TEHRAN, IRAN - JANUARY 08: Search and rescue works
Search and rescue workers at the site of a Boeing 737 plane crash near Imam Khomeini Airport in Iran. All 167 passengers and nine crew members on the Ukrainian flight died, according to a state official. (Photo by Fatemeh Bahrami/Anadolu Agency via Getty Images)
  • After a Ukrainian passenger jet crashed in Iran on Wednesday morning, speculation is mounting over what caused the plane to burst into flames.
  • The crash happened shortly after Iran fired a barrage of missiles at US forces in Iraq, but it was not yet clear whether there was any connection between the military action and the plane crashing.
  • However, the investigation will likely be hindered by the tensions between the US and Iran - the plane that crashed was a Boeing 737-800. Typically, that would mean that Boeing and US investigators would participate and provide technical expertise, but it is unclear whether this would happen, or how it would work, in the current climate.
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Speculation over what caused a Ukrainian jetliner to crash in Iran is mounting as the investigation already shows signs of political roadblocks.

Ukraine International Airlines flight PS752 from Tehran to Kyiv burst into flames and fell to the ground within minutes of taking off early Wednesday morning. All 176 passengers and crew members aboard the Boeing 737-800 were killed.

The crash occurred within a few hours of Iran firing missiles at US forces in Iraq, raising questions about whether the plane could have inadvertently been hit.

Iranian officials initially said a technical issue was to blame and later that an engine fire caused the pilot to lose control, but there have been several contradictory and confusing statements. The head of Iran's civil aviation organisation, Ali Abedzadeh, later told the Iranian news outlet Mehr that there was no evidence of technical problems, according to reporting by The New York Times. He also said that the plane had not contacted the control tower about an emergency.

The Ukrainian Embassy in Iran initially said that terrorism or an attack was not a factor, but removed the statement from its website later, replacing it with one saying that it was too soon to know what had happened.

Adding to the speculation is doubt over whether an engine failure could cause a plane to crash. Commercial aircraft are designed to fly with a single engine in the event that one fails. An uncontained engine failure, in which shrapnel from a failed engine damages the engine casing, potentially damaging or destroying the rest of the plane, is rare.

According to the airline, the plane was just three years old and had undergone maintenance checks just two days before the crash.

The airline also noted that the flight crew, which included one extra pilot due to the scheduled length of the flight, was highly experienced, and said it considered it unlikely that pilot error was a factor.

"Tehran airport is anything but a simple one. Therefore, for several years UIA has been using this airport to conduct training on Boeing 737 aircraft aimed at evaluating pilots' proficiency and ability to act in emergency cases," said Ihor Sosnovsky, Ukraine International Airlines' vice president of operations. "Given the crew's experience, error probability is minimal. We do not even consider such a chance."

The Boeing 737-800 is one of several variants from the previous generation of Boeing's 737 family of jets, the 737 NG series. The current generation, the 737 Max series, has been grounded worldwide since March following two fatal crashes caused by a faulty flight-control system. Both 737 Max crashes occurred within minutes of takeoff.

The crash has the potential to add to the crisis at Boeing that has been ongoing since the Max crashes. As scrutiny of the planemaker has continued, several potential hazards have been identified on other plane models, including the 737 NG.

Political roadblocks could make the investigation difficult

Jurisdiction over airline crashes is determined by the International Civil Aviation Organisation, or ICAO, the UN agency that manages global air travel. Article 26 of the agency's founding document, the Chicago Convention on International Civil Aviation, outlines how investigations are conducted.

Whenever an incident occurs involving a commercial plane, the investigation is led by the country where the incident occurred - in this case, Iran. Because it was a Ukrainian airline, Ukraine will also be involved.

Additionally, investigators from the country where the plane was made are also typically involved, along with the plane's manufacturer, both of whom provide technical support and expertise.

For this crash, which happened after days of escalating tensions between the US and Iran kicked off by a US strike targeting Iranian general Qassem Soleimani, that could prove difficult.

In a statement, the National Transportation Safety Board - the US agency which investigates all aviation accidents - suggested that various sanctions and embargoes on Iran - along with the recent military confrontations - could mean that the investigation will proceed differently under the current circumstances.

"The NTSB is monitoring developments surrounding the crash of Ukraine International flight 752 and is following its standard procedures for international aviation accident investigations, including long-standing restrictions under the country embargoes. As part of its usual procedures, the NTSB is working with the State Department and other agencies to determine the best course of action."

Along with assisting the investigation at the crash scene, a crashed plane's manufacturer often runs the analysis of the plane's black box, the flight data recorder.

However, Abedzadeh, the head of Iran's aviation body, reportedly told Mehr that "we will not give the black box to the manufacturer and the Americans."

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