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Flight crew O2 requirements

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Flight crew O2 requirements

Old 19th Dec 2007, 15:03
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Flight crew O2 requirements

I'm in a place where I don't have access to any Boeing data so maybe someone can pitch in here and help me with an oxygen question?

How much time would a crew of three/four have in the event of a smoke and fumes of unknown orgin problem using 100%. Lets just leave the problem itself out of the equation other than saying we need 100% for the duration. I maintain that we need what ever our ETOPS range approval is, but I may be wrong. Lets assume that our crew O2 bottle has been serviced to max or 1800 PSI. I thinking Boeing here but if the Airbus has another approach to this problem, speak up please.
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Old 20th Dec 2007, 00:20
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Come on guys. This is a killer question and I thought at least someone would have this data at their finger tips.
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Old 20th Dec 2007, 00:39
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I can't be specific

But as far as I know there is a minimum 02 pressure to allow for dispatch, this is for 3 crew members, when the 02 is below this nominal pressure, the cockpit is restricted to 2 crew members. I do not believe ETOPS duration comes into the equation, I believe the crew would reduce altitude below 10,000' then clear the smoke using the fresh air venting system.

This is not specific to Boeing, but just standard procedure as far as I know, I am a maintenance engineer not a pilot.
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Old 20th Dec 2007, 01:20
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Well thanks at least someone jumped in here. Your scenario is not a part of any Boeing QRH that I'm aware of. So if the O2 bottle is at 1800 PSI, how long can it last for 3 crew members at 100%. I think it's surprising long, maybe 3+ hours, but I can't prove that right now. I have gone to a source at Boeing so maybe I will have an answer soon.

Thanks for your comments!
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Old 20th Dec 2007, 02:23
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Try your type's FCOM for flight crew supplemental oxygen cylinder capacity. Then look at min pressure for dispatch chart(s). That will give min cylinder pressure for 2 or 3 flight deck crew for ETI of flight(s). Then get your calculator out and work out how long it would supply at 1800psi. Remember the ideal gas law PV=nRT
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Old 20th Dec 2007, 04:29
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Most pilots are shocked when they learn how little time they have when operating on 100 percent oxygen. The minimum pressure requirements typically result from the requirement to supply the cockpit crew with 15 minutes worth of oxygen at a cabin altitude of 8,000 feet. I believe one manufacturer adds an additional factor of 9 to 13 percent to account for leakage during the flight.

While certainly not intuitive, I was told by an engineer from a major oxygen equipment manufacturer, when operating on 100 percent oxygen, the rate of oxygen consumption will increase as the cabin altitude decreases. This is due to the design of the regulator. He went on to explain that if you dispatch with the MEL minimum oxygen level, and encountered the requirement to utilize 100 percent oxygen with the cabin altitude at sea level, you could find your supply depleted in as little as 10 minutes.

With a fully charged (1800 psi) 77 cubic ft cylinder installed and only a crew of two using 100 percent, you will have approximately 42 minutes at a cabin altitude of 8,000 feet. If you have a 115 cubic ft cylinder, your oxygen will last approximately 66 minutes.

The Kid

Last edited by Aztec Kid; 21st Dec 2007 at 05:30. Reason: Format
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Old 20th Dec 2007, 05:25
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smaller bottle

do you have for 49 cubic-feet bottle and two pilot ?
many thanks
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Old 20th Dec 2007, 05:52
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Just a quick look at the FAR's and don't know if ETOPS or if Swissair MD-11 has any impact.

§ 121.333 Supplemental oxygen for emergency descent and for first aid; turbine engine powered airplanes with pressurized cabins.

(b) Crewmembers. When operating at flight altitudes above 10,000 feet, the certificate holder shall supply enough oxygen to comply with §121.329, but not less than a two-hour supply for each flight crewmember on flight deck duty. The required two hours supply is that quantity of oxygen necessary for a constant rate of descent from the airplane's maximum certificated operating altitude to 10,000 feet in ten minutes and followed by 110 minutes at 10,000 feet. The oxygen required in the event of cabin pressurization failure by §121.337 may be included in determining the supply required for flight crewmembers on flight deck duty.

§ 121.337 Protective breathing equipment.

(a) The certificate holder shall furnish approved protective breathing equipment (PBE) meeting the equipment, breathing gas, and communication requirements contained in paragraph (b) of this section.

(b) Pressurized and nonpressurized cabin airplanes. Except as provided in paragraph (f) of this section, no person may operate an airplane unless protective breathing equipment meeting the requirements of this section is provided as follows:

(1) General. The equipment must protect the flightcrew from the effects of smoke, carbon dioxide or other harmful gases or an oxygen deficient environment caused by other than an airplane depressurization while on flight deck duty and must protect crewmembers from the above effects while combatting fires on board the airplane.

