In message , at
10:01:42 on Sun, 23 Jun 2013, Kai Borgolte
remarked:
buy a normal Z16 One Day Travelcard
ticket on the Friday morning and then before you travel to the airport
go to a National Rail, NOT an Underground, ticket office and ask for
an extension single (one way) ticket from Boundary Zone 6 to Gatwick
Airport. This should cost £4.90 single.

OK, I will do it this way. Less fuss and not too expensive.

How are you travelling during the week? An Oyster card is the best
choice if you are going to be using any trains/tube/buses.

Then you can buy an ordinary boundary station (eg Croydon) ticket to
Gatwick for your final leg (use the Oyster to get as far as Croydon, but
you *must* leave the train and "touch out" in order to 'complete' that
last bit of Oyster travel.) Convenient, huh?

This map shows which bits of National Rail (in addition to London
tube/bus) are valid with Oyster):

http://www.tfl.gov.uk/assets/downloa...rvices-map.pdf

--
Roland Perry