Absence of routine alarms has led investigators to believe that an Embraer 190 captain, left alone in the cockpit, deliberately disengaged multiple systems before the aircraft crashed in Namibia.

The LAM Mozambique Embraer had been cruising at 38,000ft when cockpit-voice recordings picked up the sound of the altitude pre-select being dialled to 4,288ft, then to 1,888ft and again to 592ft.

Shortly afterwards the autothrottle was disengaged and one of the air conditioning packs was deactivated.

Neither event generated a caution alarm, and the Namibian transport ministry says, in an interim statement on the crash, that this indicates the actions were intentional.

Similarly the aircraft’s mode was subsequently switched from ‘altitude hold’ to ‘flight-level change’ without any evidence of a failure of the flight-management system.

“Therefore it is possible to infer that these transitions were manually commanded,” says the inquiry. The captain had been alone because the first officer had left for the lavatory.

Autothrottle was manually re-engaged and – because the Embraer had been directed to follow a flight-level change to the lower altitude – the thrust levers automatically retarded. The autothrottle was then disengaged once more.

Flight-data recorder information shows that the jet departed from its assigned altitude and began a rapid straight-line descent that lasted for 6min 42s before Namibian radar lost contact. The aircraft struck the ground 15s later.

Some 20s after the jet left its cruising altitude the thrust levers were advanced then, 9s later, retarded back to idle. During the descent the flight-data recorder continued to capture the activation of a number of other systems.

Nearly 2min into the descent the speed-brakes were manually activated, deploying the spoilers. The speed-brake handle stayed in this position. The aircraft began descending rapidly, up to 10,560ft/min, and its varying pitch reached some 10° nose-down on occasion.

The desired speed was manually adjusted “several times”, says the inquiry, and the diving Embraer’s airspeed increased – reaching some 330kt at times – triggering overspeed warnings.

Bleed pressure dropped to near-zero, again with no caution alarm, indicating that both bleeds were disengaged intentionally.

As the aircraft descended through 17,000ft a master caution warning activated for 6s. "It was not yet possible to correlate this message with any abnormal system behaviour,” the inquiry states.

Namibian air traffic control lost contact with the Embraer at 6,600ft. Twelve seconds later the first ground-proximity alerts activated – at 5,150ft altitude when the aircraft was 2,010ft above terrain.

It crashed in Bwabwata national park and none of the six crew members or 27 passengers survived.

Investigators have not drawn any conclusions from the recorded information, but there is little in the interim statement to counter the early suspicion that the flight was sabotaged by the captain. No distress call was made by the crew, which had been in radio contact with Gaborone controllers before the sudden descent at the EXEDU waypoint.

Namibia’s inquiry states that “no mechanical faults were detected”, and that the first officer left the cockpit minutes before the crash. Recordings revealed “repeated banging”, it confirms, attributed to demands to enter the flightdeck.

Source: Cirium Dashboard