The aircraft was being flown from Adelaide to Dubbo in
accordance with instrument flight rules. At 1921 EST, the pilot
reported over Mildura maintaining 9,000 ft, and estimating abeam
Griffith at 2026 on a direct track to Dubbo.
The weather in the area was clear, with no restrictions to
visibility, and scattered cloud at 30,000 ft. Sky conditions were
dark, with no moon.
At 1958 the pilot made a routine frequency change, and 8 minutes
later advised Melbourne Flight Service (FS) there had been a loss
of vacuum and that he was returning to Mildura. In response to
enquiries from FS the pilot advised that he had 'electric backups'
and felt it safer to return to Mildura. He also confirmed his
approach and landing would not be affected, and that his estimated
time of arrival would be 2029. At 2007 FS asked the pilot for his
approximate distance from Mildura. The pilot asked FS to repeat the
request, but subsequently failed to reply. Further attempts to
contact the pilot were unsuccessful. The last recorded radio
transmission from the pilot was at 2007:49.
An uncertainty phase was declared after communication and ground
checks failed to establish the location of the aircraft. A local
resident reported seeing the lights of an aircraft shortly after
2000, and then hearing the sounds of an impact. The wreckage of the
aircraft was subsequently found some hours later. The accident was
non-survivable.
An examination of the wreckage indicated the aircraft had
impacted the ground at high speed, in a steep nose-down attitude,
consistent with loss of control. With the exception of the vacuum
system, the aircraft was considered to have been capable of normal
operation prior to impact.
The aircraft was equipped with an attitude indicator and a
directional indicator, each reliant on air-driven gyroscopes. An
electrically powered turn co-ordinator was also fitted. Examination
of the attitude indicator showed evidence of a witness mark
consistent with the gyro-rotor being stationary at impact. The turn
coordinator gyro-rotor was recovered and showed evidence of
rotation at the time of impact.
The engine-driven vacuum pump and drive coupling were recovered
from the wreckage. The impact resulted in separation of the pump
body from its base. Only a few large pieces of the rotor and vanes
were recovered. The frangible drive shaft coupling had sheared at
some time prior to impact. A specialist examination considered that
either the carbon rotor, or one or more of its vanes, had failed,
resulting in pump seizure and consequent shearing of the drive
coupling.
An entry in the aircraft logbook indicated that the vacuum pump
was installed in September 1991. From that date, until the last
periodic inspection in August 1997, the pump had operated for some
1,248 hours. No evidence was found of vacuum pump replacement
during that period.
The Mooney 20J Service and Maintenance Manual recommends that
the schedule for the primary vacuum pump replacement be either on
condition or at 500 hours, and at engine overhaul. The Civil
Aviation Safety Authority provides no additional requirements
regarding maintenance of the vacuum pump.
The pilot held a Private Pilot licence with a valid medical
certificate. His command instrument rating had expired 3 days prior
to the accident. Although no evidence could be found of the pilot
having flown in instrument meteorological conditions in the
previous 12 months, the pilot had conducted a night flight six
weeks prior to the accident. A passenger on that flight reported
they did not encounter cloud.
