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Boeing 777 flight crew wrestle with airplane for control...

FN FAL

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"Pilots on a Malaysia Airlines Boeing 777 from Perth to Kuala Lumpur battled to gain control of the plane last month after an unknown computer error caused the aircraft to pitch violently and brought it close to stalling, an Australian Transport Safety Bureau report said."


http://www.bernama.com.my/bernama/v3/news_business.php?id=156241
September 19, 2005 21:10 PM

Glitch Blamed For Out-Of-Control MAS Aircraft

From Neville D’Cruz

MELBOURNE, Sept 19 (Bernama) -- Pilots on a Malaysia Airlines Boeing 777 from Perth to Kuala Lumpur battled to gain control of the plane last month after an unknown computer error caused the aircraft to pitch violently and brought it close to stalling, an Australian Transport Safety Bureau report said.

It said the pilots fought to counter false information being fed into the aircraft's autopilot system and primary flight display, according to a report in The Australian newspaper.

Flight MH124 was about an hour out of Perth when the aircraft began behaving erratically.

The incorrect data from a supposedly fail-safe device caused the plane to pitch up and climb 3,000 feet (914 metres), cutting its indicated airspeed from 500km/h to 292km/h and activating a stall warning and a "stickshaker", the report said.

A stickshaker vibrates the aircraft's controls to warn the pilot he is approaching a speed at which the plane will have insufficient lift to keep flying.

The bureau report released last Friday revealed the pilot in command disconnected the autopilot and lowered the plane's nose to prevent the stall but the aircraft's automatic throttle responded by increasing the power.

The pilot countered by pushing the thrust levers to the idle position but the aircraft pitched up again and climbed 2,000 feet.

He notified air traffic control that the plane, carrying 177 passengers, could not maintain altitude and requested a descent and radar assistance for a return to Perth.

As the plane descended through 20,000 feet, the pilot reported the primary flight display appeared normal and separately tested the aircraft's two autopilot systems.

But he was forced to keep flying manually when the plane banked to the right and the nose pitched down during both tests. The pilot reported no difficulties flying the plane but noted that the automatic throttles remained armed.

As the aircraft was positioned to approach Perth, however, the flight display again gave a low airspeed warning and the auto-throttle responded by increasing thrust.

The report said the aircraft's warning system also indicated a dangerous windshear but the crew continued the approach and landed safely.

Shaken passengers remained in Perth overnight and were offered alternative flights the next day.

Investigations are focusing on faulty acceleration figures supplied by a device called the air data inertial reference unit.

The device, which was sent to manufacturer Honeywell and to US investigators for examination, collates aircraft navigation and performance data from other systems and passes the information to the primary flight computer.

The glitch prompted plane manufacturer Boeing to issue a global notice to all 777 operators alerting them to the problem.

Boeing spokesman Ken Morton told The Australian newspaper the incident had not occurred before or since. Operators have since been told to load a previous software version.

"There is a very simple test to do before you take off and that will tell you if your system has that problem or not," he is quoted as saying.

"To this point we haven't had any people coming back saying they've had faults," he said.

Morton said there were 525 777s in service and they had accumulated more than 10 million flight hours and two million landings.

"All incidents are thoroughly investigated and appropriate steps are taken to ensure the continuing safety of the in-service fleet," he said.

"Nothing is more important than that," he added.

-- BERNAMA
 

banned username 1

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Understand it was an ADIRU software programming glitch. AD has operators re-booting with the old program for now.

Recovery technique= take deep breath, shout explitative, click off autopilot, fly airplane. Use SAI if primary flight instrument indications are suspect.
 

C172gal05

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Cardinal

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The button is big, the button is red...Press It! And the first thing these guys do after the autopilot flips out and the regain control is reengage the autopilot? Arggghhh....
 

labbats

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Cardinal said:
The button is big, the button is red...Press It! And the first thing these guys do after the autopilot flips out and the regain control is reengage the autopilot? Arggghhh....

Time out, fuzzy.

