[Scan-DC] Squawk Mode 3

[Steve Paulson]

I heard aircraft yesterday say "squawk mode three" clearly several times.  I
found references to it at the following web pages:

http://www.ciso.fctclant.navy.mil/Sea_Combat_Air_Controller_HANDBOOK.doc
http://www.atc.gov.tw/chinese/course/PHRASEOLOGY3.htm
http://www.rduafss.faa.gov/reference/xpndr.htm

"Air Traffic Control Radar Beacon System (ATCRBS) is similar to and
compatible with military coded radar beacon equipment. Civil MODE A is
identical to military MODE 3."

" SQUAWK MAYDAY: Operate transponder in the emergency position (MODE A Code
7700 for civil transponder. MODE 3 Code 7700 and emergency feature for
military transponder.)"

Controllers generally leave out reference to the mode.  Mode A/3 simply
seems to be the normal mode in which the transponder replies to the
interrogation signal by broadcasting the code currently dialed in to the
transponder.  Mode C is an additional feature that most transponders have
which reports your altitude to ATC as well.

According to the Taiwan phraseology guide (see link above)--which appears to
be standard--a controller may say "squawk mode 3 five one two niner" or
simply "squawk five one two niner."  "Squawk mode three," however, is a
confirmation of a military aircraft.

If you hear a controller say "squawk VFR," he is referring to the code for
all VFR aircraft: 1200.

Another interesting dedicated code (I hadn't heard of this one before):
"3. Military pilots operating VFR or IFR within restricted/warning areas
should adjust their transponders to code 4000 unless another code has been
assigned by ATC."

Since 11 Sep 01, it seems that all aircraft have been specifically assigned
a squawk code but I haven't been monitoring much civilian traffic.  I
figured it was an effort to make sure there are no "unknown" aircraft out
there but this may not be the case.

--Steve Paulson
DC Metro MD