The same source indicates that after attaching the UMPK module, the weight of the FAB-500M-62 bomb actually exceeds the load capacity of the most common Russian weapon pylons, which is 500 kilograms (1,102 pounds). This may cause the bomb to detach during maneuvering.
The wing is opened after the bomb is dropped by a spring hooked to the locking mechanism. The wing opening mechanism is unreliable and “the fact that the wing is not brought into flight position is a standard occurrence for this product.”
Another disadvantage of the UMPK is that the bomb’s fuse is switched to ‘ready’ as in an ordinary bomb, i.e. at the moment of separation from the aircraft (in other winged bombs the fuse is activated later, during the glide). This means that if the wing does not open, the bomb can fall and explode, including on Russian or Russian-controlled territory. This is what the people of Belgorod faced on April 20 in an incident you can read more about
.