From TARDIS Index File, the free Doctor Who reference.
Heathrow Airport was the busiest airport in Great Britain, just outside of London.
In 1981, Tegan Jovanka and her aunt Vanessa were on their way to Heathrow (and Tegan's new job at Air Australia) when she first encountered the Doctor. (DW: Logopolis)
The Doctor later managed to get Tegan to Heathrow Airport, but in 1666. (DW: The Visitation)
The Doctor finally succeeded in getting Tegan to Heathrow, where they solved the mystery of a vanished Speedbird Concorde 192. (DW: Time-Flight)