Salute!
Maybe Wolf could contribute here, as I thot the larest H-53 series had great nav gear and radar for flying in poor weather.
Although he flew ASW, best I recall, we also have another rotorhead or two that might comment. One of which flew the monster in 'nam same time as me.
My thots are a mechanical problem, then running outta a good place to set down. OTOH cannor rule out cfit.
Gums sends...