Transponder issue

[Junkie]

Me finks its tyme for anuder ZA "first" - you know, someone like Mark wassisname to invent a wurldwyde wundergismo and retire laffin al the way to de bank

So hears my solushun

Send cheque for R100.00 to:
FLYIN' F*@K - Yes we do.. the new Wundergismo thats gonna save the wurld

We will return forthwith to u your very own personalised BLIP and Share Certificate, entitling you to free transit through any FA's of you's choice and a brighter tighter Mid-Air free new ZA

.. else they can just keep widening CTR's and dropping TMA's untill were outta bounds and up shit creek anyway

[krusty]

My post on Avcom regarding same topic:

Dougie,

Something I've been wondering about. How close together can 2 transponders be without corrupting each other's signal?

I'll explain:
The nature of a transponder is interrogation and reply, but if 2 a/c are within say 1/2 mile of each other, they're going to rx the interrogation and then tx the reply at pretty much exactly the same time. If this happens, you're effectively going to have a double transmission and the SSR won't be able to "understand" the garbled reply.

Extrapolate this to a nice Saturday morning where you have gaggles of anything from 1 to 10 microlights all taking off around sunrise from about 4 or 5 little airfields just outside (or below) the FAJS TMA. Surely this high concentration of replies is going to cause enough double transmissions to render the system effectively useless for that specific gaggle at that specific time?

I know that the tx is extremely quick and all that, but in my mind, when you're flying almost wingtip to wingtip with a whole lot of a/c, all the transponders are going to reply at effectively the same time.

Yeah, I know, distance to a/c from SSR * speed of light / (number of bits TX'd * "baud rate" of TX) = something or other. I've had too many beers to figure out what the calculation would actually be.

Point is, is this a valid technical issue or not?

[Junkie]

Jokes aside, really do hope that a cost effective solution comes up soon - in process of trolling the WWW for a nice Stick & Rudder, little wheel on back a/c (SAVAGE looks real nice so far) and want to be able to transit controlled airspace without fear or resorting to "ducking under the radar"

Everytime I try to get clearance, I get the run around and nine times outta ten left orbiting somewhere and forgotten, or told to get lost

Is it just a case of
... have TCAS, just ban the buggers, because we dont want to be bothered by the prospect of ever having to take avoiding action.....

Can understand that the guys with TCAS dont look forward to a having a dozen or so dudes painted, all potentially at or near the same altitude, uuuhhm i wonder.. do their devices tell them direction one is flying too, if you had a Mode C/S? class transponder on board ??

[Arnulf]

Junkie wrote
do their devices tell them direction one is flying too, if you had a Mode C/S? class transponder on board ??

No not actually. You just see the intruder traffic as a target moving on your navigation display. To a certain degree you can estimate the direction of the target. Gets a bit difficult if you travel at 450 kts, and the intruder at a fraction of that speed.

Regards,
Arnulf

[FAWGie]

I agree with demon...we are fighting the inevitable of the future......
If Mode C on your plane along with compulsory TCAS on fast/large metal makes it just 50% safer to prevent a mid-air, then it is worth it.....

By the way, Mode C units and TCAS are all calibrated to the same QNH reference (Like 1013mb), so the height differential reported on TCAS is realible....

[ZULU1]

By request from Alan Mackenzie...my last trike (CEW) i had a Mode C transponder from a glider. I made the antenna, mounted in a nice housing etc. It was not a problem fitting it and I made it removal with quick releases plugs. The antenna stayed in situ.

Anyway, he has requested a survey, the antenna we will make locally, and possibly laser cut and bend grd planes and brackts to suit Windlass, Aquilla and Aerotrikes. The main toys out there. I intend to approach large manufacturers with a view to a bulk purchase (prefer Mode S), this I believe looking around should be about ZAR14k all in. Now the greater plot is to make them interchangeable.

Any interested parties please send me a email rabbit1@telkomsa.net.

My thoughts on Transponders...well ATC in Deben, they treated me as a Gentleman, very, very pleasant and allowed by to fly through the airspace. Just follow the rules. Yes it was just great for South Coast runs from Ballito. A pleasure to have. Another feature is if you do get lost or whatever...you are squawking and they should see you....

