If structural integrity is in doubt ...

[TangoAir]

Hi,

What is your company or personal way to answer Boeing 737 NG QRH question regarding Emergency Descent?

How do you proceed to know if structural integrity is in doubt to decide your speed for the Emergency Descent?

Regards,

TangoAir

[compressor stall]

Not endo'd a 737, but can't see why the following wouldn't apply.

No damage = max speed
Damage = present speed

[Escape Path]

How do you proceed to know if structural integrity is in doubt to decide your speed for the Emergency Descent?

Call the F/A and ask them how's everything back there (after donning masks :E).
No hole? Maximum speed
Hole? Limited speed

[ImbracableCrunk]

I've thought a bit about this, too. My thoughts:

"Why are you doing a rapid descent?" is a good question.

Rapid decompression could be cause by a hull breach, and therefore structural integrity is in doubt. Some of the chemical milling faults in Boeings come to mind.

How many other reasons are there? Smoke is a good one, but structural integrity probably isn't an issue.

[unmanned transport]

The 747 Dreamlifter is unpressurized from a bulkhead not far from the flight deck. I wonder how many cycles this airframe will log until cracks appear in the skin of the unpressurized area.

Boeing DreamLifter - Canon Digital Photography Forums (http://photography-on-the.net/forum/showthread.php?t=911455)

[sevenstrokeroll]

this one is an easy one:

IF your first reaction is that you are annoyed as you put on the oxygen mask, proceed as if the plane is intact.

IF your first reaction is that you are scared ****less as you put on your oxgyne mask, proceed as if the plane is falling apart.

[PEI_3721]

The question should be what determines the speed/type of ‘rapid’ descent;- 'what is the nature of the problem?'.

A slowly climbing cabin could have been detected before a warning is given. Even at 10,000ft here is time for some remedial actions – check switches / close outflow valves – control the situation.

For a rapid (surprising) decompression – with the cabin altitude climbing rapidly, then a descent should be commenced immediately. There may be other system indications of what is happening which will subsequently indicate the necessary rate of descent.
Remember that you are more likely to kill passengers from hasty or misjudged actions than missing the required descent altitude by a few seconds. Beware of the actual safety altitude, no need to rush into mountains with a high rate descent.
The important issue is to get the oxygen masks on so that you can asses the situation and then decide on modifying the initial action ( SSR :ok: ) – remain in control and control the outcome.

It’s most unlikely that a rapid decompression will give ‘instantaneous’ flight / cabin altitude. Even with a window out the cabin should still have a supply of engine air and the outflow valves should be closed (and there’s always the Nun with a guitar who blocks the window).

I recall the story of a ‘Far East’ BAC 1-11 many years ago which suffered an ‘explosive’ decompression due to a ‘device’. This removed part of a fuselage panel; the crew completed a rapid, high speed emergency decent during which the power controls failed and thus required manual recovery. The FDR indicated that they pulled >3g, and with a hole in the side of the aircraft (BAC1-11 were built strong).
Some months later the same Captain suffered exactly the same symptoms; his response was to take things a little slower. With the advantage of experience, he managed the surprise - starly factor, assessed the situation (similarities), and chose a safe course of action.

In the absence of experience we have to think about these things before the event ( IC #4 :ok: ).
We should not be overly biased by a procedural training drill in simulator, few of these use realistic scenarios and might overlook the important assessment and adjustment phases.

[lomapaseo]

Interesting question, since I really don't know the answer, Ill' ask for some clarifications.

What choices do you typically choose between when deciding on speed of descent ?

Isn't it a decision to save the aircraft with as little impact on the passengers ?

Assuming that the flight crew is safe (masks work, etc.), the passengers react over a range of hazards. If this range is considered (minor impairment = ear aches etc., moderate impairment = loss of conscioness, severe = death) This consideration provides a variable in descent speeds over time. Since the optimum descent speed is unlikely to require instantaneous descision making, why not take your time in assessing the aircraft safety state and adjust in an analog fashion accordingly?

[Offchocks]

If structural integrity is in doubt, then you go down at the current Mach into IAS.
I would consider a current cabin altitude climbing to 30,000ft plus in less than 10 seconds would indicate a hole in the fuselage, there is no way of knowing if it is structual and so I would react as if it was. Once the descent is on the way there is no harm in asking CC for information, but there is a good chance a hole would not be not visable in the cabin.

[SNS3Guppy]

IF your first reaction is that you are annoyed as you put on the oxygen mask, proceed as if the plane is intact.

IF your first reaction is that you are scared ****less as you put on your oxgyne mask, proceed as if the plane is falling apart.

