Aircraft launched in 1994 can carry 189 passengers and has had some safety issues

The Boeing 737-800 model used by Ukraine International Airlines (UIA) that crashed in Tehran on Wednesday is the most popular aircraft in the sky, used by airlines from Ryanair to American Airlines.

Boeing’s short-haul workhorse is the predecessor to the 737 Max, the model that was grounded after two fatal crashes in 2018 and 2019.

The 737-800, a single-aisle aircraft that can carry 189 passengers, was launched in September 1994 as part of the 737 Next Generation (737 NG) lineup. As of February 2019 more than 4,900 had been delivered, although it has been superseded by the 737 Max, the US manufacturer’s fastest-selling model.

More recently some Boeing 737-800 planes have had safety issues, with groundings caused by cracks between the wing and fuselage in the so-called “pickle fork” structure.

The UIA plane had taken off from Imam Khomeini international airport in the Iranian capital when a fire struck one of its engines, said Qassem Biniaz, a spokesman for Iran’s road and transportation ministry. The pilot of the aircraft then lost control of the plane, sending it crashing to the ground, Biniaz was quoted as saying by the state-run Irna news agency.

However, Ukraine’s embassy in Iran dropped an initial reference to engine failure as the cause of a Ukrainian plane crash outside Tehran on Wednesday. It said in a second statement that the causes had not been disclosed and that any previous comments were not official.

All Boeing 737 NG planes use CFM56 engines manufactured by CFM, a joint venture between the US manufacturer General Electric and the French manufacturer Safran. The engines are also used on Airbus planes, including the A320.

There are more than 8,000 CFM56 engines in service on 737 aircraft worldwide, making it the most popular engine-aircraft combination in commercial aviation, according to the joint venture’s website. Last month CFM said the engines had completed a billion flight hours, the first engine family to do so.

Boeing said: “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.”

A GE spokesman said: “We are deeply saddened by the loss of Ukraine International Airlines flight 752. We extend heartfelt sympathies to the families and loved ones of those on board.”

In a statement, UIA said: “UIA expresses its deepest condolences to the families of the victims of the air crash and will do everything possible to support the relatives of the victims.”

The location of the crash – Iran – could complicate the investigation, according to the consultant air crash investigator Tony Cable. The country in which a crash occurs usually carries out the investigation, while the airline’s home country and those of the plane and engine manufacturer were also entitled to send representatives, he said. This may be complicated by the tensions between the US and Iran after the assassination of Qassem Suleimani, a senior Iranian general.

Although it was too early to ascertain the cause of the crash, the findings could potentially affect the recertification of the 737 Max, which has a similar design, Cable added.

The 737-800 has been involved in a number of fatal accidents over its long period of service.

One of the most recent fatal incidents involving a 737-800 occurred in September 2018, when a flight by the Papua New Guinea airline Air Niugini undershot the runway at Chuuk airport in Micronesia and landed in a lagoon. One of the 47 occupants died.

In March 2016 a FlyDubai flight from Dubai to the southern Russian city of Rostov-on-Don crashed while attempting to land. All 62 people on board died.

In January 2010 an Ethiopian Airlines flight to the Ethiopian capital of Addis Ababa crashed into the Mediterranean Sea shortly after takeoff from Beirut Rafic Hariri airport, killing 90.

In 2007 a Kenya Airways flight carrying 115 people crashed shortly after takeoff from Douala, Cameroon, on a flight to the Kenyan capital, Nairobi, with no survivors.

The Ukraine crash comes during a crisis period for Boeing. The 737 Max has been grounded worldwide since March after two crashes in which everyone onboard died. The UIA crash comes less than a year after the second of those, Ethiopian Airlines flight 302.

The grounding eventually prompted Boeing to fire its chief executive, Dennis Muilenburg, who had faced criticism over his handling of the crisis. His replacement, former Boeing chair David Calhoun, was due to take over formally as chief executive on 13 January.

Safran has been contacted for comment.