AIR FRANCE FLIGHT 296

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I had the opportunity last night to watch a episode of air disasters about Air France 296. It appears there never was a definitive cause to the accident or its disputed. Do any of you folks remember this accident?
 
Pretty much 100% pilot error.

Flew too low for too long, and waited too long to apply go around power.

He may have been depending on the autoflight system to allow safe slow flight (something called alpha floor applies full power in the Airbus 320, but it is disabled below 50 feet to enable landing) though opinions are mixed on that.

Lots of conspiracy claims, but they just plain flew into the trees at low speed while the engines were spooling up.
 
Originally Posted by Astro14
they just plain flew into the trees at low speed while the engines were spooling up.


The flight augmentation computer intervened to prevent a stall. The rest was history. The crew applied full power and the pilot attempted to climb. However, the elevators did not respond to the pilot's commands because the A320's computer system engaged its "alpha protection" mode (meant to prevent the aircraft from entering a stall). Less than five seconds later, the turbines began ingesting leaves and branches as the aircraft skimmed the tops of the trees. The combustion chambers clogged and the engines failed. The aircraft fell to the ground.[3]

When this happened, there was wild speculation about the fly by wire systems and the limits of the control laws. 30 years down the road, we still hear the same old reasons and excuses.

In subsequent testing various Boeing airliners flew the same profile and performed as expected, they would not have crashed.

Yes, we can blame the pilot, for judgement, thrust, speed and altitude issues. However, it's clear the airframe DID NOT DO WHAT WAS ASKED OF IT.
 
Over the decades, I've learned that unplanned events, situations and emergencies happen. Those situations may require extraordinary performance from an aircraft, even to the point of physical damage to the structure itself. When we introduce "control laws" into a aircraft, we limit performance. An example is the 60 degree bank limitation introduced on some aircraft. The reasoning is that under no circumstances should a crew need to exceed such a limit. Unfortunately, There are situations where severe maneuvering may be required. Mid air collision avoidance is one such condition, war time operations is another.

A modern large airframe may have a published 2.2G structural limit, and a 60 degree bank limit prevents any form of overstress (60 degrees of bank in a level turn creates 2G) . However, in real world terms, an airframe may be operating at 1/2 it's maximum weight and withstand 6 or 8G before reaching any actual structural limit.

It's interesting to note that on some high performance aircraft G limits increase when weight decreases. Our Extra 300L is certified for +/- 10G in single pilot operation, and +/- 8G with 2 aboard.

My point is that engineers cannot foresee all possible situations and tying the pilots hands has predictable results.
 
RememberThe FED-EX flight that had the attempted takeover by a fellow employee who used a hammer and a speargun to try and incapacitate the crew? That DC 10 did maneuvers that the designers felt would have caused a breakup in flight. It still flew for several years after that incident. It still remains the fastest speed on a DC-10 ever recorded. Had it not been able to be flown "by the pilot", they never would have survived.
 
Originally Posted by Cujet
Originally Posted by Astro14
they just plain flew into the trees at low speed while the engines were spooling up.


The flight augmentation computer intervened to prevent a stall. The rest was history. The crew applied full power and the pilot attempted to climb. However, the elevators did not respond to the pilot's commands because the A320's computer system engaged its "alpha protection" mode (meant to prevent the aircraft from entering a stall). Less than five seconds later, the turbines began ingesting leaves and branches as the aircraft skimmed the tops of the trees. The combustion chambers clogged and the engines failed. The aircraft fell to the ground.[3]

When this happened, there was wild speculation about the fly by wire systems and the limits of the control laws. 30 years down the road, we still hear the same old reasons and excuses.

In subsequent testing various Boeing airliners flew the same profile and performed as expected, they would not have crashed.

Yes, we can blame the pilot, for judgement, thrust, speed and altitude issues. However, it's clear the airframe DID NOT DO WHAT WAS ASKED OF IT.



Thank You and Astro14 both for the info. Did Airbus change anything after this crash or am I just dumb? Thank You gentlemen
smile.gif
 
Originally Posted by 53' Stude
Did Airbus change anything after this crash or am I just dumb? Thank You gentlemen
smile.gif



Yes, I believe up to this point they claimed the A320 was uncrashable. They did not continue this claim post accident!
 
I'd bet if it happened today, we'd see the FAA ground the A320 in about a country second. I can't help but think that at least initially, much of the reaction to the Max was as political as much as it was for safety. I believe I remember Europe grounded it first.

Airbus must know that what goes around comes around. What I don't understand is why Boeing moved to be more like Airbus with electronic nannies.

