EGPWS and Offshore Operations
One of the problems with the discussion of EGPWS in this thread has been that views have been expressed with assumptions that have not been stated in the posts, or stated and not acknowledge by those who have then responded. Let me explain what I mean:
Helmet fire, who commented extensively on the Cat A thread, introduced the subject by suggesting that instead of investment in performance, we should concentrate our investment on CFIT measures (it was never clear to me exactly what investment would be traded but assumed it was it was R&D and capitol against running costs of larger engines). However, this remark was made in the context of Offshore Operations as he qualified it with the phrase “full Cat A over all rig types”. HeliComparator then continued the discussion by expressing some reservations about the use of EGPWS for Offshore Operations.
The discussion then moved to a (very detailed and knowledgeable) discussion, between HeliComparator and Nick Lappos, about the efficacy of the 6 modes that are the basis of the GPWS part of the EGPWS. This discussion introduced (with no real follow up) the subject of construction and integration of alert and warning messages in the cockpit (for those who aren’t aware of it, the equipment being used a the centre of this discussion is the EGPWS on the S92 which uses the facilities contained in the ‘box’ as the generator of cockpit voice warnings - basic aircraft as well as EGPWS, TCAS etc.).
Thridle Ops Des commented on the transfer of Protection Modes from fixed wing to helicopter in onshore operations where the Protection Modes are reasonably similar but Malabo (with onshore and offshore experience) called into question its efficacy offshore.
It appears to me that while it may be necessary to ensure that the Protection Modes for onshore operations are re-examined and validated, it is absolutely essential that the Protection Scenarios for Offshore Operations are constructed so that the Protection Modes can be established. This requires that the offshore practitioners cooperate with the RTCA HTAWS in providing a detailed definition of the profiles that exist in Offshore Operations.
Other than when flying VFR, we have to use IFR procedures which constrain us into corridors or areas which are specified both horizontally and vertically and in which vertical separation is assured. Simplistically, 1000ft above obstacles (2000ft in mountains) in the cruise, decreasing in the descent to a minimum at the MDA/MDH/DA/DH which is based upon the accuracy of the aid in the vertical or lateral extents in providing obstacle clearance. Because the vertical extent of the obstacle environment offshore is non-complex (basically no obstacles higher than 500ft) we have a single MSA/LSALT of about 1500ft. The reduced obstacle clearance provided at an airport or heliport for the descent phase has to be assured by methods of surveying and safeguarding established by the State.
Specifically for offshore operations; in Europe (and I suspect elsewhere) descent below MSA/LSALT can only be achieved when on an approved procedure; this could be an en-route descent or an ARA approach but in both cases, safeguarding (in essence) is achieved by providing lateral separation from obstacles by using the weather radar - for en-route by establishing that there are no obstacles in the arc, and for approaches by ensuring that an approach and go-around corridors are free from obstacles. As en-route descents are not always associated with an immediate landing, the MDA is usually limited to 500ft.
Although not certificated for that specific purpose, the weather radar has provided us with an excellent tool for obstacle separation in a period where there was no other practical solution. The use of a real time display (weather radar) has been necessary because we usually seek to let down in an obstacle rich environment - both fixed and mobile. The MDA/MDH is set only against the MSL and not adjusted for obstacles and therefore lateral separation has to be assured. The function of the radar cannot be replaced by a synthetic visual display unless it also has real time acquisition of obstacles. Where there will be development in the future (but only for approaches to landing) will be in the provision of more accurate positional data and (hopefully) vertical guidance obtained with the use of GBAS or SBAS.
The discussion on this thread has been conditioned by an expression of sentiment which appear to be representative of most pilots; if we cannot see what is in front of us - i.e. we are visually constrained by the weather or by being IFR in or above cloud - we would like a representation of the physical world to be presented to us synthetically (using synthetic visual devices); hence towards the end of the thread pictures of annotated moving map displays appeared. The provision of data for navigation and situational awareness is achieved with the use of FMS type devices - in the past, as Reflex has said; it was with the use of moving map displays - i.e. Decca.
