QF depressurisation event

[turbantime]

https://www.sbs.com.au/news/qantas-flight-from-adelaide-to-canberra-forced-to-make-emergency-diversion

Well handled by all accounts. Wonder what the “bang” was that caused it to depressurise.

[Capt Fathom]

Interestingly was only cruising at F250 at the time of descent!

[Bug Smasher Smasher]

Interestingly was only cruising at F250 at the time of descent!
Flown into Melbourne lately? First call to Center is usually answered with “for the sequence, reduce to minimum speed, lower levels available”.

[Cunning_Stunt]

F250 is the Max altitude for dispatch with one pack inoperative.

[Street garbage]

F250 is the Max altitude for dispatch with one pack inoperative.
Anybody got the rego? XZL was flying around single pack last week...

[SandyPalms]

That twitter page states VXL

[turbantime]

Flown into Melbourne lately? First call to Center is usually answered with “for the sequence, reduce to minimum speed, lower levels available”.

Destination was Canberra so I doubt they flew at FL250 for speed reduction/sequencing purposes.

[Street garbage]

That twitter page states VXL
Thanks for that.

[Cunning_Stunt]

My understanding is that it was dispatched with a pack inop. Will be interesting to find out the details of the event.

[Ascend Charlie]

And of course, the pax were screaming, fretting, filming each other, and on the ground saying they would be reluctant to get on another flight.

Why can't the media explain to the punters that it was a non-event. After they have milked it for all it's worth, and just missed a school on short finals.

[Capt Fathom]

Lucky the passengers weren’t on a SAAB / DASH8 / ATR. There are no drop-down masks! The rubber jungle just helped to fuel the media frenzy!

[nonsense]

https://www.theguardian.com/business/2019/mar/05/qantas-flight-loses-cabin-pressure-and-forced-to-divert-to-melbourne

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/620x372/1999_0e06a65f8bd8f4ef45bebf5600987eba81ce5254.jpg

Which one is the 737?

[FullOppositeRudder]

For an excellent example of sludge reporting, including two variations on the "plunge" word, and mandatory use of "terrified" this article set new standards:

https://www.dailymail.co.uk/news/article-6771143/Qantas-flight-Adelaide-Canberra-makes-emergency-landing.html?fbclid=IwAR3Q_4kW92GCNmSnjuiz9Sxf0N5F4ko3j1RH8X CteshKClag5YZILMLHAVY

However the public can be assured with the following:

"Passenger planes losing pressure is not uncommon. Pilots are trained to descend to 10,000ft where the atmosphere has more oxygen so passengers can breathe better." :rolleyes: (https://www.dailymail.co.uk/news/article-6771143/Qantas-flight-Adelaide-Canberra-makes-emergency-landing.html?fbclid=IwAR3Q_4kW92GCNmSnjuiz9Sxf0N5F4ko3j1RH8X CteshKClag5YZILMLHAVY)

[Berealgetreal]

"Flight QF706 landed safely in Melbourne at 8.02am after making ARBEY time 54.

[Noeyedear]

Ok, so here’s a question or two for the Brains Trust.

I’m cognisant that deferring a defect under an MEL is perfectly legal. There is however a difference between ‘Legal’ and ‘Safe’. After all, just because its in the MEL, it doesn’t mean you have to fly, it means you can, if you decide its safe to do so.

All of this is typically covered in the MEL preamble and I’m not having a shot at the pilots here.

I would be curious to know how long a pack is deferrable for? The reason I ask is that, if you are flying around on one pack, and the other one fails, you are going to get the rubber jungle, an ASIR and some free media exposure. Its not a perhaps or a maybe. I’d suggest that something like a Pack should be deferred only until the aircraft stops at a maintenance base, but that’s a personal opinion.

How much does commercial pressure affect our good judgement? Do we need to modify our risk analysis? Instead of saying, “statistically, what are the chances the second pack will fail?”, should we be looking at the definite outcome when it does fail? Let’s face it, the MEL knows the second failure is possible because of the restriction to FL250 on one pack.

2 more points please:

Would this MEL item be part of the Threat and Error Management and therefore briefed to the Cabin Crew before flight? “We’re on one pack, if it fails there’ll be an Emergency Descent.”

