Southwest Airlines flight experiences engine explosion but makes a safe landing in Philadelphia... 5

[TehMightyEngineer]

zeus: I'm no expert on this but being a pilot I have read a fair bit about oxygen systems and such from my training. My understanding is that full facial coverage of the mask is important at high altitudes as the partial pressure of oxygen in your lungs is reduced. Thus, the mask needs to pressurize to some degree. This is in relation to pilot masks though, so I don't know if passenger masks have this function of providing positive pressure. However, I do know that partial coverage masks or cannulas are not to be used at higher altitude due to the fact that a few breaths not through the oxygen system can incapacitate a person (among other concerns like smoke like you indicated). For example, at 30,000 to 40,000 feet you have a minute down to fifteen seconds of effective consciousness, and as you get hypoxic you'll quickly loose all sense that something is amiss.

I'll fully admit that this risk could be a non-issue; perhaps it is fine to just wear it over the mouth for the few minutes the plane is in a dive to lower altitude. It appears to have turned out more or less okay for most passengers.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[bimr]

Flight data shows that the aircraft descended from over 30,000 feet to 13,000 feet in five minutes. After that five minutes, there was no reason to use the oxygen masks any further although there may have been a side benefit to continued use - to occupy some passengers and to muffle those passengers that were crying and screaming. "Oxygen production cannot be shut off once a mask is pulled, and oxygen production typically lasts at least 15 minutes,"

Not putting the mask over the nose would be akin to snorkeling without a snorkel.

"Passenger oxygen masks cannot deliver enough oxygen for sustained periods at high altitudes. This is why the flight crew needs to place the aircraft in a controlled emergency descent to a lower altitude where it is possible to breathe without emergency oxygen."

https://en.wikipedia.org/wiki/Emergency_oxygen_system[/URL]]Wikiedia

 

[drwebb]

" . . . place the mask over your nose and mouth and continue to breathe normally" is how I have always heard the instructions. Looks like the folks in the pic are placing them over their mouth and chin. Fitting each passenger for a respirator-class fit is hardly practical, so I have always assumed the fit is not critical to the function in typical usage scenarios (in contrast to typical respirator applications).

 

[drwebb]

The oxygen generators work from a chemical reaction, sort of like an air bag or flare, so once they're on they will go to exhaustion. Also may account for passenger accounts of smoke in the cabin despite there being no obvious fire in the accident.

 

[Sparweb]

The chemical oxygen generators get very hot.

The reaction of the chemicals produces a significant amount of heat and the generator canister in the overhead compartment can reach temperatures above 250°C. The effect of this is that an often-unanticipated burning smell may become apparent in the passenger cabin and cause alarm.

STF

 

[Sparweb]

https://flightaware.com/live/flight/SWA1380/history/20180417/1430Z/KLGA/KPHL/tracklog

Flightaware shows 3,743 feet/minute descent.


STF

 

[Compositepro]

There is only a tiny hose to the mask so it cannot possibly supply full breathing flow rates. That is the purpose of the inflatable bag, to store your exhaled breath which has been oxygen enriched, to be used again. But they do say that it is normal for the bag not to inflate. It would not inflate if the mask does not seal well.

 

[berkshire]

A minimum oxygen flow of 2.5 liters per minute is what is required at 30000 feet. That's a large soda bottle in a minute. that tiny hose is more than capable of delivering that .
B.E.

You are judged not by what you know, but by what you can do.

 

[Compositepro]

A shallow breath is more than one liter. Say that under stress a persons respiration rate is one breath per second. That is 60 liters per minute. And so my point is that 2.5 << 60.

 

[verymadmac]

A minimum oxygen flow of 2.5 liters per minute is what is required at 30000 feet. That's a large soda bottle in a minute. that tiny hose is more than capable of delivering that .

Without looking I think 2.5 ltr / min might be FAR 23 aircraft, the Part 25 freighters all get 4 ltr / min for their passengers (legally supernumeraries). The typical output of the O2 generators is 4 ltr/ min for the first 2 minutes then tapering off to 0 by 7 minute mark, there some that last for 14 mintues but I think that is for the aircraft that fly one of those routes with extended distance over 10,000 ft plus ground level (Asian to Europe typically).

A shallow breath is more than one liter. Say that under stress a persons respiration rate is one breath per second. That is 60 liters per minute. And so my point is that 2.5 << 60.