The main use of the ‘E’ function of the EGPWS is to provide situational awareness and warnings in those cases where the flight is in danger of breaching (in most cases substantially) the IFR terrain (rising ground) separation - perhaps caused by being temporarily unsure of position or not applying the appropriate vertical separation (usually resulting from being off track). We are fortunate in Offshore Operations that the terrain is always flat (give or take the sea state) and, if flying below MSA/LSALT, the main hazard is the obstacle environment (which we have already established rarely if ever exceeds 500ft).
However, and as stated above, that obstacle environment is not static and, unless there is real time updating, cannot be provided on the ‘E’ function of the EGPWS. It is therefore not clear what ‘E’ brings to the party for offshore operations; conversely, and because the display is so beguiling (see 212man’s post) it provides in HeliComparator’s words “a passing resemblance to reality…that existed some months ago”, it introduces a hazard which we would not permit following an appropriate Risk Assessment.
In a recent discussion with someone who has been closely associated with the introduction of EGPWS with a major airline we were frankly surprised at our diametrically opposed views vis-à-vis the ‘E’ function (but only with regard to offshore operations). His view was that the real benefit of EGPWS rested with the ‘E’ function and there was less-and-less reliance upon the GPWS functions (the six modes enumerated by Nick and HC). As he saw it, the problem with the GPWS functions was that in order to remove the ‘spurious alert’ (the real GPWS killer - how many before the CB is pulled), the parameters of the ‘Protection Mode’ had been widened with the consequence that only the real extremes are being signalled.
For me this raised a ray of hope because it is becoming clear that if we can establish, with some accuracy, the modus operandi (map normality) in the relatively simple terrain and vertically limited obstacle environment that obtains offshore; we can define the ‘protection scenarios’ and establish the ‘protection mode’ that can reduce CFIT offshore. However, until and unless we can provide real time updating (which is not beyond our capabilities) the ‘E’ function remains out of scope for offshore operations.
Just as a taste of what we could consider in establishing the definition of offshore operations, here is a short bullet list of items. Please feel free to use it as an Aunt Sally:
Some information for offshore operations:- obstacles rarely if ever exceed 500ft;
- pilot tend to use the radar as an aid to navigation - in some cases as a crude synthetic vision device;
- the radar is a part of the approach aid suite;
- radar is not certificated for navigation or as an approach aid;
- it is likely that pilots will carry over current radar practices to the EGPWS (as a pseudo synthetic vision device);
- in a number of world-wide locations, IFR is the norm;
- by day the main hazard is associated with the cloud break below 500ft - i.e. low cloud base and obstacles (usually obviated by checking the approach sector is clear on the radar)
- by night hazards also include lack of contact with the surface (drift down associated with fixation of the rig) or inadvertent IMC in the final stages of the approach and when flying level;
- universal limits appear to be 200ft and 0.75nm (although some States permit a closer MAPt);
- the MAPt limit is defined by the necessity to miss the target on a go-around;
- IFR descents can either be associated with a landing site or en-route (both should be associated with an approved procedure);
- the point where the gear is selected up or down is dependent upon the helicopter type and its limitations.
- the offshore landing site is always a helipad/helideck - i.e. of limited size - this means that the approach always takes the form of a decelerating manoeuvre with a terminating ground speed of zero;
- the landing site mostly sits beside a large obstacle - the presence of which must not trigger an alert;
- the landing site is never on the terrain floor (i.e. sea level);
- the helicopter rarely flies below x ft (100ft in the North Sea) above the terrain floor except when in the final stages of landing and where the ground speed is less than y kts;
- approach angles are steeper than fixed wing or for onshore approaches;
- the take-off is always associated with a spike on the Radalt as the helicopter leaves the deck (the first reading after the spike can be used in the ‘altitude sample and hold’ buffer - Mode 3) which detects descent after take-off;
- sinking below 50% of the take-off height is rare;
- weight on wheels defines the end of a sector - when offshore, that is all that is needed to define the sector (at the moment it is WOW and 30% Tq);
- shuttling can occur with wheels up or wheels down - it is difficult to delineate take-off from approach on some sectors;
- shuttling can occur at any altitude at or below 500ft (VFR)
- inter-rig flying - other than shuttling - is usually conducted at or above 500ft