Intro
On it's maiden voyage, the titanic was hailed by all as a ship that was completely
unsinkable, but we all know it to be one of histories greatest disasters.
Similarly, airplanes have gotten so advanced, that many have started to say the
same thing: that they are uncrashable. So how then did one of the most
sophistacted flying machines in the world crash into the atlantic ocean,
killing everyone on board. This project examines the events that
brought down Air France Flight 447
Flight School - (FSCHL)
Before we jump into the story and start examining
what happened, it is going to be extremely useful to
first understand the displays you see on the right hand
side of your screen. Take some time to hover over each section
to learn more about what each display represents.
FSCHL
The most important display is the main pilot display.
This is what the pilot uses to fly when they can’t
see or have very low visibility. On the flight display
their are four main features
FSCHL
The first feature is the speed indicator. This
simply displays the planes air speed in knots.
FSCHL
The second feature is what is know as an Altimeter. This displays
the planes current height in feet.
FSCHL
The third and most important feature is what is called the attitude indicator.
It displays the position of the nose of the plane in relation
to the horizon.
FSCHL
The center dot on the attitude indicator represents the
actual nose of the plane.
FSCHL
The area in blue represents the sky, and the area in brown
represents the ground.
FSCHL
If the nose is pitched up, then you will
see more blue.
FSCHL
If the nose is pitched down, then you will see more brown.
FSCHL
When the attitude indicator rotates to the left, that means that the plane
is rolling to the right.
FSCHL
If the attitude indicator is rotating to the right
that means that plane is rolling to the left. It seems very counter-intuitive
but you must remember that this attitude indicator represents
the plane in relation to the horizon.
FSCHL
The numbers on the attitude represent that angle of the airplane's
nose in relation to the horizon. So if the nose is at the 10 in the blue
area, that means that the airplanes nose is pitched 10 degrees up.
If the nose is at the 10 in the brown area then that means that the
airplane’s nose is pitched 10 degrees down.
FSCHL
Now that you understand the basics, lets pick up the story and join
flight 447 as it is cruising over the atlantic ocean.
ARARO Checkpoint - Nothing out of the Ordinary
Flight 447 is approaching ARARO point. The pilot flying is Cedric Bonin and his co-pilot is David Robert.
Bonin is sitting in the right seat and Robert is sitting in the left seat.
The captain, Marc Dubois is currently on his break in the crew quarters.
ARARO
At this stage, the aircraft is flying level at an altitude of 35,000 feet...
ARARO
and at a speed of Mach .82 (or cruising speed).
ARARO
The pitch attitude or the angle of the nose of the airplane
in relation to the horizon was 2.5 degrees and the angle of attack of
the plane was 3 degrees.
ARARO
And the auto-pilot is on. All normal and nothing out of the ordinary
here.
ARARO
The angle of attack is the angle at which the airplane wings meet the
oncoming air. The higher the angle of attack the greater the lift
efficiency, BUT (and this is a really really big but) only up to a
certain point. If the angle attack exceeds a certain amount, the
oncoming air can no longer smoothly flow over the top of the wing,
decreasing lift, which causes the aircraft to go into what is known as
a stall. This happens with all airplanes and has absolutely nothing to
do with the engines. When a stall occurs, the airplane wings are at
such a steep angle that the power and thrust provided by the engines
of the plane can not exceed the drag forces experienced by the
airplane. Now, the only way to exit a stall, is to do something that
seems really counter-intuitive. You have to push the nose of the
airplane down and dive, so that the oncoming air can begin to smoothly
flow over the wing again, thereby producing lift and taking the
airplane out of the stall.
ARARO
The aircraft is currently operating in what is known as
“Normal Law”. Under this mode, the flight computers control a large
portion of the “fly by wire” system we mentioned above. If for some reason
the pilot makes side-stick inputs erraticly or by mistake,
The computer basically says, “Im in normal mode, and i just received an input that would be too dangerous
for this altitude. Because this action would cause a stall at this
altitude, I will restrict this input from the pilot and not allow it
to go through.”
ARARO
It’s a great fail safe and has contributed a lot to
why air travel is so safe these days. AF447 is currently operating
under “Normal Law” and everything seems to be going ok, but not for
long.
