B737 crew oxygen on the 737 ng
 

Hi,
Does any one know what regulation boeing has in mind when they print the table for minimum crew oxygen bottle pressure?
I mean is there a minimum time limit on emergency/100 % oxygen somewhere?
we have a lot of flights over very high terrain and have 22 min oxygen systems on board a few of the 737s but the flight crew oxygen requirments remain the same.
how come?

This should be in your own Part A or B, Vol 1 or Vol 2 and MEL. If you don't know where to find it, ask your Engs or your Captain, how on earth do you know you are legal to dispatch? The MEl will tabulate based on number of crew, minimum for dispatch, but obviously ETOPS and OE Routes require different quantities. For pressurised flight above flight level xxx there is a minimum crew time requirement..go find! could be interview question

hi,
i have looked and asked and probed. all the time i have been flying the ng's we have seen the oxygen for dispatch as the number of crews, check the temperature and check the minimum pressure required for dispatch and match it against the indication in the cockpit. there is no indication of flow rates in different selections anywhere and thats what i am looking for
1. how much oxygen is stored in the bottle?
2. is there a calculation to figure out how long it will last the cockpit crew?
3. why does boeing define dispatch criteria only in terms of psi?

if you can direct me to the relevant pages, please do help.
thanks for the sarcasm.

Crew Oxygen
 

Check the FPPM it has a crew vs pr graph depends also on the time and route safety altitude.

NGs fitted with either 76 cu.ft or 114 cu.ft bottles. The information is usually found in the MEL/DDG.

http://i665.photobucket.com/albums/v.../737oxygen.jpg

The usage rate depends upon what mode the mask regulators are in (Normal/100% or Emergency), the cabin altitude and the pilot using the mask (some breath deeper than others!)

The FAA requires that all pilots flying their aircraft above 12,500 feet for 30 minutes or longer or at 14,000 feet or above during the entire flight must use supplemental oxygen. The amount required is 1 liter of oxygen per minute for every 10,000 feet. For example, at 18,000 feet there should be a flow of 1.8 liters per minute of oxygen available via a standard breathing device.

Ah! this is not the same question! So how much Oxygen is stored, depends on size of bottle, ( normally 76 or 114 Cu Ft) not all NGs have the same fit, only the Engineers and Boeing will know your fit, which can be found from a/c serial number and the FTM.

Boeing quote a dispatch pressure in PSI not volume as clearly, a larger vessel will have a different pressure to a smaller one, but all fits allow for the min requirement under FAA and ICAO Annex 6 requirements for flight above certain altitudes. Annex 6 refers

ICAO regs state that the mass flow rate must be capable of supplying sufficient oxygen at differrent cabin altitudes to meet the crew requirements, approx 1.4 LPM Secondary, 2.4/3.5 LPM Normal and 4.0 LPM High Demand.

To covert the size of the bottle to a time, multiply cu ft x 28.31 to get litres, then divide by flow rate, on 100% it should give you at least 30 mins.

Refs: ICAO Annex 6 section 4.3.8, 4.4.5 and 6.7
JAR OPS1 ( 1.3.8.5)
ANO sectio 45 and 54

Hope this helps.

airborne - I hope you do get an answer here! It looks as if 30 mins is falling out as the 'normal' figure, FAA-wise anyway. It may be that your company has 'worked' the figure for your routes? If 30 mins is not enough for your likely 'worst' time above 14k, it sounds like a good question for your tech pilot.

I don't think so! the pressure in the cylinder depends on when it was last serviced, and to what pressure it was filled.

Again not quite.

gas consumed = breathing rate x time x ambient pressure

The "114 cubic feet" refers to the amount of gas in the bottle(s), at sea level standard temperature and pressure when filled to the rated pressure for the cylinder. At altitude the volume will be higher.

The breathing rate or respiratory minute volume (RMV), in litres per minute (lpm) in normal conditions will be between 10 and 25 lpm. At times of high work rate or panic, breathing rates can rise to 100 lpm.

Sorry mr Checkboard, Oxygen pressure not volume, is checked prior to dispatch and the temp corrections for pressure are tabulated. Engineers fill to a agreed service level and I can assure you that the volume does effect the pressure, hence the two tables 76/114 cu ft. Obviously pressure will depend on when it was last filled as we do pre-flight oxy checks every duty start and it is bound to deplete, as you observed, temp also effects.

Oxygen systems and flows are approved according to the flow rates set down under ICAO, FAA proceedures based on average person, average workloads and then adjusted for demand, low, normal, high 100% etc.

Boeing have an estimated rate: Sedentary 14LPM
Normal 24LPM
Severe 40LPM

As defined in the Boeing operations manual.

Obviously at the pre dispatch stage we look at the route and invariably, 30 mins Oxygen will suffice. We base this on high demand rate, being the most restrictive. ( Boeing manual calculates 25 mins )

I've got no experience flying pressurised aeroplanes, so my question may be way off. But EU-OPS 1.770, which I pressume would be applicable for European operators, states:

http://img.photobucket.com/albums/v2...kH/OPS1770.png

All occupants of flight deck seats on flight deck duty

All flight time above 13 000 ft, but in no case less than oxygen for 2 hours if
certified above 25 000 ft. Reading Note 3 this is based on 10 min emergency descent and 110 min at 10 000 ft.

If I get my physics correct, the additional oxygen to be diluted into the flight deck air at 10 000 ft shouldn't be very much. But the 22 min supply mentioned in the first post, will that satisfy EU-OPS requirements really? Especially if, as first poster says, routes are over very high terrain.

The 22 minute supply mentioned in the first post refers to the passenger oxygen chemical generators. (The standard unit runs for 12 minutes.)
I think you mean that the pressure read from the gauge will indicate a different volume, depending on the volume of the cylinder fitted?

Pax Oxygen only last for between 12 and 15 minutes from the chemical oxygen generators, hence the need to have sufficient portable for 10% of the actual pax carried, the 25 mins I refer to is flight crew oxygen from the installed bottles (not portable supply) and comes out of the Boeing FTM and systems manual.
Yes, the pressure guage will indicate a different pressure according to the bottle fit.

BUY the book and stop trying to rip off the writer and publisher.
Alternatively how about you post in the Cabin Crew forums as well and irritate them as well ?

a-a he's trying to sell it!

Going ETOPS over Greenland where you might have to stay at 14000 to avoid terrain in an decompress situation, and you are looking at about 150 miles to coast around 70N. If I read you right you need spare portable bottles to cover 10% of the pax in this situation beyond the 12 min you get from the generator Also you might be flying over areas where you are no allowed to land with high terrain. Do ETOPS planes in the Atlantic req, the 25 min bottle to allow for Greenland overfly.

thanks guys,
i believe boeing had pblished a table of some sort regarding the same.
let me give you a scenario, so that you understand the situation a bit better.
flying in india we operate to an airfield calle leh, its at 10682' amsl.
on this sector we need the special 737s fitted with the 22 min pax oxy system. however the crew oxygen pressure dispatch table is the same!
so this is where i get confused. when the pax oxy requirment is being adhered to by using a larger oxy system for them, why are we being dispatched with the same requirments as any other flight?
we use the 114 cubic foot bottle if that helps.