how to handle a rapid decompression over the Pacific ?
 

is there any specific procedure for over pacific ocean?
many thanks!

Same as any ETOPS route assuming you mean a twin?

You have to breathe...so you either have the O2 system to stay up there at alt, providing for you and pax, or you come down to an alt where you the O2 system can provide for you and pax, or you come down to an alt where you can now breathe ambient air...What ever alt you end up at, to breathe and not be a pilot Popsicle, now you have to consider your new fuel burn, that if planned for, you can make to your destination.

Can your average airliner leaving LAX, once hitting the half way point, continue at alt providing O2 for everyone or do they have to come down and now have enough fuel at the lower ALT to make it to Hawaii.

It's a loaded question and I would really love someone to show me how 150 passengers could be provided 2.5 hours worth of O2 at 39000 feet.

Both ETOPS or non ETOPS flight. even 4 eng aircraft as well.
Generally "descend to 10,000ft or MSA whichever is higher and land at the suitable airport ASAP."
But I just wonder any specific procedure and considerations for when I fly over the pacific ocean.
Thanks again!

Masks on, throttles idle, nose down with an offset turn, emergency descent checklist. Make the required radio calls. Level off at the altitude planned for this contingency at the appropriate lateral offset distance. Establish planned contingency airspeed and course appropriate for contingency destination. Notify ATC as required. Hope and constantly check that your contingency fuel planning was adequate.

Hopefully your pre-flight review of the contingency planning leaves you with some modicum of confidence in your new prospects!

Considering the fuel requirement for such an occasion: Additional Fuel (called critical fuel at our outfit for such a case) should be carried on such a flight:

Critical Fuel is the fuel required at the most critical point along the routes, if a loss of one or two engines or loss of pressurisation occurs, to

• descent according to procedure and continue with LRC to a suitable AD and
• hold there for 15 min at 1.500' AAL
• and make an approach and landing

Critical fuel is of course only required, if the calculated minimum fuel is not sufficient for such an event.

Regards,
DBate

We had three fuel calculations on the paperwork OAK-HNL.

1. How much fuel we needed to fly the leg plus alternate and reserve - almost irrelevant except to plan a landing weight.

2. How much fuel we needed to get to the ETP, lose an engine, drift down and keep going in the middle 20 thousand levels.

3. How much fuel we needed to get to the ETP, decompress, dive to 10,000 and press on with all engines.

Number three was always the highest number. If we decompressed AND lost an engine I think we had a wet footprint in the middle.

quote "I would really love someone to show me how 150 passengers could be provided 2.5 hours worth of O2 at 39000 feet. "

low level fuel burn and resultant range is but one question posed by a depress burn. Those of you thinking of staying high to reduce resultant fuel burn (forgetting the pesky pax down the back and their O2 requirements) are not considering the very real danger of nitrogen coming out of solution in the bloodstream / joints .

Is there any situation for a 3 or 4 engine a/c where at FL100, greater range can be had with an engine shut down? I propose this based on the fact engines are optimized for cruise @ FL300 and up, and thus run at very low disoptimized thrust at low altitude; SFC is thus higher.

Might be better to run fewer engines at higher thrust!

:8

Barit1

I'm sure there are, the P-3 patrol planes did it regularly. But, I doubt you could do it in public transport. The data is unlikely to be available to determine when an engine shutdown would be advatageous.

GF

Nimrod also routinely shut down 2 of 4 for low level patrol IIRC. But redundancy calcs are predicated on keeping as many engines running as you can. No-one's going to encourage commercial pilots to shut down a healthy engine.

Markerinbound:

Not allowed for Part 121 ops.

Two words: Liquid Oxygen. The C-5 had 100 liters, as I remember, the system could supply everyone at FL 240 for almost 6 hours. So, no issues there. Since leaving everyone on masks for that long was a bit inhumane, we planned depressed at FL 100.

In my corporate operation, like 121 ops, we have to have a dry footprint at FL 100, depressed or dry footprint OEI at OEI optimum cruise level. Have to inquire about OEI and depressed. I suspect on most routes, it is possible.

My most challenging sector was Petropavlovsk to Taihiti, had to fly LRC to make dry prints between Christmas and Taihiti and then just barely when depressurization was planned for. Russian exit points really fouled that one up.

GF

Question: Why does the descent have to be at max speed ? Why risk a structural overspeed instead of a low-speed stall ? Surely the RoD is more important to get down to 10,000' asap ?

e.g. A320 QRH Emer Descent : "Descend at the max appropriate speed."
e.g. B737NG FCTM Rapid Descent : "Target speed MMO/VMO".