He engaged each autopilot seperately to find the malfunctioning one. It's a common phenomenon. I know that per our Ops Specs, we check each channel of a failed flight control system as well to isolate the problem and avoid any confusion on the current situation and unavaoidable write up and FAA report.
 

Swede

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labbats said:
Time out, fuzzy.

He engaged each autopilot seperately to find the malfunctioning one. It's a common phenomenon. I know that per our Ops Specs, we check each channel of a failed flight control system as well to isolate the problem and avoid any confusion on the current situation and unavaoidable write up and FAA report.

:eek: You're saying that after a violent pitch-up and approach to stall with the A/P, you'd try it again so that you'd have a more concise write-up for the MX folks? If my A/P shat on me like theirs apparently did, there's no way I'd re-engage it!
 

labbats

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Yes, I would. You can always disconnect it.
 

TheDogsBollocks

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viper548 said:
Do they have the latest version of NORTON installed?
It's probably those French bastard's from Airbus who stashed some of their software into the Boeing's computer!
 

Immelman

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You gotta wonder... being in the tech profession, when something deep goes wrong, you wonder how the hell computers manage to work at all given the complexity. Last night walking out of work after working on an intense prolem, my boss (ex-nasa space-ship guy) told me they once spent two years debugging a strange computer glitch on a certain interplanetary probe that was launced several years ago.. two separate computers had to both be executing a particular piece of software and the overlap had to be within a few picoseconds of each other; the event caused some electrical noise which created a glitch. The complexity of a modern airliner is probably not far off from that of spacecraft; I think I'm more comfortable riding around in something that has real control cables going to the actuators!
 

dseagrav

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Does the ADIRU provide attitude and heading for the PFD and ND or does it have a seperate gyro for those?
 

typhoonpilot

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dseagrav said:
Does the ADIRU provide attitude and heading for the PFD and ND or does it have a seperate gyro for those?

The ADIRU provides Altitude, Airspeed, Attitude, Heading, and Position information to the PFD, ND, and Autopilot Flight Director System (AFDS).

labbats: There are three autopilot flight director computers in the 777. There is no way to specify which one gets turned on, they have there own logic and generally all three engage with either A/P engage switch.

When this article talks about the thrust levers moving forward as they approached the stall it doesn't really state that this is a protective feature of the aircraft. If speed decreases to near stick shaker activation, the autothrottle engages in the appropriate mode and advances thrust to maintain minimum maneuver speed or the speed set in the mode control panel speed window, whichever is greater.

It's an interesting incident and it appears there was a flaw that caused the intial pitch up. After that it gets a little fuzzy,

The bureau report released last Friday revealed the pilot in command disconnected the autopilot and lowered the plane's nose to prevent the stall but the aircraft's automatic throttle responded by increasing the power.
The pilot countered by pushing the thrust levers to the idle position but the aircraft pitched up again and climbed 2,000 feet.

This part here is particularly interesting. The pilot disconnected the autopilot and lowered the nose, okay both good moves. Then the throttles advance, which they will when you get near stick shaker. He brings the thrust levers to idle, possibly because the advancing power caused a pitch-up, but probably not a good idea if already near stick shaker. The last part is hard to analyze. If he is hand flying and the thrust levers are at idle, what made the aircraft pitch up again?

I'm waiting for a more detailed explanation.


Typhoonpilot
 

dseagrav

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typhoonpilot said:
The ADIRU provides Altitude, Airspeed, Attitude, Heading, and Position information to the PFD, ND, and Autopilot Flight Director System (AFDS).

So if an ADIRU goes insane, the instruments would show it, right?

I'm waiting for a more detailed explanation.

Probably a good idea. ^_^
 

Singlecoil

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labbats said:
Yes, I would. You can always disconnect it.

You might want to re-read that Alaska 261 accident report about troubleshooting broken airplanes. I'm not at all saying that is what caused that accident, but that is one of the recommendations that came out of the analysis of it. Treat every flight control problem as a potentially catastrophic one, get the airplane on the ground, and let somebody else figure out how to fix it.
 
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