Jimmy
The Vigilant had a Mode C Transponder (not Mode S although the entire Avionics pack was due for upgrade to Mode S and 8.33 plus some glass instruments as I understand it)
Viking had nothing apart from standard VHF Radio (non-8.33), the dual battery pack of the Viking means it could easily support FLARM but also some of the new Mode S Transponders (low draw) that are being developed.
Is any of it necessary for the type of flying the ACO did (not does.............) ?- you decide..................
Arc