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When the gear was selected down only the left main gear gave a down indication. The pilot carried out emergency extension procedures which resulted in a down indication for the right main gear. During the subsequent landing with the nose landing gear trailing, the lower fuselage and propellers were abraded. Investigation disclosed that the hydraulic system had lost its oil overboard through the right engine hydraulic pump case drain.

This occurred because the left engine driven hydraulic pump main shaft seals had been incorrectly assembled.

The two seals are required to be placed back to back on the shaft, with one cup facing into the pump body and one facing away from the body. The seals had been placed with both cups facing away from the pump body. This allowed the pump to force oil past the inner seal instead of the pressure acting to positively seat the seal onto the shaft. The pump was newly overhauled having been fitted to the engine on the day prior to the accident. It had completed one flight of 1.7 hours duration.

Although the hydraulic reservoir contains an emergency oil supply, it is suspected that foaming of the contents due to pump cavitation precluded successful extension of all landing gears.

Significant factors

1. The seals on the main shaft of the right engine driven hydraulic pump were incorrectly installed.

2. The hydraulic oil was pumped overboard past the incorrectly installed seals.

3. The emergency oil supply was not able to successfully extend all three landing gears.

4. During the landing roll the nose landing gear collapsed.

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General details
Date: 05 February 1993 Investigation status: Completed 
Time: 10:14 ESuT  
 Investigation type: Occurrence Investigation 
 Occurrence type: Wheels up landing 
Release date: 16 April 1996 Occurrence class: Operational 
Report status: Final Occurrence category: Accident 
Aircraft details
Aircraft manufacturer: Piper Aircraft Corp 
Aircraft model: PA-31-350 
Aircraft registration: VH-PWA 
Sector: Piston 
Damage to aircraft: Substantial 
Departure point:King Island
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Last update 23 July 2015