AirAsia flight returns to Perth after mid-air scare

[jwocky]

So, either way, the descend rate of that plane was too low to indicate a descend with EXPED. And it was actually too low to make passengers or cabin crew alone thinking about a crash. However, if you have a relative moderate descend rate but a pitch nose down, it all feels inside a lot worse.
In FG, with many planes, you can create similar effects if you are too fast and therefore have a lot of lift and an AP tries to get your plane down as good as it can against this abundance of lift. Then you get nose down attitudes and still not much of a descent, but that usually happens in approach with the flaps out.

So the only thing, that seems to be clear here is, the cabin crew was inept and the cockpit crew idiots?

[123apple]

I see. I'd have thought for an expedieted descend, reading emergency, VMO / MMO, or at least VMO - 10 would be better, but OK.

[jwocky]

@123apple
You're right and personally, if I have cabin pressure loss or think, I will have in the next minute, I would go down fast to where people can breathe. But those AirAsia people took their good time. Vincent mentioned something,t hr oxygen masks in Airbuses have only 9 minutes? I read the ones at Boeings have allegedly 15. Still, even with 15, no need to waste time.

[KL-666]

The masks are made for 10-15 minutes. I said if you have a bad one between them, it could be 9 minutes.

Kind regards, Vincent

[HJ1an]

The masks are made for 10-15 minutes. I said if you have a bad one between them, it could be 9 minutes.

Kind regards, Vincent

Panicky people would gulp it down to >10 minutes

[HJ1an]

So, either way, the descend rate of that plane was too low to indicate a descend with EXPED. And it was actually too low to make passengers or cabin crew alone thinking about a crash. However, if you have a relative moderate descend rate but a pitch nose down, it all feels inside a lot worse.

The passengers know they are not anywhere near an airport yet, so even if it's a mild descent, and even without the oxygen masks dropping and attendants running and shouting, if there was no pilot announcement there will still be a panic of a possible hijack / rogue pilot, what would be going through their minds - a repeat of MH370 or that GermanWings one.

So, yeah, if I put myself into their shoes those 2 events would cross my mind too.

[jwocky]

Yeah, true that, didn't think about it for a moment. So, fine, they can even panic without a node down attitude. Which still doesn't explain why the pilots would chose such a moderate descend rate if the thing they have pressure loss.

[Richard]

... Which still doesn't explain why the pilots would chose such a moderate descend rate if the thing they have pressure loss.

Although I haven't checked the procedures I would imagine that the cabin pressure gauge would be a valuable reference for deciding the required descent rate. ISTR that there is a warning when the cabin pressure goes above 8,000ft and another one at >10,000 feet. The rubber jungle normally drops down at around 10k of cabin pressure, so best to avoid this if you can.

If the cabin was slowly losing pressure, providing that the flight crew are wearing their oxygen masks the emergency is almost over and the descent rate can be adjusted to keep the cabin altitude within a sensible range based on the time of useful consciousness[1], which at 15,000 feet is 30 minutes, so there is no danger to the PAX unless there is a rapid decompression and the cabin pressure is over 20,000 feet.

An appropriate measured response is that which I'd expect from the flight deck; no point screaming towards the ground unless you have to as that increases the risk of a secondary incident. You don't want to end up in an accident report that starts with "as a result of an initial incident where there was a loss of cabin pressure due to pack failure..." and ends with "....resulting in hull loss".

--------------------
[1] Table 1, page 5 : https://www.atsb.gov.au/media/27376/ar2008075_2.pdf

[jwocky]

Hummm ... do Airbuses have a display that shows the flight crew how many of the passengers put up the masks correctly? How many may entangled the hoses of the masks? How many children I have in the rear who are too small to use those masks? Nine minutes of insufficient oxygen supply to a human brain is probably already critical, but it is even more critical to children's brains. So, no offense, Richard, but if anything is wrong with the cabin pressure, ANYTHING, I expect the flight crew to bring the bird down to where people can breathe again as FAST as they possibly can. Brain damage is not a reasonable option in my book.