Boeing 737 Max8 Aircraft Crashes and Investigations [Part 5] 19

[Sparweb]

This is the continuation from:

thread815-445840
thread815-450258
thread815-452000
thread815-454283

This topic is broken into multiple threads due to the length to be scrolled, and images to load, creating long load times for some users and devices. If you are NEW to this discussion, please read the above threads prior to posting, to avoid rehashing old discussions.

Thank you everyone for your interest! I have learned a lot from the discussion, too.

Some key references:
Ethiopian CAA preliminary report

Indonesian National Transportation Safety Committee preliminary report

A Boeing 737 Technical Site

Washington Post: When Will Boeing 737 Max Fly Again and More Questions

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[dgallup]

I can hold my breath for well over a minute, why am I gong to lose brain function in 5s?

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[waross]

I thought that also, dgallup.
Then I thought:
At normal conditions we have an O2 reserve in the air already in our lungs.
When the pressure drops suddenly we loose that advantage.
The air in our lungs is at the lower pressure.
If we had anticipated the coming drop in pressure and tried to hold our breath, the excess internal pressure after the drop may be enough to cause a ruptured lung.
It's been a long time since I have been exposed to the dive tables and warnings.
Can someone confirm the maximum safe pressure differential if a diver holds his breath when ascending?
Not the bends but physical damage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zeusfaber]

Breath-holding is about not bothering to exchange air in your lungs with air outside your body (at the same pressure) and the reason you can do it for over a minute is because it takes that long for the CO2 level in your bloodstream and lungs to build to a high enough level to make you uncomfortable.

The depressurisation is different: The sudden loss of pressure on the outside of your chest will cause the air trapped in your lungs to expand and depressurise (and if, like me, your reaction is to open your mouth, excess air will vent off alongside the stream of mildish expletives). Either way, you end up with lungs full of air at reduced pressure, the alveolar ppO2 is correspondingly reduced, reversing the gradient which normally drives oxygen into your bloodstream, oxygen streams out of your blood into your lungs, and your sats plummet.

Enriching the air with oxygen helps to increase the ppO2 - but once you get to 100%, you run out of room to manoeuvre. After that, the remaining option is to cram 100% O2 into a tight-fitting mask at something over ambient pressure - and that's just not nice.

A.

 

[zeusfaber]

Bill,

Barotrauma is a risk from as little as 2-3m (so 2-300 mb pressure differential. The damage is done long before you feel anything's about to burst.

A.

 

[Compositepro]

When you hold your breath you are still consuming oxygen from the air stored in your lungs. After decompression there is almost no air in your lungs and oxygen will actually be leaving your blood in the the lungs. Its a concentration thing. I'm sure many people can last longer than 5 seconds before losing consciousness, though.

 

[waross]

Thank you for both of your posts zeusfaber.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Eufalconimorph]

The 5s is how long it takes your judgement to degrade after your lungs have been emptied (by decompression) or filled with oxygen-poor gas (by breathing in such an atmosphere). You'll still be conscious, just concentration/judgement/fine motor skills will degrade substantially. You get the same issues with confined space welding, for example.

 

[IRstuff]

Cabin pressure is supposedly comparable to 8000 ft altitude, which is just below the altitude sickness threshold for many people. Moreover, when you are holding your breath, you are facing a cooperative situation, and likely have had some preparatory breaths. In a plane, you either get explosive decompression or a gradual leak, as with the Payne Stewart case. Neither is necessarily conducive to optimum breath-holding scenarios.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Sparweb]

You guys would feel right at home in a Gulfstream, then. The recent 4, 5 and 6 models fly up to 51,000 feet. They have to deal with nasty decompression scenarios. There is a specific case related to an engine throwing a fan blade that punctures the aft fuselage skin. There's a reinforced bulkhead between the passenger cabin and the cargo bay at the back of the fuselage. If that bulkhead wasn't there, the ensuing decompression would cause the floor structure under the passenger seats to burst upwards. The bulkhead has a door that you are not allowed to open above ~35,000 feet, if memory serves me.
Enjoy your flight!

http://www.sparweb.ca

 

[Alistair_Heaton]

Explosive decompression is extremely rare and usually linked to a major structural failure which alot of the time is fatal anyway.

