Visible crew/equipment: When the dispatcher tells Copter 10 to meet Squad 51 at the five mile mark, Copter 10 lifts off, and we can see the moving shadow of the filming helicopter near the shadow of Copter 10.
Visible crew/equipment: When Station 51 is dispatched to the structure fire, just as Engine 51 rolls out of the apparatus bay, the reflections of the location shoot's array lighting and two reflector screens are visible on the side of the engine.
Continuity mistake: During the house fire, Marco's holding the hose behind Chet, while Chet is kicking open the front door just before it flashes, but in the next shot both Chet and Marco are manning the hose when the fire flashes, knocking them down the stairs.
Continuity mistake: Marco's mustache goes missing when Station 51 is dispatched to the structure fire, but then it reappears.
Visible crew/equipment: When Engine 51 and Squad 51 arrive at the training center, Captain Stanley opens the door then steps off the engine while Chet climbs down from the jumpseat, and the location's array lighting is reflected on the door's window.
Continuity mistake: During the actual rescue at Catalina Island, Johnny and Roy are now wearing water-type shoes, not their uniform shoes.
Revealing mistake: When Station 51 is dispatched to 'man trapped', just as Engine 51 rolls out of the apparatus bay and heads down the driveway, the real 127's vehicle is seen parked inside the bay, near the rear door.
Revealing mistake: After Station 51 is dispatched to the 'plane in trouble' it becomes a plane crash rescue and recovery, and when they pull out the pilot's body, who they said died on impact, his right hand moves to clasp his left wrist, and he also bends and moves his leg.
Smoke Eater - S4-E16
Continuity mistake: When Billy's mother waits in the hallway while Early examines Billy, the window behind her is on the same side as the ER's receiving entrance. Note that outside the window there's a blue metal shade at the top, which does not exist in any exterior shots of that side of the ER.
Transition - S4-E15
Continuity mistake: When Gil is assigned to ride along with Squad 51, en route to the incidents there are only two people seated in the squad in the shots shown.
Captain Hook - S6-E8
Continuity mistake: During the police helicopter rescue, Roy's, Johnny's, Marco's, and Chet's uniform shoes change to water-type shoes when they rappel down the cliff, and deal with the rescue.
Continuity mistake: After Dixie has the talk with Molly about using 51 as a crutch, it cuts to the shots at the movie studio with stunt drivers being chased, and the passenger who has his head out the car window is bareheaded, but in the closeup he's suddenly wearing a knit cap on his head.
Visible crew/equipment: When Station 51 is dispatched to an unknown type rescue, which turns out to be two people stuck on the side of a building, in the first shot of them the aerial camera tilts down and pans right to left, and as it does the reflection of the crane (supporting the camera) is visible on the building's glass siding, and the crane's outboard legs are also visible as the camera follows the squad into the lot.
Visible crew/equipment: After Early and Brackett do the tracheotomy, when Dix leaves treatment 4 and walks up the hallway, the outline of the mic transmitter and wire are visible on the back of her uniform top, and when she sees Johnny in the hallway, the outline of his mic transmitter is visible on the front of his shirt over his belt.
Visible crew/equipment: After Chet's disappearing half-dollar trick, when Squad 51 is dispatched to the gunshot wound, as Roy and Johnny get into the squad numerous set lights are reflected on the squad's chrome spotlight.
Camera Bug - S4-E10
Visible crew/equipment: After Johnny tries to take Chet's picture beside the map, when Captain Stanley walks from the office to the back of Squad 51, the reflection of crew/equipment are visible on the back of the squad.
Continuity mistake: While Johnny tries to reach the man who fell over the cliff, when the bicycle falls to the bottom of the canyon both tires break free from the frame, but when the officer retrieves the bicycle, only one of the tires is off, the other is undamaged and on the frame.
Welcome to Santa Rosa County - S6-E10
Visible crew/equipment: After Sheriff Bittner breaks the door's window to get into the clinic, when they open the door just before they walk inside, the camera's tripod, the corner of the reflector screen, and a crew member wearing a blue/white cap are all visible through the doorway by the porch area.
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.
Visible crew/equipment: When the woman drives her car up to Station 86 with the two injured passengers, the outline of mic transmitter is visible on the back of her sweater, when she gets out of the car.
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.