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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.
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 737-800, which Ukraine International Airlines said at a press conference was one of the best planes in its fleet, with no signs of trouble before the crash. It 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.
The plane is a model of the 737 NG line of aircraft, a workhorse that is considered to have a good safety record: prior to Wednesday’s crash, the over 7,000 NG planes that have been produced since 1997 had been involved in 10 fatal accidents claiming 591 lives, according to a database maintained by the Aviation Safety Network.
In what may be a sign that the catastrophe developed quickly, the pilots didn’t change their transponder squawk code to signal an emergency, according to Flightradar24 data, and the state-run IRNA news service reported that air-traffic controllers received no communications indicating that anything was amiss.
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 can take more than a year 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. Earlier in the day, Iranian media and the Ukrainian Embassy in Iran had stated that engine failure was suspected; the embassy later rescinded the statement.
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 NG does not contain the faulty MCAS flight control system that precipitated the two 737 MAX crashes. However, in November, the U.S. National Transportation Safety Board called for Boeing to strengthen the engine covers on 737 NG aircraft to ensure that parts can’t be expelled at high velocity and damage the airplane in the event of an engine failure similar to one that occurred on a Southwest Airlines jet in 2018.
The left engine of that plane failed due to a broken fan blade, with fragments from the fan cowl striking the fuselage and a window, killing one passenger.
Twin-engine airliners are designed to fly with one engine disabled, but in the rare event of an engine failure in which parts aren’t contained inside the cowling as designed, fragments flying at hundreds of miles per hour could damage critical systems elsewhere on the plane.
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.”
Boeing shares were off 1.5% to $332.17 in midday trading.
The engines on the 737-800 are made by CFM International, a joint venture of General Electric and France’s Safran. In a statement, CFM said speculation regarding the cause of the accident was premature.
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