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MERGED: Air Asia Turnback Perth 25 Jun 17

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MERGED: Air Asia Turnback Perth 25 Jun 17

Old 27th Jun 2017, 03:09
  #161 (permalink)  
 
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Originally Posted by WingNut60 View Post
Interesting.

But it all still seems very subjective to me. I would hope that there is further advice that better defines the circumstances that they are describing.
Was the vibration level observed in the passenger's video "high", as envisaged by the advice from Boeing?
Or was it "extreme"and way beyond anything they ever considered? ((Not saying it was. Just asking)

And how long did they anticipate that the vibration would last or be tolerated for?
Perhaps if the skipper had taken a walk back in the cabin past the wings, he may have reevaluated his decision, if he had finished praying, that is.
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Old 27th Jun 2017, 03:21
  #162 (permalink)  
 
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So many posters absolutely sure their opinion is correct and the Captain's was wrong. Interesting.

I know of two major airlines, not LCC, that virtually never use Learmonth as an alternate for Perth- they use Adelaide or Melbourne unless absolutely necessary. They've made the decision that it's not a place they want their A/C going unless it's absolutely necessary. Qantas would almost always use Learmonth. Who's right? Are the others wrong?

'Nearest Suitable' is a subjective term, no doubt that's intentional. Someone posted what Boeing says about it and, in my opinion, the Captain here made a reasonable decision.This Captain decided Perth was the best option. You might have made a different decision, I might have made a different decision, doesn't mean he's wrong. As evidenced by the different opinions here, it's not as straightforward as too many are making it out to be.
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Old 27th Jun 2017, 04:05
  #163 (permalink)  
 
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TineeTim that is the most sensible post on this thread.
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Old 27th Jun 2017, 04:16
  #164 (permalink)  
 
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It amuses me the way operators employees go quiet on this board when one of theirs is involved in an incident
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Old 27th Jun 2017, 04:31
  #165 (permalink)  
 
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You can't blame everyone going against the crew here.

I mean the past few incidents have all resulted in errors on the company's behalf and there's still more investigations to come. There are serious procedural breakdowns in every report that materialises, my main gripe with this mob is they continue to roll on even after acknowledging they have implemented new safety procedures. It's just not happening.

I encourage you to read past investigations (moreso if on the Airbus) to really see the issues at play. I've not seen such poor display of piloting in my entire career.
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Old 27th Jun 2017, 05:09
  #166 (permalink)  
 
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Very unprofessional by the crew to return to Perth. The crew should have a good knowledge of alternates en-route and be aware of the runway capabilities and approaches available (3047 x 45m runway with RNAV-Z approaches at Learmonth!!) and probably have them loaded into the secondary flight plan ready to go. I doubt this crew had that knowledge, based in the decision they made.
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Old 27th Jun 2017, 05:35
  #167 (permalink)  
 
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Dumb question, would they have to dump fuel to land at Learmonth? If so, how long would it take and where are they allowed to do it?
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Old 27th Jun 2017, 06:01
  #168 (permalink)  
 
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A number of major non LCC carriers don't use YPLM as an alternate because mainly due to state regulations requiring certain levels of RFF and approach capabilities. This may exclude it from being an EDTO alternate for planning purposes however once airbourne all bets are off with a major failure. Middle of the day , CAVOK with 3 km of runway and a engine with vibrations strong enough to cause a lot of alarm strewth how much suitable does it need to be !
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Old 27th Jun 2017, 07:15
  #169 (permalink)  
 
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Originally Posted by CurtainTwitcher View Post
Are they? Do you have a statistical source for this? The central assumption behind ETOPS is that cruise engine failures are independent of one another with one engine operating at Max Continuous Thrust for the maximum ETOPS time limit.

If there is a dependant relationship between the two engines (common fuel source or an engine failure damages another engine) then this assumption is no longer valid, and getting on the ground ASAP is a must. A blade failure at cruise altitude is likely to be a random event within the ETOPS time limit (ie the second engine suffering a random failure with say a 180 minute ETOPS segment is vanishingly small).

Even if there is a identical common point of failure of engine maintenance for both engines, the chances of the both failures occurring within the one flight is statistically incredibly small. In other words, the engineering is designed to get you home from the the worst case scenario. Sure, it would feel very very uncomfortable, but it will work.

