Yak-52: SB 59R/60R
|The most known is the 59R/60R couple introducing a heavy main spar and stronger wing attachments, following the 1983 fatal accident in Vilnius attributed to the failure of the main spar. It was introduced as service bulletin in November 1986 both on the newly produced and overhauled aircraft. In fact, the Bacau factory began regularly implementing it from early 1987 and the overhaul facilities, in the early 1990-s, meaning that some of the aircraft produced before early 1987 and overhauled before 1992 may still have the original less solid spar. Conscious of this, the Yakovlev Design Bureau initially limited operation of these aircraft to G factor of +5/-3. As of today, the Bureau refuse to deal with the aircraft without the 59R/60R modification.
This is the most crucial and complex Yak-52 modification. It has to be performed using certified parts in a jig at a certified facility.
The next important is the bulletin 107BD.