Maintenance is extraordinarily important for the long term usefulness of a fighter jet. There is even an official metric tracked called "maintenance man-hours per flight hour." The F-35, which was even designed to try to minimize this (while still being stealthy and lethal), requires ~5 hours of maintenance for every hour the jet is in the air. If you get cut off from parts your Air Force will be almost unable to fly in a few months.
Pretty much all modern fighters require replacement parts from the original manufacturer. There are not enough fighter jets to support an aftermarket parts manufacturer, especially one that could exist without getting sued by Lockheed, Northrop, and the like.
The main technical issue is that you have to reverse engineer the parts if you don't have original drawings and didn't get a legal license to make your own. All the technical bits on an F-35 have anti-tamper features designed to make reverse engineering almost impossible (in case a jet gets shot down over enemy territory the USA doesn't want the enemies to have an easy time figuring out the weak points or finding bugs to exploit).
If you want to see what fighter jets without legal repairability license turns into, look at Iran. The sanctions placed on Iran have meant that they've been stringing their inventory of jets along for decades without official parts. They cannibalize other jets, buy black market parts, and cobble together their own solutions to keep their Air Force going. Check out the Sedjil, which is a modified SAM, that they created to put on their F-14s because the USA stopped providing Phoenix missiles: https://en.wikipedia.org/wiki/Sedjil_(air-to-air_missile). Trying to keep an Air Force going without official permission is really challenging.
But Israel's case is a little different from the above discussion- negotiating for the rights to modify isn't really about replacement parts. They aren't that concerned that the USA will cut them off. Their negotiation is more because they want to put some of their own systems on the jet. In older 4th generation jets, integration of new systems could be straightforward; you can put it in an external pod with a standardized mounting pylon and standardized data bus. On the F-35 you obviously want to avoid hanging a bunch of extra pods off the jet, so you need to get engineering drawings and software details to figure out how to internally integrate your stuff. Because reverse engineering is hard, they pushed to get this technical information legally. The only time this effort is worth it is when you think your country's equipment outperforms what the original F-35 can do. You need a decent tech to beat the stock F-35 systems, but Israel probably has a few areas where they can do that. But even with the right to modify the F-35, Israel will be heavily reliant on original parts for maintenance. They do not have a big enough industrial base to make all the parts needed for the jet.
There are not enough fighter jets to support an aftermarket parts manufacturer, especially one that could exist without getting sued by Lockheed, Northrop, and the like.
This certainly applies to the aftermarket activities in the Westl, but entities doing that in Iran, Russia or Ukraine would not be liable to such measures. The question is more about technical capability.
> If you want to see what fighter jets without legal repairability license turns into, look at Iran. The sanctions placed on Iran have meant that they've been stringing their inventory of jets along for decades without official parts. [...]
True. Then again I see the ability for Iran to do this as a consequence of the effect of the sanctions and determination to make the best of domestic engineering potential. Quite a feat, I would say. The country has chemicals, electronics, mechanical engineering - and it trying to use it to create their own competing version of military platforms, starting with tanks, airplanes, drones, etc.
> The main technical issue is that you have to reverse engineer [...] All the technical bits on an F-35 have anti-tamper features designed to make reverse engineering almost impossible [...]
Very interesting! Almost impossible is a strong combination of words. Could you perhaps point me forward to some examples of such anti-tamper features?
Pretty much all modern fighters require replacement parts from the original manufacturer. There are not enough fighter jets to support an aftermarket parts manufacturer, especially one that could exist without getting sued by Lockheed, Northrop, and the like.
The main technical issue is that you have to reverse engineer the parts if you don't have original drawings and didn't get a legal license to make your own. All the technical bits on an F-35 have anti-tamper features designed to make reverse engineering almost impossible (in case a jet gets shot down over enemy territory the USA doesn't want the enemies to have an easy time figuring out the weak points or finding bugs to exploit).
If you want to see what fighter jets without legal repairability license turns into, look at Iran. The sanctions placed on Iran have meant that they've been stringing their inventory of jets along for decades without official parts. They cannibalize other jets, buy black market parts, and cobble together their own solutions to keep their Air Force going. Check out the Sedjil, which is a modified SAM, that they created to put on their F-14s because the USA stopped providing Phoenix missiles: https://en.wikipedia.org/wiki/Sedjil_(air-to-air_missile). Trying to keep an Air Force going without official permission is really challenging.
But Israel's case is a little different from the above discussion- negotiating for the rights to modify isn't really about replacement parts. They aren't that concerned that the USA will cut them off. Their negotiation is more because they want to put some of their own systems on the jet. In older 4th generation jets, integration of new systems could be straightforward; you can put it in an external pod with a standardized mounting pylon and standardized data bus. On the F-35 you obviously want to avoid hanging a bunch of extra pods off the jet, so you need to get engineering drawings and software details to figure out how to internally integrate your stuff. Because reverse engineering is hard, they pushed to get this technical information legally. The only time this effort is worth it is when you think your country's equipment outperforms what the original F-35 can do. You need a decent tech to beat the stock F-35 systems, but Israel probably has a few areas where they can do that. But even with the right to modify the F-35, Israel will be heavily reliant on original parts for maintenance. They do not have a big enough industrial base to make all the parts needed for the jet.