भयानक खत'राको त्यो क्षण || Two airplanes collided in the sky || Bishwo Ghatana

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Two airplanes collided in the sky
On 1 July 2002, a Boeing 757-200 being operated by DHL on a cargo flight from Bergamo to Brussels and a Tupolev Tu154M being operated by Bashkirian Airlines on a non-scheduled passenger flight from Moscow Domodedovo to Barcelona were destroyed whilst en route by a mid-air collision over southern Germany near Überlingen at night in Visual Meteorological Conditions (VMC). All 71 occupants of the two aircraft were killed.
An investigation was carried out by the German Federal Bureau of Aircraft Accidents Investigation, the Bundesstelle für Flugunfalluntersuchung (Germany) (BFU). Recorded data were recovered from the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) of both aircraft and also from the Non Volatile Memory of the Unit of the Tu154 only. ATC radar and R/T recordings were also available. A reconstruction of the flight paths of the two aircraft prior to their collision was made and is superimposed on a chart of the area in the illustration below:
Reconstruction of the two flight paths (reproduced Appendix 1 of the Official Report)
It was established that both aircraft had been under the control of Zurich ACC in accordance with a delegation agreement between the German and Swiss ANSPs. At the time of the accident, the Zurich ACC was being operated by a single controller supported by an assistant, which was as per prevailing Unit SOPs. Maintenance was in progress at the ACC overnight which meant that the radar system was functioning in the “fallback” mode under which minimum lateral separation was increased to 7nm from the normal 5nm.
The flight crews of both the aircraft involved were assessed by the Investigation as having high levels of qualification and relevant experience. The 757 was being flown by a crew of 2 who had completed initial TCAS training and had routinely received recurrent TCAS training through its inclusion in simulator details. The Tu154 had a crew of 4 and a supernumerary co-pilot on the flight deck. The pilot in the left-hand seat was a Captain under training designated as PF and the pilot in the right-hand seat was the Airline’s Chief Pilot acting as supervising Training Captain and was also, in the opinion of the Investigating Agency but contrary to paperwork for the flight, the aircraft commander. The under-supervision status of the left seat Captain was because of a Company requirement for each Captain operating to Barcelona to have completed two supervised flights before being permitted to act as a commander to that destination. The other two crew members were the Navigator and the Flight Engineer. In order to operate outside the Russian Federation where TCAS was not in use, both the pilots and the navigator had completed the required TCAS familiarisation training with their Operator. However, this had not included simulator practice because TCAS equipment was not installed on the simulator used for training. The co-pilot also present had no official function on the accident flight.
Both aircraft were at FL360, the 757 tracking north and the Tu154 tracking east. Both had been on the same Zurich ACC frequency under radar control in Class A airspace communicating with ATC in English for nearly 5 minutes when both aircraft receiving TCAS TAs as a result of potentially conflicting trajectories. Seven seconds after these TAs had been simultaneously annunciated, ATC, having become aware of the conflicting clearances which they had issued, instructed the Tu154 to descend to FL350. Five seconds later, the Tu154 initiated this descent without acknowledging the instruction to ATC, but two seconds after that, coordinated TCAS RAs were annunciated in both aircraft. The Tu154 RA was a ‘Climb’ and the 757 RA was a ‘Descend’. The 757 followed the RA promptly with AP disconnection after 2 seconds and 1500fpm descent attained 12 seconds after that. The Tu154 crew ignored the RA and continued the descent. When ATC called again to instruct the descent, this time adding ‘expedite’, the Tu154 crew acknowledged the descent instruction immediately but did not report their (ignored) TCAS RA on the contrary direction. ATC advised of traffic (the 757) at FL360.
Music Credit :
Martian Cowboy Kevin MacLeod (incompetech.com)
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