AirAsia flight returns to Perth after mid-air scare

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Re: AirAsia flight returns to Perth after mid-air scare

Postby jwocky » Wed Oct 18, 2017 5:48 pm

Or to make the poitn before even clearer: I think, the cabin crew was not the only part of the crew that sucked in that story!
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Re: AirAsia flight returns to Perth after mid-air scare

Postby KL-666 » Wed Oct 18, 2017 7:07 pm

Well, yes if they indeed descended 2000 fpm, they took their time to get exactly down in 10 minutes, fl 300 to fl 100. Not recommendable with the chemical oxygen masks, which may stop at 9 minutes.

But there is a discrepancy. 2000 fpm is really gentle. On all my jump seat rides, they did more than 2000 fpm as a standard desc. Then i wonder where the stories of plummeting come from. Those stories can be expected from a desc with full spoilers at 5000 fpm. But not from a less than standard 2000 fpm desc.

So either they descended faster than we think, or the pax make up horror stories.

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Re: AirAsia flight returns to Perth after mid-air scare

Postby HJ1an » Thu Oct 19, 2017 1:39 am

KL-666 wrote:Well, yes if they indeed descended 2000 fpm, they took their time to get exactly down in 10 minutes, fl 300 to fl 100. Not recommendable with the chemical oxygen masks, which may stop at 9 minutes.

But there is a discrepancy. 2000 fpm is really gentle. On all my jump seat rides, they did more than 2000 fpm as a standard desc. Then i wonder where the stories of plummeting come from. Those stories can be expected from a desc with full spoilers at 5000 fpm. But not from a less than standard 2000 fpm desc.

So either they descended faster than we think, or the pax make up horror stories.




I will defend the pilots here at least; just for balance. The descent is lower probably they weren't at 30,000 as we first thought... I gave it some thought and a fully laden and fueled A320 (not the usual A330 plying Perth?) would have not been at 30,000 ft, 25+- mins into the flight, considering ATC and flight plans, weight, engine type etc. Since we don't know that, I will assume the flight isn't at 30,000+, rather, somewhere below that. Let's say 27,000.

So keeping that in mind may be the case. The pilots may have tried to not induce panic by not diving like a jet fighter (and failing anyway)..

As for the passengers, well passengers as they are, they exaggerate things quite a bit. I recall many 'horror stories' from friends who flew into turbulance and saying they "fell" a great distance in a sudden drop. We on here know that this is laughable as even in the worst of turbulance a drop would be nothing more than, say, 20-30 ft (I dunno the figures, just guessing) but those who don't know would guess it at even upwards of 1000ft because their brain can't deal with what is happening.

So, in the passengers POV, this transpired:

1. Thigns go quiet (engines spool down)
1a. There may or may not be a roar (spoilers activated)
1b. Sudden feeling of drag, and an increase in feeling dropping
2. Attendants running
2a. Attendants possible shouting at people or one another
2b. Panic in attendants' face
3. Oxygen masks drop
4. PA system blarring some unintelligible nonsense (not english)
5. Flight continues go downwards
6. Pilots not coming on to say WTF is happening ("OMFG IS THIS A HIJACK??")
7. Other passengers crying, screaming, acting abnormally, reaching for phone, scmrabling for their kids / loved ones etc.

So yeah, I can imagine panic setting in pretty quickly

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Re: AirAsia flight returns to Perth after mid-air scare

Postby HJ1an » Thu Oct 19, 2017 2:42 am

update : I just read that the flight was going through FL338 when the incident occured. So disregard my above scenario .