(2) The equipment must be inspected regularly in accordance with inspection guidelines and the inspection periods established by the equipment manufacturer to ensure its condition for continued serviceability and immediate readiness to perform its intended emergency purposes. The inspection periods may be changed upon a showing by the certificate holder that the changes would provide an equivalent level of safety.

(3) That part of the equipment protecting the eyes must not impair the wearer's vision to the extent that a crewmember's duties cannot be accomplished and must allow corrective glasses to be worn without impairment of vision or loss of the protection required by paragraph (b)(1) of this section.

(4) The equipment, while in use, must allow the flightcrew to communicate using the airplane radio equipment and to communicate by interphone with each other while at their assigned duty stations. The equipment, while in use, must also allow crewmember interphone communications between each of two flight crewmember stations in the pilot compartment and at least one normal flight attendant station in each passenger compartment.

(5) The equipment, while in use, must allow any crewmember to use the airplane interphone system at any of the flight attendant stations referred to in paragraph (b)(4) of this section.

(6) The equipment may also be used to meet the supplemental oxygen requirements of this part provided it meets the oxygen equipment standards of §121.335 of this part.

(7) Protective breathing gas duration and supply system equipment requirements are as follows:

(i) The equipment must supply breathing gas for 15 minutes at a pressure altitude of 8,000 feet for the following:

(A) Flight crewmembers while performing flight deck duties; and

(B) Crewmembers while combatting an in-flight fire.

(ii) The breathing gas system must be free from hazards in itself, in its method of operation, and in its effect upon other components.

(iii) For breathing gas systems other than chemical oxygen generators, there must be a means to allow the crew to readily determine, during the equipment preflight described in paragraph (c) of this section, that the gas supply is fully charged.

(iv) For each chemical oxygen generator, the supply system equipment must meet the requirements of §25.1450 (b) and (c) of this chapter.

(8) Smoke and fume protection. Protective breathing equipment with a fixed or portable breathing gas supply meeting the requirements of this section must be conveniently located on the flight deck and be easily accessible for immediate use by each required flight crewmember at his or her assigned duty station.

(9) Fire combatting. Except for nontransport category airplanes type certificated after December 31, 1964, protective breathing equipment with a portable breathing gas supply meeting the requirements of this section must be easily accessible and conveniently located for immediate use by crewmembers in combatting fires as follows:

(i) One PBE is required for each hand fire extinguisher located for use in a galley other than a galley located in a passenger, cargo, or crew compartment.

(ii) One on the flight deck, except that the Administrator may authorize another location for this PBE if special circumstances exist that make compliance impractical and the proposed deviation would provide an equivalent level of safety.

(iii) In each passenger compartment, one for each hand fire extinguisher required by §121.309 of this part, to be located within 3 feet of each required hand fire extinguisher, except that the Administrator may authorize a deviation allowing locations of PBE more than 3 feet from required hand fire extinguisher locations if special circumstances exist that make compliance impractical and if the proposed deviation provides an equivalent level of safety.

(c) Equipment preflight. (1) Before each flight, each item of PBE at flight crewmember duty stations must be checked by the flight crewmember who will use the equipment to ensure that the equipment—

(i) For other than chemical oxygen generator systems, is functioning, is serviceable, fits properly (unless a universal-fit type), and is connected to supply terminals and that the breathing gas supply and pressure are adequate for use; and

(ii) For chemical oxygen generator systems, is serviceable and fits properly (unless a universal-fit type).

(2) Each item of PBE located at other than a flight crewmember duty station must be checked by a designated crewmember to ensure that each is properly stowed and serviceable, and, for other than chemical oxygen generator systems, the breathing gas supply is fully charged. Each certificate holder, in its operations manual, must designate at least one crewmember to perform those checks before he or she takes off in that airplane for his or her first flight of the day.
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Old 20th Dec 2007, 08:57
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I don’t believe ETOPS regulations have any impact on the oxygen requirements.

To address oxygen requirements during a depressurization, the FAA requires a supplemental oxygen flow rate of 0.8 LPM at 10,000 feet. The mask on my aircraft supplies oxygen at about 2.4 LPM when at 10,000 feet.

Charts for oxygen duration for smoke protection (100 percent oxygen) are based on a consumption rate of 30 LPM per pilot. This is why the duration is so much shorter when using 100 percent oxygen. It is also the reason that the decompression drills include a reminder to ensure the mask regulator is set to normal rather than 100 percent.

Typically, the net result is that if you have enough oxygen for 15 minutes at 100 percent at 8,000 feet, you will have more than enough to meet the two hour requirement at 10,000 feet. However, if you are flying routes with very high MEAs that would preclude an immediate descent to 10,000 feet, an analysis would have to be performed to determine the additional oxygen requirements. In some cases, it could be greater than the 15 minute supply at 100 percent.

