2010-07 · NASA ASRS report 898769
A Captain of a Short 360-300 aircraft reports not being able to retract the landing gears during initial climb; requiring an air turnback. A three-way selector valve in the right stub wing had not been reset by maintenance after they had serviced the emergency landing gear deployment accumulator and recycled the emergency 'T' handle in the cockpit.
Upon arrival to aircraft I noted the Co-pilot pre-flighting aircraft for departure. We ran through the Pre-start Checklists which include 'pre-flight inspection complete' and began our taxi for the runway. After rotation; the Co-pilot called for 'Gear Up' and I responded by moving gear selector to 'retract' position. After this action we noted that the gear remained three green 'down' [lights] even after multiple attempts to change its position. I notified ATC that we would be returning to the field and ran the applicable checks prior to our return. We landed on the runway and taxied to our hangar.On post flight inspection; we pinned the landing gear and inspected the Three-way Selector Valve on the stub wing. I verified it was in the proper position and waited until Maintenance personnel arrived. It was later discovered that the valve was slightly ajar thus preventing us from moving the gear. A conversation with maintenance personnel later in the day confirmed that they had cycled the Emergency Landing Gear deployment system and reset it only from the cockpit (must also be reset at Selector valve). In order to not duplicate this scenario again; I will be meeting with Maintenance personnel to better understand the hydraulic landing gear system. I will pass this knowledge to all pilots in our company so we can be on the lookout for these defects on our pre-flight inspections. I will also double check major parts of the pre-flight as two sets of eyes can only be beneficial when it comes to a safe aircraft.
Reporter stated the three-way selector valve is mounted in the right stub wing. There is a clear plexiglas panel on top of the stub wing held in place by thirty screws. Red and Green lines approximately one quarter of an inch wide (1/4') are painted on the plexiglas. The lines allow maintenance and flight crews to look down inside the wing to verify an indicator arm on the selector valve aligns with the green line; indicating the gear is 'ready for flight'. If the indicator arm is only a one-eighth (1/8th) of an inch; off of alignment with the green line; then that is enough to prevent gear retraction.Reporter stated the Short's aircraft have an emergency landing gear deployment system that uses a 'T' handle; located on the overhead panel; that is used when normal hydraulic system pressure is low which could affect a landing gear down and lock condition. Pilots' can pull the emergency handle which releases nitrogen from an accumulator to apply pressure to the low hydraulic system pressure and moves the three-way selector valve to a gear 'down' and 'locked' condition.Reporter stated that maintenance had earlier serviced the emergency accumulator for having a low accumulator pressure reading indication in the cockpit. He does not know why maintenance cycled the emergency 'T' handle; unless the nitrogen servicing required maintenance to move the 'T' handle. Reporter stated whenever the 'T' handle is cycled in the cockpit; then the selector valve in the stub wing must also be physically reset. That requires removing all thirty screws holding the plexiglas panel to the upper wing; physically repositioning a spring on the pull cable and moving the indicator arm on the selector valve to the 'ready for flight' position. Because that was not done; all three landing gears were already locked in the'down' position when they departed. He does not know if the Maintenance Manual needs to be revised or maintenance just missed the reset requirement in the procedures.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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