Adding to things to improve detectability:
A floatable transponder, activated by g and/or seawater, that can be interrogated by search aircraft equipped with I band interrogators. Most military aircraft will have such interrogators for IFF (Mode2)
The transponder could be set inside part of the fuselage (wing root? tail area?) and be accompanied by a fluorescent dye marker. The panel could be released by g and/or seawater battery. Might de-icing be a problem here?
Having been winched out of survival dinghies many times in my aircrew career, I know how effective dye markers are. One idiot on my crew asked what does THIS do? while pointing the day end of a day/night flare INSIDE the dinghy. Needless to say he got wet. Had this been the Med, as opposed to the Moray Firth, we would have got wet to get the orange dye off. Instead the local pub was full of men who looked like we'd just been Tango'd!!!