bad news about Air France Crash 2009

[LCHIEN]

Seems like the news about the crash analysis is not too good for the Air France crew. Freeze-prone Pitot speed indicators notwithstanding, when confronted with a stall conditions they forgot the number one rule* I learned when as a teenager 40+ years ago I read in a book private pilots license, in a stall you put the nose down and increase the engine speed, to regain speed and control. What they did was to give it mostly nose-up commands, which is akin to hitting the accelerator instead of the brakes on your car when approaching an obstacle.

When confronted by three stall warnings they angled the nose up and continued to do so until the airspeed fell to 60 knots at one point throttling the engines to idle until they basically pancaked into the ocean.

guess it was dark, turbulent and confusing with the alarms going off. Probably disoriented - they didn't feel the aircraft had stalled. Yet, all the instruments except speed were working and surely from the attitude indicator and altitude indicator they should have known they were stalled. Even a GPS speed sensor giving them ground speed would have told the story, if they paid attention to the prevalent ground speed vs airspeed difference (the difference being wind speed). Maybe by the time they realized they were stalled they had lost so much air speed the wing control surfaces no longer worked enough to point it nose down, although the engines remained 100% operational.

Why am I so worked up??? Flying Air France next Tuesday...

* the number two rule i recall from that book is that the runway number is always the compass heading in degrees dropping the last digit, e.g. runway 22 points at 220 degrees on the compass. This info would have saved that COMAIR flight in Kentucky a few years back where they took off the wrong runway. Just glance at the compass heading before gunning the engines... make sure it agrees with the runway number you've been assigned.

[All Thumbs]

Are there any scenarios in which dropping the nose and increasing throttle would be dangerous if one wasn't in a stall?

I can't conceive of a reason to ignore the warning as possibly false. I don't see the downside to following the standard procedures in this case.

I suppose if you have just lifted off and don't have the altitude yet you may be concerned with hitting a tall building or tower or something.

But they were already over the ocean, right?

I'm no pilot, but it does seem like this may be a case of over thinking in the cabin.

[woodturner]

Are there any scenarios in which dropping the nose and increasing throttle would be dangerous if one wasn't in a stall?

If the plane was already in a dive and too close to the ground, increasing speed and dropping the nose would cause a crash.

[jackellis]

Loring,

First, stop worrying. You're much more likely to be involved in a car wreck. Those you share the road with are much less skilled at managing their vehicles safely than those who fly airplanes.

Second, those of us who are pilots (amateurs and pros) are convinced the high degree of automation in the airplane is partly responsible, as are the faulty pitot tubes.

Third, if you're taking the non-stop flight, you're flying on Boeing 777s both ways. It's a fine, American-built airplane. As far as I know, the only hull loss out of 900 built was the BA accident where ice in the fuel tanks is suspected. Not gong to be a problem on your flight.

Finally, if you're ever out this way and want to sample what it's like to recover an airplane with contradictory instrument readings and NO outside references, I may be able to oblige. I have to demonstrate this skill periodically in a slow moving airplane that is quite forgiving. Jets are not.

If you're in a fast descent and you point the nose down while adding power, you can cause the airplane to come apart or make the dive unrecoverable. In this case, it appears the airplane was put in a deep stall. When they pushed the nose down to recover, the stall warning went off. When they pulled up, it stopped. I'd be confused too, because that's not how things are supposed to work.

In case I forgot to mention it earlier Loring, just relax and enjoy the flight. But definitely be very careful on the drive to the airport.

I'd much rather our National Transportation Safety Board was in charge of this investigation. There are some pretty perverse incentives to whitewash the whole accident by blaming the pilots, who can no longer defend themselves.

[Bruce Cohen]

Hey Loring,
When I was taking lessons, the SOP to stall recovery was nose down, and full throttle.
Bruce

[cabinetman]

Loring, relax. Set your mind at ease. Add one of these to your carry-on bags. I've used one many times.

.

[jackellis]

Diagram from another forum:


At 2:11, the airplane is in a deep stall. Stall recoveries may be a little different in jets (and the technique may be different when engines are aft-mounted rather than wing-mounted), but you want to get the nose down and also watch your indicated airspeed and altitude. However if you don't have reliable airspeed and altitude indications, and you have no outside references, you do have a problem.

On the other hand, some might argue that the side-to-side oscillations were an indication of a deep stall and the crew should have recognized this.

