The Beechcraft Baron aircraft was being operated on a freight
charter flight from Groote Eylandt to Darwin.
The pilot said that as the aircraft descended through 5,000 ft
the left engine fuel flow gauge reading decreased to zero and the
left tachometer indication reduced to about 1,700 RPM. The cylinder
head temperature and oil temperature readings also reduced. The
pilot advanced the engine control levers to full power and tried to
fly the aircraft at the best single engine rate of climb speed. The
aircraft continued to lose altitude and the pilot realised there
was not enough height remaining to reach an aerodrome. As the left
engine tachometer was still indicating about 1,700 RPM, the pilot,
believing the engine was still developing power, did not feather
the left propeller.
The pilot landed on a two-lane highway. The aircraft was
substantially damaged during the landing roll when it slid off the
roadway and entered a ditch. The pilot, who was the sole occupant,
was not injured.
The pilot had about 1450 hours aeronautical experience and 105
hours on the aircraft type.
Examination of the left engine found the fuel mixture control
cable had failed near the fuel control unit control lever. This
allowed the lever to move downward under its own weight into the
fuel cut-off position. No other pre-existing damage or fault was
found that may have contributed to the failure of the engine.
Both engines were only slightly damaged in the forced landing.
They were fitted to an engine test cell where they operated in
accordance with the manufacturer's standards.
The aircraft's maintenance records showed that the fuel mixture
control cable was fitted to the aircraft about 230 hours
previously. Specialist metallurgical examination of the cable,
which was constructed of one central strand surrounded by six
smaller diameter strands, showed it had broken because of fatigue
cracking. The fatigue cracking showed significant alternating
stresses had been applied to the cable during aircraft operation.
The examination also found sliding contact wear close to the break,
caused by abnormal alternating loads applied to the cable at the
point where it was swaged to the fitting. Possible misalignment of
the cable during installation may have led to the failure.
The pilot did not realise that the left engine had failed and
the unfeathered propeller was driving the engine, because the RPM
indication was higher than he had expected. He therefore was not
aware that the unfeathered propeller was causing excessive drag
preventing the aircraft from maintaining height.