Mode S transponder display to ATC?

On 2008-09-05, Thomas Borchert wrote:
In the US, the tail number is assigned an 8-digit octal number to be used as
the flight ID algorithmically by the FAA.
Hmm. Do you have a source for that?

Not directly, but I got curious to see how it was assigned, and started
poking at the FAA registration database (which includes the assigned code).
The algorithm winds up assigning 50000001 to N1, 50000002 to N1A, 50000003
to N1AA, 50000004 to N1AB,... 50000032 to N1AZ, 50000033 to N1B, 50000034 to
N1BA,... 50001131 to N1ZZ, 50001132 to N10, 50001133 to N10A, and so on. I
never got to the point of writing C code that would generate the code, but
it would be fairly straightforward. The algorithm depends on the rules for
assigning N numbers, and works left to right, with the letters in order from
A to Z (skipping I and O), then 0-9, taking all of the letter combinations
in order before expanding the number field.

Since every airline flight using a flight number rather than a tail number
for the flight ID field in the mode S data packet would break that
algorithm, it doesn't make much sense to use it in the first place.

It saves having an application process for a code separate from the
registration process. They have to come up with the number from somewhere,
and since they have a block big enough to accommodate every possible N
number, it works out easiest that way.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (FRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC

"Jay Maynard" wrote in message
...
On 2008-09-05, Thomas Borchert wrote:
In the US, the tail number is assigned an 8-digit octal number to be
used as
the flight ID algorithmically by the FAA.
Hmm. Do you have a source for that?

Not directly, but I got curious to see how it was assigned, and started
poking at the FAA registration database (which includes the assigned
code).
The algorithm winds up assigning 50000001 to N1, 50000002 to N1A, 50000003
to N1AA, 50000004 to N1AB,... 50000032 to N1AZ, 50000033 to N1B, 50000034
to
N1BA,... 50001131 to N1ZZ, 50001132 to N10, 50001133 to N10A, and so on. I
never got to the point of writing C code that would generate the code, but
it would be fairly straightforward. The algorithm depends on the rules for
assigning N numbers, and works left to right, with the letters in order
from
A to Z (skipping I and O), then 0-9, taking all of the letter combinations
in order before expanding the number field.

There's no need as it's already been done and put online.

http://www.airframes.org/

Since every airline flight using a flight number rather than a tail
number
for the flight ID field in the mode S data packet would break that
algorithm, it doesn't make much sense to use it in the first place.

It saves having an application process for a code separate from the
registration process. They have to come up with the number from somewhere,
and since they have a block big enough to accommodate every possible N
number, it works out easiest that way.

This is exactly correct. The registration number and the MODES ICAO ID are
one and the same.

The ICAO ID can also be used to selectively address the transponder (the S
in ModeS stands for "select"). So one particular transponder may be
interrogated exclusively by using the unique ICAO ID. Part of the reason
for this is the FAA was concerned about transponder saturation in areas that
have a high density of sensors. The theory was that a ModeS transponder
could be selectively interrogated by one sensor, and that sensor would share
that position data with other sensors within range. This technology was
never implemented in the US for a few reasons, but that capability still
exists within the transponder standard.

On 2008-09-05, Mike wrote:
"Jay Maynard" wrote in message
Not directly, but I got curious to see how it was assigned, and started
poking at the FAA registration database (which includes the assigned
code). The algorithm winds up assigning 50000001 to N1, 50000002 to N1A,
50000003 to N1AA, 50000004 to N1AB,... 50000032 to N1AZ, 50000033 to N1B,
50000034 to N1BA,... 50001131 to N1ZZ, 50001132 to N10, 50001133 to N10A,
and so on. I never got to the point of writing C code that would generate
the code, but it would be fairly straightforward. The algorithm depends
on the rules for assigning N numbers, and works left to right, with the
letters in order from A to Z (skipping I and O), then 0-9, taking all of
the letter combinations in order before expanding the number field.
There's no need as it's already been done and put online.

http://www.airframes.org/

Well, it appears he's written the code, but it doesn't appear to be
available...I'd like to see the actual code, just to check if my thoughts on
the programming required to go in the reverse direction are correct. I'd
also like to see if other countries assign their codes algorithmically.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (FRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC

