Aggiornamento da avherald:
On Mar 9th 2016 the SHK conducted a press conference introducing a preliminary report (The Aviation Herald later succeeded in receiving the report) to Swedish Media. Swedish Media are reporting that according to the investigator in charge the IRS (Inertial Reference System) data recorded on the flight data recorder do not match the accident flight - the investigation therefore is looking into what data the crew actually received exploring a possible theory that the crew might have received erroneous data prompting them to disconnect the autopilot. An expletive can be heard on the cockpit voice recorder after the autopilot was disconnected. 16 seconds later the distress call was made, after another 17 seconds the aircraft reached the highest recorded speed of 950kph (512 knots), the engines reduced to idle thrust, and the aircraft impacted ground at about that speed (508 knots last recorded speed) 80 seconds after the aircraft departed controlled flight. The investigation is ongoing, a final report is estimated by December 2016.
On March 9th 2016 later the afternoon the SHK released their interim report stating that there had been no significant weather along the planned route of the aircraft which took the aircraft into Swedish Airspace still controlled by Norwegian ATC. The flightplan requested FL330 for cruise.
The flight departed normally and was enroute at FL330 without anomaly until about 70 minutes into the flight and until 80 seconds prior to ground impact. About 70 minutes into the flight the captain exclaimed a strong expression, immediately after the cavalry charge (autopilot disconnect aural indication) sounded, the flight data recorder recorded the autopilot disconnect, too. The cavalry charge continued for the next 18 seconds. Following the autopilot disconnect the FDR recorded both elevators went into the nose down positions, all angle of attack sensors indicated negative angles of attack and the aircraft entered a descent reaching a vertical acceleration of -1G causing the G-Load warning system to activate issuing a triple chime, a synthetic voice alert indicated low oil pressure for both engines.
The FDR showed that the stabilizer trim went from 0.9 degrees nose up to 1.7 degrees nose down, the according clacker sound indicating stabilizer trim movement were heard on the CVR. Immediately after a high bank angle warning activated.
17 seconds after the autopilot disconnect the aircraft accelerated through 315 KIAS (VMO, maximum operating speed), the overspeed warning activated, the vertical acceleration turned into positive values.
Another 16 seconds later (33 seconds after the start of the event) the first officer transmitted a "MAYDAY" message which was confirmed by ATC, the aircraft had accelerated to 400 KIAS, the stabilizer trim began to recover and was at 0.3 degrees nose down. The captain called "Mach trim", the engines were reduced to idle thrust. The aircraft continued to accelerate however and reached 508 KIAS (last recorded speed), the vertical acceleration reached +3G, the aircraft's ailerons and spoilerons were mainly deflected to the left throughout the event.
The SHK stated: "Radar data and the accident site position indicate that the track was changed about 75 degrees to the right during the event. The crew was active during the entire event. The dialogue between the pilots consisted mainly of different perceptions regarding turn directions. They also expressed the need to climb. The aircraft collided with the ground one minute and twenty seconds after the initial height loss."
The SHK reported: "The validation of the parameters showed that four of the 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 IRU units"
The SHK continued that the pitch angle recorded by the FDR does not match the actual progress of the flight (see graphics below, showing blue the actual recorded pitch angles and green the computed pitch angles), the pitch angles were computed based on true airspeed and acceleration data, the computed pitch angles may be a few degrees off as the actual bank angles were not known. The computation of the other parameters is still in progress.
