One can fly IFR in VMC, but not VFR in IMC
The fact that one has VMC ceiling and visibility doesn't mean the conditions are such to meet the challenges involved in maintaining control and safely operating the aircraft visually. If the existing conditions meet VMC requirements, one might still not have adequate visual cue to operate safely. Flat light, featureless terrain on overcast nights, a calm sea offshore without significant surface features are examples of situations where one might have technically legal vis and ceiling that is not sufficient for safe operation.
Real world requirements to operate VFR (at least in the US) are set out in FAR 135.207, "No person may operate a helicopter under VFR unless that person has visual surface reference or, at night, visual surface light reference, sufficient to safely control the helicopter." Which is in addition to VMC minimums. If you don't have sufficient surface reference to safely control the helicopter, you can't operate VFR. Aided night vision doesn't improve the weather, it increases the flight crew's ability to acquire sufficient surface reference.
Yes, there situations that NVGs don't improve. The argument presented that the lack of aided night vision equipment was a cost issue suggests that the operating conditions in the area are such that NVGs would be effective. If this accident is finally attributed to CFIT due to lack of adequate surface reference while operating VFR at night, unaided, that million dollar charge per airframe for NVG will prove a mistaken economic priority for VFR operations.
It's easy to spend money when it not your own, easier still to criticize with benefit of hindsight a management decision. As a pilot, I'd consider the sacrifice of aircraft capability and cost to get the benefit of aided night vision good decision if I was operating outside of high cultural lighting areas.
Last edited by Devil 49; 7th Jul 2013 at 03:10.