On 10 January 2000, two minutes and 17 seconds after departure from Zurich airport, at night in instrument meteorological conditions (IMC), a SAAB 340 operated by Crossair, entered into right-hand dive and crashed.
The following is extracted from the official accident Report published by The Aircraft Accident Investigation Bureau (AAIB), Switzerland:
Take-off clearance was given at 16:54:00 UTC […] The aircraft began its take-off roll at 16:54:10 UTC in darkness. The landing lights were on and the flaps were fully retracted.
The initial flight path, at a heading of 276 degrees, followed the centre line of the runway. The radar recording then showed a deviation in the flight path by 5 degrees to the south. However, this slight deviation was reduced before waypoint DME 2.1 KLO was reached by initiating a right turn.
At 16:55:15 UTC [the aircraft] was cleared to climb to flight level 110. At 16:55:39 UTC, Zurich departure issued the instruction to turn to VOR ZUE [Callsign], turn left to Zurich East". At 16:55:45 the bank angle to the left reached a maximum of 16.9 degrees on a compass heading of 270 degrees.
After the aircraft had remained briefly at a 16 degrees bank angle to the left, it began to roll to the right. From 16:55:47 UTC the bank angle rate amounted to 3 degrees per second to the right.
[Note that from this point until the time of impact was 40 seconds]
In this phase the first officer was very busy carrying out the orders routinely issued by the commander ("CTOT/APR off, yaw damper on, bleed air on"). All relevant flight parameters in this phase indicated a stable climb with a pitch of 13-14 degrees ANU [aircraft nose up]. The communication being conducted internally did not give any indication of difficulties of any kind.
At 16:55:55 UTC, at a bank angle of 8.4 degrees to the right, the bank angle rate increased and the nose of the aircraft began to drop from 14.2 degrees to 10.8 degrees ANU.
At 16:56:00 UTC the right bank angle attained a value of 31.0 degrees, when the commander gave the order to set climb power: "set climb power". The first officer confirmed with a whispered "coming" and began to set the climb power - a procedure which takes quite some time.
Between 16:56:03 UTC and 16:56:10 UTC the commander stabilised the bank angle to the right between 39 degrees and 42 degrees by corresponding flight control inputs. The pitch reduced further and stabilised at a value of 1 degrees ANU at 16:56:06 UTC as a result of corresponding elevator inputs for four seconds. As a consequence, the trajectory reached its maximum altitude of 4720 ft AMSL.
According to information from the crew of the preceding flight SWR 014 the cloud top at that time was approx. 5000 ft AMSL. The speed of the aircraft involved in the accident increased to 158 KIAS.
16:56:10 UTC marked the beginning of a nine-second period which was characterized by destabilization of the attitude. It featured uncoordinated deflections of the ailerons to the left and right. Meanwhile, the elevator remained practically in the neutral position. Since the rightward deflections of the aileron were dominant, the bank angle increased from 42 degrees to 80 degrees to the right. Given the neutral position of the elevator, because of the high bank angle the pitch increased to 25 degrees attitude nose down (AND). The aircraft therefore quickly lost altitude and its speed increased to 207 KIAS.
At 16:56:12 UTC the first officer made the commander aware that they should turn left to ZUE: "turning left to Zurich East, we should left".
At 16:56:15 UTC, at a bank angle of 65.8 degrees to the right, the commander muttered unclearly: "oh na-na". Three seconds later at 16:56:18 UTC, DEP requested confirmation that the aircraft was turning to the left […]. The first officer responded immediately: "moment please, standby". DEP then instructed the crew to continue the right turn: "ok, continue right to Zurich East."
In the final phase of flight, beginning at 16:56:20 UTC, the aircraft went into a spiral dive. As a result of massive aileron deflections, the aircraft attained a maximum bank angle of 137 degrees to the right.
The engines still provided high power, since setting of climb power had not yet been terminated. At a speed of 250 KIAS the over speed warning horn sounded. At 16:56:24 UTC the first officer vigorously warned the commander to turn left: "turning left, left, left, left… left!"
At the end of the data recording at 16:56:25 UTC the aircraft still exhibited a bank angle of 76 degrees to the right. The nose of the aircraft had dropped to 63 degrees AND at an air speed of 285 KIAS.
Several witnesses observed the aircraft breaking out of the clouds in a steep descent and performing a right turn.
At 16:56:27.2 UTC the aircraft crashed in an open field near Au, Nassenwil, ZH. None of the three crew members and seven passengers survived the impact.”
The Report further uncovers that the medication Phenezepam was discovered in the remains of the commander:
“It is conceivable that in this period the commander’s confusion about the current attitude dominated his perceptions and that he was having trouble interpreting the EADI display at all and reconciling it with his mental picture of flight path and attitude. Once again, an enhanced effect due to the medication cannot be excluded.”
The Cause of the accident was given as:
- “The flight crew reacted inappropriately to the change in departure clearance SID ZUE 1Y by ATC.
- The co-pilot made an entry in the FMS, without being instructed to do so by the commander, which related to the change to the SID ZUE 1 standard instrument departure. In doing so, he omitted to select a turn direction.
- The commander dispensed with use of the autopilot under instrument flight conditions and during the work-intensive climb phase of the flight.
- The commander took the aircraft into a spiral dive to the right because, with a probability bordering on certainty, he had lost spatial orientation.
- The first officer took only inadequate measures to prevent or recover from the spiral dive.”
The following is stated as contributory factors to the Accident:
- "The commander remained unilaterally firm in perceptions which suggested a left turn direction to him.
- When interpreting the attitude display instruments under stress, the commander resorted to a reaction pattern (heuristics) which he had learned earlier.
- The commander’s capacity for analysis and critical assessment of the situation were possibly limited as a result of the effects of medication.
- After the change to standard instrument departure SID ZUE 1Y the crew set inappropriate priorities for their tasks and their concentration remained one-sided.
- The commander was not systematically acquainted by Crossair with the specific features of western systems and cockpit procedures."
For further information see the full accident report published by AAIB.