Much more efficient these days without the need for the calibrating aircraft to first land to drop off and set up a load of ground equipment they can just start it on their first approach inbound.
Apart from the serial which involves touching down (in reality a touch and go) the aircraft doesn't even need to land (I'm referring to my experience of CAT 1 calibrations) unless to drop off an unsatisfactory certificate to the Tels Engineers!
There used to be only one company around able to do these calibrations, in the UK there are now two that I know of, the newest one uses a PA31 that used to be owned by British Caledonian and looked lovely in their livery.