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How Iran could have mistakenly shot down a 737 airliner [video]

One of the basic tasks of an air defense battery is to discriminate between friendly aircraft and foe. But amid a state of high alert after Iran had launched a barrage of ballistic missiles at U.S. bases in Iraq, an Iranian air defense unit appears to have failed tragically, in a manner that some military experts contacted by Forbes found puzzling.

Western intelligence officials reportedly believe that two missiles were fired at the airliner by a a Russian-made Tor-M1 air defense battery, referred to by NATO as the SA-15 Gauntlet. It’s a mobile, short-range system that can accompany infantry units or provide a last line of defense for key infrastructure or military installations against low-flying jets, helicopters and cruise missiles.

Mounted on a tracked vehicle or on a truck, it can be operated singly or with multiple launchers networked together to a command post. It fires a missile with a small warhead containing 32 pounds of explosives that is designed to spray its target with metal fragments.

A properly functioning SA-15 battery would have had multiple means of identifying Ukrainian International Airways Flight PS 752 as a civilian aircraft, defense experts told Forbes. One of several head-scratchers about the incident is that radar should have shown that the Boeing 737-800 was on a commonly used flight path heading northwest from the airport—if it was inbound into the country it would be easier to explain the misidentification of the plane as a hostile aircraft, says David Deptula, a retired U.S. Air Force lieutenant general who heads the Mitchell Institute for Aerospace Studies.

“There are a lot of question marks as to why and how this could have happened,” he says.

The Boeing 737-800 was transmitting a unique transponder identification code. If the equipment on the SA-15 that picks that up, called an IFF interrogator, was malfunctioning, battery operators would typically look at the schedule of airline traffic through their area and see if the target matched with a scheduled flight, Deptula says. Flight PS 752 was delayed by almost an hour from its scheduled departure, taking off at 6:12 a.m.

The SA-15 operators also would have considered the path and speed of the plane on radar. “Is it operating at low altitude, at high speed, headed toward a sensitive area”? Deptula asks. Flight PS 752 was rising toward 8,000 feet at a relatively sedate speed of 275 knots when flight tracking data from its transponder cut out, a normal profile for an airliner, he says. “It is departing the area, climbing through medium altitude, not trying to hide its signature, looking like a routine operation.”

Complicating decision-making for the soldiers operating the battery would have been the high state of alert.

Given that Iran had launched a barrage of ballistic missiles at two U.S. bases in Iraq hours before in retaliation for the targeted killing of the high-ranking Iranian commander Qassem Soleimani, Iranian air defense forces likely were operating under looser rules of engagement in anticipation of a potential counter strike, as well as psychological pressure and fatigue after being on alert for the five days since his death.

The operators of the SA-15 battery were also likely aware that the U.S. Air Force is given to commencing campaigns by wiping out enemy air defenses like their unit to allow its warplanes to operate with greater freedom.

“Your incentive balance sways over to shoot first, ask questions later,” says Michael Elleman, senior fellow for missile defense at the International Institute for Strategic Studies.

If the unit didn’t rush, they should have had sufficient time to make a considered decision as to whether to launch an interceptor, says Carlo Kopp, co-founder of the think tank Air Power Australia. It’s unknown if Iran has integrated its SA-15 batteries with its broader air defense radar network.

If the SA-15 unit in question was operating independently, the operators’ visibility would have been constrained to its relatively short radar range of 11 to 13.5 miles. Its missiles have a maximum range of 7.5 miles.

Given the slow speed of the 737, if the plane grazed the edge of the battery’s missile range, the operators would have had a decision window of 1 minute and 53 seconds, Kopp calculates. If it directly overflew the launcher, the soldiers would have had 3 minutes and 39 seconds.

Given the multiple means of detection and the distinctive flight profile of an airliner, there’s no excuse for the deadly mistake, says Kopp.

“The only credible explanation is incompetence,” he says.

Iranian air defense forces haven’t been seriously tested since the Iran-Iraq War and their level of training is a question mark.

In 2007 and 2008, Iranian air defense units mistakenly fired on two airliners amid fears that Israel was planning to attack its nuclear weapons development facilities, according to a classified Pentagon report obtained by the New York Times. Iranian air defense forces believed enemy aircraft might mimic the flight profile of an airliner, the report said.

Iran acquired 29 SA-15 units from Russia in 2007; Russians likely trained Iranian instructors on the system, who in turn trained the operational crews, says Kopp.

“There is no evidence that Iran is training its missileers any better than the Russians do,” Kopp says. Russia has been linked to two mistakenly downed aircraft in recent years. Malaysia Airlines Flight 17 was shot down over separatist-controlled eastern Ukraine in 2014; a Dutch-led investigation concluded it was hit by a Buk missile fired from a launcher that had been brought in from Russia. In 2018, a Russian Il-18 COOT electronic intelligence plane was shot down in Syria by a Russian-made, Syrian Army S-200V long-range missile battery that was reportedly overseen by Russian military advisers.

It’s rare for air defense batteries to shoot down an airliner, but the 1988 downing of an Iran Air plane by the USS Vincennes shows that even well-trained forces can make grievous errors, says U.S. Army Lt. Col. Anthony Tingle, author of a recent paper on the incident.

While the Vincennes was under attack by small Iranian gunboats, its targeting crew misread radar data, concluding that Iran Air Flight 655 was descending toward the U.S. guided missile cruiser when it was in fact climbing, and misidentified it as an Iranian F-14 Tomcat. The Vincennes fired two anti-air missiles, striking the Airbus A300 and killing 256.

“Under duress in combat situations, mistakes happen,” Tingle says.

Given the high speed and compressed timelines of modern air warfare, Elleman says we shouldn’t be surprised by what is believed to have happened to Flight PS 752. “I’m surprised it doesn’t happen more often.”

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