ZULU1

[Fairy Flycatcher]

Yesterday I flew a PA28 from FAVG to Siteka (near Midmar Dam), and the idea was to fly flight levels. My transponder (newly repaired) packed up as I left FAPM. So Durban Approach told me to descend below the TMA and keep out of their airspace. What will happen if transponders are compulsory around a TMA as well? If for whatever reason my transponder stops working, electrical fault, etc. Must I get out of the TMA, and its environment? What does that leave for "alternate aerodromes" in your planning?

I also agree with krusty and RV4ker about the practical implications of this proposal as well. It will just not work!

A much more practical solution comes from Joe and Steve:

From SaMicro:

Joe Holmes:

Mike,
Small yachts carry lightweight radar reflector units that are suspended
off one of the mast crosstrees. These are tubular in design, about 400mm
long and 90mm in diameter, and have numerous aluminium reflector pockets
within the tube. It could be productive to mount one or more of these onto a
microlight and get them tested by ATNS radar to see if they give a big
enough footprint to make them viable. If effective they would enable primary
radar to "see" them well enough at a fraction of the cost of a transponder,
and with no electronic or mechanical parts remain functional constantly
without the pilot having to switch them on.
These reflectors are available from most yacht chandlers. Their shape
dictates that they could easily be fitted to say the kingpost, inside the
wing to the wing tubes, on the main pylon or on the undercarriage legs for
instance without adding to drag substantially.
If this design proves to be acceptable then the next step would be to
have a similar honeycomb lightweight foil extrusion manufactured and
inserted into the interior all the aircraft tube at a fractional increase in
weight, where it would serve as an out-of-sight but still operational
reflector medium. The large quantity able to be thus carried may then give a
very acceptable radar "footprint" to the enduring satisfaction of ATNS.
Cheers time being
Joe

And then Steve McCurrach

I believe I can help and I really do like Joe's idea - it very possibly
solves the problem, prevents ATNS creating an overkill (transponders)
solution and its cheap.

I have a Rainbow Cheetah - Mode C equipped, which without activating the txp
I believe would probably reflect about the same visual signature as a Trike.
How about I light up the Mode C txp and go fly a route around Durban
International without the yacht reflector, thus enabling the ATC to safely
monitor my position/separation whilst simultaneously watching my visibility
on the old primary radar. Of course I then go back around the same routing,
with the yacht reflector on board and they measure the difference, if any.
(Afterthought - my hanger mate Mark also has a Mode C equipped Cheetah, so
you guessed it; we fly a loose formation, one with a reflector and one
without.)

My employer owns a yacht with just such a reflector in the rigging, so if
you promise not to tell him, then I'll shimmy up the mast this weekend and
liberate it, in the name airborne freedom. I am also well enough acquainted
with the manager of Durban ATNS that I will go and 'do tea' in the coming
week with Kevin and set all of this up.

[Cloud Warrior]

See http://www.dg-flugzeugbau.de/radar-reflector-e.html

Looking at mounting radar reflectors in gliders to improve radar visibility.

[ICEMAN]

The reflector idea seems practical, and lightweight.

I do not have the odd or spare 10-15k just lying around and im sure most recreational pilots fit the same criteria.

The same portable 'reflector' principal is used in ocean lifeboats, when 'painted' by radar it sends a strong reflection back......... it works well.......

[Arnulf]

Hi,

Iceman wrote:
The reflector idea seems practical, and lightweight.

I doubt if this is a solution. This will only work with primary radar. Thats what naval okes have. To my knowledge ATNS is in the process of withdrawing primary radar, and replacing it with secondary radar. For secondary radar you need a transponder to be visible.

As far as I am concerned, transponders are of little benefit to microlights that stay out of controlled airspace. Only the heavy bliks have TCAS, and generally they fly in controlled airspace. As a microlight pilot I would be worried about a midair with a GA aircraft in uncontrolled airspace. Unfortunately with all these modern and fancy nav equipment lots of time is spent head down, not looking outside.

