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. See more...
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Continuity: In the climactic chase scene, when Murphy is shot through the window, he is shot in his right arm and there is a hole in the window with blood on it. When he does a 360 degree loop in the helicopter the broken window and blood appears on his left side—the opposite window to that which he was shot through.