Transponders for Sailplanes
No doubt a transponder in a sailplane would provide a measure of extra flight safety. Because of the almost total installation of anti- collision equipment in commercial transports - based on transponder data - dangerous situations with our "large competitors" can be almost completely eliminated.
Furthermore, there is a tendency to shrink the airspace for transponder participants by the installation of TMZ (Transponder Mandatory Zones). We will probably have to learn to live with the idea that in most places of the world flying without transponders will only be possible with considerable restrictions.
On the other hand the installation of transponders in sailplanes poses a number of difficult problems.
First of all, there is the question of power supply. Transponders in motor air planes need up to 1.5 ampere of power while transmitting, and 0.5 Amps while in stand-by mode. Even the large on board battery of a DG-808C would be strained to it's limits on a long flight. Some other transponders can operate at about half the above power drain, but one should install solar panels on the upper fuselage together with a transponder. One solar panel on the instrument panel would surely be insufficient.
The antenna installation in a fiberglass fuselage should pose no problem, since fiber glass is "transparent" for radar rays. This is completely different in the carbon fiber fuselage of a DG-808B:
The fuselage acts like a "Faraday's Cage" and therefore the antenna has to be placed outside the fuselage, for instance behind the main wheel.
The greatest difficulty is in the installation of the rather large instrument.
The usual transponders for motor air planes (King, Narco, Collins, ARC etc.) are usually too large. A breadth of 16 cm and a depth of 30 cm is not workable in the instrument panel of a single seater.
The old version of the TERRA by Trimble would fit in our instrument panels. But the new version is so long that installation becomes impossible. And it has no certification in Germany.
The split instrument by Becker-Flugfunk would fit better. The service module of the size of a 58 mm instrument would probably fit into any instrument panel. The other module could be put into the luggage compartment where it would not cause a problem.
In addition to the cost of a transponder, and it's installation we have the annual inspection by a licensed shop.
And finally we have to consider that in the future all transponders should operate in "Mode S" - and there are no such instruments suitable for installation in sailplanes.
Our only recommendation at this time is:
Wait and See. Wait until the authorities will have defined the standards of certification.
Please do not send us just any transponder with a new order for installation in your sailplanes, since this is often technically impossible. Please ask in advance.
Ruud Holswilder gave us his comment:
Very interesting article about transponders on your Web site.
I like your statement:
> No doubt a transponder in a sailplane would provide a measure of extra flight safety.
Because this is true.
Most of the "heavy metal" planes nowadays are equipped with TCAS (traffic advisory and collision avoidance system). TCAS functions via a mode S transponder for data communication with other TCAS equipped aircraft. This enables them to co-ordinate evasive action by climbing or descending away from a possible collision hazard.
TCAS is able to communicate with up to 50 other TCAS equipped aircraft.
TCAS is also able to see other , non TCAS equipped traffic that are using a mode A or C transponder.
A mode A aircraft is only seen as a target without altitude label (2D) and will generate a "traffic, traffic" voice alert when you are coming to close (proximity warning).
When the aircraft has a mode C transponder, a altitude label relative to the altitude of the TCAS equipped aircraft is displayed (3D) and will not only generate a "traffic, traffic" alert, but also give a resolution advisory (RA) for evasive vertical action to avoid a collision when needed.
So a glider flying in or near congested airspace will be much safer using a transponder.
There is one type that I missed in your listing:
The Garmin GTX320
This will drain a 12 Volt battery at approx. 1 AH.
The size is still a bit large for some gliders.
I'm also puzzled by the transmitter power of 200 watt pulses. I don't think it's healthy for you to have the antenna close to you in the cockpit. I rather would have it somewhere in the tail section.
Best regards, Ruud Holswilder (glider and "heavy metal" pilot)
A very interesting additional piece of information from someone who should know.
In February of 1999 there was a collision between a glider and an Airbus at Montpellier, France.
The Airbus took strong evasive action which lightly injured some passengers. Even so, there was a slight contact that scratched the Airbus but left the glider still able to fly.
But there was contact!
It is unimaginable what luck, not only the passengers, but all of us glider pilots had.
If the glider had had a transponder, probably the mishap would not have happened at all!
