AirAsia flies to Melb instead of KL . Navigation error

[sycamore]

Surely the IR systems knew where the aircraft was when it arrived at the gate,and then ground power would be connected so the systems would have been kept `alive` all the time on the ground,and only required a check for a possible bit of `drift`,rather than a reset??
It used to be fairly straightforward with a navigator..we would say ,we are `here`,going `there`,draw a line or two and we`ll be off....!

[Mags on]

I cant help but wonder why there are so many complex instruments on board to do what has become a simple task. Why not put 2,4 or even 6 Garmin1000's on board, there is space for sure, and fly on.

[BuzzBox]

The standard procedure on the A330 is to re-align the ADIRUs before every sector, so they need to be re-initialised with the current position.

[wiggy]

Sycamore

1. Can't speak for the bus but there can be problems in some types if the aircraft is unattended, the ground power drops out and the IRS's end up on battery power.

2. No idea why but where we work on the 777 we moved away from an SOP of leaving the IRSs alone between relatively short long haul sectors and we now always do a full re-align. That might be down to tighter nav accuracy requirements these days but that is only a wild guess.

[peekay4]

When you enter the company route (or manually put in from/to), the IRS initial coordinates are automatically reset to the Airport Reference Point, which is a small distance away from the actual gate location.

In this case the recommended practice is to change the coordinates to the gate location using the slew keys (up/down) -- since the amount of change will be small -- instead of manually entering the full coordinates like the Captain did in this instance.

[FlightDetent]

The standard procedure on the Airbus is also to use the slew (plus / minus) buttons to set a position for IRS INIT, as opposed to punching in the numbers.

This in order to prevent gross entry errors from crew side. Which, especially if only longitude is inserted wrong, could go undetected by the IRS verification algorithms.

Further reading in the book reveals:

IRS are automatically initialized with the GPS position. However, the flight crew can override the automatic position initialization.

And there is no recommendation (*) to enter gate coordinates at all.

Without diving in too deep, I would like to underline any and all vilas' repeated post about how non-adherence to manufacturer's S(uggested)OPs brings dire consequences, unforeseen by whoever believes they know better. Unfortunately.


(*) that's actually not 100% true, but I'd take the challenge to see the quote from OEM manuals, full, with the specific conditions when this would be the best practice.

[peekay4]

IRS are automatically initialized with the GPS position. However, the flight crew can override the automatic position initialization.

Not for all MSNs, depending on the software version, and unfortunately not for the incident aircraft.

[cwatters]

Bit surprised they haven't automated the process somehow. Perhaps a QR code on the gate read by a camera on the aircraft or a short range Bluetooth beacon?

[Chronus]

mystery of MH370 resolved!

[sycamore]

Thanks WIGGY,and Buzz...doesn`t help if you do RI-RO,and no gross/cross check of basic distance /time fuel....

[wiggy]

Cwatters

TBH there's no real advantage to inventing Bluetooth or optical processes when you've already got GPS available on many/most airframes and often that can be selected by a couple of key presses as the datum position for inertial align without needing to go down the road of entering figures long hand.

It just seems from what others have said that due to it's modification state this particular airframe lacked even the ability to align off a GPS Lat/long.

sycamore

You are welcome. Pardon the thread drift but I recall the days of our navs babysitting/ nursing an early generation inertial and being quite chuffed if the terminal error was less than 10 miles after an 1 or 2 hour " trip"........how times have changed....

[RAT 5]

IRS are automatically initialized with the GPS position. However, the flight crew can override the automatic position initialization.
Not for all MSNs, depending on the software version, and unfortunately not for the incident aircraft.

Speaking as Boeing NG pilot; why would customer opt for (if that's the case) where the GPS position can not be copy/paste into the FMC for initialisation? Or why would a systems designer create that Gotcha?Punching in Lat/Long manual is an NNC an went out with Omega.

[FlightDetent]

this particular airframe lacked even the ability to align off a GPS Lat/long.

Still, even in a non GPS aircraft, the procedure is to enter the aerodrome ID, and align to the database ARP. It makes no difference to the navigation precision or performance of the IRS. And if you need to (ehm, ehm) modify, the technique is to slew the loaded values.

RAT: no gotchas. Just a sloppy SOP set, not aligned with error/failure modes asessment of the manufacturer and designers' intention.

[peekay4]

Still, even in a non GPS aircraft, the procedure is to enter the aerodrome ID, and align to the database ARP. It makes no difference to the navigation precision or performance of the IRS. And if you need to (ehm, ehm) modify, the technique is to slew the loaded values.

The ARP could be many miles from the gate position.

