Date: 201604
Local time of day: 1801-2400
Aircraft: EC135
Operator: Air Taxi
Operating under: Part 135
Mission: Ambulance
Flight phase: Parked
Aircraft component: Oxygen System/General
Component problem: Improperly Operated
Reporter organization: Contracted Service
Reporter function: Technician
Human factors: Fatigue; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Pre-flight
Result: General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Human Factors

Narrative: While the aircraft was out of service for other scheduled maintenance I replaced the gaseous O2 bottle assembly that was due for its 36 month. After going through all the leak checks and purging procedures as outlined in the procedures for the system. I safety wired the manual shut off valve in the closed position on the regulator; it should have been safety wired in the open position. During the time the aircraft was back in service; the O2 system quantity showed full.Five days later I was contacted by the pilot stating the O2 system was full but no flow to the service ports. I was unable to quickly determine what was wrong and I was thinking while the medical interior was going back in the aircraft one of the clear flex O2 tubing was pinched; which would require a removal of the overhead and side walls of the cabin interior. We had the spare EC135 at our base so I made the call to move the crew over to that aircraft. I spent the rest of my time that night preparing the spare aircraft. I reach the end of my duty day after the spare aircraft was ready. I passed on the O2 problem on to the second base mechanic. He went thru the system and determined that the manual shut off was in the closed position. (Note in the [company's aircraft configuration] the manual shut off is not used as with other STC's AKA pilots shut off.)Two days later I came back to work and started to work the ongoing air conditioning MEL. During the course of the day I started to put the aircraft back together; I read the pass down note of where my partner left off and realized my mistake. I safety wired the manual shut off valve to the on position; verified O2 flow and installed the cover to the bottle.I have been here for about 2 months. During this time frame both of the mechanics have average over 60 hours a week dealing with scheduled and unscheduled maintenance on this aircraft with very little off time. A week before my mistake on the O2 system; I was in the hospital for a day and a half for a heart issue and I am currently on a 30 day 24 hour heart monitor. Not using this as an excuse but it is a contributing factor.It was an honest mistake made by me. All leak checks and purging was checked prior to the safety wiring of the valve. I would suggest that instead of just reading what is on the indicator and calling it good that the medical crews do a quick flow test daily as part of their routine. It was 5 days from the mistake with the safety wire and from the time it was found; 2 of those days was with the aircraft back in service for medical duty.




Synopsis: During scheduled maintenance on a Helicopter ECD-EC135 a mechanic safety wired an O2 bottle manual shutoff valve in the closed position when it should have been in the open position.