Tidal volume goes way down with rapid breathing, buried in an FAA doc on oxygen systems is a conclusion that it pretty much all comes out in the wash, total volume consumed is little changed. The bag only holds O2 that has flowed from the source while you are breathing out.


The bit that makes me think what if this had been a Boeing 787 on 330 minute EDTO (that's 5 & half hours from the nearest landing point) that had lost the window, would they have all frozen to death or be driven mad by the sound. There is a route coming from Perth, Australia to South America that goes straight over the south pole, it could be many hours before the aircraft could find air temperature above 0 deg C.

 

[zeusfaber]

@TME

For the flight crew, what you say is spot on. The doctor at aeromed school 30+ years ago used to call anything over 33,000 ft 'bandit country' - even 100% oxygen doesn't give you an alveolar PPO2 equivalent to 10,000 ft (the killer is actually the constant 50 mbar PPCO2 which starts to dominate everything else). For sustained flight at cabin altitudes between 30,000 ft and 50,000 ft, you use a pressure demand regulator, work hard to breathe out, try not to say too much and try not to spend too long there (I think my B Cat ticket restricted me to 20 min above 30,000). Getting the mask to fit and seal well enough to hold that pressure is (literally) a pain - I had to shave my beard off before we went into the chamber.

To be honest, I haven't seen a really modern airliner flight crew mask - but the ones I worked with in the 80s provided 100% oxygen at ambient rather than pressure breathing. I think that's one of the reasons commercial jets don't fly any higher than they do - if there's a problem, you can still get below 30,000 ft before becoming too hypoxic.

For the passengers, the requirement is different: The emergency oxygen supply just needs to be sufficient to sustain life during the descent, there being no real need for rational thinking, peripheral vision* or physical coordination - so a yoghurt pot with a mesh vent at the bottom and a plastic bag economiser, all fed from an ambient pressure constant flow, is ample. Even with a perfect fit, you'll still get a lot of dilution through the mesh on the front of the mask. That dilution is deliberate: It's how you persuade people to keep the masks on without feeling they're being suffocated while there's only limited flow coming through the hose.

*The hypoxic loss of peripheral vision might even be beneficial - during an emergency descent, so many bits start sticking out the wings to keep the airspeed under control that it looks like the aircraft is about to fall to bits.

A.

 

[dik]

and to help, CO2 is a respiratory stimulant...

Dik

 

[Spartan5]

FAA issues emergency airworthiness directive requiring ultrasonic inspection of fan blades within 20 days for all CFM56-7B engines having more than 30,000 flight cycles:

http://rgl.faa.gov/Regulatory_and_G...25827500759aa4/$FILE/2018-09-51_Emergency.pdf

 

[metengr]

It was recently reported that the engine manufacturer had recommended an accelerated UT inspection recommendation based on the 2016 incident with SW. The FAA, including SW or other airlines with similar engines, did not act upon this recommendation. So much for safety versus cost with major airlines, including SW.

 

[dik]

By the FAA issuing something different than the manufacturer's recommendation, they are exposing themselves to major liability, IMHO.

Dik

 

[TehMightyEngineer]

Zeus: Fantastic details. Here's my understanding what a modern flight crew mask looks like:

That makes sense about the passengers that they're not too worried about keeping them at tip-top shape, but rather just keeping them conscious and alive.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[EdStainless]

JohnRB,
I haven't flown quite as much as you, only about 3 million miles in the last 30 years.
The only time that I have seen oxygen masks deploy was due to turbulence, not depressurization.
I was on a flight that had an engine failure. JAL out of NRT bound for Singapore in a 747.
On climb out one of the outboard engines chucked parts, then black smoke, then the white fire suppression smoke.
We didn't change climb rate and headed out over the ocean on a 5 hour flight. But then we were in a plane tared to climb on 2 engines and cruse on 1 engine.
The 747 has always been my favorite plane, great ride and safety.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

The 787 dreamliner is the best plane. Been on a 747 and 787, no comparison.

 

[RoopinderTara]

Most surprising to me was the passenger in window seat *was* wearing her seat belt -- and still got almost sucked out of the plane. Could it not have been "low and tight across your lap?" RIP Jennifer Riordan.

Roopinder Tara
Director of Content
ENGINEERING.com

 

[RoopinderTara]

Southwest Airlines Flight 1380: an Uncontained Engine Failure? Article here

https://www.engineering.com/Hardwar...ight-1380-an-Uncontained-Engine-Failure.aspx.

JohnRBaker quoted.

Roopinder Tara
Director of Content
ENGINEERING.com