This page gives details of some of the aircraft types that were offered or promised to the Austrian Air Force but not delivered, cancelled official orders, and types that have been falsely reported as being in service.
British Aerospace BAe 146-200QT
Demonstrator G-BSTA was due to be leased to Austria in 1991, and was painted up in OLk colours, but the sale was cancelled at the last minute.
Grumman Gulfstream I
One Gulfstream I was reportedly operated by the Austrian Government in 1971, but it did not enter OLk service.