The Australian Transport Safety Bureau (ATSB) is advising operators of single-pilot, turbine-powered, pressurised aircraft to consider installing an aural cabin altitude pressure warning system that operates separately to the aircraft's visual warning system.
The safety advisory notice comes in the wake of a number of serious and fatal incidents involving such aircraft, when the occupants have been affected by unrecognised hypoxia. It also follows a failed attempt by the Civil Aviation Safety Authority to mandate installation.
The safety notice follows the publication of the final report into a July 2009 incident involving a Beechcraft King Air C90 on a flight with one pilot and one passenger between Perth Airport and Wiluna, Western Australia.
At flight level 210 the pilot was affected by hypoxia, became confused and descended to FL150 as he misinterpreted instrument figures and descended to avoid what he thought was a significant headwind.
Once he had descended he realised he had been affected by hypoxia and safely landed.
The investigation found there was a problem with the aircraft's left landing gear squat switch, which prevented the aircraft from pressurising in-flight, and the cabin altitude warning system was not working.
CASA issued a proposal for a mandate last October but industry response "was not favourable" and it did not find support for such a move from the US Federal Aviation Administration, it said.
Such a mandate would be unique to Australia. The ATSB says some operators have proactively fitted such systems, which cost about A$1,000 (US$970).
Source: Flight International