Wasn't there suspicion that the Air France A330 crash over the South Atlantic also involved an automated response that may have fought with the pilots' control inputs? Not sure about that one, but I remember at one point seeing at least speculation in that direction.
 
Originally Posted by IndyFan
I'd bet if it happened today, we'd see the FAA ground the A320 in about a country second. I can't help but think that at least initially, much of the reaction to the Max was as political as much as it was for safety. I believe I remember Europe grounded it first.

Airbus must know that what goes around comes around. What I don't understand is why Boeing moved to be more like Airbus with electronic nannies.

Wasn't there suspicion that the Air France A330 crash over the South Atlantic also involved an automated response that may have fought with the pilots' control inputs? Not sure about that one, but I remember at one point seeing at least speculation in that direction.


Astro as written about AF330 quite a bit here and you should search for his responses.

From what I remember he wrote, the pilots didn't realize the sensor failure that happened from ice, lost orientation and their automatic response, through training, was pull up. This lead them into a stall and fell into the ocean. One pilot realized it at the last minute and started to verbalize push down but it was too late.
 
For years Airbus aircraft would keep pilots out of the loop or "make decisions " for them. This was 100% software related as the aircraft didn't respond to the pilot's commands.
 
I'm not a pilot and only have a basic understanding of what it takes to keep a plane in the air, but I feel that computers making decisions for pilots or limiting their ability to control the plane is WRONG!

Sure, it may help the people right out of Sim training who have no actual stick and rudder experience (smaller planes, gliders) but I don't want those people carting me around at 500-700kts 30k feet off the ground when things go sideways. I want someone who can think for themselves, someone who is learned, prepared and has a "feel" for what it takes to keep that big bird aloft. Both Astro and Cujet strike me as that type of person. But I get it... Those people and the training that made them that way cost lots of money though, and who's going to pay for it? It really puts the airlines in a tough place.
 
Originally Posted by Cujet
Originally Posted by Astro14
they just plain flew into the trees at low speed while the engines were spooling up.


The flight augmentation computer intervened to prevent a stall. The rest was history. The crew applied full power and the pilot attempted to climb. However, the elevators did not respond to the pilot's commands because the A320's computer system engaged its "alpha protection" mode (meant to prevent the aircraft from entering a stall). Less than five seconds later, the turbines began ingesting leaves and branches as the aircraft skimmed the tops of the trees. The combustion chambers clogged and the engines failed. The aircraft fell to the ground.[3]

When this happened, there was wild speculation about the fly by wire systems and the limits of the control laws. 30 years down the road, we still hear the same old reasons and excuses.

In subsequent testing various Boeing airliners flew the same profile and performed as expected, they would not have crashed.

Yes, we can blame the pilot, for judgement, thrust, speed and altitude issues. However, it's clear the airframe DID NOT DO WHAT WAS ASKED OF IT.


It's not that simple.

Alpha Prot engages just before stall.

The pilot asked the airplane to do something stupid (stall) and it refused. The airplane DID PRECISELY WHAT WAS ASKED OF IT - fly just a hair above stall.

The pilot then blamed the airplane.

However, those of us who have flown the airbus (6 years in my case) strongly suspect the pilot's story.

At Alpha Prot, when above 50 feet, Alpha Floor engages, and the engines go to TOGA (full rated power) automatically. This is to recover the airplane from a stall and dig it out from the low energy state on the backside of the power curve.

He expected that TOGA would engage.

It did not.

It that's because he flew below 50 feet (an error in an airplane like this. A huge lapse in judgment).

And the airplane did not engage alpha floor because it was not in the flight regime where that works.

Pilot error. Plain and simple.
 
Originally Posted by Astro14

Pilot error. Plain and simple.


I agree that the crew was at fault. Good god, there were a pile of mistakes on their part, including not fully understanding what would happen in that situation. I make the point that engineers cannot foresee every possible situation. When everything is normal, a well engineered aircraft performs perfectly. Yet it's the performance in extraordinary circumstances that often matters.

Do we know what the stall margin was in this case? I suspect there was quite a buffer.
 
I've over-simplified this a bit as it gets technical, but your question is technical, so let's dive in...

There are seven flight control computers (FCC) that take pilot input and translate that into flight control surface movement. They operate via a set of rules known as normal law. Normal law provides envelope protection, limiting speed, AOA, bank, pitch, yaw and G. Exceeding normal law limits can over stress the airframe. It's there to keep the airplane in one piece.

