NEW AND IMPROVED?

This article was originally written in 1995 and has been changed to reflect recent features in the ADS-B system.

As far back as the 1970s the FAA was looking to replace the current MODE A system with something better: MODE S transponders.  They do seem to perform as planed however they may only be a temporary solution or a stop gap measure.

MODE S is very similar to MODE A with a few additional features.  These transponders are programmed at time of installation with your N#, speed range and aircraft category and this information is transmitted to ATC on the ground.  The benefit to controllers is mainly stress relief because they now have more options and better interfacing to the FAA database. The S in MODE S stands for "selective". With mode S they no longer must view every aircraft under their control at all times.  They can blank out slower moving aircraft,  look at helicopters only or watch it all.

MODE S did not receive a warm welcome from the general aviation public.  Many articles were written warning that "big brother is watching", and spread fear of computer generated violations notices automatically sent out each time a pilot deviates from assigned altitude. In reality this did not occur as predicted yet MODE S never caught on with most private pilots.  Probably because it was never mandated for non-commercial operators, and because the equipment is expensive.

The greatest fault of MODE S is that its designers never envisioned enough far sighted expandability.  It's pretty much what you see is what you get,  which is in these fast paced days of computer evolution, about equal to planned obsolescence.

MODE S did receive some unexpected popularity when GARMIN introduced the GTX-330 with TIS capability.

Terminal Information Service (TIS) is a very attractive feature indeed.  This system permits properly equipped aircraft to view other aircraft in several high-traffic TCAs, assuming they can afford the $15,000 (typical) or so equipment costs.  Most pilots believe this is new technology, however its been around for about 20 years and may not survive much longer.  ADS-B has made its debut along the East Coast, and threatens both MODE S and TIS.

ADS-B does everything MODE S and TIS is capable of, and much more.  Think of it as an "internet in the sky",  aircraft linked to other aircraft on the ground and in flight sharing data with ground stations and each other.  Information such as traffic (type, speed, altitude even N#), weather data both pictorial (NEXRAD) and text, even NOTAMs, all for free (no subscriptions).

The best part is that ADS-B was designed to be expandable.  It already improves your picture of what's happening beyond the cockpit as well as ATCs picture of you and everyone else in flight.  But imagine this:  As industry responds to demand internet based features for extended navigation, flight planning and cockpit resources, email and entertainment, collision avoidance, over the horizon communications more reliable than HF or VHF, even telephone service.  It has even been envisioned that the FAA could reduce its "human factor" by replacing some controllers with computers.  You will read ATC instructions on a screen, no more missed or misinterpreted calls. Weather and traffic alerts will come without delay and be more accurate than the human factor can allow.

Much of this is conjecture however we do know this much.  The system is operational along the East Coast and will expand West, and later North.  Full coverage should be by 2012 if there are no snags.

ADS-B is the reason why we do not recommend or support MODE S.  Why spend money on a soon to be obsolete system when ADS-B is around the corner  It's worth keeping an eye on for now.  In the meantime MODE A is still around and going strong.