The viz inside the aircraft will drop to under a meter and temperature will plummet down to -30 from about 20.

Most of the time there is issues with pressure high level it's either the outflow valve or a pressure seal going round a door. With both normally we feel a pressure change in our ears and everything is already being dealt with by the time the aircraft pressure gets to 13k and the rubber jungle deploys automatically. This does happen but it's not a yearly event for most pilots. I think my average is something about every 3 years.

If your aircraft is limited to fl250 you don't need drop down masks and they are not fitted. Most turboprops don't have them.

I think we have farted in the same chamber zeusfaber. Unfortunately it's not possible for civi's to do it these days I believe or if they can it's at huge expense. It's my top safety course so far in my pilot career. You only need to do it once.

 

[Alistair_Heaton]

Look on YouTube for pilot hypoxia there are loads of vids showing the chamber training.

There are also a couple of ATC recordings of controllers having to deal with getting aircraft down to a safe level with crew hypoxic.

The Helios accident in Greece was due to pilot error and pressurisation. It ended up running out of fuel killing everyone.

Also my point was more targeted towards both Boeing and the FAA knowing about a potential 25% failure rate of a critical safety system part and doing absolutely nothing about it.


I have a mate that fly's gulfs and one pilot has to sit with his mask on above I think it's fl340. And your right the SIM training is extremely involved for that event. Compared to my don mask, establish coms and decend followed two mins later taking the mask off.

 

[waross]

I think we have farted in the same chamber

Is that an effect of decompression that is never mentioned in PC society? grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alistair_Heaton]

Mate it was the most collosal fart of my life. I had been warned to go for a crap after lunch which I did.. You basically have air coming out both ends at once.

The is a vid of Clarkson from topgear doing a chamber run. He lets go a huge one as well. He had the nice controlled pressure reduction j presume they didn't want to risk hurting him.

Ours was 1 second 8k to fl350 which I think is about 0.6 bar drop. They could have gone faster as real life actually is but it gets very easy to blow ears out. They haven't yet managed to simulate dealing with a decompression after blowing both ears drums out.

 

[Alistair_Heaton]

Just to give you a bit of info so your more informed while flying as pax.

This 5s thing is the reason why your told to fit your mask before helping others. By the time you have fitted the mask to your child you will struggle getting things together to get your own on.

Most systems use chemical oxygen producers which need trigged. You trigger them by pulling down on the tubes. If you just put the mask on you will still get air movement but not 100% O2. The gas is hot, uncomfortable hot. There is one generator per seat bank with usually one extra mask for infants. If your a family of 4 with twins taking them on your knees and all the seats in the row are full. Move rows or sit either side of an isle.

These chemical O2 are a bastard to be honest the casing gets to 300-400 degrees when they fire. It used to be they could be transported on pax planes under AOG dispensation rules on DG. Thankfully that has been banned now after a pax aircraft had a fatal accident with one triggering in the hold and the hold suppression system had zero chance keeping it under control until they landed.

The 787 is a bit special because with it they changed to bottled O2 with one bottle supplying banks of three rows. You still have to pull the mask tubes to trigger it. I don't know how the arming of the system works if it's perm armed with the emergency battery bus powered or it turns on above fl100.

The issue is with the firing of the squib that releases the O2 from the bottles. Apparently getting the bottles out is a C check item where everything gets stripped out the cabin. Cost of replacing the bottles out of phase with the C check is in the region of 1 million dollars and the plane in the hanger for 2-3 weeks.

 

[LittleInch]

I'll go with the de-pressurisation thing. I was a couple of times on a pressurized jump aircraft which then purposely de-pressurized from about 2-3000 ft equivalent to 18,000 in about 5 seconds. The air went from normal to a complete fog where you couldn't see the other side of the plane. I don't recall the farting bit but likely got lost in the excitement. Mind about 7,000ft normal climb always seemed to trigger a rather noxious atmosphere in the cabin, especially on the first lift on a sunday morning...

Exiting an aircraft doing 180 knots was also rather interesting.... Slowing down to normal terminal velocity wasn't usual.

bottled O2 in a 787 eh?

