Black Box

September 26, 2009 3:14 PM

What journalists and the public often call the "black box" is typically a nearly-indestructible combination of two things: a cockpit voice recorder (CVR) which records the voices of the pilots and crew from microphones stationed around the plane, and the flight data recorder (FDR), which monitors and stores information about the flight itself, like speed, altitude, and bearing. Underwater locator beacons help search teams find submerged black boxes up to 14,000 feet under water, but sometimes even that isn't enough.
posted by MoreForMad (27 comments total)

Wait, so the AA 77 (Pentagon) recorders were found? I thought only the UA 93 (Pennsylvania) boxes were ever accounted for.

(Gonna have to turn in my tinfoil badge.)
posted by rokusan at 3:36 PM on September 26, 2009

If aircraft "black boxes" are indestructible, why can't the whole plane be made from the same material?
posted by Killick at 4:14 PM on September 26, 2009 [2 favorites]

What I don't get is why all this information can't be recorded and sent to a secure location that ISN'T ON THE PLANE!
posted by doublehappy at 4:24 PM on September 26, 2009

What I don't get is why all this information can't be recorded and sent to a secure location that ISN'T ON THE PLANE!

There are over 10,000 airplanes in the air at one time so bandwidth is a problem. You need a continuous stream of data to capture the crucial moments right up to a crash. One solution would be to spread the data out through VHF, HF and satellite. There are some current experiments along that line.

The most likely reason is that it would cost airlines millions of dollars to change at a time when they are already losing money. Considering that there are only a handful of cases over the last 50 years in which black boxes were not found, what compelling reason is there to change?
posted by JackFlash at 4:38 PM on September 26, 2009

Interesting stuff.:

FDRs are usually located in the rear of the aircraft, typically in the tail. In this position, the entire front of the aircraft is expected to act as a "crush zone" to reduce the shock that reaches the recorder. Also, modern FDRs are typically double wrapped, in strong corrosion-resistant stainless steel or titanium, with high-temperature insulation inside. They are usually bright orange. They are designed to emit a locator beacon for up to 30 days, and can operate immersed to a depth of up to 6,000 meters (20,000 ft).

posted by zarq at 5:13 PM on September 26, 2009 [2 favorites]

What I don't get is why all this information can't be recorded and sent to a secure location that ISN'T ON THE PLANE!

jackflash correctly commented that transmission might be the issue here but it should be noted that AF flight 447 did in fact transmit some information during its last minutes:

wikipedia:

An Air France spokesperson stated on 3 June that “the aircraft sent a series of electronic messages over a three-minute period, which represented about a minute of information. (...)"

(...)

The messages, sent from an onboard maintenance system, Aircraft Communication Addressing and Reporting System (ACARS), were made public on 4 June 2009.[21] These transcripts indicate that between 02:10 UTC and 02:14 UTC, 5 failure reports (FLR) and 19 warnings (WRN) were transmitted.[22] The messages resulted from equipment failure data, captured by a built-in system for testing and reporting, and cockpit warnings also posted to ACARS.[23] The failures and warnings in the 5 minutes of transmission concerned navigation auto-flight, flight controls, and cabin air-handling (codes beginning with 34, 22 , 37 and 21, respectively).[24]
posted by krautland at 5:26 PM on September 26, 2009 [1 favorite]

From the last wikipedia: Recorders may be recovered, but too damaged to read or have blanks, like in TWA Flight 800 or Swissair Flight 111, after power is cut off.

If this is true, I'm a bit disappointed that they don't have an internal backup battery.
posted by Salvor Hardin at 5:41 PM on September 26, 2009

I can't imagine that the WTC wreckage (buildings and airplane bits) weren't very closely examined. It's a bit tinfoily that they didn't recover the boxes from either plane.
posted by maxwelton at 5:47 PM on September 26, 2009

Wasn't part of the reason the towers fell that the jet fuel inferno was softening the steel girders that made up the towers? Those were a lot thicker than 1/4". It may not have melted, but the internals would certainly have cooked (based on the wikipedia link), and surviving the collapse after being in a furnace for 90 mins is a whole other kettle of fish.
posted by Decimask at 5:55 PM on September 26, 2009

(IANA materials scientist or engineer)
posted by Decimask at 5:56 PM on September 26, 2009

If this is true, I'm a bit disappointed that they don't have an internal backup battery.

Interesting response to that. In summary, the recorders get their data from other aircraft systems, so you would need a backup battery for the whole plane's electrical bus.
posted by smackfu at 6:09 PM on September 26, 2009

If this is true, I'm a bit disappointed that they don't have an internal backup battery.
many do but in the case of TWA800 the whole front third of the aircraft separated from the rest, severing among many other things the data transmission cables. Swissair 111 didn't fare much better with its massive electrical fire right behind the cockpit.
posted by krautland at 6:33 PM on September 26, 2009

the recorders get their data from other aircraft systems, so you would need a backup battery for the whole plane's electrical bus.

