It's 'exceptionally unlikely' Iran shot down airliner on purpose, says defence reporter

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A defence reporter says we can "rule out the possibility" that Iran shot down a Ukrainian commercial jetliner carrying its own citizens intentionally.

Prime Minister Justin Trudeau said Thursday that Canadian intelligence indicates the aircraft that crashed outside of Tehran on Wednesday, killing 176 people, was shot down by an Iranian missile, possibly by mistake.

Iranian officials deny the country had anything to do with the crash.

Shashank Joshi, defence editor at the Economist, says Iran's Revolutionary Guard Corps is the most likely culprit, and the country's elected officials may have been unaware of the deadly error.

Here is part of his conversation with As It Happens host Carol Off. 

How is it possible that this passenger plane could be shot down by a missile accidentally?

It's very, very unusual. Even in times of conflict, air defence units who are expecting a strike and are on high alert would, in ideal circumstances, be able to tell the difference between a war plane incoming and a civilian airliner travelling slowly, climbing in altitude, and broadcasting its location and status via transponder.

One point of speculation is that the system in question, the Russian made SA-15, which corresponds to some of the wreckage that is alleged to have been found near the site, was operated by Iran's Revolutionary Guard Corps, which is the parallel armed force in Iran, separate from the regular armed forces. 

They operate their own independent air defence network, according to some sources. And if that's the case, it's possible that they didn't have access to all the information, that they were disconnected from the radar picture provided by other sources, that they were under pressure, under stress, anticipating some kind of U.S. reprisal, and that may have contributed to some kind of mistake. 

Does it need to be considered that it wasn't an accident, that it was deliberately shot down?

It's exceptionally unlikely that it was deliberately shot down with the air defence units knowing it was a civilian airliner.

Although Iran has attacked civilians in the past as reprisals for other incidents ... they would not attack an airliner that had very large numbers of Iranian citizens on board over their own territory in a way that might have caused substantial casualties on the ground, and at a time when they had the political upper hand, having conducted what they claimed was a substantial retaliation for the assassination of their general by firing missiles at a U.S. base.

So I think we can rule out the possibility that they would have done anything like this intentionally.

What were the conditions, then? Because we know just a few hours earlier, Iran had lobbed dozens of missiles into Iraq. Are these two events associated?

We don't know, but it does seem likely that there would have been a contributing factor here from the overall crisis. Just hours before Iran had fired those ballistic missiles, and they would have had every reason to expect a potential U.S. reprisal using American aircraft that would have dropped bombs and fired missiles.

But that doesn't explain everything, because while they would have been sensitive to any suggestion of an attack and may have been trigger happy or twitchy, they would have expected to find aircraft coming in from outside of Iran's borders. They would have expected to see certain types of altitude, certain types of behaviour. They would not have expected to see an aircraft with its transponder switched on.

Despite the overall crisis, there are still some big questions to answer as to how they would have made that mistake.

How is it possible that the Islamic Revolutionary Guard Corps, a very sophisticated organization, could not know that this was a civilian plane that was taking off?

They may have not about access to the information. There may have been signal jamming involved. There may have been electronic warfare going on. It's possible that either the Iranian side or some other country may have been involved in manipulating or jamming electronic signals in order to try and pursue some military end. That may have contributed to a more confusing picture.

These sort of crisis situations can create stress. Information can be misinterpreted. People can undertake worst-case scenario assumptions. And all of that can contribute to tragic misunderstandings and misperceptions like this.

At what point would Iran have known that one of its own surface-to air-missiles had struck down that plane?

I would be open to the possibility that the Iranian elected leadership —President Hassan Rouhani, Foreign Minister [Mohammad Javad] Zarif — may still not be fully in the loop.

This is still a divided leadership. It's a leadership in which the Revolutionary Guards are very powerful and have sometimes done things without the knowledge or permission of the elected leaders.

That's not to say they're freelancing. They're still answering to the Supreme Leader. But the civilian-elected leadership, the political leadership, is not necessarily given the full details of all of these kind of things.

I'm not saying that's guaranteed, but I'm saying that in authoritarian countries, we should be open to that possibility.

Written by Sheena Goodyear with files from CBC News. Interview produced by Kate Swoger. Q&A has been edited for length and clarity.