Yes, a change of battery technology could make the difference and make it feasible.
It is still hard to make a case for putting a transponder in, since the benefit it brings is (mostly) to others and people are inherently selfish to a degree.
Transponders only send brief pulses, so even with big headline figures like 130W or 200W, the actual power consumption at the DC inlet remains pretty low and constant. They are effectively using stored energy from their internal power supplies.
A LiFe battery has much less fire risk than a LiPo. The price you pay is that it is bigger for the same capacity.
Annex 2 (now 1?) without a built in electrical system do not need to have the Txp always on when airborne, precisely to conserve battery for essential COMs and when either on a radar service or in a TMZ.
Airborne_Again wrote:
Mwah. A mode S transponder will have to reply to the broadcast requests plus requests targeted to it.Yes, but the broadcast requests should be a whole lot fewer than with mode A/C,
Why? To me, it would make sense that broadcast requests are for “who’s there/where”, and targeted requests are for “you, give me more info”? I don’t immediately see why there would be less broadcast requests. Unless you mean where ADS-B is mandatory, no need to send requests since ADS-B broadcasts without request, if I understand correctly? (If it doesn’t, how does the space/satellite-based ADS-B tracking system work? Does it send broadcast requests to the whole earth?)
Plus, I believe it is mandatory for a mode S to also squawk mode A/C?
That’s true, and when mode S isn’t compulsory the radar has to send mode A/C interrogations as well. If mode S is required, then there is no need to interrogate mode A/C.
I doubt that radar in “mode S mandatory areas” is actually configured to not send mode A/C interrogations. They allow to see aircraft that don’t obey the mode S obligation, and increases safety. But that’s only my guess.
Plus the other plane’s T(C)AS will continue sending mode A/C interrogations.
lionel wrote:
Why? To me, it would make sense that broadcast requests are for “who’s there/where”, and targeted requests are for “you, give me more info”? I don’t immediately see why there would be less broadcast requests.
One of the main reasons for mode S was to reduce the number of transponder replies. Many of the deficiencies of the original SSR system (fruit, garble…) are due to the fact that every transponder replies to every interrogation.
The number of broadcast replies are less because broadcast requests are needed only to find out what new aircraft are in range and thus they can be broadcast much less frequently than mode A/C requests which are always broadcast. The interrogator tracks known aircraft and uses individual requests to get range, bearing and altitude information. There is also a feature where a transponder doesn’t reply to a broadcast request at all if it has already replied to the same interrogator.
The table here states that mode S radars generate 4-8 times fewer replies than do mode A/C radars.
Plus the other plane’s T(C)AS will continue sending mode A/C interrogations.
TCAS interrogations have much lower power than radar interrogations so they will affect fewer aircraft.
RobertL18C wrote:
Annex 2 (now 1?) without a built in electrical system do not need to have the Txp always on when airborne, precisely to conserve battery for essential COMs and when either on a radar service or in a TMZ.
You learn something every day! Thank you!
CoA aircraft with only batteries have the same alleviation.
That is really interesting. It is also a great reason to buy an RV right away 
