Unidentified albino? in Sydney CBD

[(Matthew Taylor)]

The recent discussion of CBD peregrines has prompted me to recall a recent
sighting.  Looking out of a 20th floor office block in George St, Sydney I
saw an unusual bird flying directly towards me.  Viewed head-on, the
immediate impression was of a large pure white swift with thin swept back
wings. (Instant thoughts of a first for Australia! - but what?) It was
moving very swiftly and jinking slightly in flight.  As it flashed past and
disappeared, giving a brief side on view, it was obviously bulkier than a
swift with a bigger head - more the outline of a rainbow lorikeet.
Any records of albinos of this species, or suggestions what else it might
have been?

Matthew Taylor