Re: Odd aircraft ICAO 123456 and Reg: SPCTRLX Flight: XA0000


Dan Henry
 

On Fri, Jun 12, 2020 at 02:23 PM, Dick wrote:
In a 20 minute period I logged 38 messages from 123456 (Aircraft, Airborne).
Hi Dick,

Total trivia, but I think the VDL2 to mode-s comparison is interesting.

When I saw your original post before any replies my first thought was octal, but for a completely different reason.

On all of the military mode-s and ads-b transponders I have worked with the mode-s code is always entered in octal format.  It is usually originally "hard coded" with jumper wires or by shorting pins by maintenance in a procedure called "strapping."  Then the aircrew can display it and override the entry if needed, but always in octal format.  We also have some military aircraft flying in civilian configurations with normal transponders, also programmed in octal.

US military usually start with a hex of AExxxx.  The crew always sees this as octal 534xxxxx and that is the format displayed in the aircraft "781" maintenance forms and usually on a placard in the cockpit.  Normally mode-s / ads-b code errors that are "typos" do not look like typos unless you compare both values in octal formal.

What surprised me about your VDL2 123456 hex code, is that I had always assumed VDL2 data entry was also done in octal.  The 123456 example seems to indicate that it is actually entered or displayed in hex, the same way we see it.  Either that or the person entering the octal code for that which is not very likely! (grin)

Over the years I have used PlanePlotter data to train and correct many bad military mode-s codes in my area.  I always include a hex to octal conversion in my explanation because the octal value is the only one the aircrew ever sees.

-Dan

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