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.
