Why the Ukrainian airliner that crashed in Tehran was likely shot down

The plane crashed in darkness at 6.14am on Wednesday, about 15 kilometres north of the airport, killing all 167 passengers and nine crew. The passengers comprised 82 Iranians, 63 Canadians, 11 Ukrainians, 10 Swedes, four Afghans, three Britons and three Germans (nearly half the passengers were dual nationals, with 130 holding Iranian passports).

If it was an intentional SAM launch, it was most likely a case of mistaken identity. Iran would have been expecting an American aerial attack in response to its ballistic missile attack on US bases in Iraq nearly five hours before, and air defence crews would have been on standby at the time of the crash.

Technical problems with this very reliable aircraft type (the Boeing 737-800 Next Generation) can probably be ruled out. This particular aircraft was relatively new, having entered service in 2016. Moreover, it had been serviced only two days before. The pilot was highly qualified and the airline, UAI, also has a good safety record. This was its first crash since commencing operations in 1992. I travelled three months ago on a UAI 737-800 Next Generation flight from London to Kiev and return, and was impressed by the airline's quiet efficiency.

Mobile phone footage seen on social media shortly after the crash showed what appeared to be an aircraft on fire crashing into the ground, causing a large explosion. On January 9, 2020, a video obtained by CNN showed something being launched from the ground and hitting the plane, causing an explosion. Later that day The New York Times confirmed the video's authenticity.

[The video shows a plume of light approaching the aircraft, travelling upwards from left to right. An explosion then occurs, and the aircraft reduces speed, continuing its travel right-to-left while engulfed in flames.]

US officials claim that satellite imagery shows the aircraft was most likely shot down by an Iranian Russian-supplied Tor-M1 SAM (NATO designation SA-15 "Gauntlet"). The US's Five Eyes partners, the UK and Canada (who would have been working with the same data) have agreed with the US assessment. The US would have known where the Tor missiles were located, and would have been able to detect any launches using infrared and radar monitoring systems (this close intelligence coverage of Iran was also how the US knew fairly quickly that Iran was not planning follow-up military action after its ballistic missile launches).

The Russian Tor missile system is a mobile, modern, all-weather, low-to-medium altitude, short-range SAM system, capable of downing aircraft and cruise missiles. How many Iran has in its inventory is not information that is publicly available.

Investigators have stated that, based on the abrupt cut-off of the ADS-B tracking data and the pilot not sending a distress call, the plane would have suffered a sudden and catastrophic failure, regardless of the cause. On Thursday, Ukraine announced it was examining all possible causes, "including an anti-aircraft missile strike, a mid-air collision, an engine explosion or an explosion inside the plane carried out by a terrorist".

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Aviation monitoring group Opsgroup noted that it "would recommend the starting assumption to be that this was a shootdown event, similar to MH-17 - until there is clear evidence to the contrary", claiming that photographs "show obvious projectile holes in the fuselage and a wing section".

Some images on the internet also appear to show what could be fragments of a Tor-M1 SAM at the crash site itself. USA Today reported that British private intelligence organisation IHS Markit reviewed "photographs purportedly taken near the site of the crash to show the guidance section of an SA-15 Gauntlet" and "assesses them to be credible" - although it could not confirm the authenticity of the photographs.

On Thursday, Sweden and Canada were officially invited by the Iranian investigation team to join the probe into the crash. The US National Transportation Safety Board was also invited to join the investigation, but due to US sanctions has to seek a special licence from the US government to allow its investigators to travel to Iran. Ukraine and Boeing have also been invited to join the investigation.

Cases of military forces mistakenly downing civilian aircraft are not common, but Iranians will not have forgotten the USS Vincennes' downing with a SAM of Iran Air Flight 655 in 1988, killing all 290 passengers and crew on board.