Flight MH370 Depressurization Scenarios

[WeedWhacker]

The cabin crew have oxygen bottles which they can use.

Yes, but the POBs are small, and don't have the "EMERG" force-flow feature like the quick-donning masks in the cockpit.

(Sorry....my airline abbreviated the cabin bottles as 'POB'. Really they are oxygen cylinders, or tanks).

 

[Mick West]

There are other possible scenarios there. The 777 has oxygen generators for the passengers which last for 12 minutes. After that time, depressurising the cabin at normal cruising altitude is enough to incapacitate the passengers.

But can you override the cabin altitude limiter? That's supposed to close the outflow valves at 11,000 feet pressure. Would they just have to set the pressurization system to manual to do that?

 

[WeedWhacker]

But can you override the cabin altitude limiter? That's supposed to close the outflow valves at 11,000 feet pressure. Would they just have to set the pressurization system to manual to do that?

Using manual, yes. Also could disable the C/Bs for any other auto safety features.

(ETA: I just double-checked, in manual it does bypass the cabin altitude limiter).

Page #7 in this PDF:
http://www.smartcockpit.com/download.php?path=docs/&file=B777-Air_Systems.pdf

 

[TWCobra]

Turning the air conditioning packs off would also achieve the same result, albeit much slower.

The climb to 45000 feet doesn't make much sense from a point of view of disabling passengers. It may have been a manoeuvre to stop attempts by the crew to get back into the flight deck. There is a hatch in the cabin that leads to the Main Equipment Center under the flight deck. If there is a hatch also in the flight deck, something I haven't confirmed, it may be a way back in.

A 777 captain has a video on YouTube outlining the security problems of this hatch, just can't find it ATM.

 

[WeedWhacker]

If there is a hatch also in the flight deck, something I haven't confirmed, it may be a way back in.

That's a good point, I hadn't thought of (having not actually been trained on the B777). I do recall our DC-10s had the hatch down to the E&E compartment, but only the one in the flight deck. (IIRC). (Back in the day...Flight Attendants who asked would take some pillows and blankets down there...back when flying was a bit more fun...).

I believe I had heard about the hatch in the floor of the forward galley on the B777.

Was the YouTube video referring at all to the decompression panels in the flight deck door?

 

[TWCobra]

No, it was about access to the MEC from the cabin. The are cb's in there that disable the flight deck door lock...plus all the usual boxes... Etc etc..

 

[Balance]

A third theory is that the plane's apparent climb to an altitude of 45,000 feet early after diversion might have been designed to incapacitate others on board by inducing hypoxia - oxygen deprivation - which quickly causes disorientation and unconsciousness and can lead to death. But the radar readings are not absolutely certain and in any case Boeing-777s are certified to fly at up to 43,000 feet; counting on a cabin depressurisation just 2,000 feet above this seems unlikely. Oxygen supplies are also kept in the cabin for crew members, in addition to the oxygen masks. In all, it would be an elaborate plan with limited prospects of success.

http://www.theguardian.com/world/2014/mar/16/mh370-unanswered-questions-pilot-search

 

[WeedWhacker]

Oxygen supplies are also kept in the cabin for crew members, in addition to the oxygen masks. In all, it would be an elaborate plan with limited prospects of success.

http://www.theguardian.com/world/2014/mar/16/mh370-unanswered-questions-pilot-search

(My bolded emphasis).

Actually, as I think we've pointed out, although yes there are supplemental oxygen sources in the Main Cabin, they are quite limited in duration, compared to what's available to Flight Deck crews. Even if Malaysian Airlines had opted for the gaseous oxygen installation, for passengers (this is offered on some B777 models, per customer purchase specifications). Even with the "traditional" O2 system for passengers, it is only designed for at most about 15 minutes...this is considered sufficient for any explosive decompression event at altitude, with proper flight crew emergency descent procedures initiated to the MEA for flight segment ("Minimum Enroute Altitude"). Same goes for the Portable O2 that the cabin crew can wear with a strap over their shoulder, and then be free to ambulate around the cabin to assist passengers in their seats. It has a limited duration of usefulness.

Of course, there is also the smoke hood (or, 'PBE') for fire-fighting, with its own dedicated O2 supply (but again, it is an O2 generator), but only a scant few are usually stocked onboard. One on the Flight Deck, and one at some Main Cabin Doors, possibly in Crew Rest areas (may vary depending on specific configurations).

(That [^ ^ ^] is actually an image of a PBE replica used for initial and recurrent training, but the "real thing" is of course virtually identical...although may be yellow instead).

