The investigation was initiated by the BFU immediately after receipt on the notification.

Up to now, the investigation has led to the following results:

Aircraft/ Crews:

· The aircraft collided at a right angle. Whereas the Boeing B 757 was on a northern heading (004º) the Tupolev TU 154 M had a western heading (274º). The collision occurred at an altitude of app. FL 350.

· Both aircraft were equipped with identical collision warning devices (TCAS Honeywell 2000, Change 7). According to the knowledge gathered so far, no malfunction was found.

· Both operators had provided training programmes for TCAS and the crews had completed the corresponding training.

· Neither the history of the flight nor the evaluation of the flight data recorders indicated any technical defects on the aeroplanes.

Air Traffic Control:

· In the ACC Zurich maintenance work on the system was performed in the late evening of the accident day, during this period of time the system was operated in the “fallback mode”.

The horizontal separation minima had been increased from 5 to 7 nm. According to this, the horizontal distance between aeroplane flying at the same altitude must be at least 7 nm, which corresponds to a flight time of app. one minute. during this period of time the ground based collision warning system STCA (Short Term Conflict Alert) was not available.

The direct phone connections to the adjacent air traffic control services were not available either.

· At the moment of the collision one controller was on the sector controller workplace. He had to monitor two workplaces with radar screens. A second controller on the night shift was outside the office for a break.

In addition there was one assistant on the sector workplace. She had no traffic control tasks but was responsible only for the receipt, the processing and the transmission of reports and flight plans.

This crew composition was corresponding to the normal night shift at the ACC Zurich.

· Approximately two minutes prior to the collision the STCA system of the UACC (Upper Area Control Center) at Karlsruhe issued a warning to advise of a probable collision. The radar controller of the UACC tried several times to contact the ACC Zurich via the direct telephone line. It was not possible to establish a connection.

Exercise 9.2.2 Answer the questions.

1. What aircraft collided near the town of Űberlingen?

2. Where did both aeroplanes crash on?

3. Where was the wreckage spread?

4. How many passengers were aboard the aeroplane to Barcelona?

5. What did the previous clearance include?

6. What did TCAS warn about?

7. What did ACC Zurich instruct the crew of the Tupolev about?

8. What was the simultaneous command?

9. Who was the instruction acknowledged by?

10. What did the radar controller inform the crew about?

11. What did the crew ask for?

12. What results had the investigation led to?

13. Which system was not available?

14. What was the controller responsible for?

15. What was this crew composition corresponding to?

16. What did the radar controller of the UACC try to do?

Exercise 9.2.3 What do the following abbreviations stand for.