So modification of the init location from ARP to gate may be required to meet RNP, and is the SOP in that case (using slew keys) as recommended by Airbus.

why would customer opt for (if that's the case) where the GPS position can not be copy/paste into the FMC for initialisation?

I don't know for this case specifically. However, as alluded in a post above there has been a shift how we perceive GPS today vs. how GPS was perceived even 10 years ago.

Separating IRS entry from the GPS was thought of a "good thing" as theoretically they cross-check each other. E.g., to detect errors in case the GPS signal was degraded or spoofed. Automatically copying the GPS position would negate this "feature".

Today of course most of us trust a seemingly functioning dual GPS setup 100% of the time, at least until there's a major GPS-related incident in the future. Then people will complain about over-reliance on GPS and why there weren't more checks-and-balances in place.

Having said that, entering the Lat/Long manually from scratchpad was never the recommended procedure.

[woodpecker]

Easy mistake to make. If I go back to the B757 it didn't have GPS so the position was updated via DME/DME or DME/VOR radial. Prior to departure the airfield code was input into the FMC position update which then the appropriate (displayed) stand number. This then updated the IRS.

I enjoyed flying the aircraft using raw data so, on the day in question, NAV was not displayed on the HSI on departure, just the basic VOR radial information. Alas the copilot had earlier entered EGPH (Edinburgh) instead of EGPF (Glasgow) when updating the IRS position. The required stand was not on the list so he accepted the airfield (EGPH) position as "good enough".

All was fine during the departure until well into the climb (using raw VOR data) I engaged the autopilot and reverted to the NAV display. No sign of the magenta line!! Changing the range revealed it well removed from our position. No problem, back to the VOR display!! Continued to Heathrow with the position slowly updating (DME/DME) and when we entered the Bovingdon hold all was back to normal.

Note... The 757 didn't have a position update on entering the active runway contained in the Lnav route which the 777 does (if I remember correctly) so there was no "position error flag" when comparing the actual position to that contained in the IRS brain.

What did it say on the wall of the briefing room wall at Hamble?

"Learn from the mistakes of others, you wont live long enough to make them all yourself"

[Yaw String]

Oh well,
Just one more airline on my personal no-fly list...
Charges...1/lack of adherence to the necessary SOPs..
2/lack of attention to,and cancelling of,crew messages/cautions/advisories....
3/ lack of system knowledge...etc etc..
Crikey,sounds like me as a 17 year old PPL holder!
With retirement just around the corner,I think I will avoid reading the cruise ship forums too!!!!

[edmundronald]

Having at least one navigation system that is autonomous and does not rely on a vulnerable reference seems a good idea. GPS spoofing has been tuned into an art form by the electronic warfare specialists.

Edmund

[RoyHudd]

Local CM1? Malay "boss" in the left seat calling the shots? Inadequate or P2F FO monitoring?

Certainly this event has displayed either a company or an individual arrogance beyond belief that would allow such a deviation from crucial Manufacturer's SOP's. Both MH and Air Asia have demonstrated a shocking list of screw-ups along 3 full-on fatal crashes in the last 3 years.

[wiggy]

Having at least one navigation system that is autonomous and does not rely on a vulnerable reference seems a good idea.

Apologies before hand if I'm teaching you to suck eggs but this might be of interst to others.

Possible problems with GPS is of course why modern long range nav systems en-route don't just use GPS as a sole reference, they'll look at GPS/Inertial/conventional radio aids and in the background whilst en-route are running fancy algorithms/confidence checks, and in extremis can veto out anything it considers to be an erronous source. Of course if at the start of play the PIC is determined to "tell" the system where it is, regardless of where it really is, HAL has a problem................

I think most of us here mentioning the use of GPS are talking about it's use before flight on the ramp, as providing the reference position for aligning the inertial system. If you do that (as we do in our SOPs) there should still be a credibility check to ensure the GPS position isn't wildly in error, for whatever reason ( spoofing, lack of coverage, etc). That usually means in part selecting the electronic MAP display and comparing the real world seen out of the window with the virtual one. For example checking a 16R departure via Dunes from SYD if all was OK I'd at least expect to see the departure runway and the Dunes waypoint displayed on the map display a short range scale.

Apologies again if etc....

[Capn Bloggs]

Originally Posted by Wiggy

If you do that (as we do in our SOPs) there should still be a credibility check to ensure the GPS position isn't wildly in error, for whatever reason ( spoofing, lack of coverage, etc).

Get with the program, Wiggy, it's only because of GPS we now have jets ducking down deep valleys to a 350ft minimum, GLS approaches to Cat 1 and soon Cat 2 and, of course, quick, simple, always-accurate IRS initialisations.