Revealing mistake: After Station 51 is dispatched to "traffic accident with injuries," when they're on scene at the plant with the injured tanker driver, pay particular attention to the background behind Engine 51 while Roy is on the Biophone with Rampart. When Brackett says, "51, can you give me any more information," we can actually see Station 51 aka 127, directly behind Roy.
Continuity mistake: When Roy and Johnny get to the airport and start talking to the boy flying the plane, the clock reads 11:55, but when Frankie puts the oxygen mask on his father it's 12:15, then when Roy reassures the boy about flying straight and level, it's 12:40, and so on, even though it's really supposed to be only a few minutes between these shots.
Continuity mistake: When Frankie lands the Cessna, the red seatbelt is in place behind him. When Gage and DeSoto reach the plane that seatbelt has been pulled across the side wall, over the door, with its end pushed between the windshield and ceiling. Done deliberately so Gage can enter that door unhindered.
Deliberate mistake: At the station, Gage is washing dishes and talking about his idea for a new poker game. In this shot the camera is positioned behind the kitchen's top/lower cabinets and sink, facing Gage. The fact that we can see the back side of the cabinetry (paper towel dispenser which hangs over sink is gone) ruins the illusion of this POV from the wall that should be there.
Continuity mistake: When Squad 51 is dispatched to the attempted suicide, the dispatcher states that he's in apartment 2A, and when Roy and John arrive at the scene the police officer also says he's in apartment 2A, but when they get to the second floor they pass apt 2A and go to the apartment at the end of the hall.
Continuity mistake: When the firemen cover the tanker in foam, the paramedics and ambulance drivers extract the tanker driver and place the patient on the stretcher they all get covered in foam, including the stretcher. Next shot, the stretcher, the patient and the men are all clean.
Continuity mistake: At the airport, when Roy is being told about young Frankie flying the airplane because his father had a heart attack, we see that Roy's wearing his uniform shoes, but in the shot of Roy following the airport employee while they're running into the building, Roy (perhaps his double) is wearing tan work boots. The uniform shoes are back when Roy uses the grounded plane's radio mic.
Continuity mistake: At the scene of the traffic accident, after removing the injured driver from the overturned tanker, when Roy gets the Biophone from the squad and John runs over to the ambulance stretcher, notice the red rectangular material adhered to the front of Engine 51's cab. We know that Engine 51 does not have a license plate on the front of its cab, and during this scene Engine 51 is being played by the real Engine 127, whose license plate is at the front of its cab.
Continuity mistake: When Roy brings the injured tanker driver into the ER, the attendants wheel the stretcher down the hallway passing treatment 3, and after Roy asks Brackett and Early a pointed question about the trucker's condition, the doctors also walk down the hallway passing treatment 3, in the direction of the nurses' station. But then we see that Early and Brackett are with the patient in treatment 3, which is right beside the ER's receiving entrance.