The airport scenes were filmed at Coventry Airport (at the start of the episode when they enter the airport, you can see the sign saying Coventry airport) but the runway scenes were filmed at Stanstead Airport - Source: ChuckleVision Wikia
@@submale5892 The thing is, it’s not on other channels. I don’t know exactly which clips were used for the aircraft takeoff and Flight 175 crashing into the South Tower.