Black box replaced with continous data transfer?

[Spinnor]

If the amount of data contained in a aircraft black box was not too large could such info be sent out on an additional aircraft radio channel and collected for all aircraft in real time thus eliminating the need for physical black boxes? At least then we would not have to search the bottom of oceans for them.

Thanks for your thoughts.

 

[FredGarvin]

That's a good idea. While I can think of big issues that would have to be worked out, I can see one major problem right off the bat;

When an aircraft is in flight, it gets "passed" along to various controllers along the way that monitor it and keep in contact with it. This same procedure would have to happen with the transmittal of flight data as well all the while maintaining integrity of the data (or they would have to be able to transmit incredible distances). I am not in that area of engineering, so perhaps that wouldn't be such a tough thing, but I would think that would be a real hassle.

 

[Danger]

For continuous coverage, would it be possible to piggy-back the data stream on the GPS signal?

 

[Mech_Engineer]

For continuous coverage, would it be possible to piggy-back the data stream on the GPS signal?

GPS is one-way (as in the satellites only transmit, the receiver only receives) but the idea of a global satellite network to cover the planes seems like a feasible (albeit expensive) one.

 

[FredGarvin]

I am not any kind of expert or even play one on TV, but in the case of GPS, I think we're talking about transmitting a signal versus receiving one. The aircraft is now the transmitter, not the satellite.

 

[Danger]

GPS is one-way (as in the satellites only transmit, the receiver only receives)

Now I'm confused. Don't things like LOJAK and cell phones transmit GPS signals? If not, how do they track cars and phones and cargo containers?

 

[Pengwuino]

Now I'm confused. Don't things like LOJAK and cell phones transmit GPS signals? If not, how do they track cars and phones and cargo containers?

http://en.wikipedia.org/wiki/Lojack#How_it_works

LoJack apparently works on typical radio frequencies. Cell phones with GPS capabilities actually have GPS receivers built in. As far as the GPS thing, I always thought GPS satellites only transmit and the receiver does all the calculations based off of the signals from the satellites. I have a feeling tracking is done off separate satellites.

 

[mgb_phys]

Cell phones with GPS capabilities actually have GPS receivers built in.

Some do, others use cell towers to triangulate your position. Older GPS chips use a lot of power to do the calculations, the newer ASICS are a lot better.

As far as the GPS thing, I always thought GPS satellites only transmit and the receiver does all the calculations based off of the signals from the satellites. I have a feeling tracking is done off separate satellites.

The tracking is normally done over GSM by sending SMS messages

Modern commercial aircraft do transmit a diagnostic messages via VHF radio link as small text messages, called ACARS.
Some planes also send a lot more data over their satelite data links.

Rolls-Royce for example, lease the engines to the airlines and constantly monitor the engine performance, the system I saw logs about 1Gb of engine data on a long flight. It's stored on removable hard drives in the engine management system. On planes with internet they can also send a lot of this data back live so the airline get notified about upcoming maintenance before the plane lands, they can also advise the crew of any potential problems well in advance.

 

[FredGarvin]

If a LoJack unit is activated, every police car within a 2-3 mile radius and equipped with a tracking unit will automatically be alerted that the vehicle is near.

There you go. It is radio based, not GPS and because of the size of the transmitter, has a pretty small range.

The GPS receivers do the location calculations based off of triangulations between at least 3 satellites. So your handheld device just has to be a receiver. I wonder how much power a GPS satellite transmitter is...I am sure I could find it easily if I had the gumption to do so.

 

[mgb_phys]

I wonder how much power a GPS satellite transmitter is...

It's tiny , about 50W. The receiver does an amazingly clever correlation on incredibly weak multiple signals on the same frequency.

 

[Danger]

Okay. Thanks for the clarification, guys. It makes more sense now.

 

[Pengwuino]

The GPS receivers do the location calculations based off of triangulations between at least 3 satellites. So your handheld device just has to be a receiver. I wonder how much power a GPS satellite transmitter is...I am sure I could find it easily if I had the gumption to do so.

This is a tad bit off topic but a friend and I were wondering how many GPS satellites are required to theoretically and practically determine your exact location (altitude included). I would think you need 4 satellites to determine your exact position. Why do you need just 3? I've heard you need 3 but that it doesn't determine your altitude. That doesn't make too much sense to me since only 3 should simply reduce your possible positions to 2 points, not 1 point with an unknown altitude.

 

[MATLABdude]

GPS is one-way (as in the satellites only transmit, the receiver only receives) but the idea of a global satellite network to cover the planes seems like a feasible (albeit expensive) one.

Why not use the existing satellite network?
http://en.wikipedia.org/wiki/Satellite_phone

Still expensive, and the number of planes in the air, all simultaneously transmitting telemetry, instrument status, etc. would probably consume a great deal of the available bandwidth. That or they'd just text their status:

<PI_IN_SKY_AC314: 06-03-2009 1:31:00 AM> c'ing skys ov blue
<PI_IN_SKY_AC314: 06-03-2009 1:31:10 AM> clouds o white
<PI_IN_SKY_AC314: 06-03-2009 1:31:15 AM> bright blessd days
<PI_IN_SKY_AC314: 06-03-2009 1:31:20 AM> dark sacrd nights
<PI_IN_SKY_AC314: 06-03-2009 1:31:30 AM> and me think to mesef
<PI_IN_SKY_AC314: 06-03-2009 1:32:00 AM> OMG fire n ngine 3!
<PI_IN_SKY_AC314: 06-03-2009 1:33:00 AM> ...OMGWTFBBQ?!