Explanation appreciated.

Is it possible you'd get a slightly better range because of one less engine. Just wondering...

ross, in case you were responding to my post, I was referring to a rapid decompression over the Pacific (the original subject of this thread) assuming both engines running, therefore OEI and terrain issues are irrelevant. Perhaps I didn't make myself clear.

@ReverseFlight:

I was responding to MarkerInbound. My question was whether a ( decompression + lost engine ) be better than just a decompression from range considerations alone.

Regululations would not allow an airliner to cross the Pacific and not have a procedure to land at destination or return without everybody alive. We had a rogue chief pilot that wanted to fly from LAX to HNL with no supplemental oxygen even though we had the space. I refused and told the company why I wouldn't do it because ditching was the possible outcome. Common sense will prevail in these matters.

Yes, for the 737 that is the case.

If you look at the long range cruise tables at 10,000'. Fuel Flow is about 10% more for the 2 engine case.

Our company works on decompression (2 engine) as the most fuel critical scenario for ETOPS planning. They don't use LRC as the speed schedule, but the result is the same - decompression (2eng) is more limiting.

For us, planned speed is simply that - planned speed to establish the area of operation. There is no need to actually fly at that speed if you had a decompression.

How about this one: lose cabin pressure halfway, and have to descent to 10000 ft into heavy convective weather. I did. Wasn't fun.

- a fairly common military procedure on combat aircraft, but remember that generally mil engines are 'optimised' for full power (leaving the Jaguar out of it :D) and so fuel consumption tended to be better at top end RPM, whereas civ and other transport a/c are 'optimised' for cruise RPM bands. Standard low fuel diversion in the BAC Lightning was one shut down if it was for any significant distance and we used to 'loiter' on CAP one-engined..

Whoever it was suggested staying at cruise altitude unpressurised - don't so it with me on board please. - where do you fly that has an offset procedure at 10,000' or below?

Highest ROD is achieved at max speed. You want to get down asap so use max speed unless a structural problem (i.e. structural damage) is known/suspected in which case most aircraft say to descend at current speed.

Engine out = longer range??
 

I'm fully aware of P-3's, Nimrods etc shutting some down when on patrol, but that's done for greater ENDURANCE, not RANGE. My question yesterday was whether range could be extended by this practice.

Potsie Weber surprised me with his 737 response - I guess I wasn't expecting a twin to behave that way (trim drag, y'know) but I now stand enlightened! :)

The genesis of my range question goes back 35 years: A F/E at KLM theorized the DC-10 was "hobbled" by the nose-down moment of the high #2 engine, causing excess stab trim drag. He proposed running #2 at reduced thrust in cruise to lessen trim drag.

He would have been correct, too, if it weren't for the unfortunate fact that engine SFC deteriorates with the reduced thrust, thus eating up any gains in trim drag. :sad:

Thanks @Potsie Weber!

What's the analog for a quad? Say a 747. Get's interesting ; would the adverse trim drag on a single engine failure be compensated by an additional symmetric engine shutdown. Only an academic question; doubt anyone's doing that.

Hi ross_M,
747-400 has flown LAX-LHR on 3 engines.
http://www.caa.co.uk/docs/33/factor200623.pdf

- see post #21? Endurance not toooo much of a problem on an emergency diversion:hmm:

Of course not. In case I didn't state it clearly enough, the planned speed I was referring to is the speed at which the flight planned time and range assumptions at the ETP for the contingency being considered are based. The actual situation at the time of occurrence may give cause to select a different speed. But since the fuel burn estimates used in the flight plan contingencies were calculated using a specific speed, it's a good place to start until the actual situation can be assessed and the plan adjusted accordingly.

Summarizing oceanic planning considerations into a format suitable for the purposes of a discussion like this is challenging to say the least. A comprehensive computer based flight plan package contains far too much information to whittle down to a few paragraphs. And there are more things to consider than can be accounted for in a few words. The automation of flight planning provides fast accurate data, but also makes understanding the assumptions and decision matrix more challenging. It all seems a bit more sensible when marked up on a plotting chart.

westhawk

Ha ha! Nowhere of course. The offset is intended to provide lateral separation from other traffic on the same track while descending.

There's at least an even chance you'll be changing course for a diversionary alternate or return anyway. I did not mean to imply that one must continue on the offset track once the descent is completed. If a real emergency, going direct might be most appropriate.

BA didn't quite make it to LHR. had to stop a bit earlier if i remember correctly.

