This is similar to the error in 'Back To the Future III' - Murphy lands the helicopter on a railway line so an oncoming train will destroy it completely, and this happens exactly on cue with huge, dramatic explosions and flying debris. Apparently the train driver doesn't think this is important enough to interrupt his busy schedule - he doesn't stop the train. We do not hear brakes being applied - the wheels would make a noise like the sky coming down - and the train doesn't slow down at all - it just keeps on going.
The registration number N77GH is visible on a gold placard on right surveillance camera' but only civilian aircraft are given November numbers. Military helicopters only have a series of numbers like on the tail. You aren't supposed to notice Blue Thunder's real "N" number, but it is there throughout the movie making it known it was truly a civilian helicopter.