Ah, I see - that makes sense. It seems like passive devices like microphones should keep working though. Of course, it's hard to engineer something that will keep gathering data if the plan breaks into multiple pieces...
posted by Salvor Hardin at 6:52 PM on September 26, 2009

Actually, now that I think about it, most black boxes must have a battery on board if they transmit a locator beacon.
posted by Salvor Hardin at 6:53 PM on September 26, 2009

I can't imagine that the WTC wreckage (buildings and airplane bits) weren't very closely examined. It's a bit tinfoily that they didn't recover the boxes from either plane.

The Straight Dope article on the "why don't they make the planes out of the same material?" question mentions that in an airline crash in Thailand "the recorder landed in a pool of flaming fuel and basically got cooked." So clearly blackboxes can melt under great heat. As the two planes that struck the tower were held in place by the structures on impact and during the subsequent explosion and fire, it's not impossible that their blackboxes pretty much became molten.
posted by Marisa Stole the Precious Thing at 6:57 PM on September 26, 2009

So why not have more than one black box, in different sections of the plane? In case one or more fail, I mean.
posted by marble at 7:50 PM on September 26, 2009

> It's a bit tinfoily that they didn't recover the boxes from either plane.

From a comment above, they had to move the black box from the midsection to the tail because the midsection tended to crush the boxes. What do you think a skyscraper could do?
posted by xorry at 7:54 PM on September 26, 2009

Ah, Marisa got it. It wasn't in a comment, but the Straight Dope link.
posted by xorry at 7:54 PM on September 26, 2009

(Gonna have to turn in my tinfoil badge.)

Oh, so now we need tinfoil badges in addition to the hats? I'll tell you this and I'll tell you right now: we don't need no stinkin' badges.
posted by telstar at 10:51 PM on September 26, 2009

smackfu, all you would need would be a couple of diodes to isolate the backup battery from the rest of the aircraft's power. I'm a rather rusty EE, though.
posted by rfs at 10:58 PM on September 26, 2009

I can't imagine that the WTC wreckage (buildings and airplane bits) weren't very closely examined. It's a bit tinfoily that they didn't recover the boxes from either plane.

I think it's pretty clear what went wrong on those flights.
posted by doublehappy at 4:38 AM on September 27, 2009 [2 favorites]

For those interested, development is underway on Black Boxes (they're actually orange) that eject from the aircraft when certain parameters are exceeded (i.e. - hey something's really wrong here!) and then float. Also, if you look at the Air France flight, the ACARS system sent out burst messages when things started going wrong.

I think in the near future you're going to see an improved upon combination of the two technologies.

Although some companies want to get rid of the black box entirely.
posted by matty at 11:52 AM on September 27, 2009

more on ACARS - I think the current cost to send a message is $0.25. That doesn't sound like a lot, but it adds up to a significant expense for an airline over time, especially considering ACARS usage:

dispatcher rerouting and messaging
weather
maintenance messages
atc communication
emergency burst messaging on performance

More often than not when your aircraft receives a routing change for 'whatever reason', that change was approved and communicated by the airline company's dispatch office in coordination with ATC and sent over ACARS.

Long story short, real-time data via ACARS would be crazy expensive, so it'll be interesting to see what technologies industry comes up with if they want to pursue a real-time data connection.
posted by matty at 12:18 PM on September 27, 2009

Although some companies want to get rid of the black box entirely.

Which is silly. Comm links drop all the time for various reasons -- indeed, when a data dropout happens on the Shuttle, the standard answer is "wait 15-30 seconds for it to come back."

It's obvious that CVR/FDR technology is pretty good. The best way to make that data stream safer isn't to replace CVR/FDRs, it's to augment them. Yes, if you can manage the data, have a real time data stream uplinked somewhere -- but record that same data stream to the CVR/FDRs on board.

95% is pretty reliable, but two 95% reliable systems are vastly more so.
posted by eriko at 12:22 PM on September 27, 2009

@Eriko: 'Which is silly.'

I agree.
posted by matty at 12:39 PM on September 27, 2009

I can't imagine that the WTC wreckage (buildings and airplane bits) weren't very closely examined....

It's the Pentagon one that surprised me.
posted by rokusan at 1:19 AM on September 28, 2009

For those interested, development is underway on Black Boxes (they're actually orange) that eject from the aircraft when certain parameters are exceeded (i.e. - hey something's really wrong here!) and then float.

This already exists - at least for helicopter platforms. My work has installed them on Australia's SeaHawks. Check out the big orange thing on the side of the aircraft here.

It has a number of deployment triggers - manual signal from pilots, crush switches just under skin and water immersion sensors.

All CDR/FDRs are certified under regulations which give minimum time to survive in a fire of a certain temperature. You can't make them completely indestructable - everything is a tradeoff.
posted by trialex at 5:37 PM on September 29, 2009