Some of the newly trained Bulgarian Mig-29 pilots are refusing to fly their Russian made aircraft because of safety concerns. This unprecedented action by the pilots was triggered by the recent revelation that six of ten replacement engines for Bulgarian MiG-29s were found to be defective and are being returned to Russia. Four of the RD-33 replacement engines were new while six were refurbished and these were the ones found unsuitable. This sort of thing is not unique because Algeria returned all its recently purchased MiG-29s because of poor quality.
For Bulgaria the Cold War never ended because Russia has continued to find ways to punish Bulgaria for abolishing the communist government Russia imposed after World War II and, as far as the Russians were concerned, switching sides by joining NATO. To become a full-fledged member of NATO Bulgaria needed to upgrade or replace a lot of its military equipment. The most expensive item to replace or upgrade was the MiG-29s that comprised the most modern warplanes Bulgaria had. But these aircraft were notorious for how difficult and expensive they were to keep flyable. Currently only six of the 15 remaining Bulgarian MiG-29s are considered capable of taking off and given the poor quality of Russian replacement parts and technical support many of the new MiG-29 pilots would rather risk losing their jobs than flying the MiG-29s they are assigned to.
Most of these pilots are recent graduates of a MiG-29 pilot training program that had been halted for budgetary reasons in the late 1990s and revived in 2009. Such training had stopped because during 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. But these needed upgrades to meet NATO standards. The other Cold War era equipment consisted of a few combat and support aircraft that did not require updates. In addition most air bases were shut down, and nearly all the 200 Russian made aircraft (most of them obsolete) sold for scrap.
The MiG-29s were kept because they were, on paper, competitive with Western fighters and NATO required that Bulgaria have at least twelve flyable NATO quality het fighters to be a member. 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 batch of new MiG-29 pilots. That training was completed by 2010. But these new pilots were more aware of the sorry state MiG-29 reliability as well as the poor Russian support of the aircraft they exported. In 2011 Bulgaria found that Poland had developed an affordable program for bringing MiG-29s up to NATO standards and Bulgaria had put six of their MiG-29s through that program. But one major MiG-29 replacement part still had to come from Russia; the engines. Bulgaria bought ten of these in part to get another four grounded MiG-29s flying again and keep others in service.
There was also another option. In early 2017 Bulgaria decided to buy eight Gripen fighters from Sweden. But that effort ran afoul of political opposition and was now stalled for renegotiation or switching to another aircraft (like used F-16s). Bulgaria is scrambling to get at least a dozen of its MiG-29s fit to meet NATO standards and that is proving to be one embarrassing problem after another.