Expert: Bomb or missile likely cause of Iran plane crash

Three Britons were among the people killed after the passenger plane crashed moments after take-off on Wednesday.

All 167 passengers and nine crew on the Ukraine International Airlines Boeing 737 flight from Imam Khomeini International Airport in Tehran to the Ukrainian capital Kiev were killed minutes after take-off at 6.10am local time (2.40am GMT) on Wednesday.

David Learmount, consulting editor at aviation news site FlightGlobal, said such a sudden crash would only have a small number of causes.

The former RAF pilot said: "Whatever it was, it was very dramatic and very sudden because the crew were not able to make an emergency call.

"They had plenty of height which would have given them the time to make a call. They were at around 8000 or 9000 feet and all of a sudden they were not talking to anyone.

"You try to work out what very dramatic thing can go wrong with an airliner and you can't really come up with anything.

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"If it was a missile strike, that's dramatic. If it was a bomb on board, that's dramatic.

"If you have either of those two things that might well damage the aeroplane to such an extent that the pilots are simply fighting for control and therefore they don't have the capacity to tell anybody what's going on."

Officials in Iran blamed an engine fire while the Ukrainian president has ordered a criminal investigation into the crash.

UIA has ruled out any chance of human error given the experience of the crew.

Learmount said the crash could have been caused by the "catastrophic mechanical failure" of an engine, however he said this would not match the significant wreckage that has been reported by the Iranian media.

He continued: "That would not be as dramatic as what we appear to have witnessed because although it could have damaged the aeroplane significantly, it would have been able to fly on the other engine alone.

"It has never happened before that both engines have failed for completely unrelated reasons at the same time.

"That is the only catastrophic thing that could have happened to the aircraft without any interference from the outside."

Learmount said it was rare to have both engines fail, which has been previously caused by a crash into a flock of birds.

However, at a height of between 8,000 and 9,000 feet, the UIA plane was too high to be affected by birds, he said.

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"You don't get a four-year-old modern airliner falling apart in the sky and bursting into flames, it just doesn't happen," he added.

The Iranian military disputed suggestions the airliner was brought down by a missile, something Downing Street added there was "no indication" of, after the Ukrainian authorities refused to rule out the prospect.

Tony Cable, a former senior inspector of the Air Accidents Investigation Branch (AAIB), told Sky News there was likely a "loss of control" which led to the crash.

When asked what may have caused this, he said: "A multitude of things really, all sorts of aircraft faults and failures, hostile action, whatever, many, many causes potentially."

Cable said the aeroplane is thought to have had a normal ascent before suddenly dropping.

"It suggests something pretty catastrophic," he said.

The investigation into the crash is ongoing and will involve the plane's manufacturer, Boeing, as well as the United States.

However, tensions are high in the region after the US killing of Iranian General Qassem Soleimani.

Graham Brathwaite, Professor of Safety and Accident Investigation and Director of Transport Systems at Cranfield University, said: "These are safety investigations, not to apportion blame or liability, but to focus on what the industry can learn.

"The investigation will be led by Iran as 'the state of occurrence' with Ukraine acting as an accredited representative. One of the other states that would normally participate is the state of the manufacturer, in this case the United States National Transportation Safety Board (NTSB).

"They could bring in technical advisers - in this investigation that would be the manufacturer, Boeing. This ensures the independence of the investigation's findings."

Brathwaite added that a third, neutral country may be involved in aspects of the investigation including decoding the flight data recorder, commonly known as the black box.

The OPS Group, an aviation monitoring group, have published a report suggesting the possibility that the plane was shot down.

It described "obvious projectile holes in the fuselage and a wing section ... whether that projectile was an engine part, or a missile fragment is still conjecture".

A number of commercial airlines have rerouted flights to avoid possible danger amid escalating tensions between the United States and Iran.

The UK has urged Iran not to carry out further "reckless and dangerous" attacks after Tehran fired missiles at military bases in Iraq hosting British and US troops.

British Airways rerouted flight 134 from Mumbai to Heathrow mid-way through the flight, to avoid crossing Iraqi airspace. The plane flew in a circle and was then diverted to the Greek capital Athens for refuelling.