It usually works great. But if the FCCs lose an input from a sensor, as was the case in AF 447, then they can't accurately determine the envelope, and some of those protections are removed, allowing the pilot to fly beyond what would normally be allowed, since those limits might be inaccurately determined from faulty sensors. This regime is known as alternate and AF 447 was operating in alternate law.

The flight control system, in normal law, provides auto-trimming up to alpha prot (protection). You must hold back stick to fly an AOA above alpha prot. Release the stick and it returns to alpha prot. The airplane will be squawking at you the whole time you're at, or above in AOA, alpha prot by saying "speed, speed, speed" because you're at an unusually low speed. An unusually high AOA.

The airplane will limit AOA to alpha max. It can't be flown above that. It will stop increasing pitch.

Somewhere between alpha prot and alpha max, the flight control system engages alpha floor, and puts the engines in TOGA (full thrust). This is, as I mentioned, a safety limit to prevent a stall, and dig the airplane out of a low energy state.

Alpha floor and the speed warning are inhibited for landing (alpha max still applies, but the fuselage will hit the ground long before its reached) and this makes sense, you don't want a gust or momentary alpha sensor perturbation to suddenly put the engines in TOGA while landing - that would cause a crash all by itself. That inhibition happens at 100 feet (I was mistaken when I said 50).

Nothing in the FCOM (Airbus handbook for the airplane) or my airline flight manual states how much margin exists between these values. They're just a few knots apart, from alpha prot to alpha max, at normal landing speeds, and a good 20 knots below a normal landing speed. REALLY slow...but I've got no precise answer for you in either AOA or airspeed.

So, what really happened in this case?

First, the pilot flew well below the altitude that he should have. He, by doing that, removed the alpha floor and speed warnings.

Then, he continued to fly low, and didn't select TOGA power until the airplane was hitting trees. Usually, adding power before you crash works out better than adding power AS you crash...

Why?

He claims that "the airplane didn't respond" - which implies that he was expecting alpha floor to engage as he increased AOA. But it didn't because he was flying where it was inhibited for landing.

Had he selected TOGA before the end of the runway, the airplane would've flown away.

Had he stayed above 100 feet, as he should have, the airplane would've flown away.

Had the airplane allowed him to exceed alpha max, it would've stalled and crashed anyway.

So, it's not really a case of "airplane didn't respond" - it's far more like Asiana 214. It's a case of "pilot didn't understand his airplane" and flew it into a place (low, slow, engines at idle) where it couldn't be recovered.
 
Last edited:
Originally Posted by Astro14
Alpha floor and the speed warning are inhibited for landing (alpha max still applies, but the fuselage will hit the ground long before its reached) and this makes sense, you don't want a gust or momentary alpha sensor perturbation to suddenly put the engines in TOGA while landing - that would cause a crash all by itself. That inhibition happens at 100 feet (I was mistaken when I said 50).

Had he stayed above 100 feet, as he should have, the airplane would've flown away.


Is there any warning given to the pilot that the alpha floor and the speed warning systems are inhibited when the plane goes below 100 feet so he knows he's in a potentially dangerous flying condition?
 
No warning is given that the airplane is below 100 feet, except that, well, you're below 100 feet! Radio altimeter. Trees. Lots of clues.

It's not dangerous to be below 100' with those warnings inhibited, or every landing would be "dangerous".

It's normal. That's how the airplane was designed. That's how it works.

If you left those systems active on landing - where you could get "surprise" full power during the landing - THAT would be dangerous...

The real danger: a pilot that doesn't understand how his airplane works.
 
Last edited:
Originally Posted by Astro14
It's not dangerous to be below 100' with those warnings inhibited, or every landing would be "dangerous".

It's normal. That's how the airplane was designed. That's how it works.


Of course, but he wasn't landing, he was trying to fly at extremely low altitude. Gliding in under low power to make a landing isn't quite the same as flying level at low speed, (which it sounds like he was doing), especially if he was trying to make any kind of turns at slow speed and low altitude.

Even though there should have been instrumentation info and other signs he was too low, maybe he didn't realize just how low and didn't realize that those systems were deactivated. Maybe if he got a warning those systems automatically deactivated he would have realized he was in a danger zone and wouldn't have lost it.

Originally Posted by Astro14
The real danger: a pilot that doesn't understand how his airplane works.


Yes, that's true about any machine a human is piloting, driving, riding, etc. But proper instrumentation and warning systems do help give needed info in critical times, especially in complex aircraft.
 
Now, with all this alpha this and beta that computer stuff, a question remains. If the airplane were equipped with traditional cable and roller flight controls, would any of this have even been an issue?
 
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