Old 8th Sep 2016, 05:48
  #43 (permalink)  
Algol
 
Join Date: Jan 1999
Posts: 275
Buzzbox and Curtain twitcher, thanks for the link to the report, I hadn't seen it before questioning ATC's actions. The OP only put up the Guardian article which seemed to say the crew were left blindly flying around and found their own way to Melbourne. Happy to withdraw any criticism of ATC, they helped enormously.

Now regarding the criticisms of this crew. Some on this thread have lambasted them for lack of systems knowledge. I think its also rather unfair. My own decades long experience and knowledge of INS systems wouldn't have anticipated the behaviour seen in this event. Its perplexing.

Several yonks ago when I did my ATPL I remember the instructor telling us that an INS will NOT align if you input a grossly inaccurate position. The reason being that the INS platform compares the input position to the local 'vertical' and this would not resolve if the 'expected' vertical didn't match the 'sensed' vertical within narrow limits.

A decade later I flew INS equipped B747's (before the days of GPS) and those INS's behaved exactly as was taught. They were twitchy buggers and would fail to align even if a wind was making the aircraft move around, or the loaders were being a bit boisterous. A few degrees disagreement to the sensed vertical was enough to fail the process.
In this AK case the difference between 'input position vertical' and the real 'sensed vertical' was huge - 136deg - and yet it seems the INS accepted the error and aligned to the wrong location. A very 'robust' INS, no doubt. Is that such a good thing?

When I went on to my first Airbus there was no GPS. The first commercial GPS system was only set up around 1995. Before that it all relied on INS (IRS).
In those days we had to confirm a valid 'Position Update' of the aircraft symbol on the ND to the runway on start of the take off roll. It would happen automatically when thrust levers were advanced. It was reliable. I never saw it 'not work'.

In this AK event the report says the Position Update did not happen at start of take-off, because "the error was too great". Seriously!? You mean Airbus designed a navigation system that simply goes 'idle' when you've created a massive error - exactly when you most need it to work? Or at least WARN you that it isn't working?

When GPS was introduced we were told this would (when available) prevent any more gross errors in Nav, as the GPS would automatically update the 'mix POSN' and eliminate gross errors. Surely a pair og GPS's in agreement are more reliable than even 3 INS's?
But no. Now we discover that if the GPS doesn't agree with the INS's it will effectively vote itself out of the system, and the only warning you'll get is one single chime after it has thought about it for ten minutes (or more)! Incredible.
By the way, its not at all unusual to have 'mystery chimes' go off which never reveal themselves. Perhaps a flicker on the ECAM which you can't read, and which can't be recalled. So what do you do? Stop everything? Go back for engineering inspection? Not likely in the real world.
The lack of a proper clear warning of a primary navigation failure is again unbelievable.

Airbus aircraft seem to regularly do this to their crews - they fail, and dump everything in the crews lap with little hint as to what's really going on. This incident reminds me so much of the Air France AF447 accident - another crew let down by hard to diagnose Airbus systems failures, with obscure (out of normal envelope) systems behaviour contributing to their confusion. They were extremely lucky this didn't end up the same way. Perhaps if it had been night time?
Those saying there was an obvious action - what is it? When the EGPWS starts shouting at you at 400' after liftoff you know you've got problems - but when you realise now your ND compass is giving you erronoeous information (because ATC tell you) what would be expected except confusion and shock?
Reverting to raw data sounds an obvious first step - but the ND is still wrong, and you can't steer unless you realise it and focus on that micky mouse compass. All very easy to describe from the comfort of an armchair. Ever steered by a magnetic compass? If so you'll know its not that simple.

Did the AK crew screw up? The Captain input the position manually. Is that Air Asia procedure? If so - why? If that's what they train them to do, who's at fault really?
In my INS days the position entry had to be done together with a second crewmember, and double checked. This didn't happen here - is that how they're trained?
Why weren't they trained to use the slew buttons? We were trained to use them and we all much preferred it - its so much easier than struggling with conversion of Lat/Long to Airbus formats.
Why were they even required to insert the Gate rather than just accept the ARP (which will be updated anyhow at take-off)?
Why wasn't the maintenance mod done by AK? The Align would have been automatic - as it is in the Airbus I fly now. Human error is largely removed entirely.

What I'm saying is that the armchair heroes are good at boasting about their own knowledge of the systems - after the fact.
The keyboard warriors get some self satisfaction from slating their fellow pilots - inferring to the rest of us how 'skilled' they themselves are? They let the manufacturers and regulators and the airlines entirely off the hook. Haven't you learned by now that the next guy to swing is you!?

Last edited by Algol; 8th Sep 2016 at 06:00.
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