Why did Flight 447 head straight into a monster?

[Guest guest]

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Koring

Why did Flight 447 head straight into a monster?

From Monday's Globe and Mail, Sunday, Jun. 07, 2009 08:38PM EDT

In the still-whirling maelstrom of speculation a week after the catastrophic end

of Air France's flight 447, only a few facts have emerged, all of which point

ominously to a seemingly inexplicable situation.

How did it happen that highly experienced pilots flying a very sophisticated,

nearly new jetliner for a world-class airline ended up in a monster thunderstorm

when the wall of violent weather should have been starkly evident on the cockpit

weathers radar and when the risks are well known.

Meanwhile, the last few short coded fault reports, sent automatically by the

aircraft's sophisticated flights systems to Air France, paint a frightening but

incomplete picture of multiple systems failing just before the catastrophic end.

A minute of two earlier there are tenuous hints that indicate failing speed

sensors – perhaps iced over – could have forced the autopilot to shut off,

leaving the pilots to hand-fly the big, twin-engined jetliner in the treacherous

violence of a night-time thunderstorm.

No one yet knows the cause of the crash and it will take investigators months –

perhaps years – to determine the chain of events, even if they manage to recover

the treasure trove of detailed information from the flight data and cockpit

voice recorders, now on the sea bottom.

But violent weather seems certain to have played a role, although likely only

part of a sequence of the disaster. The ill-fated Airbus 330 with 228 people on

board was flying a route directly into the kind of monster storms that all

pilots know to avoid. Other pilots reported thunderstorms, but nothing

particularly out of the ordinary.

Still, some were huge, soaring to more than 50,000 feet, with internal

aircraft-flipping gusts of more than 160 kilometres per hour and vicious cold

spots that can also cause severe icing. The inside of a thunderstorm can produce

what is called extreme turbulence – which bears no relation to the

stomach-churning bounces that has passengers white-knuckling the arm rests.

Extreme turbulence can flip an aircraft out of control. It is defined by

aviation regulators as having the potential to cause " structural damage and

prolonged loss of control of the aircraft. "

As night fell over the crash site Sunday, searchers had recovered half a dozen

bodies from a debris field roughly 6,500 km northeast of the de Noronha

islands off Brazil's northern coast. The area was about 60 km south of the last

electronically reported position of Flight 447, but floating objects have been

at the mercy of currents and winds for almost a week.

" We're sailing through a sea of debris, " said Brazilian Navy Capt. Giucemar

Tabosa Cardoso said.

France sent a nuclear submarine, the United States flew specialized listening

equipment that will be towed deep underwater near the crash site in an effort to

detect the signals sent by finger-sized locator beacons attached to the two

bright-orange recorders, often referred to as black boxes.

Finding them will be a race against time. The beacons are supposed to function

for at least 30 days but only have a range of a few thousand metres. With the

precise crash site still uncertain, searchers are faced with trolling for the

signals over a wide area and in depths of up to 4,000 metres.

If they are recovered, the cockpit voice recorder should reveal the pilots' last

half-hour of conversation, as they considered the weather and their awareness of

the sequence of faults in flight systems.

From the flight's data recorder, investigators should be able to build a

detailed reconstruction of the aircraft's systems, its speed, and manoeuvres.

Far less detailed, but still very useful, data is available from fault codes,

automatically generated by the Airbus 330's flight computer system, which were

sent by satellite. Although the pilots last radioed air traffic control with a

routine position check-in about 40 minutes before the crash, they also sent a

manual text message saying their were flying in heavy or hard weather (Air

France hasn't released the exact text) a few minutes before the crash. Then, in

the last minutes of the flight, a flurry of fault codes, including one showing

the autopilot had been disconnected, were received.

One emerging, but still tentative, theory is that the airspeed sensors – known

as pitot tubes and protruding into the air stream – may have iced up, a

previously known problem in high-altitude cruises of Airbus 330s.

There are several pitot tubes and the autopilot depends on them being in

agreement. If there are discrepancies, the autopilot would disengage and the

pilots would have been alerted to hand-fly the aircraft. Icing is a known hazard

in the upper reaches of thunderstorms where upwelling chilled air can create

roiling turbulence.

Air France was part way through a planned upgrade of all pitot tubes after

several previous cases of ice-related failures but the aircraft that crashed had

not yet been upgraded. Since the crash, the airline had said it will quickly

install newer-model, icing-resistant pitots.

However, ice-blocked failure of one of more pitot tubes would not, by itself, be

a catastrophic problem.

