Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Communication Breakdown; Time Pressure; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action; General Maintenance Action
Aircraft; Procedure; Manuals; Company Policy; Human Factors
During preflight I performed the Crew Oxygen Test in accordance with the AOM. During the test; I observed a noticeable drop in oxygen pressure. The AOM Crew Oxygen Test description states; 'If there is a drop in oxygen pressure during the test; corrective Maintenance action must be performed prior to flight.' I made a logbook entry and contacted MX Control through my Dispatcher. The first MX Controller instructed me to order Contract MX; and we hung up to wait. Not long afterwards; I received a message to Contact MX Control. When I reestablished contact; a different MX Controller insisted that the test was normal; and the system was functioning normally.He stated that his manual described the test to be successful only if there was a pressure drop. He went on to explain if the valve was closed; the pressure would drop to zero. When I asked about a partially closed valve; he said the system was operating normally. When I told him I had never in my experience seen an O2 pressure drop like the one on the aircraft today; he told me I should pay closer attention. We got the Chief Pilot on Call on the line; but the MX Controller would not let us have a conversion without constant interruptions. He continued to the point of berating me; mentioned about how long it would take to check the valve; all the time getting more agitated and emotional. He then stated when the Contract Mechanic arrived; nothing would change; and he would write in the logbook that the system was normal. When the Contract Mechanic arrived; I watched him inspect the valve on the O2 tank installed forward of the forward bulkhead in the forward cargo compartment. He removed the Safety wire; and turned the valve handle counter clockwise; and reinstalled the Safety wire.I returned to the cockpit; and again performed the Crew Oxygen Test. The pressure indicator did not move; indicating normal system operation. When the Contract Mechanic returned with the logbook; I checked it to make sure the discrepancy was signed off. The entry was to the effect that the valve was in the full open position; and the system was normal. I asked the Mechanic why he had not written that he fully opened the valve. He said the MX Controller told him to clear the discrepancy as if the system had operated normally the whole time.Upon arrival; the flight delay report [included] the explanation: 'UPON BOARDING COMPLETION CAPT CALLED MX CONTROL AFTER CLEARED BY MX CONTROL CAPT STILL WANTED TO CALL CONTRACT MX.' The Agents comment demonstrates a fundamental lack of understanding of the pre-flight procedures; the details of the event itself; and more worrisome a focus on blame for the late departure without any concern for the Safety aspect of the flight. 1. Check to see if the AOM and MX manuals agree about the details of what constitutes a successful or failed Crew Oxygen Test. 2. Remove the pressure on Ground Operations and Technical Operations (MX) to push on time at all costs. 3. Change the metrics so the sole focus by which Stations and Departments are evaluated is not on time performance. 4. Re-emphasize to all Operational Departments that SAFETY is our number one priority. 5. Treat all Employees with respect; and recognize that Pilots are professional observers with valuable inputs that can help resolve problems.
I felt that Maintenance Control was attempting to pressure the Captain to continue the flight without a Maintenance check of the oxygen system. This; despite the fact that he had already made a logbook entry; and contacted the Operations Center regarding the issue. I'm not really sure why Maintenance was trying to get us to press on; when at the very least; the logbook entry would need to be cleared by Maintenance; even if nothing was found. According to our manuals; a possible reason for a drop in oxygen pressure is that the valve of the oxygen bottle could be closed; or only partially open.I don't think I have to state here what would happen if there were smoke and fumes in the aircraft at cruise; and the Crew oxygen valve was closed. When Contract Maintenance finally arrived; we described the problem; and he checked the valve in the cargo compartment. According to the Captain that watched him; the valve did move a significant amount of turn when he checked it.The Captain also relayed that they checked the oxygen mask again; and it appeared to pass the test after the adjustment. (I was not present then). Finally; the logbook entry came back saying there was nothing wrong with the system; and our delay reason blamed the Crew. My assumption is that Maintenance Control directly influenced both writeups. After the logbook was signed; we finished pre-departure prep and departed expeditiously.
B737-700 flight crew reported the crew oxygen pressure dropped significantly during the preflight procedure. The valve was found to not be fully open; however the signoff did not indicate so; and the delay was charged to the crew.