Is there such thing as a FAR that regulates how many passenger masks must be on a plane. Online quite a few people have said it has to exceed the number of seats by 10%, and I assume that makes up for the infants in lap, right? (but they never quoted a FAR)

Or are people who said that confused by this

"from FAR 121.327
(1) For flights of more than 30 minutes duration at cabin pressure altitudes above 8,000 feet up to and including 14,000 feet, enough oxygen for 30 minutes for 10 percent of the passengers."

or

(e)Passenger cabin occupants. When the airplane is operating at flight altitudes above 10,000 feet, the following supply of oxygen must be provided for the use of passenger cabin occupants:

(1) When an airplane certificated to operate at flight altitudes up to and including flight level 250, can at any point along the route to be flown, descend safely to a flight altitude of 14,000 feet or less within four minutes, oxygen must be available at the rate prescribed by this part for a 30-minute period for at least 10 percent of the passenger cabin occupants.

Also as if I didn't already ask enough...

(c) The equipment required by this section must have a means -

(1) To enable the pilots to readily determine, in flight, the amount of oxygen available in each source of supply and whether the oxygen is being delivered to the dispensing units; or

(2) In the case of individual dispensing units, to enable each user to make those determinations with respect to that person's oxygen supply and delivery; and

(3) To allow the pilots to use undiluted oxygen at their discretion at altitudes above 25,000 feet MSL.

Does this mean that the PAX must be able to see their oxygen flow indicator?

I'm not too familiar with aerospace, FARS, or any aircraft regulations, but is that the type of thing that would be listed in a FAR? - how many PAX oxygen masks for a commercial twin-aisle aircraft, or is that left to the discretion of an airliner. Also is this a good place to discuss FARS, or is there a different forum for this? I have more questions about regulations on different topics (and no one to go to that knows about them)

At least one for each seat is the simple answer. Certainly not discretionary. not uncommon to sea a row of three seats and four overhead masks if that is a potential configuration option, Of course there are masks in the lavs and crew rest areas as well. and different kind of masks on the flight deck.

The pax masks are usually good for 15 minutes 9enogh time to get down to 10,000'). There is an option for 20 minutes if it's an operational issue,

Thanks BravoOne, yeah I've noticed that they provide more masks than the amount of seats.

I'm looking for a law/regulation that states the required amount. I've read this online, but there wasn't any connection to any law, from any civil authority. "When an airplane flies at over 25000 ft, the total number of oxygen dispensing units and supply terminals must be at least greater than the number of seats by 10%"

You can find it in §25.1447 Equipment standards for oxygen dispensing units.

"(c) If certification for operation above 25,000 feet is requested, there must be oxygen dispensing equipment meeting the following requirements:

(1) There must be an oxygen dispensing unit connected to oxygen supply terminals immediately available to each occupant, wherever seated, and at least two oxygen dispensing units connected to oxygen terminals in each lavatory. The total number of dispensing units and outlets in the cabin must exceed the number of seats by at least 10 percent. The extra units must be as uniformly distributed throughout the cabin as practicable. If certification for operation above 30,000 feet is requested, the dispensing units providing the required oxygen flow must be automatically presented to the occupants before the cabin pressure altitude exceeds 15,000 feet. The crew must be provided with a manual means of making the dispensing units immediately available in the event of failure of the automatic system."

Thank you N0dak, that was exactly what I was looking for.

Actually, there are more masks than Pax. I would guess about 25% more. Each row of three has 4 masks as an example. You have to remember that people move around the cabin during flight and might not be at their seats when an emergency takes place.

(2) In the case of individual dispensing units, to enable each user to make those determinations with respect to that person's oxygen supply and delivery; and

The statement applies only to walk around bottles which could have leaked or been used and restowed. The supply for the planes O2 system is monitored by gauge in the cockpit and if O2 generators are the supply, no gauge is needed because they are either ready to go or fired off and depleted and it is obvious and known if they have been discharged.

(2) In the case of individual dispensing units, to enable each user to make those determinations with respect to that person's oxygen supply and delivery; and

Ah okay, I see your point. I thought that is why the flow indicator existed in some passenger oxygen systems. Why wouldn't they use "portable" in the statement. These rules are so confusing.

§25.1449 Means for determining use of oxygen.
There must be a means to allow the crew to determine whether oxygen is being delivered to the dispensing equipment.

Do you think this means that the crew must see that the passenger oxygen is flowing, or just that their own portable oxygen is flowing? I see this rule as an aid to help flight attendants help passengers.

So where are you going with this thread? Do you suspect there are violations in the present procedures or pax O2 designs?

NewFlightBird wrote:

Do you think this means that the crew must see that the passenger oxygen is flowing, or just that their own portable oxygen is flowing? I see this rule as an aid to help flight attendants help passengers.

Crew must see that passenger oxygen is flowing. All Boeing 727 thru 787 have a light and message (those equipped) to indicate the system is functioning and the masks have dropped. As for the crew they have confirmed their system is working properly before flight and when the masks are donned in flight they will be able to visually confirm operation (flow indicator), aurally confirm operation (clicking of flow indicator) as well as breathing oxygen.

NewFlightBird wrote:

(2) In the case of individual dispensing units, to enable each user to make those determinations with respect to that person's oxygen supply and delivery; and

Ah okay, I see your point. I thought that is why the flow indicator existed in some passenger oxygen systems. Why wouldn't they use "portable" in the statement. These rules are so confusing.

§25.1449 Means for determining use of oxygen.
There must be a means to allow the crew to determine whether oxygen is being delivered to the dispensing equipment.

Do you think this means that the crew must see that the passenger oxygen is flowing, or just that their own portable oxygen is flowing? I see this rule as an aid to help flight attendants help passengers.

The more common name for individual dispensing units is walk-around O2 (Oxygen) bottles and for use by the cabin crew so that they can move about the cabin in an emergency. Each O2 walk-around bottle has a pressure gauge to show quantity. The only thing that the cabin crew does in regards to PAX is to ensure that everyone has their mask donned correctly. No monitoring of oxygen flow is possible or required by the flight or cabin crew. The PAX O2 operation is automatic and also can also be deployed by the flight crew with the switch on the P-5 panel.

When the PAX O2 is depleted, it is just plain old gone. The only purpose of the PAX O2 system is so that if the aircraft suffers a decompression, the PAX can be kept alive while the aircraft descends to an altitude that can support human life. Depending on the the carrier, the PAX O2 system is good for approximately 20 minutes.

The flight crew O2 system is separate from the PAX O2 system and has an adjustable diluter demand regulator with a flow indicator and the pressure (quantity) of the flight crew system can be monitored in flight. Also, flight crew O2 is used during normal flight dependent on altitude and if a flight crew member leaves the cockpit above a certain altitude.

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