The US has issued a licence allowing Boeing to do business with Iran for the first time since the US embargo of 1979.
The licence covers a "limited period of time" and allows Boeing only "to provide them spare parts that are for safety purposes".
Boeing will still not be allowed to sell new planes to Iran, a company spokesman said.
The licence was granted by the US Treasury Department in the context of an interim deal between world powers and Iran over its nuclear programme signed in November, the spokesman said.
At the end of February, another US company, General Electric, indicated it had requested permission to sell spare airliner parts to Iran, but so far it has not received a response.
The US and European nations have imposed severe economic sanctions in recent years aiming to pressure Iran to reduce permanently, or at least long term, the scope of its nuclear activities to make it extremely difficult for it ever to develop nuclear weapons.
Iran has always denied any such ambition.
The sanctions were partially lifted in January after Iran agreed to freeze a part of its contested programme.
The West and Iran are currently negotiating a definitive agreement that would guarantee Iran's nuclear programme would be peaceful and would ultimately lead to all sanctions being lifted.
The US severed diplomatic relations with Iran in the aftermath of the 1979 Islamic revolution.