Do transponders even work?

[DulceDecorum]

"Turn your transponder OFF as you approach Lake Parker". That is in the official FAA Sun'n Fun arrival NOTAM. Too much traffic, all those airplanes will overload the radar, so turn it off.
Is that a joke? Isn't the whole purpose of Air Traffic Control to keep airplanes from running into each other? And doesn't the chance of collision increase when there are lots of airplanes?
Why do we have transponders anyway? They don't do anything to help the pilot, just take up valuable space on the panel, add weight and battery drain, increase antenna drag. It ain't for us, fellow pilots, the transponder is to help ATC do their job. And their job is to keep us from bumping. So why do they tell us to turn it off when it is needed the most?
Because they can't handle very many replies, that's why. The system overloads and goes haywire. Not at Lakeland, but at Orlando and Tampa where the airliners go. And ATC can't have that!
The problem isn't limited to Sun'n Fun and Oshkosh. Mark Twombly wrote in January AOPA PILOT about flow control through Jacksonville Center that kept aircraft separated 20 miles in trail because of frequency congestion. And this was because of some football game! What ATC didn't tell him was that it's not communications overload, it is overload of the 1090 mhz transponder frequency. Friends, if the capacity and safety of our airspace is upset by a ballgame, we're in deep ----, er, trouble.
http://www.gtwn.net/~keith.peshak/atcrabs.html
http://www.gtwn.net/~keith.peshak/taillight.htm

Excerpts:
September 11, 1999
RE: Transponders becoming invisible
The only replies to the question I posed back in 1995 dealt with similar anecdotal problems...but no explanations. The radar technicians never did provide a plausible theory to this mystery. The FAA certified avionics shop was baffled too, especially since the transponder passed their repeated tests with flying colors. Then, some time later, the problem mysteriously went away. All indications pointed toward the newly running ASR-9 radar...but then something changed. It was sort of like the transponder magically got better. It didn't make sense. I now understand, having read your report, that modifications have been made to the Mode S ground radar interrogations (as described on page 18) to fix the "Terra problem." That is the most plausible explanation as to why these anomalies occurred.
I feel it is important to bring this to your (and the industry's) attention because it attests to the possibility of a more widespread problem in the fleet of GA transponders than may be realized or reported. This concerns me a great deal, as proper operation of transponders is the backbone of the ATC radar beacon & TCAS systems. It is disconcerting to realize that possibly 1 in 5 transponders, those that exhibit this "Terra like characteristic," are likely to be invisible to TCAS equipped aircraft!!!
The pieces of this puzzle all point to Mode S interrogations.
On an unrelated, yet extremely similar topic, I have enclosed a copy of my paper, "Real Targets - Unreal Displays..," as reprinted from the March '92 issue of the Journal of Air Traffic Control. That paper has nothing to do with transponders, or radar, or Mode S. It is purely a radar data processing problem...a result of ARTCC software not being able to handle the voluminous amount of excellent radar data available. However, it results in a similar condition...aircraft becoming invisible to the controller. Having visited Cleveland Center just last June, I observed that the problem still exists.
Sincerely,
Thomas G. Lusch
cc: FAA Administrator Jane Garvey, AOPA, ATCA, EAA, NASA-ASRS, NATCA, and others...
http://home.columbus.rr.com/lusch/talotta.html

James Zerbe, Airport Engineering Specialist of the Wisconsin Department of Transportation in Madison had requested of the FAA regional office that we be allowed to flight demonstrate the system. The FAA response was threat to arrest.
I also discussed the major error in Technical Standards Order C74c dated 2/20/73, the section entitled 2.6 Decoding Performance c Side-lobe Suppression. If you build transponders to work as specified, then you will not see equipped aircraft on the new FAA radar, nor the Airline Traffic Collision Avoidance System.
<snip>
I have received the following "offer" from the FAA: They will "certify" that I said that my system meets TSO C74c, thereby allowing people to use it. They know full well that I have told them in no uncertain terms that it does not. Of course, it does the exact opposite of what is specified in that TSO, or it wouldn't work (ignores a pulse following P3, suppresses on a pulse following P1).
That last sentence is also true for every other aircraft transponder. You suppress on a pulse following P1, in opposition to the TSO, not a pulse following P3, in accordance with the TSO. If you suppress on a pulse following P3, then you will not appear on "radar" or TCAS.
http://www.avweb.com/news/osh2002/184055-1.html

What's going on then?
Let us put September 11, 2001 aside for a moment.
Do transponders ever work?

[buckeye1]

1. The primary purpose..

is to indicate the altitude of the plane. Ground based radar cannot determine it. Thats why there are AWACS type planes they can. Of course,other information can be sent also. After a plane leaves the vicinity of the airport it follows corridors similar to highways that are controlled by regional FAA centers.

Airliners have an on board radar that prevents head on or rear end collisions. If the planes are too close a warning sounds and if no action is taken the plane drops altitude to avoid collision.

[MercutioATC]

2. Your description was a little off...

(Traffic Collision Avoidance System)

It operates in 360 degrees (not just ahead and behind) and provides alerts to possible traffic to the pilot with suggested remedies. It does NOT EVER control the aircraft by itself.

[Flightful]

3. TCAS needs transponders

TCAS interrogates the transponders of other aircraft and will not detect aircraft that do not have them. Also, the transponder provides more than altitude- the original implementation provided for a 12-bit ID code only, altitude and airspeed data were added later.

[DulceDecorum]

4. But do the transponders really work?

If the FAA has accepted that they have major shortcomings with transponders which almost ALL routinely fail tests and also with the technology behind the entire enterprise.

In the 1960's, the United States air traffic control (ATC) system was in disarray. Delays were increasing, efficiency was low, and air traffic was growing at an rate that the system was unprepared to handle. By the end of the decade, a number of converging factors, on several different fronts, came together to solve these problems. The solution was Mode S, an air traffic control data link technology designed by MIT's Lincoln Labs to alleviate the existing problems of the day as well as to meet the challenges of future growth. Today, Mode S is an integral component of the Traffic Collision Avoidance System (TCAS), which is an international standard for commercial aircraft.
http://web.mit.edu/6.933/www/Fall2000/mode-s/index.html

The way I understand it,
the whole system is faulty
and does not now
and never has worked properly.
EVER.

On a good clear day,
with everything going well a
nd everyone doing what they are supposed to be doing,
transponders ROUTINELY vanish off the screen.

THAT is the message that I am getting from a cursory look at the system known as Mode S.
Remember this crash?
http://news.bbc.co.uk/1/hi/world/europe/2115425.stm
Well, it would appear that this was caused by a systemic technological failure.
http://web.mit.edu/6.933/www/Fall2000/mode-s/technology.html