February 11th, 1991, 100 passengers had an unforgettable flight on the former DDR airline Interflug.
читать дальшеThey had boarded at Berline Schoneveld for a flight to Moscow. The flight was uneventfull, until they started the landing.
Just before 11 o'clock the flight is on approach to Sheremetyevo. The flight is on a ILS approach to runway 25L. The plane is on full auto-pilot.
As usual during such a landing the pilots are preparing the landing. That includes the second pilot setting the go-around altitude of 3.580 foot (1.090 meter) in the auto-pilot's computer. The plane is on approach wtih flaps and slats out at 1.550 foot (472 metres) when the pilots are informed by ATC that the runway is not clear. They are instructed to do a go-around. The pilots put the throttle in go-around mode and correct the settings of the flaps. They also change the altitude settings for the go-around computer tpo 1.640 foot (500 meter), the altitude assigned by ATC.
As the graphs indicate the Airbus climbed at 10:56:41 as expected on auto-pilot. The pilots believe the plane is climbing too steeply. Therefor they disconnect the auto-pilot. When they hear the stall alert they try to push the nose down. However, at this point the auto-pilot was not totally disconnected. Therefor the manual change in attitude is counteracted by a auto-pilot change of trim level.
Only when the go-around altitude is reached is the go-around autopilot disconnected. However, the pilots fail to realise this. They are still trying to correct level of the climb. Due to this "fight" between pilots and auto-pilot the plane is at climbing at full power, but with very slow speed. At a height of 4.327 foot (1.318 meter) the speed is just 34 knots (63 kph). This is well below the stall speed and the wings barely provide any lift. The crew did not notice the stall alerts.
At this point in filght the plane dips to the left and goes into a nearly uncontrolled vertical dive. 23 Seconds later it's at 1.487 foot (453 meter) when at 10:57:46 it starts to climb again. This time is climbs for 29 seconds up to an altitude of 5.787 foot (1.763 meter). During the climb the speed again drops and again it dips to the left.
At 10:58:40 the process repeats. At an altitude of 1.775 foot (541 meters) it starts to climb again. This time for 31 seconds till it reaches and altitude of 7.355 foot (2.241 meter). This time it dips to the right.
These uncontrolled climbs and descents are repeated four times. Only after decreasing the engine power does the crew regain control and land safely at 11:05:58.
While the passengers and crew where terrified, there where no injuries. As was usual during those days (NOTE: cold war) no information was revealed about this incident. The accident investigators (FUS / Flugunfalluntersuchungsstelle) filed it under "flight disruption". In the investigation (file number: 6 X 002-0/91) the cause is noted as failure of the crew to notice that the auto-plot had disengaged. They where under the impression that the auto-pilot could not disengage, and paid insufficient attention to various warnings.
The pilots had not noticed that the auto pilot had changed trim level. This meant the plane was out of control between 10:56:50 abd 11:03:00.
Only after changing the power and trim level did the pilots, unwittingly, regain control. In desperation the captain had also pulled several fuses in an attempt to disable the auto-pilot. This did not work, as the wrong fuses where pulled!
No technical issues were found on the plane. The auto-pilot disconnected certain modules due to the strange flight path and resulting unreliable data.
That leaves the crew's qualifications. The captain had 6.399 flight hours including 5.699 hours on the Il-18 and 730 hours on the A310. The second officer 6.778 hours of which 5.509 on the Il-18 and 1.269 on the A310.
That the pilots had skipped two generations of planes between the Il-18 and the A310 was summarised as such by the FUS: "The crew did not follow essential rules of "Crew Coordination" and "Cockpit Resource Management". They lacked the required skills to operated a modern 2-man glass cockpit".
The lead investigator said: "The incident was caused by a disruption of communication between crew and plane. In a modern plane several safety controls are in place such as flight envelope protection. During a critical phase the pilots tried to override the auto-pilot, not fully realizing the potential consequences".
The alsmost crashed A310 is currently part of the Luftwaffe's VIP fleet, flying under serial number 10+23. The two other former Interflug A310s are now also part of the Luftwaffe.