"Question: Why does the descent have to be at max speed ? Why risk a structural overspeed instead of a low-speed stall ? Surely the RoD is more important to get down to 10,000' asap ?

e.g. A320 QRH Emer Descent : "Descend at the max appropriate speed."
e.g. B737NG FCTM Rapid Descent : "Target speed MMO/VMO".

Explanation appreciated. "


For the safety of the humans on board. rapid decompression at high altitudes can cause DCS (also known as the bends). Have to get down asap to get that nitrogen back into solution in the blood. plus, it might be a bit chilly.

whereas the DH 121 Trident had its centre-engine momentum drag above the c/l, and the thrust about in-line.
Slight assistance with trim drag :ok:

====

An historic miljet (1945 Gloster Meteor) regulary positions to airshows with one engine shut down. These are RR Derwents, some the earliest production Whittle based engines, and are stopped and started with complete confidence it seems, even in such an old warbird. They are a trifle juicy, so this makes a healthy improvement to its realistic range, as well as reducing hours on each engine (they both still have plenty left, fortunately :ok:)

D. P Davies pointed out that there are at least two ways of getting down fast.

The Mmo/Vmo route, anticipating the switch altitude to pickup Vmo.

Then it was possible to decelerate at constant altitude, hang out a few drag producing devices (e.g. u/c and/or spoilers ) and then come down slower & steeper.

For a veriety of reasons, the former is usually the best method, especially as it starts to get the cabin altitude down immediately....

Both methods (he suggested) required a sensible margin above level-off height (e.g. 10,000 ft) to initiate the levelling off in good time.

*The ear also doesn't like (can't handle) rapidly increasing pressure as much as reducing pressure. I believe I was once told that comfortable rapid descents should be limited to about 8000 ft/min... for that reason, though of course oxygen content of the cabin air would rate higher on the wish list, than some discomfort.

* Am quite prepared to be corrected on the above anecdote

Thanks for all your answers. I guess the max RoD is achieved at max speed (MMO?VMO) rather than min speed (Vls), although I have no reference for this. My A320 FCTM just says :

33 posts later and the question of the day is how to push the nose over and not exceed Vmo in a rapid decompression event.

How about some of the experts in here tell me how a 737 past the half way point to Hawaii, will either provide 150 passengers with O2 at altitude for the remainder of the trip or have enough fuel to fly the last 1100 Nm at 12500 feet.....

The explanation is based on the balance of forces in the dive.

At constant speed, the drag of the aircraft is balanced by the thrust and the gravity component along the flight path. The gravity component increases as the dive steepens, so for the steepest dive angle you want the most drag and the least thrust. Drag being proportional to speed squared, the faster you go the steeper the dive angle can be.

Furthermore, what counts is not dive angle but rate of descent. The faster you go for a given dive angle, the higher the ROD will be.

Therefore, for a given aircraft configuration, the faster you go, the higher the ROD will be, and its probably something like a cube factor on the speed. So speed is a very powerful determinant of ROD.

The only slight caveat is the statement "for a given aircraft configuration". Obviously if you change the configuration to achieve more drag, you can achieve a steeped angle. BUT if you give up speed limits in order to achieve a steeper angle, you may well (and in many cases do) lose out on ROD.

Going up the back side of the drag curve doesn't work because you get a fair amount of drag, but even if you could get the same dive angle as at Vmo, your rate of descent, which depends on both speed AND dive angle, will be anaemic compared to the VMO case - perhaps only 1/3 the ROD.

- heard of ETOPS?

You might break out of your FAR 91, small plane world and refer to FAR 121.333 and FAR 121.646. Airliners are REQUIRED to provide for a depressurization in passenger operations at the ETP. Wet footprints are NOT allowed.

I don't have a B737 FPCCM, but you can be assured that the plan has fuel for a diversion at the ETP, either onward to HI or return to CA. We do it in business jets, the airlines do it. Simple or you don't go.

GF

g.f.

I flew 121 quite often LAX-HNL and return. But, my experience was limited to TWA's L1011-100.

Westbound, once out of LAX about 300 miles SFO was our diversionary alternate until passing the ETP, at which point it became Hilo. Otherwise the wet footprint would be a problem.

Don't know whether that holds true to the 777 or A330 with their awesome range, but it seems like a B737-800 would be more critical than the L1011-100.

BTW, I am in Kauai this week. Landing at Lihue (PHLI) on Friday there was an Alaska Airlines 737 (800?, NG?) parked at the terminal. I presume it came from PANC. Or,perhaps Seattle? Anywhere else seems a bit of a stretch.

I think AS does PLHI-KSEA and PHLI-KLAX right now. -800SFP. All the islands are a stretch in a 737, really.