About a year or so ago, a VirginBlue 73 had its nose wheels lifted off the ground during push back at YPDN.
The story I heard through the grapevine was, that some weeks prior a "pushback person" replaced a sheared shearpin with a bolt and forgot to remove the bolt. On the night of the incident the pushback commenced with the brakes still applied, and the nose wheels were lifted clear of the ground as the aircraft rotated about the main wheel axles.
I believe the aircraft ferried to BNE for inspection with the gear down, after blocking one of only three aerobridges for most of the ensuing day.
