[Scan-DC] Squawk Mode 3

[Sheldon Daitch]

Steve,

There is also mode S transponder coding.

A quick review is at:

  http://www.tc.faa.gov/its/cmd/visitors/data/ACT-300/modes.pdf

Also, see a few indented notes below.

Sheldon


Steve Paulson wrote:
> 

> 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.

	True, but Mode C altitude squawk also requires either an 
	encoding altimeter or a blind altimeter (sending) unit that 
	provides the altitude information to the transponder.  On
	occasion, you will hear the ATC request that the A/C not
	give the altitude squawk, if the encoded altitude information
	is incorrect by a certain amount, as this triggers altitude
	alerts for the ATC system.  SD 
	

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

	1200 is pretty much a US standard, but many other countries 
	use different VFR squawk codes for aircraft not in the ATC system.
	Aircraft operating under VFR conditions, but in communications
	with ATC most often are assigned a specific transponder code
	for flight tracking, unless there is not much traffic in the 	
	area. SD 

> 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.

	Aircraft not in contact with ATC and operating under VFR
	would not have a discrete transponder code, but would normally
	be squawking 1200.  Once they have made contact with an ATC 
	facility, they might or might not be assigned a transponder
	code, depending on where they are, where they are going, and
	the traffic in the controller's air space.  SD