Mode S transponder display to ATC?

On 2008-09-05, Thomas Borchert wrote:
Mode S transponder have the option of setting a flight ID or the tail
number in a data field designated for that info. This is broadcast with
the Mode S data packet and is independent of the unique transponder hex
code. In airline operations, the flight crew normally sets the flight ID
for each flight, e.g. UA011 for United flight 011. In GA operations, the
aircraft tailnumber is set by the installer.

In the US, the tail number is assigned an 8-digit octal number to be used as
the flight ID algorithmically by the FAA. I don't know what other countries
do. Since it's algorithmic, it's possible to go backward from ID 51577524 to
N55ZC.

Controllers with mode S radar equipment have the option of displaying
this data field next to the "blip". I do not know how common such
equipment is in the US, but it is getting more and more widespread in
Europe.

Apparently, it's not used in the US at all.

AFAIK, the big database correlating call signs and hex codes inside the
radar equipment is a myth.

If other countries do it the way the FAA does, there's no need for a
database.
--
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,

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? 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.

--
Thomas Borchert (EDDH)

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.