The crash of a Boeing 737-800 operated by Ukraine International Airlines on Wednesday morning near Tehran promises to spur intense speculation as to its cause, coming hours after Iran launched missile strikes on U.S. bases in Iraq and amid the international grounding of the latest model of the 737.
Flight PS 752 appeared to be climbing normally after taking off from Tehran’s Imam Khomeini airport at 6:12 a.m., two air safety experts said, with heading, altitude and airspeed consistent with the same flight on previous days, based on transponder data from Flightradar24. That data cuts out abruptly roughly three and a half minutes into the flight, with the plane at an altitude of 8,000 feet.
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It’s unusual for a crash to begin in that phase of flight, said John Goglia, a former airline mechanic and board member of the U.S. National Transportation Safety Board.
“The risky part of the takeoff is behind them,” he says. “Eight thousand feet is an altitude that the crew is comfortable and the airplane is settling into the flight.”
The disaster killed all 176 on board the plane, which Ukraine International Airlines said at a press conference was one of the best in its fleet, with no signs of trouble before the crash. The plane was delivered to UIA in 2016 directly from Boeing and had last undergone scheduled maintenance on Jan. 6. The airline said the pilots were highly experienced.
In what may be a sign that the catastrophe developed quickly, based on Flightradar24 data, it appears that the pilots didn’t change their transponder squawk code to signal an emergency.
A video shared online by the Iranian Students’ News Agency is purported to show the aircraft descending in flames and exploding on contact with the ground, however it hasn’t been verified and photos haven’t surfaced yet that show an impact crater, said Kristy Kiernan, an assistant professor at Embry-Riddle University and a former air safety officer with the U.S. Coast Guard.
An image of the entire debris field hasn’t been made public yet, which would provide important clues, but Kiernan said pictures of the wreckage that she’s seen suggest an inflight breakup or explosion may have taken place. “It is deformed prior to contact with the ground, and dispersed in a way that is not consistent with the collision of an intact aircraft with the ground,” she said.
While Goglia cautioned that it’s premature to draw conclusions, he said investigators likely will be considering whether the plane was brought down by a bomb or a mistaken military strike.
Shortly after 1 a.m. local time, Iranian forces had fired missiles at two U.S. bases in Iraq, and they were likely on alert for a counter-attack.
Determining the cause of a crash usually takes months of analysis. The cockpit voice and data recorders from the plane have been found, but the head of Iran’s civil aviation agency, Ali Abedzadeh, said it has not been decided yet where they will be sent for analysis, and they will not be shared with Boeing and U.S. authorities, according to the Mehr news agency. Customarily the aviation authorities of the country that governs the plane’s manufacturer participate in the investigation.
Abedzadeh said there was no evidence of technical issues with the plane.
The disaster is another worrying development for Boeing, which has been rocked by the grounding of the 737 MAX, the newest version of its bestselling plane, after two deadly crashes within five months that killed 346.
The 737-800 that crashed in Iran is part of the previous model generation, known as the 737 NG. It’s considered to have a good safety record: prior to Wednesday’s crash, 20 planes have been lost in accidents since the NG debuted in 1996 with 591 fatalities, according to a database maintained by the Aviation Safety Network.
Boeing said in a statement: “This is a tragic event and our heartfelt thoughts are with the crew, passengers, and their families. We are in contact with our airline customer and stand by them in this difficult time. We are ready to assist in any way needed.”