Installing a Terra Transponder in a DG Glider
The following e-mail came from Marc Silverman
Hi Karl, I thought I would let you know how I installed the newer Terra transponder in my DG-300. I traded places with the radio which is usually installed in the pedestal base that holds the panel. The Newer Terra transponder is of course longer, but by angling the rear end of the unit down I was able to get the unit in with out sticking out the front of the pedestal base. The radio is now in the panel. I do have a custom panel that is larger than the factory DG panel but I still thought that the on the factory panel you might be able to fit a radio in depending on the other instruments.
Good Flying Marc Silverman WV
New Insights from the AERO in Friedrichshafen
Commercial aviation increases by 5% every year and determines the future developments in the airspace.
It also determines politically what can be demanded.
To minimize the safety margins in the airspace, and that is the only way the increased traffic can be handled, more precise procedures are necessary.
The military have to consider this, too.
"Eurocontrol" has been given the political task to manage a smoother traffic flow without detours and waiting times.
For the future security of our flights in controlled airspace outside airspace "G" (above 2500 ft.) it will become necessary for all aircraft to be equipped with transponders.
The following must already be equipped with an "S mode" transponder:
- every IFR aircraft, and every new VFR aircraft from 2003
- all aircraft in airspace which requires transponders from 2008
"Aircraft" means ALL aircraft, including sailplanes, kites and ultra lights . For presently licensed aircraft installation it must be complete by 2008. That was decided as binding by the "Eurocontrol" in Maastricht. But "S-Mode" transponders for sailplanes do not yet exist, and the manufacturers are at this time not willing to develop one, because the necessary standards have not been developed yet. They are waiting in great anticipation for the government agencies to get together to set standards, and only then to resume the development of a small S-Mode transponder and to license it. At the same time the prevailing opinion is that the proposed deadlines cannot be achieved anyway.
Certainly not all ground stations of the air control will not be updated by then and only then would a introduction of S-Mode transponders be meaningful. It is quite possible that there will be delays, and that perhaps sailplanes can be equipped with Mode A/C transponders.
Transponder Modes
It would make sense to clarify the various transponder types in light of their development history.
A
I'm sure you are aware that the radar beam of the air traffic control incites the transponder to respond, in the case of Mode A by means of a light point next to the transponder generated number. The controllers used to see not only a small dot as the primary flying target but instead a light space containing the identifier. The paper strip in front of them, and which was continuously updated by their assistants, showed the detailed data of the aircraft behind the identifier. These radar units, which showed the controller on his screen the conditions directly in front of the radar antenna, are not in use any more.
C
Soon the transponders with altitude encoding appeared, the "Mode C" . They contain an altimeter. That means a connection to static pressure. When a transponder is hit by the radar beam it responds with it's identifier and the altitude. Radar antennas these days have a range of several hundred kilometers. With this radar a precision approach to a distant airport is possible. The controller also receives an updated computer view of the airspace by remote transmission. All non relevant echoes, such as mountains, moving trains or high-rise buildings are screened out. Air space limits, control zones etc. are put into his picture. The primary target is shown on the computer screen as a small cross. The target shows identifier, altitude, speed and course. The latter are calculated from several data by the computer. The controller receives a clear picture of the targets He can remove targets he does not want, such as VFR aircraft identified as below 5000 ft. Of course he can no longer give them traffic information.
With the increase in air traffic came a technical problem. The radar bean has a width of about 3 degrees. All the transponders in this small area respond with their code as soon as the radar beam hits them. A major installation can handle up to ten codes simultaneously. But if on a nice Sunday several hundred VFR air planes are about the situation has arisen where the targets could no longer be properly separated, with the result that the important echoes of commercial traffic disappeared in the maze.
The controller can erase the VFR echoes, but when the radar con not read them anymore the legibility of the remaining echoes is not improved. In addition, the military with they friend/foe identification system uses the same frequencies. Because of these problem it has been decided to close down the Mode A/C. But when?
S
Faced with these problems the new Mode S standard was developed but unfortunately was not completed. With a Mode S transponder the radar "knows" which targets are in the area. This knowledge is gained because the radar beam transmits further coded information and asks: "Who is new in the area?" Only the transponders which have not previously replied will respond giving altitude and identifier of the aircraft. The radar selectively calls on the transponders whose information is to be considered. Unimportant targets are not queried at every antenna revolution, but only after given seconds or minutes or not at all. In this way the radar works only as many targets as it can handle and sets aside those at great distance from other aircraft or in a height band that is not of interest.
This is similar to the TCAS System of the heavy transports, which operates on the same frequency, and only calls transponders in aircraft on a possible collision course. The capacity of the Mode S system is several thousand times greater than the A/C System.