 

[Mech_Engineer]

This is a tad bit off topic but a friend and I were wondering how many GPS satellites are required to theoretically and practically determine your exact location (altitude included). I would think you need 4 satellites to determine your exact position. Why do you need just 3? I've heard you need 3 but that it doesn't determine your altitude. That doesn't make too much sense to me since only 3 should simply reduce your possible positions to 2 points, not 1 point with an unknown altitude.

1 satellite gives you in theory enough information to be located somewhere on a sphere's surface. Trilateration from 2 satellites will give you two overlapping spheres, so your location is somewhere on a circle (at this point some receivers can assume the third required sphere is Earth at sea level). A third satellite can give you two intersection points (if you assume you're on the point "closer" to the Earth, you're done although not very accurate due to measurement error). More than three satellites will be able to give you increasingly accurate positioning information.

Basic Concept of GPS

Article on Trilateration

 

[mgb_phys]

Why do you need just 3? I've heard you need 3 but that it doesn't determine your altitude. That doesn't make too much sense to me since only 3 should simply reduce your possible positions to 2 points, not 1 point with an unknown altitude.

With 3 fixes you do have two points, but one is one is on Earth and the other is one orbital height above the satelites - which is not usually the case unless you are really lost.

In all practical cases you need four to also give you the time correction. I seem to remember the original design was to use 3 and be able to ID the individual satelites and together with their known orbits calculate the time correction - I don't know if this was ever implemented on the original military kit.

There are 31 active satelites (out of an intended 24) and usually about 6-8 above the horizon depending on where you are. So most commercial receivers are 12 channel and can track 12 signals, this doesn't stop manufacturers advertising units with 48 and 60 channels!

 

[gmax137]

Back to the original topic, I think* the reason planes have the black boxes is so that, in the event the power / radio goes out, there is a record of the subsequent events. I thought the black box is a recording system, which is independent of the systems whose failure could lead to a crash. So, unless the data streaming from the plane to some remote receiver is powered by a redundant, self contained, blah blah blah system, it just doesn't meet the same specs as the black box.

*Maybe I'm way off base here, since I have no idea of what I'm talking about.

 

[mgb_phys]

Back to the original topic, I think* the reason planes have the black boxes is so that, in the event the power / radio goes out, there is a record of the subsequent events.

The reason for having a black box is that it's required. Aviation is rather conservative and there are a lot of aircraft out there that would need upgrading. The main reason for fitting direct data links is to save money - by scheduling maintenance or replacing components in advance.
The drawback of the black box is that you have to find it.

I thought the black box is a recording system, which is independent of the systems whose failure could lead to a crash. So, unless the data streaming from the plane to some remote receiver is powered by a redundant, self contained, blah blah blah system, it just doesn't meet the same specs as the black box.

The black box doesn't contain it's own power source so in the event of an electrical failure there is no further data recorded. This has been a problem in a few accidents. There was a suggestion that it should carry 30mins of backup power but there is a concern that it would enable the device to keep recording and overwrite the critical data - the cockpit voice recorder only records the last 30mins.

 

[gmax137]

The reason for having a black box is that it's required.

Ok... so why is it required?

The black box doesn't contain it's own power source so in the event of an electrical failure there is no further data recorded.

Wow that surprises me. But like I said, I don't know anything about this. Thanks for the correction, mgb

Gregg

 

[mgb_phys]

Ok... so why is it required?

The idea came about before data links. The first black boxes were fire bricks with holes in them and asbestos washers. Test pilots put a washer into a labelled hole to indicate what had gone wrong - before they crashed!

There are two flight recorders, the data recorder shows the position of the controls and some data about the flight, it's fairly low data rate an on modern aircraft much more data is sent back over the data links form the engine management etc.
The cockpit voice recorder stores the communications and sounds in the cockpit, it only records the last 30mins but would take a lot more bandwidth to send back live.
There are also legal implications - the pilots object to being continuously recorded at work - especially in a country where a comment about one of the cabin crew could mean a $M harassment claim. Fairly reasonably they claim that safety would be impacted if they were constantly thinking about not saying anything to upset the company, FAA or colleagues while flying.

Most US airlines and pilots associations resisted fitting the full instrument package that BA uses on the grounds that it would leave them liable for every slight violation. I think in the end it was agreed on the basis that it wouldn't be used to measure individual's performance.

Wow that surprises me. But like I said, I don't know anything about this. Thanks for the correction,

Since the data recorder records data form the flight instruments it makes sense for it to be powered by the aircraft, if you have no aircraft power then there is no instrument data to record anyway. The CVR could provide useful data in the event of a total power loss but as I said there is a concern that if it ha batteries it could overwrite data after a crash