The Flight Data Recorder of the Canadair CRJ-200 cargo plane that crashed in Sweden on January 8, showed incompatible data, according to the interim report released by the Swedish Accident Investigation Authority. The FDR recorded pitch values increasing to +85°, which in realilty was descreasing to -40°.
The accident aircraft departed Oslo-Gardermoen Airport, Norway at 23:10 hours local time on a mail and package flight to Tromsø, Norway. The take-off, departure and climb to cruising altitude, flight level 330, were performed according to normal procedures. The flight was uneventful until one minute and 20 seconds before the impact.
After one hour and ten minutes of flight the pilot in command, who was seated in the left seat, exclaimed a strong expression. Immediately thereafter the aural warning for autopilot disconnect activated. The warning sounded continuously during the following 18 seconds.
After the autopilot disengagement FDR data indicates that both left and right elevators moved towards aircraft nose down position. Left and right side angle of attack went towards negative values. The aircraft entered a descent with vertical acceleration values that reached a negative load corresponding to -1G.
After a few seconds of negative G-load the aircraft’s warning system was activated by a so-called Triple Chime followed by an aural warning for low engine oil pressure on both engines.
FDR data shows that the trim to the movable horizontal stabilizer was activated manually and the trim position went from -0.9 degrees nose up to 1.7 degrees nose down. An aural signal of the stabilizer trim movement, signifying a manual input longer than three seconds, was activated in connection with this. Immediately thereafter a warning for high bank angle was activated.
After 17 seconds from the start of the event, the maximum speed (VMO), 315 knots was exceeded. The over speed warning was activated and the vertical acceleration turned to positive values.
Another 16 seconds later, the first officer transmitted a “MAYDAY” message that was confirmed by the air traffic control. The indicated airspeed then exceeded 400 knots and the stabilizer trim was reactivated and dropped to 0.3 degrees nose down. The Pilot in Command called “Mach trim” after which engine power was reduced to idle.
During the further event the last valid FDR value shows that the speed continued to increase up to 508 knots while the vertical acceleration values were positive, with maximum values of approximately +3G.
The aircraft collided with the ground one minute and twenty seconds after the initial height loss.
During the investigation it was concluded that four of the Flight Data Recorder’s parameters could not be compatible with the aircraft’s actual movement. The concerned parameters were pitch angle, roll angle, magnetic heading and ground speed. Those parameters emanate from the airplane’s Inertial Reference Unit (IRU). During the even the FDR recorded a continued increase in pitch from 0 to about 85° nose up in about twenty seconds time. In reality the aircraft attained a nose down attitude from 0 to about -40° in those twenty seconds.
The investigation is ongoing and a final report is expected to be published in December 2016.