Essentially, usually below 14,000 most people will not suffer any brain damage from oxygen starvation. Healthier/younger individuals can tolerate higher altitudes, but there are other factors. In designated "mountainous terrain" regions, MEAs are rarely above about 14,000 feet, and in those regions we always have diversion scenarios to go off-route, in the event of a need for emergency descent due to pressurization problems.

All the above may be overkill as an explanation, and not relevant to this MH370 speculation, except to illustrate that "The Guardian" article needed a bit more expansion.

 

[Balance]

My bad, I was looking more for criticism or confirmation about the stated depressurisation theory, rather than detail of oxygen supplies after the event. ie Would you agree/disagree it's an unlikely plan?

 

[TWCobra]

Would you agree/disagree it's an unlikely plan?

With the apparent level of forethought that has gone into this, I would say it is likely.

 

[Balance]

With the apparent level of forethought that has gone into this, I would say it is likely.

I have to admit, I wasn't expecting that and am keen to know how this theory plays out, (if you're free to discuss it?)

Is the intent of causing a depressurisation to disable others on-board?
Given the oxygen supplies, how long would this take and
Is it not possible someone might try using a cell phone to raise the alarm or send a message?

 

[Mark Barrington]

I have to admit, I wasn't expecting that and am keen to know how this theory plays out, (if you're free to discuss it?)

Is the intent of causing a depressurisation to disable others on-board?
Given the oxygen supplies, how long would this take and
Is it not possible someone might try using a cell phone to raise the alarm or send a message?

Cell phones would be useless where they were, as there are no cell towers anywhere near, and cell towers are optimized to send signal near ground level. If someone had a satellite phone, they could possibly have raised an alarm, but those are fairly rare.

 

[Balance]

Cell phones would be useless where they were, as there are no cell towers anywhere near, and cell towers are optimized to send signal near ground level. If someone had a satellite phone, they could possibly have raised an alarm, but those are fairly rare.

I vaguely recall mention of allowing/pushing for cell phone usage in-flight after the events of 9/11, so I guess it never happened as fast as I assumed it would?
http://en.wikipedia.org/wiki/Mobile_phones_on_aircraft
http://airfax.com/blog/index.php/tag/inflight-connectivity/

The Malaysia Airlines CEO, Ahmad Jauhari Yahya, said investigators were looking at mobile phone records to see whether anyone on board tried to make calls or send texts, but so far there was no evidence of attempted contact.

I guess I'm trying to explore all possible "risks" of this theory/plan. Would the crew not be alerted before losing consciousness, and what could they have done in the time the might have had?

 

[Ray Robertson]

Is it possible that a depressurization event also incapacitated the oxygen masks and the crew only had those 30-60 seconds to try and set the autopilot to fly to their airport of departure and made mistakes in setting the autopilot, even mistakenly turning the transponder off. Conditions would be harsh, very cold, painful to breathe, windy and difficult to see. One of their bodies could have pulled back on the yoke making the plane climb to 45000, where it stalled and AP only managed to get it out of the stall at 23000.

 

[WeedWhacker]

Is it possible that a depressurization event also incapacitated the oxygen masks and the crew only had those 30-60 seconds to try and set the autopilot to fly to their airport of departure and made mistakes in setting the autopilot, even mistakenly turning the transponder off. Conditions would be harsh, very cold, painful to breathe, windy and difficult to see. One of their bodies could have pulled back on the yoke making the plane climb to 45000, where it stalled and AP only managed to get it out of the stall at 23000.

Short answer: "No".

I think you may be referring to a video posted a while back by "Sky News"? No, in an explosive (or rapid) depressurization the first action is to don the O2 mask. This is standard airline pilot training and really quite obvious.

ETA, the rest of your post asked another question re: the autopilot, and also the answer is also "No" to that scenario. Doesn't work that way.

 

[Ray Robertson]

I haven't watched any videos with regard to the cockpit being torn open. In my question I asked whether the oxygen masks can be incapacitated or removed by a breach in the cockpit. Meaning, there is no working oxygen masks to don.

 

[WeedWhacker]

I haven't watched any videos with regard to the cockpit being torn open. In my question I asked whether the oxygen masks can be incapacitated or removed by a breach in the cockpit. Meaning, there is no working oxygen masks to don.

Oh I see. Well, the one such scenario would be for the coincidence of an explosive decompression combined with the simultaneous failure/loss of the crew oxygen cylinder. The odds against that seem to be pretty large. **

**ETA: Well, just did a quick search and there was once an incident on a Qantas B747, when one of the O2 tanks for the passenger oxygen system exploded (they had the gaseous supply, in lieu of the chemical generators).

