As title says, massive FPS drop, going from 80-60 down to 3-1 or less even, when an explosive of some sort detonates nearby you. If explosives are shot into the air these FPS drops do not occur.
I found this includes all explosives, the faster the rate they are going off the bigger the drop. 30MM auto-cannons, jet main cannons, anti-air tank cannons, helicopter main cannons all cause huge drops.
Have multiple explosives detonate around you in a short amount of time.
This glitch has been around for a long while, and was patch around a year ago. It came back with the 1.54 update. I don't know which patch fixed it.
Cant reproduce. Only where there are big number of explosions. Did you tried updating video drivers? Dont know your GPU but Radeon released Crimson edition drivers boosting GPU (mine) about 30% without overclocking. BTW - are you using ACE 3? There is file responsible for big FPS drops on mentioned explosions - ace_frag which produces houndrets of frags while explosion appear - it eat lot of CPU resources.