(Bloomberg) -- The helicopter crash that killed Iran President Ebrahim Raisi is the latest reminder of the poor state of many aircraft operating in the Islamic Republic after almost half a century of US sanctions. 

Iran has been largely barred from purchasing new aircraft or aircraft components from US or European suppliers since the revolution of 1979, leaving both military and civilian operators cut off from heavyweights Boeing Co. and Airbus SE and reliant on patched-up vehicles from earlier eras. 

Iranian airlines operate some of the world’s oldest aircraft, with an average fleet age of over 25 years. Some domestic services are operated by models that have long been retired in the rest of the world, including the McDonnell Douglas MD-83 and Airbus A300 and A310. 

McDonnell Douglas was acquired by Boeing some 27 years ago. 

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The BBC identified Raisi’s helicopter as a Bell 212, a US model that first entered service in 1968 and stopped being made in 1998. 

Another Iranian Bell 212 crashed in the Persian Gulf in 2018 during an emergency airlift for an offshore oil worker, according to the Iranian oil ministry’s website. 

Germany had been preparing to help upgrade Iran’s helicopter fleet after the 2015 nuclear accord with the US, an agreement that briefly eased sanctions. But those new supplies never materialized as the agreement fell apart under the Donald Trump administration.

Old, Basic 

As a result, Iran flies some of the oldest and most basic helicopters still in use and relies on the skills of its engineers to find ways to keep them in operation with limited access to new materials. 

While Iran most likely does source some supplies from Russia and China, it has extremely limited access to the most modern technology produced in the US and Europe. 

Raisi was returning from an event on the border with Azerbaijan in a party of three helicopters when his craft went down with nine people on board, all of whom died. There was dense fog in the region, making conditions difficult for rescue teams. The other two helicopters landed safely.

--With assistance from Siddharth Philip and Arsalan Shahla.

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