Investigators have been unable to explain conclusively why a passenger on the ill-fated Malaysia Airlines flight MH17 was found wearing an oxygen mask following the Boeing 777’s destruction over Ukraine.

The Dutch Safety Board states that the aircraft was shot down by a Russian-built surface-to-air missile but it has not been able to determine much detail about the situation in the passenger cabin following the initial detonation.

Dutch prosecutors disclosed in October last year that a single passenger had been found with a mask during the recovery operation.

All three crew members in the cockpit were killed instantly by the hail of shrapnel from the warhead, and the 777 subsequently broke up as a result of aerodynamic forces.

Investigators determined that electrical power to the aircraft was abruptly lost – halting the aircraft’s surveillance transmissions and both flight recorders – at 16:20:03 local time on 17 July 2014.

The aircraft’s internal cabin altitude had been 4,800ft before the missile detonation, indicating that the oxygen system would not have activated prior to the explosion.

While the sudden depressurisation of the fuselage should have triggered the deployment of masks, the inquiry found that this was prevented by the loss of electrical power.

Investigators recovered some 50 oxygen generators from the crash site, all but one of which had been activated – which normally occurs as a passenger dons the mask, tugging it and pulling the generator’s firing pin.

The inquiry sought to learn whether passengers on board MH17 had been able to access the oxygen system in the aftermath of the missile explosion.

One passenger was found to be wearing a mask strap around their neck, with the mask at their throat. But no DNA or fingerprint analysis could be conducted, says the inquiry, to explain its presence.

“It remains unclear whether the person concerned put on the mask in a reflex or that it was done by someone on the ground,” the Dutch Safety Board adds.

But it states that the oxygen system was “unlikely” to have activated in the normal manner, and that masks probably fell from their storage hatches as a result of dynamic forces from the break-up.

The inquiry points out that only a small force is required to remove the firing pin from the oxygen generator and that they could have been activated by the missile detonation or during the crash sequence.

Investigators found that the non-activated generator had been installed in the crew rest, rather than the passenger cabin, and might have been protected by the compartment structure.

While the cockpit crew sustained immediate fatal injuries the inquiry could not determine the length of time for which the passengers and cabin crew might have remained conscious.

But it says the occupants were probably “barely able to comprehend” the situation after the initial explosion, given the overwhelming sudden cacophony and the presence of a high-speed cold airstream and debris.

“No indications were found that point to any conscious actions,” it says, highlighting the absence of any photographs or text communications from mobile devices, although it states: “It cannot be ruled out that some occupants remained conscious for some time during the [60-90s] for which the crash lasted.”

Source: Cirium Dashboard