REVELATIONS the body of an Australian passenger from Malaysian Airlines Flight 17 was found with an oxygen mask should come as no surprise, an aviation expert says.

Former pilot and air traffic control operator Peter Smith said it was “extremely unlikely” the Buk surface-to-air missile that brought down the Boeing 777 would have killed everybody on board immediately.

All 298 crew and passengers, including 38 Australian citizens and residents, died when the Malaysia Airlines Flight 17, flying from Amsterdam to Kuala Lumpur crashed on July 17.

Mr Smith said the bulk of the shrapnel from the missile would detonate under the target, impacting the underside of the wings and the fuselage and causing “catastrophic damage”.

“The aircraft would be rendered instantly unflyable but this would not in itself be enough to cause the deaths of everybody on board,” Mr Smith said.

“The most likely scenario is that passengers closest to the point of impact might well have been killed or mortally wounded by the detonation of the missile which would also have punctured the pressurised cabin causing an explosive decompression.”

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Despite the damage, a number of the aircraft emergency systems would probably still have been working, including the automatic deployment of oxygen masks, Mr Smith said.

“It is entirely likely that a number of passengers may have been able to begin breathing through the emergency oxygen system in the depressurised cabin of the aircraft as it fell to earth,” he said.

“I know this is not what the relatives of passengers on board the aircraft would probably wish to hear but in my view it is certainly probable that many, perhaps even the majority of the passengers would still have been conscious and alive as the aircraft dropped out of the sky.”

Those who did not manage to breathe emergency oxygen would have been rendered unconscious quite quickly, perhaps within one to two minutes, he said.

“Realistically we will not know the details of exactly which systems were working until the flight data recorder information can be processed and analysed and even then the picture may not be entirely clear,” said Mr Smith.

“But I am reasonably certain that many of the passengers would have known precisely what was happening to the aircraft as it fell from the sky, even if they had no idea why.”

Mr Smith’s comments were made after Dutch prosecutors revealed that the passenger aboard Malaysia Airlines Flight 17 was found wearing an oxygen mask was an Australian. Earlier Dutch Foreign Minister Frans Timmermans revealed on national TV in The Netherlands that a passenger was found with an oxygen mask on.

The revelation raised questions about how much those on board knew about their fate when the plane plunged out of the sky above eastern Ukraine.

Prosecution spokesman Wim de Bruin says the passenger did not have the mask on his face, but its elastic strap was around his neck.

De Bruin says it is not known “how or when the mask got around the victim’s neck”.

However Australian and Dutch authorities investigating the MH17 flight have refused to confirm the admission.

The Dutch Safety Board refused to respond to Mr Timmermans’ claim saying, “The investigation is ongoing and is based on various sources and kinds of information,” a board spokeswoman said.

“We won’t bring out any details until the final report is issued.”

The Department of Foreign Affairs referred questions about the comments to the Australian Federal Police.

“The AFP is part of a multinational, Dutch led investigation (into the downing of MH17),” said a statement released by AFP to News Corp.

“The AFP does not comment on ongoing operations. Further questions should be directed to the Dutch authorities.”

Oxygen masks automatically drop from an aircraft’s overhead compartment when there is a loss of pressure in the cabin. They may also be released during severe turbulence or particularly rough landings.

Dutch investigators said last month the plane was likely struck by multiple “high-energy objects from outside the aircraft,” causing it to break up.

The latest revelation comes after Dutch Foreign Minister Frans Timmermans indicated that some of the passengers and crew on board may have remained conscious after the aircraft was shot down by a Buk surface-to-air missile fired by pro-Russian separatists 50km from the Ukraine-Russia border on July 17, BNO News reported.

The scheduled international passenger flight from Amsterdam to Kuala Lumpur crashed near Torez in Donetsk Oblast, Ukraine. All passengers, including 38 Australians, and crew died.

Timmermans, who was being interviewed on the Dutch national broadcaster’s show Pauw, answered a comment from host Jeroen Pauw that the final moments aboard Flight MH17 were not as suggested during Timmerman’s speech at the UN Security Council in the week after the atrocity.

“No, they did not see the missile coming, but did you know that someone was found with an oxygen mask over his mouth? So someone had the time to do that,” Timmermans said, dismissing Pauw’s question.

Timmermans added that there was no evidence to conclude that the final moments could not have been as he said in his UN speech.

Timmermans suggested that passengers had remained conscious after the airliner was struck by a suspected missile during his UN speech on July 21.

Experts later said everyone on board was likely killed immediately or, if not, became unconscious within seconds.

“I’ve been thinking how horrible the final moments of their lives must have been, when they knew the plane was going down,” Timmermans said during his speech at the UN.

“Did they lock hands with their loved ones, did they hold their children close to their hearts, did they look each other in the eyes, one final time, in a wordless goodbye? We will never know.”

A preliminary report by the Dutch Safety Board said that puncture holes in the aircraft’s wreckage suggested that small objects penetrated the aircraft in both the cockpit and forward sections. Holes were also found on the cockpit floor. Through analysis, the damage to the body of the aircraft is consistent with “high-energy objects” piercing the aircraft from the outside, they said.

Forensic experts have so far been unable to recover all bodies from the site of the crash due to ongoing fighting in the area. A total of 228 coffins have been flown back to the Netherlands for identification, but some of the coffins contained only partial remains, and it is unclear how many bodies remain unaccounted for.