I believe duration for a full bottle is simply a linear relationship. So for a full 49 cubic ft cylinder and two pilots, I would estimate that you would have approximately 26 minutes at 100 percent and 8,000 feet.

Please keep in mind that I am definitely not an expert in this area. I am simply conveying what was told to me by the engineer.

Regardless if you are miles away from land or directly over a suitable airport, dealing with smoke in the aircraft would be an extremely challenging task for even the most proficient flight crew. Keep in mind; while the pilots may have a limited oxygen supply, other than a few PBEs, the cabin crew and passengers have nothing. This may be one of the reasons that regulators do not dwell on the limited crew oxygen for smoke protection.

The Kid

Last edited by Aztec Kid; 21st Dec 2007 at 05:28. Reason: Format
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Old 20th Dec 2007, 09:32
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Forgive me for not answering the original question.

Based on the information I have, for a full cylinder when using 100 percent oxygen at 8,000 feet:

For a 77 cubic ft cylinder:
A 4 pilot crew will have 21 minutes, and a 3 pilot crew will have 28 minutes.

For a 115 cubic ft cylinder:
A 4 pilot crew will have 33 minutes, and a 3 pilot crew will have 44 minutes.

The Kid

Last edited by Aztec Kid; 20th Dec 2007 at 09:33. Reason: Format
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Old 20th Dec 2007, 12:49
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O2

My AB book says that we need enough O2 for all occupants from decompression to the time we reach 10000'. Being an A300F, fitted with 4 115 cu/ft bottles, in "normal" mode, 2 pilots plus 7 occupants need 900 psi (average per bottle at 21 deg) to last 120 min. There is no provision for 100% and it would be hypothetic to mention emergency since that with an actual fire on board the AC structural integrity would probably not last more than 20 min...
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Old 20th Dec 2007, 14:34
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This would seem to fly in the face of the previous posters CFAR 121.333. I have a B777 acceptance document here in front of me and it appears that it also references the 10 minute descent, including the two hour supply for the crew. Does not mention crew size or 100%. More to come from Boeing later today, I hope.

Thanks everyone!
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Old 20th Dec 2007, 17:53
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Aztec Kid is on the mark.

An actual event from a few years back showed what Aztec Kid posted is 100% correct. The crew diverted to LPLA with smoke in the cabin and landed with a nearly depleted pilot oxygen system (they fixed the problem before landing). When their story started to spead, we began to ask a lot of questions. There was simply not as much available time on 100% O2 as we thought.

Our minimum for ETOPS went from 1000 to 1100psi, and we notice that we are normally around 1600 now...thank to the crew´s statements.
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Old 20th Dec 2007, 19:21
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Maybe we have started a dialouge here that will enhance someones awareness of an issue that perhaps we have taken for granite to long?
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Old 21st Dec 2007, 06:46
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The following comes from one flight manual.
Two crew and two 514 cubic inch cylinders. Red figures 100% oxygen.
OXYGEN DURATION - HOURS
Cockpit GAUGE PRESSURE - PSI
Altitude 1800 1500 1200 900 600 300
35,000 7.80 6.50 5.20 3.90 2.60 1.30
7.80 6.50 5.20 3.90 2.60 1.30
30,000 5.63 4.69 3.74 2.80 1.86 .93
5.63 4.69 3.74 2.80 1.86 .93
25,000 4.34 3.62 2.89 2.17 1.44 .72
5.47 4.56 3.64 2.73 1.82 .91
20,000 3.30 2.75 2.20 1.65 1.10 .55
6.17 5.15 4.11 3.09 2.06 1.03
15,000 2.65 2.21 1.77 1.33 .88 .44
7.49 6.24 5.00 3.75 2.50 1.25
10,000 2.12 1.76 1.42 1.06 .71 .35
9.94 8.29 7.44 4.97 3.72 1.86

Last edited by Brian Abraham; 22nd Dec 2007 at 01:45. Reason: try to sort formatting (unsuccessfully)
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Old 21st Dec 2007, 16:55
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Brian,

The duration figures you posted seem to make sense in relative sense. When in the normal position, above approximately 27,500 feet, the mask regulator is designed to supply 100 percent oxygen. Above 30,000 feet, you will get 100 percent with positive pressure (emergency mode), regardless of what mode you have selected. This is why the durations you listed are identical for normal and 100 percent when at 30,000 and 35,000.

You can see at the lower altitudes, your duration is significantly reduced when comparing 100 percent to the normal position.

However the magnitudes do not seem to be correct. If you have two bottles with 514 cubic inch capacity, that is only 0.6 cubic feet. Unless I am making an error, this would only supply one pilot for 48 seconds.


Best regards,
The Kid
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Old 22nd Dec 2007, 12:38
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Aztec - I don't know how you are doing the math but I can asure you we ran out of fuel long before we got close to running out of oxygen.
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