This did pierce the pressure vessel, and cause an explosive decompression. Interesting if it HAD been the crew O2 bottle!!

http://en.wikipedia.org/wiki/Qantas_Flight_30

So, as speculation goes re: MH370? Maybe we can add it to the "list".

 

[Ray Robertson]

http://atsb.gov.au/publications/investigation_reports/2008/aair/ao-2008-053.aspx

Oh, we found the same one.

 

[TWCobra]

The QF 30 incident was a " Black Swan" event. An exploding oxy bottle was totally unprecedented in the annals of civil aviation. The captain and first officer went from thinking about getting a cup of coffee to oxy masks on, depressurisation checklist complete and aircraft commencing emergency descent in the space of 20 seconds.

(I know a lot about this one due to going through pilot training with the captain and my pilots association duties at the time)

If you are following the investigation of MH370 you can see that the known path of the aircraft includes a descent to 5000 feet and manoeuvres and actions intended to mask the aircraft from radar. They aren't the actions of an oxygen starved crew.

It hasn't even been ascertained if the aircraft was depressurised either deliberately or by a malfunction.

 

[Hama Neggs]

I'm a bit confused about any definite radar info. Did the plane, for sure, go to high altitude and then drop back to 5000 ft? I'm not clear on why it wasn't followed on radar if it re-crossed the land mass heading west. Is 5000 feet too low to be detected on radar?

 

[WeedWhacker]

I agree about the safety of the O2 cylinders. The one on QF 030 apparently failed on the bottom, and not where you'd most likely expect, at the valve.

But, I mention it because in SCUBA the tanks are pressurized to about the same PSI, and there are scant few instances of tank failures there, either. Except of course, mishandling that can break the valve.

 

[TWCobra]

I'm a bit confused about any definite radar info. Did the plane, for sure, go to high altitude and then drop back to 5000 ft? I'm not clear on why it wasn't followed on radar if it re-crossed the land mass heading west. Is 5000 feet to low to be detected on radar?

They get the info from the Primary air defence radars of the RMAF. They would be reasonably accurate.

The image of an taut air defence system with fighter aircraft on alert 5 ready to scramble 24 hours a day is not how it happens in a time of low military readiness.
Especially in Malaysia.

There were no fighters on standby at 1.00 am on a Saturday night and the operators of the radar may not have even been looking at the screens. The radar information is recorded however, and checked later.

 

[Con-fidential S-ource]

Condensation in O2 cylinders present corrosion issues- during storage off the aircraft, such as in a depot or MX base or general neglect in service. Problems may develop inside a cylinder: This would be undetectable to most techs.

 

[Hama Neggs]

They get the info from the Primary air defence radars of the RMAF. They would be reasonably accurate.

The image of an taut air defence system with fighter aircraft on alert 5 ready to scramble 24 hours a day is not how it happens in a time of low military readiness.
Especially in Malaysia.

There were no fighters on standby at 1.00 am on a Saturday night and the operators of the radar may not have even been looking at the screens. The radar information is recorded however, and checked later.

Yeah, hence my question. Don't they know if it recrossed Malasia or not and how firm is any altitude info?

 

[TWCobra]

No they didn't. They seemed to be avoiding Sumatra as well. There are some big mountains in Sumatra and I am assuming this is where the terrain masking reference comes from.

 

[Hama Neggs]

Evening news just said two contradictory things. They said the plane was seen to "turn around", but was last known to be still "heading north".

 

[Balance]

Evening news just said two contradictory things. They said the plane was seen to "turn around", but was last known to be still "heading north".

There's too much contradiction coming out daily. The tweet about rumours in the evening, denials the next morning is proving to be an apt rule.
They're today saying the first officer made the "Alright Good night" sign-off but are rescinding the confirmation the ACARS was turned off deliberately.
They're also not sure the plane climbed to 45000feet.

 

[Hama Neggs]

There's too much contradiction coming out daily. The tweet about rumours in the evening, denials the next morning is proving to be an apt rule.
They're today saying the first officer made the "Alright Good night" sign-off but are rescinding the confirmation the ACARS was turned off deliberately.
They're also not sure the plane climbed to 45000feet.

Yes, they said that now they don't know when the thing was turned off.

 

[Balance]

Let me correct myself.

The last spoken communication from the missing Malaysia Airlines plane came from the flight's co-pilot, investigators believe.

