I've taken some people flying recently for fun, and they noticed some hot-air balloons and asked me if they had transponders. In San Diego (Southern California) I often see hot air balloons well within the Mode C Veil (a 30 NM radius circle surrounding from a Class B airport). Do hot-air balloons need transponders when they are within the Mode C Veil?
I've gotten this question enough times to look up the regulations and answer my own question :)
14 CFR 91.215 lays it out quite nicely. Particularly section B(3):
(3) Notwithstanding paragraph (b)(2) of this section, any aircraft which was not originally certificated with an engine-driven electrical system or which has not subsequently been certified with such a system installed, balloon or glider may conduct operations in the airspace within 30 nautical miles of an airport listed in appendix D, section 1 of this part provided such operations are conducted -
(i) Outside any Class A, Class B, or Class C airspace area; and
(ii) Below the altitude of the ceiling of a Class B or Class C airspace area designated for an airport or 10,000 feet MSL, whichever is lower; and
Where I see the balloons is definitely outside of the Class B airspace and below 10,000 feet MSL, so the answer is, no, they don't need a transponder.
When do I need to get a transponder?
Within the UK FIR, Mode S Enhanced (EHS) has been mandatory for all aircraft flying IFR as GAT within notified Mode S airspace since 31 Mar 05 (with a 2-year transition period until 31 March 2007), as per AIC 49/2005 (YLO 171).
The carriage of a Mode S Elementary (ELS) transponder within remaining UK airspace has been mandated by 31 Mar 2008. It is likely that there will be a 2-year transition period until 31 March 2010, to allow for any implementation difficulties.
Within other European Mode S implementing states, the target for Mode S (EHS and ELS) implementation is 31 March 2008, with no exemption period!
What is Eurocae ED115?
ED115 is the agreed technical standard for LAST Mode S transponders.