Date: 201502
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Weather elements / visibility: Excessive cold
Light: Daylight
Aircraft: Eurocopter AS 350/355/EC130 - Astar/Twinstar/Ecureuil
Operator: Air Taxi
Operating under: Part 135
Flight phase: Parked
Aircraft component: Oxygen System/Pax
Component problem: Design; Improperly Operated
Reporter organization: Air Taxi
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Attendant
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Human Factors; Chart Or Publication
Primary problem: Human Factors

Narrative: I was performing some Approved Aircraft Inspection Program (AAIP) inspections on a spare   AS-350 aircraft on the roof top pad. I was doing the maintenance on a maintenance delay. Since I was on a delay I wanted to take advantage and top off the Liquid O2 (LOX). The LOX is contained in the aircraft R/H baggage hold. I removed the LOX container and took it into the hospital to service it with LOX. After the converter was full I let it sit in the hospital for awhile to thaw the frost that builds up during the fill process. I continued with the inspections. At some point I took the container back out to the ship and re-installed it.  The LOX has two electrical wires for quantity indication; and two flexible hoses; one for vent; and one for pressure. After I installed the full converter I checked the installation for O2 flow by turning on the O2 shutoff valve and the flow control on the O2 panel. I had O2 flow and the quantity indicated 8 liters +. I learned this morning when I returned to work that I had left the pressure hose disconnected. Because of this no O2 was available from the aircraft O2 cabinet. I was informed the flight was ok because there was back up gaseous O2 available. This was very confusing because I had O2 flow during the post installation flow check. Today I was at another base working on my normal ship. It also has LOX system. I attempted to duplicate this situation. I found that even after the LOX pressure hose is disconnected from the LOX container there is still enough residual O2 in the system that it is possible to get a flow from the O2 panel. If the flow control is not set to high flow rates it is possible to get flow for longer than one would expect. [Recommend:]1.While performing multiple tasks better planning can be done to avoid starting and stopping midway thru a task. 2.When checking flow from the O2 panel one must turn the flow control full on and run the O2 until such a time as the quantity indicator shows a decrease in quantity. The quantity display is very sensitive and will indicate even a small amount of O2 use.3.The medical crew needs to be alerted when the LOX is serviced so as to implement an additional layer of checks.

Callback: Reporter stated medical evacuation helicopters require specific Supplemental Type Certificates (STC) to install a medical cabin. A medical panel is built into the aft bulkhead of the cabin fuselage section. The panel faces forward. The LOX container is a round stainless steel sphere with a heat exchanger located in the baggage pit below the transmission deck. On the LOX sphere is a pressure transducer that is a digital readout of the LOX quantity in liters. There is no other pressure gauge required per the STC after the LOX sphere.Reporter stated the Manual OFF-ON O2 handle for the LOX system is located on the left aft side of the Captain's seat; which is the right seat position on their single pilot aircraft. The shut-off handle operates a push-pull cable to a regulator that is downstream (after) the LOX heat exchanger and before the medical O2 panel. The medical panel has four oxygen outlets. Two outlets that provide full O2 vapor pressure and two individually regulated outlets that use flow control. Medical Staff must look aft at the aft bulkhead to verify O2 is flowing; but would not be aware when looking forward if the O2 flow suddenly stopped. In the past; even pilots have unknowingly moved the Manual Off-ON O2 handle; which is near their left seat belt attachment and shutting off available O2 to the medical panel without the Medical Staff being aware of the condition; since the only pressure gauge is at the LOX sphere. Since technicians and pilots can unknowingly create an unsafe condition; he recommends the STC require adding a LOX Low pressure light to the center panel on the forward side of the medical cabin that is an additional alert to the Medical Staff that a drop in available oxygen to a patient has occurred.



Synopsis: An Aircraft Maintenance Technician (AMT) was informed he had left a pressure hose disconnected from an LOX sphere after reinstalling the serviced oxygen sphere on an AS-350 Medical helicopter. Residual pressure in the oxygen system line was enough to show oxygen flow at the O2 panel during his O2 check. Technician recommends the Medical STC require a low pressure O2 light be added to the center panel to alert Medical Staff of sudden O2 loss.