US can't put a ban on Aircraft sales to Iran as it is in direct violation of the JCPOA and if they do - Iran has every right to walk from the deal as per agreement. I am sure the world doesn't want that and any violation by the JCPOA will turn in protest. I am sure that many of you might think I am naive, but till now all deliveries are on track and tomorrow to IranAir delivery team will fly to Toulouse a head of the delivery of 2 new ATR72 aircraft (msn 1477/1478). Also don't be too surprised to see other deliveries of Airbus in the coming months. I am sure Airbus and EU are lobbying very well to prevent any blockade.
There is no law that says that anyone has too sell to somebody else if they don't want too. You cannot force me too sell you goods or services and even if there was, I would price it so exorbitantly high, that it wouldn't be worth your while to buy from me.
The point is, they don't even have to put a direct ban on aircraft sales, just any parts in a particular aircraft that are U.S. made/designed. If there is an aircraft out there, with absolutely zero U.S. content, then there would be nothing that the U.S could do to stop that aircraft being sold to Iran, but good luck finding one that would be worthwhile. If Iran was to walk away from the JCPOA agreement, then unfortunately you would probably see the reinstatement of other sanctions. Airbus wouldn't be the only ones lobbying to stop any potential ban, Boeing would be at the front of that line, they want to sell to Iran, most U.S. companies probably do, but if the government was too ban trade with Iran, there is nothing they could do about it.
Nothing against ATR72 aircraft, but in the grand scheme of things, they really are insignificant at this point in the argument, it is the bigger, higher profile aircraft that will be affected first by any ban. Eventually though, even the ATR's would suffer the same fate, no engines (even if it is Pratt Canada) no deliveries, no spares being available, etc.
As much as the less narrow minded people in the world don't like it, the U.S.A. carries the big stick, just as the E.U. Russia and China do to a lesser extant. It is the economic and techno logic reality and as long as that is the case, there is very little that rest of the world can do, except play along.