# Why don't black boxes have their own GPS?

In too many cases of unfortunate incidents, hunting for FDR (or CVR also) is a major challenge.1 There are many or all answers recorded on that device.

Why a locator (GPS linked) cannot be included in the black box? It has its battery which runs for several days and very rigid outer shell.

Ordinary cell phones are GPS enabled which pinpoint their location with the accuracy of a couple of feet. So why there cannot be a more sophisticated technology added to the black boxes?

1: I am aware that most of FDRs/CVRs are eventually recovered.

• GPS is receiving only the satellite doesn't know what devices are getting its signal, to send you location to a receiver you need a radio connection of some kind, if we could do that then we wouldn't need the gps location in the first place Mar 24 '14 at 21:34
• It would not be possible to get the (enormous) power required to transmit something through 5000 feet of water. Even submarines can't do that and they have something of an advantage over a small box. Mar 24 '14 at 22:45

First let's and define what "too many cases" means in terms of cold, hard, unfeeling numbers (as best we can):

Wikipedia has a list (admittedly incomplete) of crashes where the CVR/FDR was not recovered. There are 16 crashes listed. I'll further add Air France 447 (which took "a long time" to find), and MH370 (which is currently unrecovered), bringing the total to 18.

As Wikipedia admits their list is incomplete I'll double-and-round that in the name of being pessimistically conservative and say that since 1965 there have been 50 cases where it has taken "a long time" to recover the flight recorders (or they were never recovered).

In a single year there can be over 100 "incidents". Even if we assume the CVR/FDR data wouldn't be useful for all of them there are still many hundreds (if not thousands) of incidents since 1965 where the cockpit voice recorder and/or flight data recorders have been recovered along with other wreckage or damaged airframes - often within a matter of days or hours (as soon as investigators can get to the wreckage). That's a pretty good track record.

One could certainly argue (legitimately) that "one unrecovered flight recorder is too many", and indeed the goal is to always find the recorders and analyze their contents.
If we're being realistic about this though we're going to have to accept the fact that sometimes you're just not going to recover the recorders: Aircraft crashes are messy, high-energy affairs and often involve inhospitable recovery environments like "the bottom of the ocean".

If someone has better statistics close at hand I would love to review them and update this answer. Otherwise, it should be obvious that the above is an extremely rough off-the-cuff estimate, and should not be taken for any research or investigative purposes.
In case it's not obvious - well I just said it.

Now, to the meat of your question:

Theoretically you could include a locator beacon in the CVR or FDR - incorporating a 406MHz ELT into the black box design is possible (you could even add a GPS to encode the device's location, though it would be of limited additional value with the inherent location accuracy of the 406MHz locator signal and satellite search system).

So why don't we do it?

As Lnafziger pointed out, airliners are already required to carry emergency locator transmitters - in any case where such a beacon would function including one in the CVR/FDR would be redundant with existing equipment in the aircraft.

Further practical problems arise when you consider the kind of abuse a "black box" is subject to -- These things need to survive a crash (up to 3400 Gs), crush forces, fire, and immersion in water under pressure.
Your typical distress beacon requires an antenna and a view of the sky, both of which would be in serious doubt after a crash: The black box may be inside or under wreckage, required external antennas may have been torn off or burned away, and distress beacon signals are unlikely to be received if the recorder is under water (this is why current generation recorders have sonar "pingers" to assist in locating them).

To easily illustrate the sort of problem radio devices have with "stuff" between them and the sky, try this experiment: Take your cell phone, wrap it in aluminum foil to simulate the skin of a plane, put it in a zip-lock bag, and take it to the bottom of a pool. I bet you won't be able to get a call on that phone.

Given the numerous failure modes (all of which are fairly high-probability in a real-world crash scenario), and the fact that we usually have a pretty good idea of where an aircraft is when a crash does happen, there isn't much to be gained by including additional locator technology in the CVR/FDR designs at this time - it just adds more components that would need periodic testing and recertification to ensure they are functioning properly and would activate appropriately in the event of a crash, while not appreciably improving our odds of finding the recorders.

• Thanks for the thorough answer. I agree FDRs are eventually found but many times it takes longer. What I had in mind was a way/technology to announce its position when it could not be located. Using the existing technology, there are many limitations (which you have pointed). Maybe in future someone can invent something which could help tracing objects easier. Of course some people don't like to be "traced" all the time.
– Farhan
Mar 25 '14 at 17:25

If you can receive a signal from the device, then you can already home in on where that signal is coming from. The signal does not need to include the position.

