Oxygen System Abnormals

- James Albright (a former G450 driver)

Updated: 2015-01-21

There isn't much here, about all I have to say on this is how to restow the cabin oxygen masks if you happen to inadvertently deploy them.

Everything here is from the references shown below, with a few comments in an alternate color.

 Oxygen mask restow

Some say "there are those that have and those that will" when it comes to the mistake of getting the oxygen system switches wrong. It can happen two ways:

• The pilot blindly turns the knob to the right from "Off" to "Man" when he or she meant to go from "Auto" to "Off." The masks will drop.

• The pilot gets the order wrong and turns the passenger system to Auto before turning the total system On. The masks might drop.

The solution, of course, is to never touch the passenger oxygen system knob without first checking the oxygen system switch. But if you do drop them can you just stuff the masks back into their containers and be done with it? Perhaps. If there isn't any electrical power on the aircraft and your system isn't especially tight the answer could be yes. Otherwise, you have a checklist to guide you but that might not be enough.

If you remember the circuit breaker and are methodical about it, you can get this done in about five minutes. Since you don't do this often, keep three things in mind:

1. There is a procedure in the QRH that tells you what circuit breaker to pull. But that isn't enough . . .

2. There is an expanded procedure in the Operating Manual that tells you how to fold the mask and tubing. But that isn't enough . . .

3. Chances are you will be in a rush. You need to deplete the oxygen pressure in the lines or the masks will just pop right out again or the mask covers may refuse to seat. Instructions below.

Procedure

[G450 Quick Reference Handbook, page EH-14]

IF THE PASSENGER OXYGEN MASKS ARE INADVERTENTLY ACTIVATED, EITHER ON THE GROUND OR IN FLIGHT, THE FOLLOWING PROCEDURES APPLY:

1. Passenger Oxygen Controller . . . OFF

   Don't skip this step, it is critical that you bleed the pressure from the system.

2. Passenger Oxygen Masks . . . RESTOW

   Not yet! More on that below.

   RESET PASSENGER OXYGEN CONTROLLER AS FOLLOWS:

3. WARN LTS PWR #5 CB (REER) . . . PULL & RESET

   NOTE: The circuit breaker is pulled and reset, to reset the logic of the Passenger Oxygen Controller.

   There are those "who have" and managed to restow all the masks without incident and without having touched the circuit breaker. It seems the aircraft electrical power was off and the logic of the system was not affected. If you had power on at any point, it seems, pulling the circuit breaker would be prudent.

[G450 Maintenance Manual, §35-21-01, ¶C.(2)]

a. Pull REER A25.

The operating manual puts this later in the procedure but it doesn't seem to matter as long as you do it. If there is no power on the aircraft you can skip this step.

b. Stow head strap inside of mask face piece.

You will have a great deal of difficulty getting the covers to close unless you deplete the oxygen pressure first.

c. Fold breather bag flat by overlapping edges toward center, one lap for each side.

d. Fold breather bag into mask face piece using accordion type folds.

e. Coil tubing in a neat spiral inside of face piece. Ensure no kinks exist.

f. Invert mask (face piece opening toward presentation unit).

Deplete Oxygen Pressure Prior to Restow

The mask is held in place by a decorative cover on a spring loaded cover pin that is pushed by an oxygen actuated plunger. So long as there is pressure in the passenger oxygen lines, that plunger will have pressure on it. (It is shown here with the plunger already retracted.) Do not confuse the pin holding the cover to the one tethered to the mask. In the photo, the cover pin is missing because the plunger pushed it out of its receptacle. The oxygen mask pin is still in place, connected with a string to the mask.

If the masks were deployed and not used, there will probably be residual pressure in the lines. You need to find the mask that is furthest from the cockpit and pull the pin attached to the mask with a string. You should hear an audible hissing from the mask. Give the system a few minutes to deplete all the residual pressure. Once that is done, you should be able to reseat the pin and restow all the deployed oxygen masks.

 References:

Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013

Gulfstream G450 Quick Reference Handbook, GAC-AC-G450-OPS-0003, Revision 34, 18 April 2013