“Tower, look at to the south, there's an aircraft crashing”
On Veterans’ Day in 2001, an airplane carrying
260 people dropped out of the sky shortly after taking off from JFK.
“An aircraft just crashed to the south of the field”
The top fin of the plane broke off and fell into Jamaica Bay,
and the rest of the plane crashed into a residential neighborhood in Queens. Everyone onboard and
5 people on the ground were killed. This was just 2 months after September 11th,
and it was reasonable to assume, as many people did, that New York was being attacked again.
But investigators concluded that it wasn’t terrorism that took down Flight 587.
And they knew that because of what they found on the airplane’s black box.
What the press calls the “black box” is actually 2 orange flight recorders.
The idea dates back to the 1950s, when the first commercial jet had 5 accidents in its
first 2 years of passenger service, and investigators realized how useful it
would be to have a record of what was happening on the plane before the crash.
Early generations of flight recorders etched the data onto metal foil.
By the 1970s they’d switched to magnetic tape, and by the 90s, solid-state memory chips.
But overall, the concept has remained basically the same, with 2 components:
The cockpit voice recorder stores the last 2 hours of sound from cockpit and from the
pilots’ headset microphones, on 4 different channels.
In some cases, these audio recordings alone can reveal what happened, as they did when
a Germanwings flight crashed into the French Alps in 2015.
NBC report: “The plane begins to descend. Air Traffic control calls. No answer.
The captain begins banging on the door, yelling, ‘For God's sake, open the door.’
Passengers scream in the background.” In the case of Flight 587, that's the plane that
crashed into those houses in Queens -- the cockpit voice recorder offered some hints
about what happened. The transcript showed that before crashing,
the plane ran into some wake turbulence from the large 747 that took off just ahead
of Flight 587. But that turbulence alone wouldn’t have
been enough to take down the flight. So investigators needed information from the
second box: the flight data recorder. It captures at least 88 types of data about the plane’s
position and instruments for the past 25 hours. That data feeds into computer animations of
what happened before the recorder lost power.
And the black box data revealed that the pilots lost control of the plane
over the course of about 10 seconds.
And this line in particular stuck out -- it shows what the copilot, who was flying the
plane, was doing with the rudder pedals in response to the turbulence.
Pilots can maneuver planes along 3 axes, pitch, roll, and yaw, which is what the rudder controls.
But they rarely use the rudder, because as you’ve probably noticed, they can change direction by rolling.
Investigators concluded that the copilot probably
didn’t realize that his aggressive rudder pedal movements were making things worse,
that they were putting enough pressure on the the vertical stabilizer, that it detached
causing the plane to crash. Because of the flight data recorder, authorities
could rule out both terrorism and mechanical failure, and instead, blame pilot error and poor training.
No two airplane accidents are the same, but
the flight recorders are useful for every case, provided that they survive the crash.
And they usually do. The recorders are installed near the tail of planes where the force of
the impact is somewhat lessened. And the memory boards are kept in steel
or titanium cases and surrounded by materials that protect against high temperatures.
Often, the rest of the box will be destroyed, but that doesn’t matter as long as the memory
unit is intact. Of course, flight recorders that are never
found are useless. They do have a beacon that activates underwater
and sends an ultrasound signal every second for 30 days. That signal can travel through
14,000 feet of water.
But as flight MH 370 showed, sometimes investigators aren’t even within that range.
BBC report: "But the batteries from MH 370 black boxes
are almost certainly starting to fail.
If they haven't already."
That’s why some have proposed new systems that don’t leave the data on the plane,
but rather transmit it in real time to satellites or ground stations.
There are privacy and cost concerns to consider, but in the future, they might not need to
find a box, in order to find the answers the that investigators,
and families need.
Why does the press call it a black box when it's orange?
Very good question. The term "black box" is not actually used within the aviation industry.
I was told when I originally came here there were a couple of different theories.
One, that the term black box is often used in engineering for a device where you have a lot of inputs.
It may go back to the early days of the recorder, where they used light-sensitive paper to record
traces from the stylus. And that equipment was housed in a light-protected black box.
There's also the idea that, as a result of the accident, once they've been expose to heat and fire,
that they turn black or a dark brown.
Nobody really knows where the term came from. But as I say, they're more appropriately called
flight recorders or onboard recording devices and they're always painted a very bright orange.