Date: 201202
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: B747-400
Operator: Air Carrier
Operating under: Part 121
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
Aircraft component: Oxygen System/Crew
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Inspector
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Workload; Situational Awareness; Training / Qualification; Fatigue; Communication Breakdown
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; General Maintenance Action
Contributing factors: Chart Or Publication; Company Policy; Environment - Non Weather Related; Procedure; Aircraft; Human Factors
Primary problem: Human Factors

Narrative: A B747-400 aircraft was on the ramp at a Contract Maintenance Repair Station facility. The [Flight] crew was in the flight deck.  I asked the First Officer (F/O) to verify that there was adequate oxygen flow through his mask.  He pressed the button and held it for about ten seconds.  Oxygen continued to flow at a normal rate.  I was satisfied that the Crew Oxygen (O2) was turned 'On' because of the duration that the oxygen was flowing.  I did not physically verify that the Crew Oxygen bottle was turned 'On'.   Assuming that the bottle was turned 'On'; I entered this statement in the Aircraft Maintenance Log Corrective Action block; 'Crew O2 turned on' and signed the Mechanic signature/Certificate # block.  The next day I received a call; telling me the B747-400 aircraft had diverted because of a Crew Oxygen light. When the aircraft landed a Mechanic discovered that the Crew O2 bottle [valve] was turned 'Off'.  That was when I realized my failure to physically verify that the Crew O2 bottle was turned 'On' caused this event.  I should never have assumed that the Crew O2 bottle was turned 'On' based on oxygen flow from the crew mask alone.  No exceptions. No shortcuts. The bottle must always be physically verified that it is turned 'On' by checking the bottle valve handle.

Callback: Reporter stated he is one of the Maintenance Inspectors' for his Air Carrier (ACR) that oversees the maintenance work done by a Contract Maintenance Repair Station.  The B747-400 cargo aircraft was in for an  A-Check. His ACR requires the Gear pins be installed and the Crew Oxygen bottle valve be closed during the  A-Check and that information entered in the Logbook. But; all their A-Check Jobcards state is to 'Open' the Crew Oxygen bottle. No reference is made about 'Closing' the Crew oxygen valve.The Reporter stated the Captain had already tested his oxygen mask with good flow when  the First Officer was asked to perform a Ten-Second Test of his mask; where there was adequate air flow and no pressure drop-off. In fact; that same Flight crew flew a one hour aircraft repositioning flight from the Contract Repair Station and only hours later did the long haul outbound Flight crew have a Crew Oxygen light come on and a diversion.Reporter stated his ACR does mix and match steel and composite Crew Oxygen bottles in their newer B747-400s. His mistake was not visually and physically verifying the Crew Oxygen bottle valve handle was full open. He does not know if a composite bottle was involved with his incident. He has never had a problem with a steel oxygen bottle valve handle 'not' being fully opened when the valve handle was turned to open.



Synopsis: A Maintenance Inspector was informed; after he had signed-off a Logbook item stating 'Crew O2 turned On'; a B747-400 cargo aircraft had diverted due to a Crew Oxygen (O2) light illuminating in flight.   A Downline station Mechanic found the Crew O2 bottle valve handle 'Closed'.