A Line Mechanic reports a B767-400 he worked earlier required an Air Turnback for a left Main Landing Gear (MLG) door unsafe indication. Gear door had not retracted and the Bypass safety pin was still installed in the MLG door safety valve.
Synopsis
A Line Mechanic reports a B767-400 he worked earlier required an Air Turnback for a left Main Landing Gear (MLG) door unsafe indication. Gear door had not retracted and the Bypass safety pin was still installed in the MLG door safety valve.
Narrative
A B767-400 departed but did not have safe indication for the left main landing gear door. The aircraft returned to gate where Maintenance reported finding the bypass pin installed in the bypass position of the left Main Landing Gear (MLG) door safety valve. The compartment itself was found properly closed. I had installed the bypass pin at the conclusion of the aircraft's most recent Maintenance event; believing it was properly in place and installed. The safety block on the safety bypass valve door is intended to prevent closing the compartment door with the bypass pin installed in the bypass position. Apparently; this door's safety did not function as intended; and the door was closed with the safety bypass pin installed. This inadvertent action caused the left main landing gear door to remain open in flight.My suggestion for prevention of a recurrence would include but; not be limited to the following: a fleet-wide inspection to determine if any other aircraft's safety device attached to the safety valve compartment door are not effective in their intended function. A caution placard be placed in plain view in the safety valve compartment stating that the design will allow bypass pin to be installed in the valve while any hydraulic pressure is present.
NASA callback
Reporter stated with hydraulic pressure 'on'; he activated the gear close switch; closing the Main Gear doors. But; he inadvertently installed the Bypass safety pin into the Main Landing Gear (MLG) door safety valve Bypass location hole; instead of the hole for stowing the safety pin. Both positions are located in the same Safety valve compartment area. Reporter stated the safety block on the compartment door should contact the safety pin if the pin is installed in the Bypass position; preventing the door from being closed. From what they could determine later; the safety pin can actually move sideways enough; while in the Bypass position hole; to allow the safety block to slip pass the safety pin and allow closing of the compartment door. No warning streamers are attached to the Safety Bypass pin. As a result; the B767-400 departed with the Bypass valve in 'bypass' position. Although the landing gear door would open; it would not close after the the gear retracted.Reporter stated he was one of three Mechanics closing the gear doors. The gear doors close much slower on the B767-400's on the ground; compared to the B767-300's; which are very quick and more dangerous to be around when operating.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.