I think that's probably the best explanation I've heard on the subject.

[glhcarl]

I wonder how many cycles this airframe will log until cracks appear in the skin of the unpressurized area.
It depends on the loads experanced. The un-pressurized wings skins are a lot thicker than fuselage skins but that can start cracking a very low hours/cycles!

[sevenstrokeroll]

generally speaking the loss of one window in the cabin could just about be compensate by a fully closed outflow valve.

So, if the plane's cabin has climbed to 30,000 feet in an instant, it is probably a bigger hole than a window!

have some confidence in your decision...and remember that Aloha 737 made it with real structural failure!!!

thanks guppy, sometimes the soul has more knowledge than the mind.

[galaxy flyer]

Well, for FL 510 certification, a simulated hole equal in area to a cabin window is instantly opened. On a GLEX, the cabin rises about 800-1000fpm, maximum. I suspect that is standard test profile and, yes an outflow can just about compensate. So, what seven stroke said!

GF

[Sciolistes]

Cracking a cockpit window open on the ground will release 200' of pressure in a second or two. Therefore, I would have thought the loss of a cabin window would result in a rapid depressurisation (6,000 to 12,000 fpm) even if it isn't instant.

[Checkboard]

Loss of a "large" window:

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Piaggio P-180 Avanti rapid depressurisation demonstration - Cabin at sea level, aircraft at 7000', bleeds off, outflow valve full open (cabin goes from sea level to 7000' in about 15 seconds):

CS9UH8Pg_aY

[Centaurus]

With a 737, gear and speed brake extended and thrust levers idle the rate of descent is as near as dammit to the high dive at max speed. Barreling down at 320 knots in IMC is good fun in the simulator because there are no thunderstorms to run into on the way down.

Opinions vary, but having done a high dive at max speed in IMC for real on a bloody black night, next time I would opt for the low speed descent with gear and speed brakes extended. Less strain on the airframe for one thing and if descending into heavy precipitation, Boeing recommend reducing speed to minimise possibility of engine instability due rain ingestion at high speed.

If your speed is aleady back to around 250 knots IAS (same IAS in cruise at high altitude), then you have covered the heavy rain/thunderstorm case since the speed covers best turbulence penetration as well.

So much depends on circumstances at the time of depressuriastion. Sound professional knowledge of the pros and cons of high speed versus low speed descent helps. But you need to delve into more than just the FCOM advice as this only gives you the bare bones of the subject. Search the internet.

[Centaurus]

generally speaking the loss of one window in the cabin could just about be compensate by a fully closed outflow valve

Generally speaking is understandably just another personal opinion not based on fact or a measured test. No offence meant of course and I mean that.

On the other hand the Boeing 737-300 flight simulator operating hand book explains that operation of the "uncontrollable depressurisation" selection on the instructor panel simulates loss of all cabin pressure in three seconds caused by a passenger window blown out. Closing the outflow valve makes no difference. Of course different types of aircraft may have different depressurisation characteristics.

[sevenstrokeroll]

remember, if you are flying along and your outflow valve is almost completely closed in normal ops, it won't help that much when you blow a window.

planes develop leaks along their lives and I remember one flight attendant telling me how they proped a piece of soap in the lavatory basin drain...this would suck all the foul smelling odors out of the lavatory...but affected our pressurization especially in a reduced power descent.

but if your outflow valve is fully open and you lose a window, the size is comparable take a look at the outflow valve(s) the next walk around...about the size of a window.

not that it will be comfortable in the cabin

[lomapaseo]

planes develop leaks along their lives and I remember one flight attendant telling me how they proped a piece of soap in the lavatory basin drain...this would suck all the foul smelling odors out of the lavatory...but affected our pressurization especially in a reduced power descent.



I don't understand the reason for the pressure differential in a lavatory that explains the above.

Does this mean that if one were to seal the lavatory from inside using wet cloths etc. around the doors and then left the sink drain propped open that you would eventually suffocate ? Or just smoke your ciggie with your head over the sink basin.

[misd-agin]

sevenstrokeseven - you can't compare a wide open outflow valve on the ground with the loss of a window.

The open outflow valve is obvious on the ground. The outflow valve is nowhere near fully open inflight.

[sevenstrokeroll]

the whole idea is that there is some reduction in immediate climb from 8000' to 35,000 feet in an instant...(cabin alt).

indeed there are federal regulations regarding this.

I encourage you to read as much as you can on the subject.

[TangoAir]

Thanks for all your responses,

Regards,

TangoAir