A Piper PA-31-350 Navajo Chieftain had completed an uneventful flight from Fairbanks International Airport to Galena Airport in Alaska, USA with a pilot and seven passengers on board. When the aircraft was configured to land on runway 26, the landing gear would not extend. The landing gear handle was cycled, to no avail, the landing gear would not extend.
A quick check of the circuit breakers in the cockpit was followed by the checklist to manually pump the landing gear down. This required the opening of a cover, extending the pump handle and 70 (Seventy) strokes, with not much resistance. The landing gear would still not come down. A broadcast was made on the Galena traffic frequency that they would be circling overhead. When circling the pilot contacted the maintenance organisation for the airline. There was one last possibility (Pneumatic blowdown) which she could attempt to get the landing gear down but wanted to consult with maintenance if it was better to do so at Galena or return to Fairbanks. With the latter having the pilots having the pilot preference, maintenance confirmed it was better to return to Fairbanks.
After diverting back to Fairbanks the pilot contacted maintenance again and followed the checklist for blowdown of the landing gear. After following the checklist the left main landing gear and the nose landing gear indicated down and locked, and the red transit light remained on. A low pass over runway 02R was flown, and ATC confirmed that the right main landing doors were open but the landing gear was not down. The pilot then asked for clearance to fly to the practice area to the southeast of the airport, after this was granted the aircraft headed to the practice area while climbing to 5000 feet After arriving in the practice area some manoeuvres were flown to increase the G-loading on the aircraft while exercising the manual pump handle. This did not free the right-hand main landing gear. The passengers were briefed for an emergency landing and the aircraft was then configured according to th emergency checklist. An approach to runway 02L at Fairbanks was flown, just before landing both props were feathered and the engines shut down. The aircraft touched down on the left main gear and the nose landing gear, a short while later the right wingtip touched the runway. The pilot managed to keep the aircraft on the runway, after coming to a stop she confirmed the passengers were ok and shut down the aircraft.
Damage to aircraft was limited.
The damaged wing tip (Source; Kathrynsreport.com © FAA)
The aircraft was inspected by an FAA Inspector who inspected the aircraft aftre it was moved off the runway.
The hydraulic reservoir was almost depleted and minimal fluid existed
in the system. After servicing and testing the hydraulic system, a leak was observed at the fitting between the right main landing gear door close line and the right MLG unlock actuator. The hydraulic line was removed, and the threads on the actuator assembly connection were stripped. The fitting was capped and the system functioned normally.
The company also tested the pneumatic blowdown system and discovered that the right MLG shuttle valve was stuck in place. The shuttle valve was removed and disassembled, and water and corrosion were present inside.
The damaged hydraulic fitting on the right-hand main landing gear (Source; Kathrynsreport.com © FAA)
The National Transportation Safety Board concluded that the probable causes for the accident were;
The improper installation of a hydraulic line at the right main landing gear (MLG) unlock actuator, which resulted in a total loss of system hydraulic pressure and failure of the landing gear to extend. Contributing to the accident was the failure of the right MLG shuttle valve due to corrosion, which prevented the right MLG from extending during the emergency blowdown activation.
The NTSB report, which was one of the sources for this blog, can be accessed by clicking on the .pdf file below;
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