ATA 35

During an operational check of an aircraft oxygen system, it was determined that a passenger oxygen drop down mask would not let oxygen flow. The fault was in the connection between the smaller tube and the larger tube attached to the barbed fitting on the oxygen drop down box. There is supposed to be clearance for oxygen to flow, in this case the smaller line was squeezed shut and would not allow oxygen to flow to the mask. The part number in question is a 174080-31 Rev “K”. The, Batch was LC0526K. This lot had been shipped around July of 2005. A thorough inspection of the masks that are installed in your aircraft is recommended. This inspection should include a functional test of the mask as well as the aircraft system.

Please refer to the IAI AMM 35-00-00 Oxygen system adjustment and test paragraph 1, Steps (1) thru (36).

ATA 35

Passenger Oxygen Masks
On February 19 our Service Center, Trimec, reported that during an operational inspection of the passenger oxygen drop down masks, there was one that would not let oxygen flow thru the connection between the larger line attached to the barbed fitting on the oxygen drop down box and the smaller line that goes to the mask. In this case the smaller line was squeezed shut and would not allow oxygen to flow to the mask. The part number in question is a 174080-31 Rev “K”. The, Batch was LC0526K. This lot had been shipped around July of 2005.
A thorough inspection of the masks that are installed in your aircraft is recommended. This inspection should include a functional test of the mask as well as the aircraft system.

Please refer to the IAI AMM 35-00-00 Oxygen system adjustment and test paragraph 1, Steps (1) thru (36).

This may be the time for you to accomplish your chapter 5 requirements: 6- 8 year factory overhaul or 20 life limit.

A follow up investigation of the event is underway and if any fleet action is required it will be communicated accordingly.

ATA 35

Passenger Oxygen Mask Check
When our customers are bringing their aircraft in for an 800-hour “C” inspection, we encourage them to deploy the passenger oxygen masks, simulating an actual cabin de-pressurization. This familiarizes the pilots with what goes on during a mask drop-out. Our procedure is as follows:
• Level the aircraft at 16,000 ft.
• Slowly open the manual dump valve (red knob). Watch for ”10,000 ft. cabin” light on annunciator panel to illuminate at 10,000 ft. cabin altitude. The cabin should level off at 13,000 ft.
• Select Ram. The cabin will climb and you should get the red “Pass Oxygen On” light on the passenger oxygen control panel on the copilot’s side console and a simultaneous drop of the passenger masks.
If any of these events do not occur, you might have a problem with the system, and corrective maintenance should be accomplished.