A Line Mechanic reports he serviced all three Crew High Pressure Oxygen bottles on a DC-10 aircraft that indicated zero pressure; instead of removing the bottles. Reference in the DC-10 Maintenance Manual to refer to an incomplete General Manual; plus concerns about making scheduled departure time contributed to the incident.
Synopsis
A Line Mechanic reports he serviced all three Crew High Pressure Oxygen bottles on a DC-10 aircraft that indicated zero pressure; instead of removing the bottles. Reference in the DC-10 Maintenance Manual to refer to an incomplete General Manual; plus concerns about making scheduled departure time contributed to the incident.
Narrative
A DC-10-10 landed [and the] Captain indicated with a Logbook entry that all three of the aircraft's High Pressure Oxygen bottles indicated '0' psi on the cockpit gauge. After the aircraft blocked in; I opened the forward electronics bay door to look at two of the three O2 bottles. The bottles direct reading gauges read very low. I could not determine if the two O2 bottles in the electronics bay were completely empty. The remote gauge for the #3 bottle read very low as well. Using DC-10 Aircraft Maintenance Manual (AMM) 12-15-01-3 and General Manual (GM) X-Y-700 I serviced all three bottles to 500 PSI. I waited a few minutes to determine if there was a leak. The gauges on both bottles held at 500 PSI. The indirect reading gauge on [the] #3 bottle held its pressure as well. I went upstairs [to cockpit] and checked all of the Crew and Observers masks. I tested each mask with use. The Captain of the flight told me he thought the First Officer's mask was left 'On' after she used it during the flight. Also; one of the jumpseaters told me the right-hand Observer's mask [oxygen] was free flowing then stopped; when I first started the O2 recharging procedure. I filled the three bottles to the required departure pressure and did the leak checks on the [supply] manifold and [servicing] fill areas.Note: The DC-10 Maintenance Manual (MM) 12-15-01-3 refers you to GM X-Y-700. In GM X-Y-700; there is a Section 6-D-3 that gives rules for charging high pressure oxygen cylinders. The high pressure recharging procedure does not have a requirement to change an empty bottle. In DC-10 MM 12-15-01; Section 4-C states 'Any cylinder that is determined to be completely empty cannot be recharged on the aircraft'. I'm not sure the O2 cylinders were completely empty. The GM had no requirement to change the bottles in the Recharging High Pressure bottles section. And the MM 12-15-01 section 4-C requires cylinder to be completely empty and it cannot be recharged on the aircraft.
NASA callback
Reporter stated their General Manual (GM) states that Low Pressure Oxygen bottles must be replaced if the gauge reads 'Zero'. But their DC-10s do not have Low Pressure bottles which are serviced to 700 LBS PSI; nothing in the GM states to remove a High Pressure bottle for 'Zero' indication. Mechanics can't tell if the High Pressure Bottle is really empty because the gauges don't really peg-out at 'Zero'. So they just service the bottles to 1;800 LBS PSI.Reporter stated he recently learned there is a concern about moisture building up inside a depleted steel oxygen bottle and developing internal corrosion. He has submitted a change request to their manuals for better clarity. He also realizes he was distracted by his concerns about making scheduled departure time.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.