In the future everyone should be able to fly everywhere. Control zones are no longer needed because targets on a collision course are warned in time and can change course. Will that ever become reality?
Current Drain
For us soaring pilots the Mode S system means additional cost, but also additional safety. It has another advantage. Because the transponder has to respond only infrequently but requires an impulse of 250 watts (only for a few thousands of a second) the current demand is considerably less and saves the cost of solar panels etc.
"Eurocontrol" is also considering that a small aircraft transponder has to have a "low power" warning. It won't do to have a target suddenly disappear because the battery gave up it's ghost. The discussion of these problems is
not over.
Market Observations
Becker as well as Filser offer a transponder with a 56 mm service module and a separate instrument housed in the baggage compartment Prices were quoted by Becker of Euro 2,700 and by Filser of Euro 1,800 without taxes or installation.
Most interesting was a French product offered by the Zimmermann company but which is not be licensed in the moment. Price is also Euro 1,800, but the entire instrument will fit in the instrument panel. No other unit is necessary.
Such a transponder can be used at least until the year 2008, but probably much longer. We think this is a real innovation and can improve safety considerably.
Antenna
The installation of the aerial is quite easy. Because of the strong impulse it should not be put next to the pilot. It won't make you sick, but it doesn't contribute to your health, either. There have been no adverse effects among the manufacturer's personnel. The emission of the antenna has to be downward, so the area behind the landing gear and before the fuselage gets small, would be a good location. It would also prevent antenna damage if you land gear up. The antenna is a short piece of wire or could be an aerodynamic fin.
- friedel weber - May 1999 -
translated by Albin Schreiter CDN
New facts from the Aero Exhibition 2001
The most significant knowledge after going over the past article is: “ Nothing has actually changed regarding the unclear situation concerning the specifications of future transponders. The responsible bodies of experts have not come to an agreement on the specifications. Therefore no developer has even begun developing a "Mode S" transponder so far. What should he develop?
What is known is the fact that the controlled airspace will be greatly widened. An entry to controlled airspace will only be granted with a transponder. This can not be achieved with mode A/C transponders due to the fruit problem. The radar facilities would be overloaded. The "Mode-S" transponders will come resulting in a mandatory deployment in all aircraft even for paragliders.
The small French transponder distributed by Zimmermann is, to our knowledge, still not available.
The mentioned Becker Transponder with a separate operations and transmitting device has recently been substituted by a new, smaller transponder. That transponder is ready to be approved and sold in the last part of 2001. It is - to our knowledge - the best Transponder for gliders due to it's size (57 mm and 192 mm in depth). It consumes roughly only about 0,4 amp for transmitting and receiving. It appears to be well suited for every glider. The transponder only weighs about 725 grams.
It's believed to be sold for about € 2000.-- in addition to the altitude encoder, antenna an deployment. The whole system should run at about € 2.500 + tax.
But then there is still the risk about the operation time for the "Mode A/C" transponder. The final date is still 2005 but is extended up to 2008, if the glider already has an A/C transponder.
Then there is finally the device from Filser that is similar to the device from Becker. It differs in the following cases:
There is no separate altitude encoder required. It's included. The price should run at about €2100.- It's believed to be approved in the last part of 2001.
The development is based on the idea to simply change the basic layer in the transponder once "Mode-S" is approved. That way the operation and handling of the transponder would be the same. Only the electronics would have to be altered. It's certainly an impressive idea to grant security of upgrades and updates in the future.
But it has to be seen if such a slight alteration is practicable at lower costs than for a new transponder. Only the future will show that.
Safety conscious pilots should now deploy transponders to their planes even if it's only for 4 – 7 years. For all others the saying: “Wait and see” is the way to go.
Betreff: Transponders
Von: Pecklund
Dear Sir:
Thanks for the transponder articles. I have a Terra 720 installed on my carbon fiber glider. I placed the antenna on the top of the instrument shroud in the cockpit. There has never been a weak signal as verified by Air Traffic Control in the Denver Class B airspace. I cannot comment about the health risk from mounting it at that location. I get clearance to fly in Class B airspace, if the traffic configuration for Denver International Airport allows it. Sometimes they will allow me to follow cloud streets that curve in non-linear directions. I am enthusiastic about the safety it provides me from jet traffic with TCAS installed which directs airliners to make evasive maneuvers in case of conflict.
Phil Ecklund
Boulder, CO