We accept this engineering rational every time we go flying in a twin. Here is a primer from EASA on the IFSD rates and engineering assumptions: Extended Range Operation with Two-Engine Aeroplanes ETOPS Certification and Operation. Have a look at section 3: RISK MANAGEMENT AND RISK MODEL (page 35), see Figure 1 and look at the IFSD rates per 1000 flight hours, and how they derive Figure 2 and the IFSD rate as ETOPS segments goes out towards 10 hours (0.010 failures per 1000 flight hours). If the second engine still works after the first blows up, it will keep working until you land.

Recent incidents that shows that dual engine failures were dependant: US Airways Flight 1549, QF32 and Air Transat 236. In all cases, there was a dependant relationship between the failures (external, birds for Sully, engine disintegration causing a second engine problem for QF32 and the Air Transat crew mishandling a fuel leak causing a common point of failure for the Azores Glider)


Having said all that, in this scenario I would be proceeding to the nearest runway that I believed was safe given my knowledge of the local environment. For me, YPLM is OK, for another pilot who is less familiar with the area that may be YPPH.

This short video shows where a random independent process becomes dependent one. The final simulation appears to defy logic and reason and does not produce the expected normal distribution.

All very interesting.
I personally know a pilot that had an engine failure with return to land in Singapore. A day or two later he departed in the same aircraft once it was fixed and the OTHER engine failed!!
Work out the stats for that!
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Old 27th Jun 2017, 07:20
  #170 (permalink)  
 
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Originally Posted by Matt48 View Post
Perhaps if the skipper had taken a walk back in the cabin past the wings, he may have reevaluated his decision, if he had finished praying, that is.
Thats a very good point. Do we know if he went back to do a visual inspection and vibe appraisal? I sincerely hope he did, I suspect he didn't.
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Old 27th Jun 2017, 07:32
  #171 (permalink)  
 
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If the captain did put it down in Learmonth, what possible punishment could he be dealt?

Little or non is my guess.

Not a great look for an airline firing someone for putting their customers safety first I would have thought?
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Old 27th Jun 2017, 08:11
  #172 (permalink)  
 
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There's a big difference between nominating an airport as an alternate and using it as a diversion port in an emergency.
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Old 27th Jun 2017, 08:41
  #173 (permalink)  
 
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Originally Posted by TineeTim View Post
So many posters absolutely sure their opinion is correct and the Captain's was wrong. Interesting

'Nearest Suitable' is a subjective term, no doubt that's intentional. Someone posted what Boeing says about it and, in my opinion, the Captain here made a reasonable decision.This Captain decided Perth was the best option. You might have made a different decision, I might have made a different decision, doesn't mean he's wrong. As evidenced by the different opinions here, it's not as straightforward as too many are making it out to be.
"Nearest Suitable" is clearly defined in at least one major Australia airline's procedures, there's nothing subjective about it. Flying past an Adequate or EDTo Alternate is subjective, flying past a Suitable is not.
I do however acknowledge that Learmonth may not have been designated as Suitable or equivalent to AirAsia, and that other factors may have precluded a landing in Learmonth or favoured a return to Perth.
But hopefully not those factors affecting safety, like passenger convenience, accommodation etc.
Then, with an Airbus, you get this ECAM alert..."LAND ASAP" in either red or amber, depending on the severity of the situation.
I've heard a number of interpretations on this one, to me it's pretty clear.
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Old 27th Jun 2017, 13:27
  #174 (permalink)  
 
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On a different but not unrelated question: when Qantas start their non-stop flights to Perth from the UK soon what is their alternate for a full 787 if, having reached Perth and found that they can't land, they are forced to divert?

