Helicopters:
1970's.
Decca moving map - very dodgy but works for supertankers.
1980's.
TANS (Tactical Air Navigation System) used Dopplar cross refer TANS to a radio beacon and update 'FIX' (DME/TACAN) in the overhead, followed by a set pattern to parallel the runway outbound at 1.5nm offset to begin a turn in at 7nm from the threshold. Pretty much an SRE talkdown but internally from the crewman.
1990's Super TANS / RNS252 (Racal nav system) - similar to above but GPS input replaces dopplar. GPS less likely to go walk about than dopplar was. FIX could be offset as long as TANS and other radio aid agreed with one another. Pattern was the same downwind at 1500'agl IIRC.
Deep doo doo:
Radar Altimeter monitored let-down ideally over the sea. Wind farms and gas/oil rigs make this very iffy.
and/or
Establish hover on the Rad Alt at a pre determined height and get crewman to open the door and look down - why? - because slant vis (pilot) is not as good as vertically down (crewman); and this procedure may just prevent you wearing a wires necklace in the event of high tension wires being nearby.
Practised all of the above weekly and used it once:- In Belize after Radar (SRE) piped up "Loss of radar contact due to radar clutter (weather)" just at the time when we needed ATC more than ever and options were few if any. In fairness we were already halfway down the approach at 3nm+ when this event occurred. The rain was so heavy that having the wipers on was a wasted effort. On an ILS/PAR/SRE the TANS/GPS was always set up to act as a back-up.