"Jay Maynard" wrote in message
...
On 2008-09-05, Mike wrote:
"Jay Maynard" wrote in message
Not directly, but I got curious to see how it was assigned, and started
poking at the FAA registration database (which includes the assigned
code). The algorithm winds up assigning 50000001 to N1, 50000002 to N1A,
50000003 to N1AA, 50000004 to N1AB,... 50000032 to N1AZ, 50000033 to
N1B,
50000034 to N1BA,... 50001131 to N1ZZ, 50001132 to N10, 50001133 to
N10A,
and so on. I never got to the point of writing C code that would
generate
the code, but it would be fairly straightforward. The algorithm depends
on the rules for assigning N numbers, and works left to right, with the
letters in order from A to Z (skipping I and O), then 0-9, taking all of
the letter combinations in order before expanding the number field.
There's no need as it's already been done and put online.

http://www.airframes.org/

Well, it appears he's written the code, but it doesn't appear to be
available...I'd like to see the actual code, just to check if my thoughts
on
the programming required to go in the reverse direction are correct. I'd
also like to see if other countries assign their codes algorithmically.

The algorithm is part of the ICAO standard, so if other countries aren't
doing this, they are doing so outside the standard.

If you could find the written version of the standard in the ICAO
conventions, it would probably verify your suspicions, but ICAO standards
are a bit hard to find without paying for a copy as ICAO would like you to
do.

On 2008-09-05, Mike wrote:
The algorithm is part of the ICAO standard, so if other countries aren't
doing this, they are doing so outside the standard.

Uhm...since the US algorithm is quite dependent on the US rules for
assigning registration numbers, it would not work at all for, say, the UK.
(Although, in fairness, the UK's algorithm, as well as that for countries
that use all-alphabetic registration systems, would be quite a lot simpler
than the US one.) That either says it's not in the ICAO standard, or else
there's more than one.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (FRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC

"Jay Maynard" wrote in message
...
On 2008-09-05, Mike wrote:
The algorithm is part of the ICAO standard, so if other countries aren't
doing this, they are doing so outside the standard.

Uhm...since the US algorithm is quite dependent on the US rules for
assigning registration numbers, it would not work at all for, say, the UK.
(Although, in fairness, the UK's algorithm, as well as that for countries
that use all-alphabetic registration systems, would be quite a lot simpler
than the US one.) That either says it's not in the ICAO standard, or else
there's more than one.

I haven't read the standard, but the hard wired serial number in the ModeS
transponder is refered to as the ICAO ID. I'm also quite sure the standard
exists in the ICAO convention.

Peter writes:

The UK CAA have a public database linking Mode S codes with tail
numbers (google on G-INFO) so it would be easy enough to trace a
specific aircraft from the 24-bit ID.

Odd that such a database would be public in a country that forbids listening
to ATC.

Peter wrote:

You would however get into trouble if you recorded ATC and then openly
published the recording, e.g. on a website. I don't know why there is
this sensitivity because UK ATC are generally highly professional;

Maybe a parallel to Germany might help. In Germany, tapping into any
communication not intended by the sender to be heard/read/whatever by
oneself is illegal (regardless of whether there are measures taken to
prevent this) under privacy laws. There are some exceptions, but that's the
general rule. ATC communication is only intended for a limited circle of
recipients. Plane spotters are not the intended recipients, thus, they may
not listen.

It has nothing to do with perceived professionality of the ATC people, and
everything with protecting the privacy of ATC and pilots.

Peter,

which display aircraft
registrations do it by containing software and database to decode the
24-bit code.


Why wouldn't they simply use the flight ID data field?

--
Thomas Borchert (EDDH)

"Thomas Borchert" wrote in message
...
Peter,

which display aircraft
registrations do it by containing software and database to decode the
24-bit code.


Why wouldn't they simply use the flight ID data field?

For one, not all ModeS transponders have that capability as it's implemented
as a level 2 function. I know that many, if not all, areas of western
Europe require a ModeS transponder, but I'm not sure if they require a level
2 ModeS transponder.