GPS would also be of limited use. In most scenarios, it would probably be unable to receive a signal underneath water, terrain, weather, and wreckage. The GPS and antenna would also have to survive in order to function.

• +1 This is the crucial information: GPS doesn't work well in typical crash scenarios. It actually doesn't work at all below a not so thick layer of water (surely no more than couple meters).
– yo'
Mar 25 '14 at 17:13

To answer this question, you need to understand how GPS works. GPS satellites just keep continuously beaming the time the message was transmitter, and the position of the satellite at the time of the transmission.

The GPS receiver/client then interprets your location based on the transit time of each message and computes the distance to each satellite.

This means, the satellites or anyone other than your GPS receiver don't know your location. To transmit your location to anyone, you need a medium (such as the internet or GSM network), which is absent at the bottom of the ocean.

Source: Wikipedia

Actually, modern 406 Mhz ELT's do have GPS built-in and they transmit their location to satellites when activated.

Since they are required by US regulations, it would be redundant to require the black box to have its own.

From Wikipedia:

GPS-based, registered
The most modern 406 MHz beacons with GPS (US300+ in 2010) track with a precision of 100 meters in the 70% of the world closest to the equator, and send a serial number so the responsible authority can look up phone numbers to notify the registrator (e.g. next-of-kin) in four minutes.

The GPS system permits stationary, wide-view geosynchronous communications satellites to enhance the doppler position received by low Earth orbit satellites. EPIRB beacons with built-in GPS are usually called GPIRBs, for GPS Position-Indicating Radio Beacon or Global Position-Indicating Radio Beacon.

However, rescue cannot begin until a doppler track is available. The COSPAS-SARSAT specifications say [7] that a beacon location is not considered "resolved" unless at least two doppler tracks match or a doppler track confirms an encoded (GPS) track. One or more GPS tracks are not sufficient.

• In the US, ELTs are not required on air carriers (scheduled air carriers), and an ELT is not a FDR. §91.207 ecfr.gov/cgi-bin/text-idx?rgn=div8&node=14:2.0.1.3.10.3.7.4
– CJBS
Mar 24 '14 at 23:04
• @CJBS I never said that an ELT is an FDR, and I had forgotten that it isn't required for scheduled air carrier flights. Mar 24 '14 at 23:10
• You're right, but I think it's somewhat implied -- the question isn't about ELTs, it's about black boxes. Regarding the U.S. FAA not requiring ELTs for scheduled carrier services, it's this crash type that tends to attract the most media attention, most likely hence the question. For what it's worth, I had also assumed that ELTs would automatically be on air carriers too (from GA pilot training), only to be reminded that that's not the case for scheduled services. Doesn't really make sense that they're not required, does it?
– CJBS
Mar 24 '14 at 23:19
• @CJBS I know that it isn't about ELT's, but having an ELT negates the need to add one to the FDR, which is what I wrote.... Mar 24 '14 at 23:37
• This is true. Presumably the reason that they're not required on air carrier services is that air carriers typically know where their craft are.
– CJBS
Mar 25 '14 at 0:08

The answers are missing the point. Some companies have real time GPS enabled tracking on fleet trucks. You can go on a computer and check where these trucks have been 1 week back. When some of you say GPS signals can't penetrate deep waters, it would have at least sent it's last known coordinates before impact that could have been recorded if there was a system in place to record. Then we could better pinpoint impact areas.

• Sent by what mechanism? Tracked trucks are seldom out of cell phone range; intercontinental flights are seldom within cell phone range. And, in any case, all systems on aircraft can be switched off so that faults can be isolated. Mar 26 '14 at 10:20
• @DavidRicherby Sent by satellite is one option... Mar 26 '14 at 13:27

Completely agree with Thilak. With a GPS receiver attached to a black box, only the black box will be able to know its own location. We are able to use GPS for tracking assets becuase those devices transmit the location information received from GPS, using various channels such as GPRS or satellite connectivity. In the case of black box - (a) GPS signals from satellites reaching the receiver is not guaranteed at all places e.g ocean beds. (b) If the black box did had the channel to transmit GPS information (Which it does not have) to back office, it could rather send much more actual data.