A bit more background on the issue

https://www.bbc.co.uk/news/business-50293927

I suppose the key issue, apart from the safety culture issue, is that testing a single use item is virtually impossible if you can't easily replace it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Alistair_Heaton]

Its a weight saving feature.

787 has a humidity control system and also it gets clean cabin air instead of using bleed air from the engine compressors. Its cabin is lower at 6000ft typically.

From the mates that fly them, it works well and they notice a big difference. The ones that used to fly the 777 say when they get on a triple now it stinks like a workshop and they can feel thier eye balls drying out in the climb and sinuses clogging up.

Out with the emergency false tears and decongestant nasal sprays.

 

[Alistair_Heaton]

oh on the subject of Decompression sickness and flying.

The FAA have a safety leaflet on the subject.

https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/dcs.pdf

I too used to scuba dive a lot in Scotland at uni. I just tried to calculate a saturated body at 1 bar going to 0.24 bar at Fl350 and put it through the tables.

By my calcs you would need to sit for 16-24 hours on pure 02 at sea level not to get a CNS bend if you went straight from FL08 to FL350 in seconds.

And if you spend 8 hours at 6 meters under water on air then pop up your also into the trouble area of the graph. At 9 meters its 4:30 hours and 10meters 4 hours.

BTW those numbers are from 30 years ago and the current ones will be much more conservative. When I started diving in Scotland it was single 12 ltr steel cylinder, single DV, toilet seat ABLJ with fenzy bottle and a dry suit. We did have one club member get a bend after diving all day at 10 meters training so did about 5 hours underwater with 30 min breaks between dives and when we were travelling back to Glasgow over the rest and be thankful at 2000ft it hit her. The rest of us were fine which the medics put down to the boys finishing off the beer on the way back in the minibus.

 

[zeusfaber]

Wouldn't get that experience these days - 40% nitrox is a real boon if you're doing back to back shallow bounces (and what's the chances of ever finding the Rest and be Thankful open to traffic these days)?

A.

 

[VEBill]

This might be a rehash of older news:

https://www.bnnbloomberg.ca/delays-in-boeing-max-return-began-with-near-crash-in-simulator-1.1345067

 

[Alistair_Heaton]

It is and it isn't.

The sim crash was the reason why they went for a frankin furter dual FCC setup. This is a "leak" into what actually happened. Dual FCC and dual sensors actually does nothing when the system kills itself in the event of mismatch and then dumps everything on the pilot and leaves the uncertifiable flight dynamics that MCAS was installed for still there. To get to the next level of failure you need 3 of everything. Which would take at least a year.


Right the next bit has zero factual content and is purely rumour from this side of the pond.

The FAA have been told that if the max can't be started to be delivered by Jan then Boeing is going to be split into Mil and space and a few other entities and commercial airlines are going to be on there own. Production will be stopped and Chapter 11 declared. All debt will be with commercial and liability. Pensions will be dumped for all production staff if working now or retired will be screwed. The blackmail factor will be the possibility of the type approval entity going which will result in basically all Boeing models loosing there type approval over night because there will be nobody responsible for engineering oversight. Which will mean every single Boeing in the world will have to stop flying overnight.

And the context includes EASA and the other regulators. The American market isn't big enough to save things which is why they are asking to be able to deliver and then sort out the training later. Basically the world aviation market is screwed if the regulators don't agree if the rumours are correct and they pull chapter 11. Airbus can't supply the product in the amount required so 45% of the single isle market 180 seat plus production has disappeared over night. Tis is extremely serious. Linked into the pickle issue with the NG potentially grounding a further 20% of that size with zero spare parts and worse extremely limited jigs to do the fix to the airframes. And long haul.... carnage its Boeings only plus point with 777 because the A380 is pish along with A340. A330 is sort of ok if you don't mind pax dying of cancer enroute because its so slow and climbs like undernourished penguin.

To be honest I really can't comprehend the amount of issues if the Boeing type approvals were to evaporate over night if it was pushed to that point.

It will be now certified in Dec I am 100% sure. My bum and my family (apart from the mother in law) will not be sitting in it.