If so, and this is an ethical and theoretical question that goes to Duty of Care, do you believe Passengers should be told before flight of the aircraft status and possible outcomes? I know this is a controversial question and impractical in the real world, but surely Pax have an expectation that their flight is as risk free as possible? I imagine if this were the case, the commercial pressure would shift from the pilots, to the company, as that’s not a conversation the Company would want to have. Surely, that’s a good thing?

[porch monkey]

Depends greatly on the form the pack failure takes. Depending on that form, and the crews awareness/attentiveness, an emergency descent is not inevitable at all. A managed descent is quite possible. n Let me add another variable if you like. Cruising at 380, 1 pack from 2 fails. Perfectly OK to remain at 380 if I like. 1 pack. How does that change things? Discuss.

[neville_nobody]

If so, and this is an ethical and theoretical question that goes to Duty of Care, do you believe Passengers should be told before flight of the aircraft status and possible outcomes? I know this is a controversial question and impractical in the real world, but surely Pax have an expectation that their flight is as risk free as possible? I imagine if this were the case, the commercial pressure would shift from the pilots, to the company, as that’s not a conversation the Company would want to have. Surely, that’s a good thing?

Welcome to the quagmire that is aviation. Reality is that flying involves risk. How much risk are you prepared to take is the question.

Most of your questions are only going to be answered definitively if either:

1. A passenger sues an airline or captain even though they followed manufacturer's approved procedures
or
2. A pilot refuses to fly an aircraft with a particular MEL applied and is fired and then claims unfair dismissal and tests it in court.

Until either those happen I would suggest we will never have an answer.

[tdracer]

I would be curious to know how long a pack is deferrable for?
I no longer have access to the MMEL to give a definitive answer to the question, but everything in the MMEL (Master MEL - published by the airframer - operators can go more conservative than the MMEL, but not more liberal) has been statistically analyzed and approved by the regulators.
My best guess is 3 days, but that's just an educated guess.

[porch monkey]

10 days or 240 hrs.

[Capn Bloggs]

Let’s face it, the MEL knows the second failure is possible because of the restriction to FL250 on one pack.
Hmm. What's the maximum altitude after one of two serviceable packs fails (or is turned off under a QRH procedure) in flight?

[porch monkey]

As far as the 737 is concerned, it's good up to certified ceiling, according to Boeing. (FL 410) Subject to some caveats, of course. Not that I would necessarily advocate same......

[morno]

I know in the 320, if the second pack fails, you don’t get a rapid depressurisation. So depending on your height when it fails, you may not actually get the rubber jungle at all.

The FL250 restriction is interesting though. The 320 doesn’t start placing restrictions unless the speed brakes are inop.

[porch monkey]

Just to clarify, on the 737 the FL250 limit is at the planning stage only. (MEL) Not a requirement after dispatch.

[morno]

Just to clarify, on the 737 the FL250 limit is at the planning stage only. (MEL) Not a requirement after dispatch.

Thanks porch monkey, sounds more realistic

[machtuk]

ALL MEL's have two meanings. one at the planning stage & another when airborne!

[allthecoolnamesarego]

Just to clarify, on the 737 the FL250 limit is at the planning stage only. (MEL) Not a requirement after dispatch.
this is from the DDG.
Except for ER operations, one may be​ inoperative provided flight altitude remains ​
at or below FL​ 250

[das Uber Soldat]

if you are flying around on one pack, and the other one fails, you are going to get the rubber jungle.. / .. Its not a perhaps or a maybe

Its not a certainty.

[mustafagander]

I am reliably informed that there was a time in the recent past when a certain airline in Oz had four A380s each with one pack inop, leaving one working. This went on for several weeks coz it is a major job to replace a pack even if you have the spares, which they didn't.
Trust the statistics, you'll get away with it!

[Bootstrap1]

I am reliably informed that there was a time in the recent past when a certain airline in Oz had four A380s each with one pack inop, leaving one working. This went on for several weeks coz it is a major job to replace a pack even if you have the spares, which they didn't.
Trust the statistics, you'll get away with it!


More that they need the groundtime to be scheduled to replace the heat exchangers. It is not a simple job like on other aircraft. It can take up to 4 shifts to remove rebuild and reinstall an A380 pack.

[mustafagander]

Bootstrap 1,
That's what I also heard. If the parts become available the ground time needs to be also there and then we need at least 2 crews for, as I am told, about 24 hours to do each aircraft.
Still, it was eventually done and they got away with it. Think of the hours saved on the a/c packs coz they weren't fitted - a big saving of component hours. My friends used to tear their hair out, now they just shrug.