Loss of Air Speed- LoAS
Robert notices that they are headed towards an area of
intensive activity and asks Bonin if he can move the aircraft left, so
that they can dodge this activity. Bonin rolls the plane 20 degrees to
the left and also reduces the airspeed from .82 mach to .8 mach. This
slightly increased the angle of attack on the airplane. The sound of
tiny ice crystals hitting the windshield of the aircraft could clearly
be heard in the cockpit. Hit the start animation button to see what happens.
LoAS
Unknown to both pilots, these ice crystals were clogging up
the airplane’s pitot tubes. The pitot tubes are located on the front
of all major aircraft and are instruments that provide vital airspeed
data to the aircraft’s computers. Because the ice crystals clogged up
the pitot tubes, accurate air speed data stopped being sent to the
flight computers, and without accurate airspeed data, AF447’s
autopilot turned off, sounding an alarm in the cockpit, handing
control of the aircraft fully over to the pilots.
LoAS
This also switched the mode on the flight computers from the existing “Normal Law” to
“Alternate Law”. In alternate law, the pilot’s inputs are not as
scrutinized by the flight computer as under “normal law”, which means
that the flight computers can’t prevent any errors or prevent stalls
from happening.
LoAS
Everything that just occurred was a normal and logical
response by the airplane and was designed this way by the airplane
engineers. At this moment, Bonin verbally says “I have the controls.”
LoAS
Now remember, the airplane is currently flying level (both
wings and nose level to the horizon) and the engine thrust set to
consistently deliver a nominal .8 mach. The only significant error was
the loss of the indication of airspeed, not the actual airspeed
itself. All Bonin needs to do is keep the aircraft straight and level
and maintain these current conditions.
LoAS
As a result of the loss the auto pilot, the plane begins to roll slightly to the right.
To correct this all Bonin needs to do is move his side stick a little bit to the
left to counteract the roll right. But for some unknown reason, Bonin
makes a nose up and left input.
LoAS
Now its not a slight pulling back of the side stick.
Bonin jerks the side stick back considerably and to
the left. Because Bonin makes this nose up and left input, an alarm
(Altitude alert C cord) in the cockpit sounds warning the pilots that
the aircraft has left its recommended altitude and has begun climbing
because of Bonin’s nose up input. The airplane then sounds the stall
warning twice in a row. Now remember, the plane’s computers are in
alternate law so it is not going to correct Bonin’s mistake. Neither
pilot acknowledges the altitude or stall warning.
LoAS
The airplane is now climbing at a blistering rate, almost
7000ft/minute. Both pilots acknowledge that they have lost their
airspeed indications. But as the aircraft continues to climb it’s also
losing a tremendous amount of speed. During the next ten seconds Bonin
brings the pitch of the aircraft from 2.5 degrees to 11 degrees.
LoAS
During these next ten seconds, Rober starts to read out the warning
messages in a disorganized manner. He verbally says “Alternate Law
Protections”, which means that the airplane has moved from normal to
alternate law and that stalls can occur. But each time the stall
warning sounds, both pilots seem to not acknowledge it at all. It’s
not clear that Robert processed what he was reading from the screen or
if Bonin ever heard anything that Robert was saying at this time.
Because if they did, they would have acknowledged the stall warnings
and instead of pulling up, Bonin could have pushed the nose of the
plane down, to recover from the stall.
Almost Saved - ALSAV
Robert tells Bonin, “Pay attention to your speed. Pay
attention to your speed.” By this Robert probably means the vertical
speed because their air speed is still currently invalid.
ALSAV
Bonin responds, “Ok, ok, I am descending...”
ALSAV
Robert tells Bonin, “Decend… It says we are going up… It says
we are going up.... Descend.”
ALSAV
Now during this whole time, Robert has actually no
idea whether or not Bonin is making the necessary side stick inputs.
That is because Robert’s side stick and Bonin’s stick are not linked.
This is how most Airbus aircraft are designed. If Bonin moves side
stick, Robert’s side stick stays stationary. If both pilots move their
side stick at the same time, then a warning sounds off saying “Dual
Input”, and flight computers split the difference.
ALSAV
If Bonin and Rober were flying a Boeing aircraft, they would both have what is called
yolk. Its a long column that sits in front of the pilots seat. Now if
one pilot moves his yolk or control column in a boeing, the other
pilot’s yolk/control column would move as well because both are
linked. Robert would be able to identify exactly what Bonin was doing.
In this A330 that was unfortunately not the case.
