On 1 August 2005, at about 1000 Eastern Standard Time, a Piper
Aircraft Corporation PA-31-350 (Chieftain), registered VH-LMB,
departed Adelaide on a scheduled passenger flight to Port Augusta.
The aircraft was being operated under the instrument flight rules
with a pilot and seven passengers, including an aircraft
maintenance engineer. On arrival in the circuit area at Port
Augusta the pilot selected the landing gear down. The landing gear
appeared to operate normally, but the right main landing gear
down-light did not illuminate, the gear selector did not return to
the neutral position and the transit light remained on.
A number of landing gear retractions and extensions produced the
same result. With the assistance of the engineer in the copilot
seat, the right gear-down indicator light was changed and the
manual extension procedure carried out. However, the landing gear
unsafe condition remained and the pilot conducted a low pass to
allow an aircraft maintenance engineer on the ground to observe the
gear. The landing gear appeared to be down and locked, but the
inboard gear doors (flipper doors) remained extended, indicating
that the extension cycle was not complete. The pilot attempted to
engage the right main landing gear down-lock by manoeuvring the
aircraft and repeating the normal and manual gear extensions, but
was unsuccessful.
The pilot reported that, consistent with the operator's
procedures, he elected to land with the landing gear retracted. The
passengers were briefed and the engineer moved to the seat adjacent
to the emergency exit. After a total of about 1 hour 40 minutes in
the Port Augusta area, the pilot landed on runway 33. The
propellers, underbelly skin and flaps were damaged. The occupants
were not injured.
Aircraft maintenance engineers who inspected the aircraft after
it was lifted, found that when the landing gear was manually
extended, the right down-lock assembly was stiff and did not
completely engage. A force applied to the down-lock assembly
completed its engagement and actuated the right down-light. The
operator advised that an engineering report would be completed once
the aircraft was recovered and full retraction tests carried
out.
The aircraft manufacturer issued Service Letter 755C in November
1985. Part I of the service letter addressed inspection and
lubrication of the landing gear lock actuator rod and rod end
bearing assemblies. This was recommended at each 50 hours of
operation and whenever landing gear and wheel areas were washed.
Part I included the following statement:
It has been determined that the location of the exhaust outlets
on the … PA-31-350 … aircraft are such that an increased frequency
of inspection and lubrication is recommended. It is also
recommended that the inspection and lubrication includes downlock
latch and pivot bolts.
Although operators were not required to comply with service
letters, the operator's Chieftain System of Maintenance included a
50-hour maintenance schedule that specified inspection of the main
landing gear down-lock rod and cable assemblies and referred to
Piper Service Letter 755C. The 50-hour maintenance schedule did not
specifically require lubrication of the landing gear, and the
aircraft's main landing gear down-lock had not been lubricated at
the recent 50-hour inspection.
A search of the Australian Transport Safety Bureau occurrence
database showed that in each year from 1997 to mid 2004, there were
up to two occurrences that involved Chieftain main landing gear
down-locks. In the 12 months prior to the occurrence, there were
four Chieftain main landing gear problems involving stiff or sticky
down-lock assemblies. The operators or maintainers of those
Chieftains indicated that inadequate lubrication was the main
reason for the down-lock stiffness or stickiness.