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Data Entry Blunders Force Air Asia Pilots To Land in Melbourne Instead of Malaysia (mashable.com)
A flight from Sydney to Malaysia ended up in Melbourne after the captain incorrectly entered the plane's location in its navigation system just before take-off, according to a safety investigation, whose conclusion was published this week. Mashable reports:The Air Asia pilots made several errors in entering data into the aircraft's navigation system, which caused them to follow an incorrect flight path out of Sydney, according to Australian transportation officials. While troubleshooting the incorrect flight path, the pilots were unable to fix the issue, and may have compounded it. The aircraft's systems would not allow the plane to be flown in instrument conditions and the weather also had deteriorated in Sydney by the time the pilots decided to turn back. They were directed via radar to a visual approach in Melbourne where they could land safely. The pilots did not believe the airport was located in Malaysia.
Navigation grade inertial nav systems need to know their initial position in order to perform accurately. According to the Australian Transport Safety Bureau report, an erroneous longitude value was entered prior to takeoff. This is very curious, as initial position is supplied automatically from GPS, unless (1) GPS is not available; or (2) the system is very old and doesn't have that feature. If the latitude is correct but the longitude is wrong, the INS will probably align properly, but it really won't know where the heck it is.
This is a much more complicated and interesting story than the headline or first glance would suggest. (because as is common, the headline makes it sound like a bunch of bungling pilots from a LCC airline were flailing about stupidly, which is not the case)
The omission of a trailing zero digit in the manual entry of longitude during system initialization caused serious autopilot/navigation problems that were not resolved by automated cross-checks that should've caught it. (Error #1)
Then, as a result of trying to fix/diagnose the problem on the fly, the flight display/instruments were put into a failure/safe mode where only visual flight conditions could be handled (Error #2).
It turned out ok in this case (just a diversion), but if the weather had been poor or other combinations of conditions existed, it could've easily gone wrong. Very interesting...
This is kind of a false idea since a Boeing has the exact same error potential. I was on a flight one time where a navigator messed up the whole inertial reference system and we lost all positional awareness (just like in this article). We didn't get "lost" because I navigated by other means. However, it was on a Boeing airplane. Airbus and Boeing, and while we're at it: Embraer, Sukhoi, Canadair, etc. have the same mode of failure in their navigation systems.
The Airbus is highly automated but it is very well thought out. In the worse case, it can be flown like a more traditional airplane (Boeing). In fact, all the systems revert to a "direct law" system where the pilots have full authority over all flight control systems and the pilots can break stuff by exceeding limits. Honestly, more pilot error happens with Boeings than with Airbus. Think of an older Boeing (e.g. 737) as an old circa 1980's chevy with electronic fuel injection but nothing more. Think of an Airbus as that plus systems such as automatic breaking that keep you from rear ending another car. Worse case, that automatic system can be shed so that you can crash into the car in front of you.
These pilots made logical choices which ended in a null condition. Unfortunately, this is what happens when people only know their job and not the theory behind how everything works. I doubt these guys were airplane computer engineers so without the deep knowledge of the systems (e.g. at the code level), anything they would have attempted was probably a guess. The manuals also may not have been specific to this situation and thus might have put them in this negative condition.
Nevertheless, I can't help but to wonder if they tried using traditional terrestrial navaids to determine their position or if they were simply in oceanic airspace and inertial reference was their only means of positional awareness.