And also, ACARS was turned off, was suposed to read "transponder was turned off"

Though the article I'm referring to has maybe confused the two also.

 

[jaydeehess]

On the issue of cell phones. On a/c that do give passengers the ability to use them on board, the aircraft itself has a cell "tower" that connects to the ground via a separate comm link, often via satellite link. However that being the case the pilots could turn off that comm link. A sat phone could work but there's another issue.
This is at night and given a non-drastic manouver, the passengers may not ever notice a problem is developing as they become sleepy due to oxygen deprivation, again, its night time and it would not surprise passengers that they are getting sleepy. In addition, thought roceses he harder as the brain gets less oxygen. Even if a passenger realizes something's wrong the first instinct will not be to make a call, instead it will be to try and get the flight attendant. Even then if they perceive a problem, the mental confusion may be such that they cannot even recognize a cell phone or not recall how to use it or decide who to call.

 

[jaydeehess]

On the issue of supplemental oxygen, there is an atmospheric pressure at which simple masks won't work. Unless one is wearing a pressure suit or oxygen is actually being forced into the lungs, the body cannot create enough draw. Though that might not be until 60K feet, I don't recall.

 

[Hama Neggs]

On the issue of cell phones. On a/c that do give passengers the ability to use them on board, the aircraft itself has a cell "tower" that connects to the ground via a separate comm link, often via satellite link. However that being the case the pilots could turn off that comm link. A sat phone could work but there's another issue.
This is at night and given a non-drastic manouver, the passengers may not ever notice a problem is developing as they become sleepy due to oxygen deprivation, again, its night time and it would not surprise passengers that they are getting sleepy. In addition, thought roceses he harder as the brain gets less oxygen. Even if a passenger realizes something's wrong the first instinct will not be to make a call, instead it will be to try and get the flight attendant. Even then if they perceive a problem, the mental confusion may be such that they cannot even recognize a cell phone or not recall how to use it or decide who to call.

No, the oxygen masks would drop. I doubt the pilot can keep that from happening.

 

[WeedWhacker]

No, the oxygen masks would drop. I doubt the pilot can keep that from happening.

Well, if this was a pre-planned scenario and someone didn't want the pax masks to drop, it would be simple enough to find and pull the circuit breakers before raising the cabin altitude above the level where the Auto system will activate. Since the PSU doors are electrically actuated solenoids, removing electrical power to them renders them inop.

 

[WeedWhacker]

Unless one is wearing a pressure suit or oxygen is actually being forced into the lungs, the body cannot create enough draw.

That got me wondering because I couldn't remember! So:

http://en.wikipedia.org/wiki/Pressure_Suit

...while above 40,000 ft (12,000 m) oxygen must be under positive pressure.

 

[Balance]

yet there is no evidence the plane ascended above 45000feet, other than speculations. At which point, anything is possible.

 

[jaydeehess]

Sure, be like that, all factual and stuff.....dang!

At least I was half right.

 

[Balance]

Sowwy

 

[jaydeehess]

Sowwy

I was referring to the mask drop.
OTOH weed whacker explains even that could be worked around.

So, passengers put to sleep, at night, no air mask drop, little chance of cell phone capability and even sat phones probably not used as passengers lose cognitive power to do so. Masks w/o positive pressure are useless anyway while the plane is at 45000 ft pressure.

If the cabin remains at 45K feet pressure for more than three minutes passengers are either dead or brain damaged.

 

[jaydeehess]

Interestingly I read this
http://books.google.ca/books/about/Mayday.html?id=ARCjngEACAAJ&redir_esc=y
A novel in which an aircraft suffers rapid depressurization at high altitude, passengers and crew are completely incapacitated except for three people who have the nightmare task of bringing a badly damaged a/c to safe landing while evading those who would rather the aircraft simply disappear.

 

[WeedWhacker]

Interestingly I read this
http://books.google.ca/books/about/Mayday.html?id=ARCjngEACAAJ&redir_esc=y
A novel in which an aircraft suffers rapid depressurization at high altitude, passengers and crew are completely incapacitated except for three people who have the nightmare task of bringing a badly damaged a/c to safe landing while evading those who would rather the aircraft simply disappear.

Ya know that this novel was made into a movie? (Made for TV movie, anyways).

http://www.imdb.com/title/tt0465537/

I think I recall seeing snippets of it, and well...it was cringe-worthy!! (But, at least Dean Cain some some work....)

LOL!! One of the first "glowing" reviews:

"I would rather look at the bricks on my wall."