As a matter of interest:
SASless on another thread asked me if Europe had a rule for visual flying that was equivalent to that in FARs. The quick answer is no, there is no equivalent rule; in that respect, FAR 135.207 is a superior text.
However, nothing is quite as simple as that. There are three threads running which are attempting to tease out one simple principle - what represents adequate visual cues for visual contact flying. In FAR 135.207 the objective is set but without a method of compliance. The term adequate visual cues is a combination of: the ability to fly the aircraft by using external cues (inversely proportional to aircraft stability); the ability to see and avoid obstacles; all conditioned by the ability of the pilot (innate skill, training and recency).
For a helicopter to be certificated to fly on instruments, it has to meet the stability requirements of Appendix B of Parts 27 or 29. This requirement is called up from Part 27/29.141(c)
"Have any additional characteristics required for night or instrument operation, if certification for those kinds of operation is requested. Requirements for helicopter instrument flight are contained in appendix B"
Note that night is also included in the requirement for 'additional characteristics' but nowhere in the airworthiness code is to be found an equivalent appendix. This is dealt within the operational code of some States which require control augmentation - simplistically - by making a requirement for an autopilot with heading and height hold for flight at night.
In passing, it is worth mentioning that this problem is not only confined to night, we have seen a large number of accidents occurring in daylight when the visual cue environment degrades such that control is lost - the most prevalent being inadvertent entry into cloud. This loss of control is insidious (a word which perfectly describes the process)
Most understand that, as the visual cues diminish, it becomes progressively more difficult to maintain control without augmentation. In any case, because it is more difficult to control a helicopter without external visual cues, certification in appendix B is largely concerned with stability – i.e. making the 'mechanics of flying' easier (compare flying a Robinson R22 to an S76 in cloud and on instruments). This permits the (even single) pilot to undertake the other tasks that are associated with navigation and spatial awareness. For a fully automatic flight control system, almost all attention can be provided to the tasks of external scanning and/or navigating
when the pilot is flying VFR.
The rules for VFR overwater flight referred to in an earlier post are an attempt at setting the conditions in an environment where visual surface light reference is largely absent. Without external light (in the form of moonlight and/or stars and/or a visible horizon), the pilot can still fly VFR if obstacles can be seen – i.e. because vessels are required to carry light sources. Even though not provided for this purpose, the weather radar has shown itself to be extremely useful for showing obstacles on the sea surface (within tolerable limits) and sight of such obstacles can be anticipated (and distances measured) and missed laterally even if their vertical extent is not known.
The fact is that most flights on the North Sea are conducted under IFR; the issue then is how the transition between IFR and VFR is mandated and managed. There are two alternatives: the pilot lets down from the en-route altitude/FL and, having descended visually below MSA, continues the flight VFR (more usually by day); or an instrument let-down procedure at the destination is utilised.
In order to facilitate an en-route let down, companies can have discrete instrument procedures permitting a descent through MSA to achieve VFR; to ensure that this does not leave the pilot exposed there are limits on the descent altitude - specified in the Operations Manual and accepted by the NAA. These limits are underpinned by a rule which specifies the minimum cloud base and visibility for VFR flight by day and by night.
The only practical instrument let down procedure available (at the moment) is the Airborne Radar Approach (ARA); this procedure is conditioned by the fact that the largest obstacle in the approach area is the destination to which the flight is being conducted. Whilst most instrument procedures rely upon a vertical clearance of obstacles in the approach and missed approach segment, because the pilot is heading towards a large object, the ARA has to rely upon lateral clearance (along an obstacle clear corridor and missed approach segment). In view of this constraint (and simplistically stated), in the latter part of the approach there are three distinct phases: the descent phase (which is in effect the cloud break); the level phase (where the pilot is clear of cloud and driving towards and beyond the MAPt); and the landing phase – this is no different from the point-in-space (PinS) procedures (defined in ICAO) which have ‘proceed visually’ or ‘proceed VFR’ as their final element.
Because of the requirement for lateral avoidance, the procedure has to have either: an offset approach – which, using accurate guidance, takes the pilot a set distance from the target and provides a straight ahead missed approach (this is usually based upon fixed tracks); or the introduction of a divergent heading to ensure that the pilot tracks away from the target - with a turning missed approach from the MAPt; this procedure can be omni-directional and into wind. The length of the level segment should be from the OIP to the MAPt and from the MAPt to landing manoeuvre. The position of the OIP, the heading offset and the MAPt are all based upon margins of error which ensure that a late missed approach will still provide a probable miss distance of 400m from the target (depending of course on how wide the target is).
The procedure should be flown stabilised and the landing manoeuvre commenced only when sufficient references are available to permit the landing pilot to take control and perform the landing. From the previous passages you can see that there is a world of difference between visual sighting of the target and adequate cues to permit a visual contact flying and landing. This is most evident when flying to a single light source which is narrow – like a well-head platform - where, if the approach is flown without assistance (be it from another pilot on instruments or using the automatics), all sorts of twisting and turning of the target can be experienced.
The more assistance that can be made of the automatics (or the second pilot) in the level segment, the less the visual pilot has to fly the aircraft – concentrating instead on ensuring that it is positioned accurately for the landing manoeuvre. Regardless, at some point in these latter phases there has to be a decelerative manoeuvre – if the level phase is conducted at the minimum altitude (200ft by day and 300ft by night), and it is not windy, this decelerative manoeuvre will be whilst the aircraft is level.
At the point where the automatics have to be switched out, perhaps because of speed limitations, the visual pilot will have already decided that there are sufficient visual cues to perform the landing; if there are insufficient cues, or at any time in the level segment if the aircraft becomes unstable, a go-around should be flown. (This is not the missed approach of the ARA - which can only be initiated up to the MAPt.) Because this go-around is likely to take the pilot into reduced visual cues, it will have to be flown on instruments and in line with company procedures – hopefully it will not resemble a recovery from unusual attitudes which is a measure of desperation.
This last paragraph applies equally to approaches which are not instrument let down procedures. There is basically no difference between the last phases of an ARA and an approach which is conducted at night from shuttling (except that the lowest level phase in shuttling is 500ft).
Jim