Regards,
Arnulf

[Arnulf]

Finger trouble!
Post deleted by Arnulf

[ICEMAN]

I doubt if this is a solution. This will only work with primary radar. Thats what naval okes have. To my knowledge ATNS is in the process of withdrawing primary radar, and replacing it with secondary radar. For secondary radar you need a transponder to be visible.

pity about that, i was hoping to annex a few boxes of tin foil from Mrs Ices kitchen and wrap my wing.....

so let me get this straight: Primary radar is passive, it paints the target and interprets the reflection.. the newer secondary radar systems relies on the A/C actively announcing its presence by tx??

Will secondary radar be effective with the well used second (or third or fourth) hand aircraft used for passengers, operated by some of these small african countries that are renowed for poor maintanace of their craft......

[unicorn]

Yes, the advantages of secondary radar over primary radar are that aircraft can be positively identified with the aircraft's SSR code or call-sign displayed on the radar screen, usually together with the aircraft's pressure altitude, its groundspeed and the rate of climb or decent.

When a Mode C transponder is installed in the aircraft with an encoding altimeter, other aircraft will be able to see the altitude of the aircraft displayed on the screen.

Mode S transponders, which answer only when inerrogated, are also used in Traffic Collision Avoidance Systems (TCAS), where the aircraft's transponder interrogates the transponders of near-by aircraft and display that information in the cockpit. Airborne Collision Avoidance Systems (ACAS II) take this one step further and also offer a traffic resolution to the pilot.

[DarkHelmet]

Transponders are so archaic! Surely there are slimmer more advanced and more accurate systems available (not to mention less pricey?)

Our skies are unfortunately dominated by the think big think expensive technology mindset that a cost effective alternative is not an option.

Personally, yes, if it makes the skies safer and is the only technology available I fear we will have to give in. But as stated before, years ago people were up in arms about radios. I shiver and cringe when I take off without mine!

[Lester]

The ability of ATC to know the position of every aircraft in their area is obviously great but has a number of associated difficulties.

1. The use of Primary radar to detect aircraft is limited to a blip giving a distance and a bearing but without altitude information. In addition, microlights will in all probability appear and disappear as the radar's noise rejection algorithms come in to play as they are considered to be too slow for a real aircraft. It will be up to the ATC to interpret whether a target is real or not. My guess is he'd rather be doing other things. I doubt that a radar reflector (as used by yachties) will improve visibility significantly but I suppose its worth investigating. Also, without a transponder, aircraft will not be visible to other aircraft using TCAS equipment.

2. The use of SSR is preferred by ATC because every target is known to be a REAL aircraft. Unfortunately there are many problems associated with this technology particularly when congestion takes place.

An aircraft transponder is triggered by the SSR every time it sweeps past (every 12 secs) and this goes for all transponders on the same radial at any altitude. When more than one transponder resonds at a time, all but the very strongest of signals will be obliterated in the resulting noise. The SSR has a very clever solution to this loss of signal - It simply predicts where the aircraft were based on their previous tracks and speeds. There is a story of one of the 911 airliners (which stopped abruptly inside a tall building) being tracked for some minutes into upstate New York before finally "crashing". I can imagine that with the random meandering that most of the microlights I've seen, following suitable emergency landing sites or just the pretty sites, such predictions would be hopelessly wrong.

Adding to the interference would be the TCAS of suitably fitted aircraft intorrgating transponders in its vicinity. Once again, mutiple transmissions will cause all responses to be lost. The more transponders there are, the less reliable the system!

Microlights will probably also have very poor transponder installations. Not because of poor workmanship but because of poor transmission platforms lacking a good ground plane. Power output (200W albeit for a very short duration) is very high for our limited supplies. Also to be sitting with your sensitive bits only inches away from a microwave antenna chirping every few seconds is not something I like to think of.

If the problem is "collision avoidance in controlled airspace" then to my mind we should be avoiding entering the airspace in the first instance rather than the detection of transgressors.

GPS units are a dime a dozen now (relatively) and can surely be loaded with a suitable database of controlled airspace details such that anyone venturing too close can immmediately be warned. I'd rather be forced to carry a suitably configured GPS unit than splash out on a transponder. The GPS even has other uses besides policeing (OK so the transponder can also be used to cook bacon and eggs at the next breakfast flyin).

Other collision avoidance devices (based on GPS) also look promising but perhaps its early days to consider fitting these to all aircraft.