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On 16 July 2009 the pilot of a Beechcraft King Air C90 aircraft, registered VH-TAM, departed Perth Airport on a flight to Wiluna, Western Australia with one passenger on board.

Sometime after becoming established at flight level (FL) 210, the pilot became affected by hypoxia, which resulted in him becoming fixated on the 'distance-to-run' figures on the aircraft's Global Positioning System equipment display and incorrectly interpreting those figures as the aircraft's 'groundspeed'. That confusion resulted in the pilot interpreting the lower-than-expected figures as a significant headwind and in him descending the aircraft to escape the winds. Once established at FL150 for a significant period of time, he realised that that he had been affected by hypoxia. The pilot descended further before landing at his destination.

The investigation identified problems with the aircraft's left landing gear squat switch that prevented the aircraft from pressurising in flight. In addition, the cabin altitude warning system was non‑operational due to the incorrect connection of the switch wiring during previous maintenance.

Following this occurrence, the aircraft manufacturer changed the aircraft type's maintenance manuals and documentation and the Civil Aviation Safety Authority (CASA) issued a letter to owners and operators of Australian-registered pressurised aircraft that proposed mandating the fitment of aural cabin pressure warning systems in those aircraft. As a result of that industry consultation, CASA determined that a uniquely Australian installation requirement could not be justified.

Notwithstanding, as a result of the ongoing risk of serious incidents and fatal accidents in which the occupants of single-pilot, turbine‑powered, pressurised aircraft have been affected by, or have succumbed to unrecognised hypoxia in an unpressurised cabin, the Australian Transport Safety Bureau has issued a safety advisory notice. That notice encourages all operators of such aircraft to consider the installation of an aural cabin altitude pressure warning system that operates separately to their aircraft's visual warning system.

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Safety issues

AO-2009-044-SI-01 - AO-2009-044-SI-02 -  

Cabin Altitude Warning switc wiring diagram

The cabin altitude warning pressure switch maintenance manual wiring diagram did not provide a clear indication of the wiring connections for the superseded switch.

Safety issue details
Issue number:AO-2009-044-SI-01
Who it affects:Owners, operators and maintenance venues for Beech King Air 90 aircraft
Status:Adequately addressed


Replacement of cabin altitude warning switch

The aircraft maintenance manuals did not include the operating specifications of the replacement cabin altitude warning pressure switch hampering the required verification of switch serviceabilty.

Safety issue details
Issue number:AO-2009-044-SI-02
Who it affects:Owners, operators and maintenance venues for Beech King Air 90 aircraft
Status:Adequately addressed

General details
Date: 16 July 2009 Investigation status: Completed 
Time: 10:30 WST  
Location   (show map):74 km NE of Perth Airport Investigation type: Occurrence Investigation 
State: Western Australia Occurrence type: Landing gear/indication 
Release date: 21 September 2011 Occurrence class: Technical 
Report status: Final Occurrence category: Serious Incident 
 Highest injury level: None 
Aircraft details
Aircraft manufacturer: Beech Aircraft Corp 
Aircraft model: 90 
Aircraft registration: VH-TAM 
Serial number: LJ-919 
Type of operation: Charter 
Damage to aircraft: Nil 
Departure point:Perth, WA
Destination:Wiluna, WA

Safety Advisory Notice

Operators of single-pilot, turbine-powered, pressurised aircraft
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Last update 14 November 2018