Never seen such a 30 years regulation on official documents. Is the Turkish Özgür upgrade done with US approval? Always wondered about that ...
My guess is, such modification permissions are results of direct negotiations between US gov and foreign states.
As an example, Israeli F-16s had major modifications regarding airframe design and avionics:
- F-16 A/B had software changes of mission computer and avionics to integrate Israeli made-weapons.
- F-16 C/D had major structural changes of the airframe (done by General Dynamcis then)
- F-16I Sufa differs fundamentally to conventional F-16s (dorsal spine compartment with Israeli "electronics equipment", Elbit mission and avionics computers etc. High suspicion that Israel received relevant source codes from the get go. As an US incentive to give up its own Lavi fighter project)
- F-35I are also extensively different to other configurations (esp. Israeli avionics, sub-systems)
ROKAF upgrade program for KF-16 was a major clusterfuck until recently:
1. Upgrade:
35 F-16 C/D Block 32 upgraded since 2010s to Block 52 level (by Lockheed Martin for $250 mil.), no hiccups so far.
2. Upgrade:
134 KF-16 C/D Block 52 (mostly license-built by Samsung Aerospace = now KAI) contract won in 2012 by BAE Systems US subsidiary. First upgrade deal awarded to a non-OEM company for a
fixed-price of $1,05 billion (AN/APG-84 AESA radar by Raytheon, new databus, Link-16 and avionics etc). Two KF-16 were already converted by BAE Systems in the USA.
Then things went sour over the years: US gov classified the deal as Foreign Military Sale and not as Direct Commercial Sale. Price hikes of $471 mil. by US gov and $282 mil. by BAE Systems for project delays resulted in
$753 mil. added costs = $1,7 bil. in total!
Korean gov and public freaked out, cancelled the whole deal in 2014. BAE Systems USA sued SK gov for financial losses. Koreans went total apeshit and US-ROK relations reached a low point.
Finally in 2018 Lockheed Martin as original manufacturer obtained their upgrade contract for
$1,2+ billion: now with AN/APG-83 AESA radar by Northrop Grumman and other modifications to Viper standards. Koreans are still pissed off to no end ... US "blood ally" my ass.
Good overview of said events and F-16 upgrade saga found here:
ROKAF KF-16 (click to view full) In July 2009, The Korea Times reported that ROKAF was looking to upgrade its F-16C/D fleet's radar and armament, as part of the 2010-2014 arms acquisition and management package submitted to President Lee Myung-bak for approval. Under the Peace Bridge II and II...
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