Revealing mistake: On the roof of the jail, Roy buckles his safety belt around his waist, with an extra belt for the prisoner hanging from it as well. When Roy removes the second belt from his own, we can see two carabiners that are now attached to his lifebelt, which go down into Roy's pants. Those carabiners are presumably attached to extra support under Roy's pants.
Revealing mistake: During the rescue of the two mountain climbers who are stuck on the side of a building, when Johnny and Roy are hanging from the lines which are attached to the lifebelts buckled around their waists, we can also see that attached to their lifebelts are carabiners, which are tucked inside their shirts. Those carabiners are presumably attached to extra support under their clothing. Johnny's is particularly visible, while Roy tries to cover his carabiners with his hand.
Revealing mistake: When Station 51 is dispatched to "plane that hit building," after they rescue the two aboard the plane, just before the explosion when the orange combustible drum is propelled into the air, we can see the stunt's projectile to get the drum airborne.
Revealing mistake: When Station 51 is dispatched to "accident with injuries," en route one of the camera angles is from the POV behind Roy and John, where the back of the squad is located. The problem is that there's bright sunlight on their backs as they’re driving, when it shouldn't be there. Artistic license is acceptable, but having so much sunlight where it should not be reveals that Squad 51 is not in its normal state.
Revealing mistake: When Station 51 is dispatched to the hang gliding accident with two men trapped on a cliff, as the squad and engine roll out of the bay, we can see the real 127's vehicle is still parked in the apparatus bay, near the rear door.
Paper Work - S6-E11
Revealing mistake: At the start of the episode, when the camera zooms in on the words 'Los Angeles County Fire Station 51' which are attached to the side of the building, we can see that this shot is actually played in reverse - notice the cars/trucks behind the station are driving backwards. Additionally, note that the real 127's rig is seen in the driveway to the right. Also interesting to notice are the upper/lower metal bars which are attached to the bricks, where we can see the bars are much longer after 'Station 51', with a space for something missing, due to the fact that is was made to hold '127' on it.
Revealing mistake: At the gas station, when the pump sparks and catches fire, we can see that it's not gasoline on the ground with the water from the fire hose, but instead it's floating thick gobs of stunt fire gel with burning flames.
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.