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Re: AirAsia flight returns to Perth after mid-air scare

Postby jwocky » Thu Oct 19, 2017 2:23 pm

Okay, lets think here, what makes a 2000fpm descent or as I calculated 2200fpm feel like something real bad and makes pop up words like "plummeting" in people's heads? See, what passengers feel is not the actual rate of descend till the Messiers Newton and Keppler start to work on them. What passengers feel is rather the attitude of the plane. So imagine, you speed is already high, by all means, you were already set up for cruising at mach 0.80 or something in high altitude. Now warning light and emergency descend. So, how are you doing an emergency descend? Has an Airbus maybe a button for that? Because if not, it would AP off, press her manually down, spoilers out to reduce speed. Only, lets say, you forget the spoilers. Then you go from fast to faster. The result are more warnings, the computers drown an anyway panicking cockpit crew, alarms produce that nerve killing sounds and the pilot presses on his tiny little toystick to get her down to 10,000 and he can't really descend? Why? Because his airspeed is high, his lift is high. And that is how you have a plane maybe at a pitch at -10 degree and still descending moderately at best. And a pitch of -10 degrees feels for the passenger like catastrophe and probably also the cabin crew.
There are two pieces of data, I so would like to see, but can't find anywhere in the press. The actual weight and the distance, the plane traveled horizontally while doing this descend. The weight was probably still far under MTOW. AirAsia is a cheap line with 1 class configurations. There were according to the press articles 146 passengers on board, while the A320 has in one-class usually something about 180-185 pax? So, the bird was still not as heavy as it could have been and that makes it even harder to make her descend if you are too fast.
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Re: AirAsia flight returns to Perth after mid-air scare

Postby Wecsje » Fri Oct 20, 2017 1:41 am

So here I am with some more facts abput tbe A320:

2000/2200fpm descent is very normal for approach and so on, passengers shouldn't be thinking that they will crash.

Now, IF there was a cabin depress warning, the emergency descent procedure should have been followed: set AP to descend to FL100, then full spoilers (this part at any speed), if needed, landing gear may be extended, but speed must be lower then of course. The plane will be able to descend at a max V/S of 7000fpm, from FL390 (service ceiling) to FL100 it would take 4 minutes and 40 nm to descend. The procedure recommends leaving AP and A/T enabled, A/T will pull idle as usual on descend.

SO, if there was a depress warning, pilots must have been idiots. If there was never one, explains the whole thing.

I found this checklist/procedure online aswell: http://aviationenglish.club/emergency-descent/

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Charlie (Wecsje)

PS: so there is no emer desc button. But the AP works it out for you anyways, with use of ecam messages/procedures.
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Re: AirAsia flight returns to Perth after mid-air scare

Postby SHM » Fri Oct 20, 2017 2:28 am

Wecsje wrote:PS: so there is no emer desc button. But the AP works it out for you anyways, with use of ecam messages/procedures.

There is EXPED
You will get a scary vertical speed and the consequent dropoff in airspeed to green dot speed because the EXPED button engages Expedite mode which uses pitch to get you to the altitude selected in the FCU with the maximum vertical gradient. There are two types of expedite mode: EXP CLB and EXP DES. EXP CLB commands green dot speed while EX DES commands 0.8 mach.

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Re: AirAsia flight returns to Perth after mid-air scare

Postby Wecsje » Fri Oct 20, 2017 2:32 am

True, but then people will really think they will crash ;D

Do love it however when the ATC asks you to expedite descent, and you be like *vertical mode engaged, here we go*.

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Re: AirAsia flight returns to Perth after mid-air scare

Postby 123apple » Fri Oct 20, 2017 2:53 pm

SHM wrote:
Wecsje wrote:PS: so there is no emer desc button. But the AP works it out for you anyways, with use of ecam messages/procedures.

There is EXPED
You will get a scary vertical speed and the consequent dropoff in airspeed to green dot speed because the EXPED button engages Expedite mode which uses pitch to get you to the altitude selected in the FCU with the maximum vertical gradient. There are two types of expedite mode: EXP CLB and EXP DES. EXP CLB commands green dot speed while EX DES commands 0.8 mach.


I thought that it commanded MMO / VMO, in EX DES?

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Re: AirAsia flight returns to Perth after mid-air scare

Postby SHM » Fri Oct 20, 2017 4:42 pm

123apple wrote:I thought that it commanded MMO / VMO, in EX DES?

No, its M0.8/340kts


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