FLARM for SAR

On Tuesday, November 20, 2012 3:30:04 PM UTC-5, Don Johnstone wrote:
At 11:50 20 November 2012, pcool wrote:

Of course, what else could it be held inside that few characters?

Time of course, Flarm Id, lat-lon, altitude, speed, direction.

The whole story is about sorting out the flarm id from a long list of

collected logs, to understand when was the lost glider before it

disappeared.



The flarm protocol did not change, to my knowledge, after the latest

compulsory update.



Actually all that is needed is ID, time, position (lat/long), and altitude

everything else can be calculated from that data using consecutive fixes,

exactly what a logger does and who has not seen maggot racing?. Breaking

code where the contents of the encoded message are unknown can be a long

process however where you know exactly what the message should be cracking

the code is very very easy.

It all depends on how badly you want to do it and whether using FLARM for

SAR purposes is the best way to go when there are other better suited

devices on the market.

Having said that an instrument that takes on the functionality of FLARM and

SPOT, with the security and reliabilty that such critical devices should

have, would be a major contribution to safety but where is anyone going to

recoup the developement costs? Not from glider pilots that is for sure, the

market is just too small.

So what we have is glider specific instruments, produced with minimal

development costs and almost no certified quality control or an instrument

produced for the GA with official certification, and all the expense that

entails, and never the twain shall meet.









"Roel Baardman" wrote in message

...



I think this is unlikely, as the format of the data in these records is

quite likely the packet format on the air.

It appears to have changed a little from the specification from 2008 (what



was post here at least), but not a whole lot.



I would not be surprised if these records are just packet dumps. This is

consistent with the story of later on finding out what you can do with

them.

Also, I wouldn't want to release their specification if I were to send

them



on air aswell. Encryption over the air was in 2008 not very complicated

(and

the processor used has little room for

complex encryption), so revealing this format (and thus the packet format

on

the air) again opens up the market for protocol-compatible devices. You

could just brute-force the encryption using a

regular PC.



Disclaimer: this is all guessing from what I could read from the data. I

haven't actually decoded these records. And I'm not sure I would want to,

if

it means Flarm will have to change formats

again.





I don't understand all the discussion over how/why to contort FLARM's purpose into SAR application when there are much better devices already purposed with emergency location. The FLARM folks shouldn't be badgered / forced to support every hacker wanting to try their hand at SAR software. Just use a Spot or ELT and be done with it.

-Jim