen (lapse of attention) turning it into a charge of
Pflichtverletzung (breach of obligations), which carries a heavier penalty. As a result, an arrest warrant was issued, and the train dispatcher was held in
pre-trial detention from 12 April 2016. The prosecutors brought the charges to the court in Traunstein in mid July 2016 with accusations on twelve accounts of
fahrlässige Tötung (
involuntary manslaughter) and 89 accounts of
fahrlässige Körperverletzung (involuntary
battery). The main trial was scheduled for seven days between 10 November and 5 December 2016. On the first day of trial, the defendant confessed to the charges brought by the prosecutors, but his lawyer wanted the degree of guilt to be evaluated during the subsequent proceedings. Although he showed a degree of compassion for the victims, the defendant refused to answer questions on the intensity of his preoccupation with the mobile game. The expert witness from the EUB investigation board had shown in court that while the documentation for the interlocking section () was outdated, slightly incorrect and did not contain directions for the emergency radio, the actual interlocking setup was logical and fully functional in a way that an experienced train dispatcher could handle correctly. The defendant had not followed general guidelines, including a
block signal test (), nor did he radio to the train driver to proceed slowly under the unusual circumstances. The original error had occurred somewhat earlier: with one of the trains running late, he chose to move the train crossing from Kolbermoor to Bad Aibling by juggling some of the signals. With a delay of only four minutes, this action was not warranted. The verdict was final, as his lawyers renounced any appeal a week later. In July 2018 he was released on probation after having served two-thirds of the prison sentence, in accordance with German law (§57 StGB). A preliminary report was published by the German investigation agency on 7 March 2017. The report stated that the infrastructure was fully functional, but that some documentation was slightly outdated (for example, an unused GSM-R radio infill station was listed). The reconstructed timeline showed that an emergency call was first initiated 35 seconds before the crash, but to the wrong emergency call group. The emergency code for track workers had been selected twice (code 569, "Trackside maintenance groups: High-priority call", "", labelled "") instead of the general GSM-R emergency number (code 299, "Train groups: Emergency call", "", labelled "").
Timeline The reconstructed timeline shows that the westbound train 79506 entered the section to Kolbermoor at 06:37. The first action in the following series of events occurred at 06:38 when the train dispatcher set the signals for the train allowing both entry to Kolbermoor station as well as allowing exit towards Bad Aibling. The westbound train reached the station at 06:40. The train was supposed to wait until 06:45 at the platform for the eastbound train to arrive. The eastbound train 79505 arrived at Bad Aibling station at 06:42. Since the exit signal at Kolbermoor was set to passing, the signal box did block the single track section to Bad Aibling for this train. Nevertheless, the train dispatcher tried to set the exit signal for the eastbound train from Bad Aibling towards Kolbermoor. He resolved the situation by assuming a technical error using the replacement signal "order" at 06:43 for the exit signal at the station and another replacement signal at the following station Bad Aibling Kurpark at 06:45. Now both trains were clear to enter the single-track section in opposite directions. The eastbound train left Bad Aibling station at 06:43:38. The time was taken from the train recorder as the train passed over an active
PZB inductor at the signal at danger. The westbound train 79506 at Kolbermoor waited for the regular departure time, leaving the station at 06:45:02. The train recorder of the eastbound train 79505 showed a stop at 06:45:14 in Bad Aibling Kurpark, quickly continuing on the single-track section. The signal at danger at Bad Aibling Kurpark was recorded at 06:45:46 (see picture). Shortly later, the train dispatcher recognized the situation with both trains showing up on the same track whereas the train drivers could not see each other due to a curve near the Bad Aibling sewage works. At 06:46:20 an emergency signal was radioed by the train dispatcher and received by other workers but not the train drivers. Both train recorders show an emergency brake at 06:46:55, only a second before the crash. Before the emergency braking, the trains were travelling at 56 km/h and 92 km/h respectively. The last entries on the train recorders at 06:46:56 show remaining speeds of 52 km/h and 87 km/h. The energy supply for the overhead catenary was automatically shut down at 06:47:02. == Recommendations ==