ALSAV
Bonin eases back on the stick and for slight moment the
aircraft begins to pick up some speed as the nose is lowered. A few
degrees lower and Bonin can reduce the climb and get the aircraft back
on track, but for some reason Bonin does not do this. He push back on
the stick again.
Deep Stall - DPSL
Even though the plane is actually beginning to level Bonin continues to make nose up inputs,
raising the pitch of the aircraft back up to 13 degrees above the horizon.
Again the stall warning sounds. The aircraft begins to shake violently.
DPSL
Not knowing what is happening, Robert makes a call to
Captain Dubois asking him to come to cockpit immediately.
DPSL
Bonin continues to make nose up inputs, raising the pitch of
the aircraft to 13 degrees above the horizon. Again the stall warning
sounds. The aircraft begins to shake violently.
DPSL
The aircraft reaches its maximum altitude of about 38,000
feet. With the engine at full power and an angle of attack of 16
degrees, the plane begins to decend and fall out of the sky. If Bonin
just let go of the side stick, the plane’s pitch would decrease,
increase the flow of air over the top of the wings, and pulling the
plane out of the stall. But Bonin, doesnt let go and pulls and holds
the side stick all the way back. At this time, the plane is shaking so
much that it’s extremely difficult to keep the plane's wings level.
DPSL
We can never really know the true reason
Bonin kept pulling his side stick back,
but there are some possible explanations.
DPSL
One possible reason was that both pilot’s were more focused on leveling the plane,
trying to understand why the auto pilot was turned off and why they lost their airspeeds
DPSL
Another reason may be that Bonin was trying to reach clear skys, by flying higher,
because they were at the edge of the cloud layer.
DPSL
And the last reason may include that the presence of turbulence prior to loss
of autopilot may have changed their perception of the planes movements.
Confusion - CFUS
Robert takes control of the plane for a few seconds, without
letting Bonin know that he was taking control. Almost immediately
after Robert takes control of the plane, Bonin takes control back.
CFUS
Captain Dubois finally comes in the cockpit to see what is
happening. Captain Dubois asks, “What the hell are you doing?”. And
Bonin responds that they have lost control of the airplane.
CFUS
The aircraft falls back down to it’s original altitude of
35,000 feet but continues to descend at a rate of almost 10,000ft/min.
At this moment the stall warning stopped sounding because the angle of
attack was so high that the flight computers rejected the data as
invalid. The recorded angle of attack was an incredible 41 degrees.
CFUS
The right wing was down by about 30 degrees causing the plane to arc
way off its set flight path. The aircraft would maintain these
characteristics all the way till it hit the Atlantic ocean.
CFUS
Now because the stall warning had stopped sounding, the
pilots may have assumed that all was ok again (when in reality things
were not ok). Each time bonin actually did lower the nose of the
plane, the computer began to receive accurate data again and the stall
warning began to sound. Thinking that he was in stall again Bonin then
pulled back on his side stick, increasing the pitch of the plane, and
increasing the angle of attack, such that the computer rejected the
data being provided, and the stall warning stopped. This was a
nightmarish negative feedback loop. The plane was now loosing altitude
at a rate of 15,000ft/min/
Final Moments - FNMT
Robert asks Captain Dubois, “What do you think? What do you
think? What should we do?”
FNMT
Captain Dubois says, “I don’t know.” Captain Dubois urges
Bonin to level the wings but that does extremely little to solve their
actual problem.
FNMT
Robert quickly takes back control, pitches the nose of the
airplane down, but as he does that Bonin pushes the nose of the plane
up. The Dual Input warning sounds again and the plane maintains a
upward pitch. Bonin says, “We are reaching flight level 100.” , which
means their current altitude is 10,000ft. This was the last moment in
which a recovery would have been possible. There are only a handful of
pilots who would have been able to execute the maneuver necessary to
save this plane.
FNMT
Robert tells Bonin, “Climb, Climb, Climb…”. Bonin responds,
“But I have had my stick back this whole time!”. To this Captain
Dubois says, “No, do not climb!”. What Captain Dubois meant to say was
“Do not pitch up!” because it was because their high pitch that they
were falling out of the sky. They actually needed to “climb”.
FNMT
The ground proximity warning system began to sound because
it detected the ocean was fast approaching. Warning of “Sink Rate” and
“Pull Up” began to sound.
FNMT
The recording stops.