However, loss of airspeed sensors – resulting in the autopilot disengaging and

leaving the crew to hand-fly in the very difficult and demanding nighttime

conditions if they had strayed inadvertently into a major thunderstorm or been

caught by one rapidly rising from underneath them – could create extreme

conditions.

Louis Arslanian, the lead investigator for the French aviation-accident

investigation agency probing the crash, cautioned it was too early to draw

conclusions about the role of pitot tubes in the crash, saying " it does not mean

that without replacing the Pitots that the A330 was dangerous. "

Nor is it clear yet whether the crew manually disconnected the autopilot,

perhaps to fly around or between the thunderstorm cells that on the night of the

crash towering to more than 50,000 feet, far higher than the 35,000-foot

assigned cruising altitude.

If the pilots had elected a major detour – crews sometimes fly hundreds of

kilometres off planned routings to avoid the well-known risks of penetrating a

thunderstorm – they would have told air-traffic control to avoid conflicts with

other aircraft. So it seems likely that Flight 447's pilots believed they could

dodge among the thunderstorms.

Meteorologists who have conducted a painstaking review using satellite data of

the conditions along Flight 447's route at the time of the disaster have found a

line a huge storms, including several very severe ones welling up at about the

time the Airbus was passing. But the weather, while dire, wasn't unusual for the

route and avoiding the storms would have been relatively routine for highly

experienced crews.

[Guest guest]

Supposedly a warning was sent out to replace the probes because of known problems with them. It doesn't appear that was done with this plane. One would also think that is that autopilot was so good that it could have looked at the onboard radars and decided that storm was far too dangerous to fly into and gone around it. Then again, maybe because of its failure, if it indeed failed, the pilot couldn't regain enough control of the plane to avoid the storm, or it was too late because the machine hadn't corrected in time.

I also wonder how much the reliance on carbon fiber might have played in this crash. That stuff is supposed to be stronger than metal but I've heard of cases where it has failed in the past.

In a message dated 6/7/2009 9:05:41 P.M. Eastern Daylight Time, no_reply writes:

Why did Flight 447 head straight into a monster? A Good Credit Score is 700 or Above. See yours in just 2 easy steps!

[Guest guest]

Autopilot is NOT an automatic pilot, any more than cruise control is

an automatic cruise control. It is likely that the autopilot was set

to follow GPS waypoints, maintain altitude and airspeed. I have no

idea why the flight crew attempted to fly through the storm rather

than around it, other than a systems failure that would have forced a

landing, which should have been reported. A question I have is can the

aircraft switch to using INS and GPS based speed modes? The reason bad

pitot tubes can confuse the autothrottles (subset of autopilot

functionality responsible for handling engines to maintain a speed and

tune output between engines) is that the autothrottles control each

engine independently to make sure the engines are not producing

asymmetric thrust.

The new pitot tubes may not have been installed yet because parts tend

to take a while to build, ship, and mount.

>

>

> Supposedly a warning was sent out to replace the probes because of known

> problems with them. It doesn't appear that was done with this plane. One

> would also think that is that autopilot was so good that it could have

> looked at the onboard radars and decided that storm was far too dangerous to

> fly into and gone around it. Then again, maybe because of its failure, if it

> indeed failed, the pilot couldn't regain enough control of the plane to

> avoid the storm, or it was too late because the machine hadn't corrected in

> time.

>

[Guest guest]

Excuse me for the typo: First line should read " any more than cruise

control is an automatic *driver*. "

> Autopilot is NOT an automatic pilot, any more than cruise control is

> an automatic cruise control. It is likely that the autopilot was set

> to follow GPS waypoints, maintain altitude and airspeed. I have no

> idea why the flight crew attempted to fly through the storm rather

> than around it, other than a systems failure that would have forced a

> landing, which should have been reported. A question I have is can the

> aircraft switch to using INS and GPS based speed modes? The reason bad

> pitot tubes can confuse the autothrottles (subset of autopilot

> functionality responsible for handling engines to maintain a speed and

> tune output between engines) is that the autothrottles control each

> engine independently to make sure the engines are not producing

> asymmetric thrust.

> The new pitot tubes may not have been installed yet because parts tend

> to take a while to build, ship, and mount.

>

>

>>

>>

>> Supposedly a warning was sent out to replace the probes because of known

>> problems with them. It doesn't appear that was done with this plane. One

>> would also think that is that autopilot was so good that it could have

>> looked at the onboard radars and decided that storm was far too dangerous to

>> fly into and gone around it. Then again, maybe because of its failure, if it

>> indeed failed, the pilot couldn't regain enough control of the plane to

>> avoid the storm, or it was too late because the machine hadn't corrected in

>> time.

>>

>