ASDE-X in US. Why Mode C comment?

[nnc0]

The following note is in effect on the Jepp pgs for FLL as well as several other US airports:

ASDE-X SURVEIILLANCE SYSTEM IN USE: PILOTS SHOULD OPERATE TRANSPONDERS WITH MODE C ON ALL TWYS AND RWYS.

The wording seems to imply you must use Mode C. Does that make any sense? Most large commercial aircraft use Mode S transponders and I'm inclined to think thats sufficient (Mode S XPNDRS interrogate and reply to Mode C equipment.) There is no way to specifically select Mode C.

I guess my question is that if I'm operating a Mode S XPNDR in an ASDE-X environment, am I complying with ASDE-X requirements?

[Radarspod]

I think what they mean is to report altitude when on ground as opposed to not. Your Mode S transponder will reply to Mode S derived altitude requests or Mode C derived altitude requests. The use of the term "Mode C" in this context is confusing.

Rs

[nnc0]

Thanks Radarspod

Certainly sounds like that is the intent doesn't it? I was thinking the message was targetted at operators who turn XPNDR off after landing or at GA aircraft who don't have Mode S but your thought makes more sense.

Caused quite a stir here as folks started running around trying to figure out what we needed to do to make our Mode S XPNDRS operate in Mode C only on the ground.

So then you call the FAA for clarification and they start using terms like ON or STBY which only confuses the matter more when the terms are actually XPNDR functions/switch selections.

Whooo boy - good night nurse!

[Spodman]

As I understand it Mode S is supposed to operated all the time. The only reason Mode C isn't as the discrimination of the regular Terminal Approach Radar is not good enough to stop Mode C returns garbling. Garbling results in spurious returns and the odd emergency code activation. That mouthful-of-letters machine is better than a regular TAR, so the ground returns can be displayed, and should be.

Operate the Mode S all the time. At 'normal' airports select on/C when entering the runway. When this instruction exists on/C when the motors are running.