Can I use Oyster OAYG or Contactless card to/from the airport.

Heathrow. Sometimes, valid on some but not all modes…
Yes on Piccadilly Line.
Yes on tfl buses. (Remember tfl buses in the immediate vicinity of the airport are free).
Not valid on Heathrow Express or Heathrow Connect.

London City. Yes
Yes, valid on DLR. There are no gates to the platform, so remember to “beep in” on the validators tucked away (not in your sight line) opposite the escalators to the platform.
Yes, valid on tfl buses. (There are limited bus routes from LCY, and bus is rarely a wise choice).

Gatwick. No, not valid.
The rail operator has expressed a desire to extend use of Oyster to Gatwick, but at the moment it’s not accepted.

Luton. No, not valid.

Stansted. No, not valid.

Southend. No, not valid.