[TempoTCu]

What I don't understand is, how come CASA haven't already bypassed legislation and issued a directive to say that no RPT operation is to commence unless that acft has three packs installed (the third one being for an extra level of redundancy), and that no flight is to operate if any one of those three packs are unserviceable ('cos there is always the possibility of a double pack failure). After all, safety is number one.

[Australopithecus]

Well, not that, but perhaps it might be time to revisit the wisdom of applying the pack MEL for certain failures that led to the pack being inop. This is the second (and yesterday, third) time in a year a Qantas aircraft has done the dirty dive subsequent to dispatching with a pack MEL.

[mrdeux]

I am reliably informed that there was a time in the recent past when a certain airline in Oz had four A380s each with one pack inop, leaving one working. This went on for several weeks coz it is a major job to replace a pack even if you have the spares, which they didn't.
Trust the statistics, you'll get away with it!

I wouldn't be surprised if there is a tad more redundancy within the 380 pack system than that of the 737.

The question I'm left with though, is why did they end up with a rubber jungle. The aircraft cabin altitude shouldn't climb all that rapidly in the case of a second pack failure, so why didn't they beat it down?

[Nkosi]

Outflow valve motored towards fullopen?

[tdracer]

What I don't understand is, how come CASA haven't already bypassed legislation and issued a directive to say that no RPT operation is to commence unless that acft has three packs installed (the third one being for an extra level of redundancy), and that no flight is to operate if any one of those three packs are unserviceable ('cos there is always the possibility of a double pack failure). After all, safety is number one.

Why limit it to A/C packs? MEL operation is all about operating with reduced redundancy.
So simply ban all MEL operation for Australian based operators. Simples.
Of course, within 12 months there would no longer be any Oz based operators, but what the heck...

[tdracer]

Well, not that, but perhaps it might be time to revisit the wisdom of applying the pack MEL for certain failures that led to the pack being inop. This is the second (and yesterday, third) time in a year a Qantas aircraft has done the dirty dive subsequent to dispatching with a pack MEL.

Packs are normally extremely reliable - maybe it's time to look at how the packs are being maintained/overhauled if they are failing at that rate. I don't see anyone else having these issues with the packs.

[ECAMACTIONSCOMPLETE]

Why limit it to A/C packs? MEL operation is all about operating with reduced redundancy.
So simply ban all MEL operation for Australian based operators. Simples.
Of course, within 12 months there would no longer be any Oz based operators, but what the heck...

i think that the point that everyone is making is that with most MELs there is still a level of redundancy. Operating 1 pack inop with only 1 pack remaining gives zero redundancy. You lose that one pack, you’re going to have a depressurisation event.

[Capt Fathom]

you’re going to have a depressurisation event

Maybe even a depressurisation Non-Event.

[tdracer]

i think that the point that everyone is making is that with most MELs there is still a level of redundancy. Operating 1 pack inop with only 1 pack remaining gives zero redundancy. You lose that one pack, you’re going to have a depressurisation event.

Ah, if you look at an MEL, you'll find a number of systems where "Number installed" is 2, "Number required" is 1 (sometimes zero). MEL operation, pretty much by definition, means reduced safety relative to a full up aircraft. The effect on safety is very, very small (assuming the MEL limitations are observed), but if you're going to take Dick Smith's position of absolute safety regardless of cost, you need to ban MEL operation.
Or you can live in the real world.

[ECAMACTIONSCOMPLETE]

Who is arguing to get rid of MELs? There are plenty of aircraft defects that are simple no go items. Perhaps operating with only 1 pack operable should be a no go defect. I have flown with plenty of captains at my airline who have refused an aircraft before due to an MEL being applied which may be legal to operate with but which in their opinion has too large an impact on the safety of the operation.

[mustafagander]

Tempo,
As I am reliably informed, the A380 has two "twin packs" so actually four but, and a big but, is that the common items can and do regularly fail taking out one "twin pack" leaving only one. Still, statistics say it won't happen today so what the hell, let's just apply the MEL and go for a few weeks. Bonuses all round!

[tdracer]

Who is arguing to get rid of MELs? There are plenty of aircraft defects that are simple no go items. Perhaps operating with only 1 pack operable should be a no go defect. I have flown with plenty of captains at my airline who have refused an aircraft before due to an MEL being applied which may be legal to operate with but which in their opinion has too large an impact on the safety of the operation.