I'm instrument rated (means I can fly solely by reference to instruments, as on a pitch black night or in the clouds). At every proficiency check, I have to demonstrate an ability to fly with certain instruments covered up. It's not that difficult with a little practice, but it's also not realistic. Instrument indications don't go away, they become inconsistent and unreliable, and failures typically happen slowly rather than all at once, so a problem may not be obvious until recovery becomes much more difficult.

I've also flown in the clouds with an iced-up pitot tube, which was unexpected and occurred over the mountains of western Montana. When the pitot tube ices up, it gets confusing in the cockpit. This link explains the erroneous indications on the three pressure-sensitive instruments. I had about five hours of solo instrument time. The airplane I was flying (a rental) happened to have a device that indicated ground speed independently of the airspeed indicator (ground and air speed diverge with altitude). As we descended into warmer air on a radio-guided approach to Butte, the ice melted and we had accurate indications on the airspeed indicator and altimeter again.

[LCHIEN]

Jack, I'm not really that worried, I made it here last Monday OK on probably the same 777 I'll be going back on.

I just like reading about technical stuff and like to understand what goes wrong in high tech disasters.

It was already common knowledge among airbus users that the pitots had problems, they were slated to be replaced. Was there not a general warning to watch out for these problems to the pilots?

Clearly at 35,000 feet the danger of nosing down is very small.. and they'd already discussing flying higher was not an option due to the air density/temperature mix. Maybe I'm jumping to conclusions but if the facts released by the BEA have been given accurately so far, there's clearly a pilot error involved. Once nose-up the forward speed dropped precipitously, the air flow over the control surfaces was insufficient to make the plane nose down again even if they had tried, and the engines just had enough bite at the attitude of pointing up to keep the plane from sliding backwards. They dropped like a rock, belly-flopping into the water at a terminal velocity of 11,000 feet per minute or 124 miles per hour. Their forward speed was but 60 mph.

My conclusions:
they made the wrong decisions. Initially it was savable but went past savable when they went up and did a deep stall.
Maybe they were confused. Maybe their training failed them.
The reactors melted in the first few hours. Whoops, wrong tech disaster.

[jackellis]

they made the wrong decisions. Initially it was savable but went past savable when they went up and did a deep stall

I'm not so sure. I'm also a little suspicious of Airbus, Air France and the BEA based on my limited and highly biased knowledge of how the French government and business establishments work.

If this was a small airplane like mine, I'd agree that it's a case of pilot error, because unless the attitude indicator failed, they'd have a reference for pitch, and any pilot worth a **** should be able to maintain level flight and avoid a stall with pitch and power. Maintaining altitude would be more problematic, though modern handheld GPS receivers would provide a rough idea. However, this is a jet, not a piston airplane, so the story might be more complicated, or not.

The autopilot and the way Airbus uses automation have to be contributing factors in this accident. I haven't had a chance to read the detailed accounts.

[scmhogg]

The article that I read said the Captain was not in the cockpit, and had to be paged. It said they were at 38,000 feet. It took 3 1/2 minutes for that terrifying plunge into the ocean.

This at least the second or third accident, that I have read about recently, that involved a pitot tube. Don't we have better technology.

Steve

[radhak]

T It said they were at 38,000 feet. It took 3 1/2 minutes for that terrifying plunge into the ocean.
Steve

That part of the report scared me like very little else does : I cannot imagine being a parent in that plane with a scared, screaming child asking its parents to help, and the parent unable to. For all of 3½ minutes...I think those would be a very long time period. When I think of the roller-coaster rides that last much less, fall faaar less, and yet could be scary, the end moments of those unfortunate souls come so alive now. May they have peace.

[LCHIEN]

That part of the report scared me like very little else does : I cannot imagine being a parent in that plane with a scared, screaming child asking its parents to help, and the parent unable to. For all of 3½ minutes...I think those would be a very long time period. When I think of the roller-coaster rides that last much less, fall faaar less, and yet could be scary, the end moments of those unfortunate souls come so alive now. May they have peace.

