|
     
|
    
|
TransponderThere is a lot of discussion going on around the requirement to carry a mode-S transponder for VFR flights in Europe. An official deadline, 31. March 2008, by which all aircraft performing VFR flights have to be equipped, exists. This date has however slipped in the past and there seems to be a lot of hope in the general aviation community that this will happen again. For me however the case is made easy by the Swiss Federal Office for Civil Aviation, which requires Mode-S for all aircraft which are issued with a first certificate of airworthiness on or after 31. March 2005. The question for me is therefore not which type of transponder to select but only which product. Mode-S Transponder exist in 4 different levels with increasing functionality. Most available transponders for General Aviation purposes are level 2. This level is also specified as minimal requirement today. Even within the level 2, differences in functionality exist however. First there are two classes of level 2 mode-S transponders. Class 1 transponders deliver at least 125 W at the antenna, Class 2 transponders at least 71 W. Class 1 transponders are required above 15´000 ft and 175 kts cruise speed, below these values Class 2 is sufficient. Most kitplanes fall into this category. For aircraft above 5700 kg max. takeoff weight or 250 kts cruise speed additional requirements exist (enhanced data transmission EHS, antenna diversity etc.). Most of the transponders listed under the above link do not provide these functions. Just about any kitplane does however not fall into the enhanced requirements category. Then there is ADS-B transmission ("extended squitter"), which transmits additional data directly to other airplanes. Again this is currently not required, might however get standard in the future. Anyway it seems an advantage to me to have it. A good article (in German) about the basics of Mode-S can be found on the Pilot und Flugzeug web page. A quick look at the marked showed the following mode-S transponders as being available and appropriate for the purpose of a homebuilt kitplane plane:
GarrechtVT-01The Garrecht VT-01 is a Level 2 transponder of a very compact size. The front panel can be detached from the main unit, which reduces the required depth to 45 mm. An altitude encoder is integrated, simplifying installation. The VT-01 is available as Class1 as well as Class 2 unit. Entering squawk-codes through only one rotary knob is a little tricky however. The VT-01 is also available as VT01 UltraCompact without detachable front panel.
Garrecht also announced the VT-02
(Class 1, Level 2), which is mostly meant for retrofitting, as it fits
into the mounting tray of the Bendix/King KT-76 without requiring changes
to the wiring.
Garmin
GTX330
The GTX330
is a Level 2, Class 1 Transponder. It supports extended squitter and is
therefore ready for ADS-B. Entering squawk codes is simplified in the GTX330
as it has a numerical keys.
The GTX330 requires an external
altitude encoder or air data computer.
The GTX330D also supports antenna
diversity and transmits EHS data. It can therefore be used for aircraft
with a cruise speed above 250 kts and an MTOW of more than 5.700 kg. GTX328Garmin has recently announced the GTX328, a simplified version of the GTX330, tailored to the European VFR Mode-S requirement.
Filser
TRT 800/800H/800AThe TRT800
is available in three versions. The standard version, the TRT800, is a Level 2,
class 2 transponder, the TRT 800H is class 1. Both are fitting in a space
saving 57 mm standard instrument hole. The squawk-code is entered using
four rotary knobs.
The TRT800A
is a level 2, class a transponder
fitting in a standard avionics rack.
The Filser transponders have been developed especially for the European market. They are supporting some specific functions, like switching VFR codes at 5´000 ft (used in Germany until spring 2007). Filser transponders include an altitude encoder. BeckerBXP6401
The Mode-S
transponder BXP6401from Becker is a level 2es (Elementary Surveillance)
device available as class 1 or 2. It requires an external altitude encoder,
which is available as attaching unit from Becker.
Die BXP6401 can be used with a second control panel BXP6402, which is especially handy for aircraft with tandem seats.
HoneywellKT73The KT73 is designed as a "plug and play" replacement for the KT70 Mode A/C transponder. It is built as a level 2 (Elementary Surveillance), class 1 unit.
TRIGTT31The TT31 is designed as a "plug and play" replacement for the KT76A Mode A/C transponder. It is built as a level 2 (Elementary Surveillance), class 1 unit and supports ADS-B Extended Squitter and TIS Traffic Information Service through software options. I have not been able to find any price information. The manufacturer is new in the avionics business and the TT31 is their first product.
Summary
*) BE6401-1-(01) up to 20’000 **) available with second control pan
ConclusionWe initially tended towards installing the Becker Transponder, but finally went for the Garmin GNX330. We got a good price and it integrates nicely with the GNS430 we chose as radio. |
|
© 2006-2007 Bernhard Stamm last update: 01.02.2009 |