ECAM, you're missing my point. MEL relief is based on the probability of the next failure which could cause a problem - along with the potential severity of the problem. Packs are normally extremely reliable. Hence if dispatching MEL with an inop pack before the problem is fixed, the probability that the other pack will fail is very small during the 10 day MEL relief. If there really have been three events in the last 12 months where Qantas dispatched MEL with a pack inop, and the second pack failed, it doesn't mean there is something wrong with the MEL - 737 operators all over the world are operating to the same MEL and not having a problem (and the in-service 737 fleet is huge). It probably means there is something wrong with the way Qantas is maintaining their packs.

[Derfred]

No, to the best of my knowledge, QF have never had an event of a second pack failing after dispatch with a PACK MEL.

Well, not that, but perhaps it might be time to revisit the wisdom of applying the pack MEL for certain failures that led to the pack being inop. This is the second (and yesterday, third) time in a year a Qantas aircraft has done the dirty dive subsequent to dispatching with a pack MEL.

Unless Astral is referrring to an event I haven’t heard of, s/he may be referring to the event out of ADL a couple of years ago (or more), whereby the aircraft with a PACK MEL climbed through 10,000’, and shortly thereafter got a cabin altitude warning because the remaining systems for some reason were not maintaining cabin pressure. I don’t think a dirty dive resulted, but of course the pilots went on oxy and descended back to 10,000’. I never heard the actual technical reason for it, but I recall it was surmised that it wasn’t pilot error or maintenance error. It was another more insidious system problem that for some reason only revealed itself under single pack operation.

Rumour so far is that the recent event happened under similar, but not identical, circumstances. But this one didn’t happen climbing through 10,000’, it happened at high altitude (presumably well into cruise because they diverted to YMML rather than back to YPAD). The other pack didn’t fail, but apparently it couldn’t maintain cabin pressure. (It had nothing to do with the outflow valve or cabin pressurisation controller. The outflow valve was closed.)

That Astral refers to the second event as having happened “twice” (and therefore a total of 3 times) is a bit misleading... it happened again during a ferry (or test?) flight the next day after some maintenance (no passengers on board, management pilots flying). So whatever initial maintenance action that intially took place couldn’t identify the problem on the ground. They chose to send it into the air again with no pax, and the same problem happened again, and not immediately, only again after some time in cruise. That flight apparently helped them to finally identify and finally fix the problem (which apparently was related to bleed, not pack) and the aircraft is now back in the air.

Of course without detailed knowledge, it’s hard to speculate other than to suggest that perhaps Boeing’s requirements for dispatch under a PACK MEL need to include additional checks for reliable function of remaining systems, issues with which may have previously gone undetected under dual pack operation. These checks may be difficult on the ground. I imagine it isn’t easy to conduct tests of pressurisation and bleed systems on the ground other than BITE tests, and from what I’ve been told, all indications so far are that all BITE tests initially conducted were fine.

To suggest a hypothetical: the MEL says that a single PACK may be INOP provided the remaining PACK operates normally.

That’s fine, but how do you determine if the remaining PACK is operating normally? You can test it on the ground: yes, it tests to be operating normally. But when was it last tested at cruise altitude under single pack operation? Can you even test it for this condidtion on the ground? Can you be sure that it can maintain cabin altitude even if restricted to 25,000’? What if there is a more insidious fault such as a blockage or lack of bleed air that doesn’t show itself in BITE tests, and doesn’t cause a pack or bleed TRIP?

Possibly, the Boeing maintenance procedure for the application of PACK MEL on the B737NG needs to be reviewed, or other aspects of pack/bleed ongoing maintenance needs to be reviewed. I note that this involved one of the older of QF’s 737NG’s (16-17 years?) but that’s not old by 737 standards.

Having said that, I note that at the end of the day, the flight got airborne with an acceptable MEL. That happens all the time. Boeing (and ICAO, and FAA?) statistics say it’s virtually impossible for you to have a similar independent failure on the same flight. So either this was the one a a zillion, or the statistics are wrong, or... or (hang on), or... it wasn’t a similar independent failure. That little insidious fault might have been sitting there for years, maybe it even rolled out of the factory that way, they just didn’t find it until they had to run single pack operation. Hmmm.

It would be interesting to hear from anyone with knowledge of B737NG pack/bleed engineering/design.

And, I’d like to add, thanks to the crew for getting it back to 10,000’ and to YMML with a minimum of fuss. Nice work. That’s what we do.