A roller coaster ride jerks you side to side and up and down so you can feel the motion.
Actually, with the plane in a flat stall accelerating to terminal velocity, they would have felt no untoward falling motion - the wings would have provided enough drag to vertical motion that they would not have floated weightless off the floor. The reports said that most likely they would have felt a slight rocking of the wings not unlike riding in turbulent weather and would not have felt the fall. They did not pitch, roll or spin. This is also why the pilots were possibly disoriented, the instruments can tell them they are falling but their senses don't confirm what the instruments say - they already have conflicting speed info so maybe they chose to ignore the other instruments and follow their senses.

Some of the news reports said that the Victim's family organization was privately advised by the BEA prior to release of the report that the victims probably felt nothing more than maybe popping ears until the impact. The "terrifying fall" or "horrifying plunge" part of the news headlines is either sensationalism or perhaps describing what we feel when we hear of the fall, Not necessarily what the passengers experienced:


From the Guardian.co.UK http://www.guardian.co.uk/world/2011...-crash-inquiry
According to the BEA, the French air accident investigation agency, one of the pilots called the cabin crew two hours and six minutes into the flight to tell them: "In two minutes we should enter an area where it'll move about a bit more than at the moment, you should watch out." Just over eight minutes later everyone on board was dead following a descent that, according to experts, none of the passengers would have noticed.

"The aeroplane probably felt more or less under control. The passengers probably would have felt their ears popping as it descended but the aircraft was held in a consistent pattern until it hit the sea," said Guy Gratton of Brunel University and a member of the Royal Aeronautical Society.

Another A330 Pilot wrote:
Despite what the pilots must have been going through in the cockpit, the pitch attitude remained fairly constant throughout so the passengers would not have sensed something was seriously wrong. They would have felt mild buffeting of the stalled airflow over the wings and the initial sinking feeling. That's all.

[All Thumbs]

If the plane was already in a dive and too close to the ground, increasing speed and dropping the nose would cause a crash.

Right. But they knew their altitude and that even if they were in a dive that it would be some time before they'd impact. It took between three and four minutes for them to fall.

My casual playing with a flight simulator (it has been some time) would seem to indicate that getting out of a stall didn't take long at all.

So you point the nose down and increase the throttle. If the stall warning stops, you were in a stall. If it doesn't, well, you are probably in a bunch of trouble.

How long would it normally take to correct a stall on a big jet like that? If you had all your senses and were following protocol? My flight simulator experience may not be indicative of how long it actually stakes to correct a stall condition.

[LCHIEN]

Normally if you still have adequate forward momentum then pointing the nose down is simply a matter of operating the tail elevators to push the rear up.

However, consider that you have been speeding along just above stall speed and then you lose speed indication and maybe you point your plane up... the instrument recordings indicate quite a bit up - then you start slowing rapidly below stall speed and the airflow over your wings is nil and then your elevators don't work well - loss of control surface effectivity. You can flap your elevators all you want and they won't work.

The next thing you do is go to max power and try to literally push more air over the wings to regain control surface effectivity. But, if you are at high altitude (thin air), and you nose is angled up, and you are not in a high performance aerobatic airplane with a high thrust to weight ratio, but a large lumbering jetliner, then your engines may not be strong enough to increase your airspeed significantly when pointed up and your airplane is literally trying to slide backwards.

When you get to this state, ineffective elevators, nose up and gaining no speed, then you end up in a flat fall like a leaf, only heavier, where it drops nearly straight down, only the flat surface of the wings providing some cushion that keep if from falling faster and faster- they apparently reached a fall speed of 11,000 feet per minute quickly and then stayed there - so called terminal velocity. where the downward force of gravity equals the retarding force of the air drag.

Had the plane not been so balanced the nose might have naturally eventually pointed down (like a dropped dart) and possibly been able to pull out. But an unbalanced plane is hard to fly normally as it keeps wanting to nose over, so that's not an acceptable answer. BTW planes have been known to crash when unrestrained cargo shifted forwards in a descent causing the plane to nose over uncontrollably.

[jackellis]

This at least the second or third accident, that I have read about recently, that involved a pitot tube. Don't we have better technology

There have been cases where the crew forgot something as simple as turning on the pitot heat. Insects are known to build nests, which is why we use pitot tube covers.

There's nothing better than a direct measurement of dynamic air pressure, which is what a pitot tube measures, and it's what determines whether and how the airplane flies. In fact, accidents involving the pitot-static system are pretty rare. Loose nuts sitting in the left seat are a bigger hazard in any airplane. However, there's just no way to drive the risk of any activity to zero.