Bulgaria has hired a Polish firm to upgrade six of their MiG-29 fighters. Poland was selected because in 2014 Poland completed upgrades required to make their own MiG-29s compatible with NATO standards. This was necessary because Poland is now a member of NATO and could not afford to replace its MiG-29s with Western fighters. Poland has the largest fleet of MiG-29s in NATO (32 operational) and other East European nations that recently joined NATO are in a similar situation.
The Poles didn’t do it all themselves but figured out who the most effective partners would be. Thus a Polish firm worked with an Israeli company to make the MiG-29 electronics compatible with NATO equipment. Mechanical controls were replaced with electronic (“fly by wire”) ones. This involved a much more efficient cockpit and some amenities which make life much easier for pilots. All this gave the MiG-29 electronics similar to those in the 48 F-16s Poland has purchased.
The Bulgarian upgrades are less about new electronics and more about keeping the Bulgarian MiG-29s flyable. This being done despite protests from Russia who insist it is illegal for anyone but the Russian manufacturer to perform such upgrades and refurbishment. But the Russians want a lot more money for the work than Polish, or even Western European firms can do it for. Moreover the current Russian hostility towards NATO does not make Russia a reliable source of such services.
Bulgaria has to be careful with what it spends on military equipment because the country was never rich to begin with. After Bulgaria broke free from communist (and Russian dominated) government in 1989 it turned to the West for help. Reforms (and reducing the chronic corruption) took time. Thus it wasn’t until 2009 that Bulgaria was able to resume training new MiG-29 pilots. Such training had stopped, for budgetary reasons, in the late 1990s. Throughout the 1990s, and until 2004, Bulgaria was busy disbanding its Cold War era air force of 226 aircraft. By 2009 all they had left was 18 MiG-29s (which needed upgrades to meet NATO standards), some Su-25s (for ground attack), a few MiG-21s (on their way out), some Su-22s (used for reconnaissance) and a few dozen transports and helicopters. One by one, most air bases were shut down, and the Russian made aircraft (most of them obsolete) sold for scrap.
Western aircraft are being bought, but the MiG-29s are being kept because they are competitive with Western fighters. That is important because East European nations found that Western warplanes were too expensive. Meanwhile by 2009 the existing MiG-29 pilots were getting old and many of them had already left for more lucrative commercial flying job. Thus the need for another dozen MiG-29 pilots. That training was completed by 2010.
In late 2011 Bulgaria announced that it would postpone a decision on the purchase of a new multi-role jet fighter until at least 2012. Bulgaria originally committed itself to buying a NATO-type fighter as part of its alliance integration process. However, the economic recession cut into procurement funds and that situation never got better. Soon plans for buying Western warplanes was dropped as well. Then the Poles showed it was possible to upgrade MiG-29s on an East European budget.