Presumably similar questions have been asked (& answered) about Learmonth's suitability etc irrespective of the situation the aircraft and/or passengers are in?
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Old 27th Jun 2017, 14:08
  #175 (permalink)  
 
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AMM Requirements

Originally Posted by Sailvi767 View Post
I certainly would not want to be on that airframe again until the entire pylon was changed and a full inspection of the wing box and pylon attach points.
There is an inspection criteria in Chp 5 and/or 71 of the Aircraft Maintenance Manual for failure of engine post a blade off event. The whole engine, fan cowlings, nose cowl, C Ducts and Common Nozzle Assembly must be removed and quarantined (the CNA is matched to the engine so would be replaced anyway). The Engine pylon mounts will also be removed and replaced. There is then a progressive inspection of the pylon which will require deeper inspections depending on level 1 findings up to level 3 (from memory) if required. A pylon replacement would be dependent on inspection level findings. I would also think Airbus have requested the QAR/FDR data to determine the level and frequency of vibration which they will then base further airframe inspection requirements on also.

Last edited by Tom Sawyer; 2nd Jul 2017 at 15:04.
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Old 27th Jun 2017, 14:22
  #176 (permalink)  
 
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Ditching

Several credible sources have referred to the possibility of the flight ditching being raised at some point.

- If - the capt was contemplating ditching one moment then a diversion to Perth the next, then the thinking is definitely questionable. No doubt the return to Perth was for commercial reasons instead of the much closer and adequate alternate, YPLM.

The ditching talk has gone quiet though.

Matt, this fad of referring to "souls" on board is repugnant and as unprofessional as the capt asking everyone to "pray" that he'll be able to do his job and get them on the ground in one piece. Unless you have wings growing out of your shoulders, let's leave religious claptrap out of aviation please.
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Old 27th Jun 2017, 15:04
  #177 (permalink)  
 
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Originally Posted by Eclan View Post
Referring to "souls" on board is repugnant and as unprofessional as the capt asking everyone to "pray" that he'll be able to do his job
You are kidding me, Souls on Board has been a common reference for ATC services in many countries.

Let go of anti-religious clap trap, its tiring.
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Old 27th Jun 2017, 16:21
  #178 (permalink)  
 
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Originally Posted by CurtainTwitcher View Post
Its covered in the EASA ETOPS document.
Page 34/65 -

This test must be run with the high speed and low speed main engine rotors unbalanced to generate at least 90 percent of the applicant’s recommended maintenance vibration levels. Additionally, for engines with three main engine rotors, the intermediate speed rotor must be unbalanced to generate at least 90 percent of the applicant’s recommended acceptance vibration level.

**************

I've reached vibration limits and they weren't noticeable. Ninty percent would be a lower figure.

So what level is the pylon and wing certified to when the entire plane is shaking?

How long is the good engine certified to operate when exposed to level X vibration? What level are they tested to, especially for 90+ minutes.

I don't know the answers. I doubt 1/100, perhaps 1/1000, or 1/10,000 pilots know the answers. Absent that knowledge I'd do whatever I could do reduce the vibrations and land ASAP. We don't operate with " I think it will stay together" as a hope. Absent knowledge, or if there's significant doubt about the safety of the aircraft, landing and solving the trouble shooting, or investigation, on the ground is the most prudent course of action.

And none of this addresses the requirement to land at the nearest suitable after the lose of an engine.
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Old 27th Jun 2017, 16:27
  #179 (permalink)  
 
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You don't dilly-dally dumping fuel when it's not required. An overweight landing, even single engine, isn't a dire emergency. It's standard risk assessment. With the much vibration I'd land overweight vs delaying and subjectng the aircraft to additional stress from the vibration. And it's not like an overweight inspection will delay the next departure because that airplane isn't going anywhere for days.

Hopefully the investigation gives flight crews more insight into what is, or isn't, acceptable limits if we experience this ourselves.
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Old 27th Jun 2017, 16:31
  #180 (permalink)  
 
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Originally Posted by Awol57 View Post
I have been to the airport there a few times, I guess I was just playing a bit of "what if" as well.

Living in the NW I have a fair idea of the resources available and I just suspect it wouldn't be as straightforward as some people seem to think if it did all go pear shaped I guess was more my point. Sure if you have no options I'd be headed there but I can only presume at the time with the information they had they decided PH or somewhere further south was a better option was all.

An extra 359 in a town of about 2500 is a fair impost even with an airline potentially throwing money around.
The industry has diverted airliners into towns who's population numbers less than the passenger total of the a/c diverting.

Here's an aviation truth - being on the ground is better than wishing you were on the ground.
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