When operating under JAR-OPs, as the three big offshore companies do, one has Ops Manuals.
The OMA (Ops Manual A) is company specific, it covers rules, minima and procedures which apply to all aircrew whatever aircraft type they fly.
The OMB (Ops Manual B) covers the specific helicopter type. Each type has its own book which looks very like the RFM, and includes Limitations, Normal SOPs, Emergencies, Performance, Weight and Balance, and more.
Under JAR-OPs a performance class one helicopter, being flown two crew, day or night, can depart an offshore deck in 250m vis, clear of could with surface in sight. The commander must ensure the path ahead is clear. This authority will be found in the OMA. These are IFR departure minima only, see JAR-Ops 3.430(a).
For performance class 2 helicopters its 800m vis until achieving PC1 capability. Currently the UK CAA allows PC2 offshore. Still an IFR minima. JAR-OPs 3.430(a)(3)(ii)
However, specifically, for the AW139, if the OMB reflects the RFM there will be a limitation saying "minimum airspeed under IFR is 50 KIAS".
If this is so (check your OMB), the OMB is more restrictive, in this case, than the OMA, as at night to maintain VMC thus complying with the Visual Flight Rules - until at 50 KIAS - you need inflight vis of 3km in UK Class G airspace, i.e. offshore. That is for as long as there is not a 50 kts hoolie, when immediately, you are permitted to comply with the Instrument Flight Rules.
(The UK 'VFR at Night' rules are notified in Civil Aviation Authority INFORMATION NOTICE Number: IN–2012/145 which supersedes the ANO.)
During the day one would be limited to 1500m (Class G) as the ICAO alleviation for just clear of cloud in sight of the surface in VFR below 1000ft above terrain is not permitted in UK airspace.
We are a little off tread. But the point Crab makes is an interesting one. The point is not that one can't fly solely on instruments below 50 KIAS in an AW139. Simply, that before reaching 50 KIAS one is not allowed to operate under Instrument Flight Rules, therefore you have no option but to comply with Visual Flight Rules.
This is not simply about weather, as the Visual Flight Rules and Instrument Flight Rules comprise more than just weather limits.
Crab noted that something has been given a "damned good ignoring", he is right, but as I say, it is not that you can't fly solely on instruments below 50 KIAS in a AW139, well not as the rule are currently written.
As the wording stands, the rules say, you can not depart offshore, (or from Gillingham - same airspace), in vis below 3km, clear of cloud and with the surface in sight, at night in a AW139 in UK Class G... unless the wind allows you to see 50 KIAS on the ASI.
This would still not allow one to depart from Gillingham as one could not comply with the IFRs i.e rules 33 and 34 of the ANO, assuming a private flight, or your OMA under JAR-OPS. I'm afraid in the Gillingham case one must have, a) 3km, b) to maintain clear of cloud and c) be in sight of the surface simply to conform with the Visual Flight Rules. Forget everything else, towering take offs, TDPs, sole reference - forget it.
If you drive a AW139 in the UK, apply the VFRs to the airspace you take off from, and explain how, without 1500m by day - 3km by night, clear of cloud, in sight of surface or 50 KIAS (50kts+ on the nose), you do it without breaking a limitation?
Are you legally allowed to break limitations on a wholesale basis? Have the Authority granted a waiver? Or has it just been given a "damned good ignoring".
By the way, if you fly a PC1 profile you will also comply with PC2 as PC1 is clearly more restrictive. This is required in the OMB of at least one of the large three operators in the UK.
That's as I see it. Please correct me if I'm wrong.
I'll leave it at that.
Over to the legislators and lawyers...