Avionics confusion had hand in Crossair Saab 340 accident

 - January 30, 2007, 11:11 AM

Nearly four years after the accident, the Swiss Aircraft Accident Investigation Bureau (BFU) published its final report on the Jan. 10, 2000 crash of a Crossair Saab 340B at Nassenwil near Zurich Airport. The unusual delay stems from appeals filed against the BFU’s conclusions, the most publicized objection coming from Moritz Suter, Crossair’s CEO at the time of the accident. One day after the report’s publication the Swiss governmental appeal board was asked to review it, meaning it might not be “final” after all. The BFU confirmed its findings as published in an intermediate report in September 2002, which singled out pilot error as the main cause of the crash.

Crossair Flight 498 took off from Runway 28 at Zurich Airport at 4:54:10 p.m. GMT for a scheduled flight to Dresden, Germany. The twin turboprop crashed two minutes 17 seconds later in a field near the village of Nassenwil. All 10 occupants died and the aircraft caught fire. The flight crew included a 42-year-old captain who was a native of Moldavia and a 35-year-old first officer from Slovakia. They had flown together on nine flights during the previous four days without incident or known personality clashes. English was their only common language, but while the first officer spoke fluent English the captain had only sufficient command of the language to accomplish his job.

During the climbout from Runway 28 the captain had chosen to fly the aircraft manually, rather than use the autopilot. He was cleared to the KLO VOR, where he was to make a 180-degree left turn and continue the climb toward the ZUE VOR (also called “Zurich East” by ATC). According to the BFU’s findings, problems for the ill-fated flight started 2.1 nm before reaching KLO, at 4:55:39, when ATC cleared the pilot direct to the ZUE VOR with an immediate left turn. Without waiting for instructions from the captain, the first officer reprogrammed the FMS accordingly with a “direct to” entry. As he had not entered a left or right indication, the system chose a right turn as the shortest way and displayed that indication.

The captain started a left turn as per previous ATC directions, but after 4:55:47 the aircraft started a roll to the right. From 4:56:10 to 4:56:19 the flight data recorder showed several uncoordinated aileron deflections left and right. The FO repeatedly told the captain they should turn left, but ATC then chose to give clearance for a right turn to Zurich East. The bank angle to the right continuously increased and peaked at 137 degrees at 4:56:20. Because of the excessive bank, the aircraft started losing altitude and gained speed. At 4:56:25, its nose-down pitch had reached 63 degrees and forward speed exceeded operating limits. The Saab then entered a steep spiral and crashed at 4:56:27.

BFU experts concluded that the captain lost spatial orientation in the dark sky “with a probability bordering on certainty” and caused the aircraft to dive in the attempt to correct an excessive bank angle in the wrong direction. Contradictory indications and orders in a language that he did not fully master apparently proved too much for the Moldavian pilot, who had flown Russian-built airplanes, where the attitude is displayed by a moving aircraft symbol in front of a fixed horizon, as opposed to a fixed aircraft symbol in front of a moving horizon as in the EADI fitted in the Saab 340.
A superficial impression of a Russian instrument indicating a 30-degree bank to the left resembles a Western instrument indicating a similar bank to the right. The BFU noted that confusion caused by this difference in display technique has caused several accidents in Russia after introduction of Western aircraft there.

Other elements cited by the BFU as main causes of the crash are the captain’s decision not to use the autopilot in the climbout phase and an inadequate response from the first officer to prevent or recover from the final spiral.

The captain’s flight bag contained an open package of Phenazepam, a sedative produced in Russia, and a very small concentration of that medicine was found in his muscular tissue. The BFU did not consider it was a primary cause of the accident.
The Moldavian pilot had been directly hired as a captain by Crossair. Despite the fact that he had been a Saab 340B captain with Moldavian Airlines from 1997 through 1999, and that he had gone through the Crossair training center in Basel on behalf of Moldavian, BFU said he had not been systematically trained by the company to get fully acquainted with the aircraft’s specific features and Western systems.