Don't know when the last Avro to get airborne was, but the one you are referring to was the War Memorial aircraft which was restored by QF apprentices in Hangar 11 at Mascot in the late sixties.
If my memory serves me correctly the pilot was supposed to have a taxi around in front of hangar 96 for the cameras, a gust of wind might have suddenly caused it become airborne momentarily, dunno, the pilot was some bloke named Sir Hudson Fysh apparently he'd had flown an Avro 504K previously.
