For the seven staff of miner Sons of Gwalia, the trip to the company's operation at Leonora should have been routine.

The aircraft, a Beechcraft King Air 200, was trusted and the pilot Ken Mosedale was experienced.

It was a short flight and the weather on Monday, September 4, 2000, was fine.

According to air crash investigators, the tragedy of the ghost flight that was about to unfold could have been avoided.

The plane, VH-SKC, left Perth at 6.09pm and climbed without incident towards an initial flight level of 16,000ft.

Next the air traffic controller cleared the pilot to the planned cruising level of 25,000ft.

At 6.20pm, the controller cleared the pilot to fly directly to the position called Debra, a waypoint on the Cunderdin to Leonora route. The pilot acknowledged.

A few minutes later as the plane climbed through 25,600ft, the controller asked the pilot to verify the aircraft's altitude.

Mr Mosedale replied: "Sierra Kilo Charlie-um-standby."

That was the last communication with the pilot.

For the next 10 minutes as the air traffic control radar display showed the aircraft's altitude increasing, the controller tried in vain to raise the pilot.

WA MINER'S TOP TEAM LOST TO JUNGLE

The automatic recording of transmissions contains one unintelligible syllable, sounds of a person breathing, two chime-like tones, similar to those generated by electronic devices and background sound consistent with engine/propeller noise. Chillingly, the pilot did not answer further radio transmissions by the controller.

The King Air continued to climb on auto-pilot on the Debra to Leonora track and at 7.02pm it left radar coverage 404km north-east of Perth while climbing through an altitude of 32,500ft.

Australian Search and Rescue moved into action and asked the crew of a business jet to fly near the King Air for a short period, near Leonora.

The jet crew reported the King Air was maintaining 34,300ft.

Tragically they detected no movement aboard.

At 9.35pm, the King Air was sighted north-west of Alice Springs by the crews of two other aircraft who were asked to intercept and follow. Again, no movement. Finally the plane's fuel ran out and the engines quit one by one.

It descended and crashed about 65km south-east of Burketown in Queensland.

There were no survivors.

The Australian Transport Safety Bureau report found the pilot and passengers were probably overcome by hypoxia, or oxygen starvation, after the plane's pressurisation system failed.

Because of the severe damage to the plane, the report said it was not possible to say why the cabin had depressurised. It was unable to determine whether the failure of the pressurisation system was caused by a malfunction or because it had not been turned on.

The ATSB said the tragedy might have been prevented had the King Air been equipped with an aural warning system for depressurisation - as recommended nearly a year earlier - and had the visual alert been set to operate at 10,000ft.

The plane had a visual alert set to activate only at 12,500ft.

According to former ATSB investigator Alan Stray, "two different forms of alert are better than just one".

"We think they should now mandate aural alerts because there have been several of these occurrences and this one led to eight people losing their lives," he said.

It was thought possible that because the King Air was flying east, the setting sun might have been shining on the cockpit instruments, masking the red pressurisation warning light.

Investigators from the safety bureau warned the Australian Civil Aviation Safety Authority on October 7, 1999, of shortcomings with the King Air visual pressurisation warning systems after an incident involving the same type of aircraft in June 1999.

In that case a pilot was overcome by hypobaric hypoxia and a passenger, who was also a pilot, took over until the pilot recovered and landed the aircraft.

CASA responded on January 28, 2000, that "whilst CASA accepts the board's point of view that the onset of hypoxia usually degrades visual acuity before hearing, this incident does not provide sufficient justification to mandate retrofitting of audible cabin altitude warnings".

The ATSB report said vision was particularly sensitive to hypoxia and the rate and magnitude of the decline in vision was greater than the corresponding decline in hearing.

Most King Airs are fitted with aural pressurisation warnings.

The West Australian

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