Efficacy of EGPWS

[jolly girl]

For those who have had the opportunity to fly with it, how effective is EGPWS proving to be in supporting / enhancing awareness of terrain / obstructions?

[Troglodita]

In a 412EP it will annoy you with "Tail Low, Tail Low" if you hover at anything below 15 feet - a great shame since the recommended hover height is 4 feet!

Also lots of terrain warnings in areas where the highest obstruction is a golf course flag.

[maeroda]

EGPWS

Troglo,

about 412 tail low in hover....you still don't know how 139 hovers, right?
First thing when hovering a 139 is to riconsider 412 low tail hovers as "very hight tail hovers"!

EGPWS,
on my recent flight experience on 139 I would sugest everybody performing night unaided flight on mountain terrain to buy one or get pilots well trained to use it.
I had been flying in mountain hems for last two years; it happens after sunset+30' you are on remote hospital pad at 6000ft and have no way to climb over 12.000ft to get the 30 minutes long straight route home due to weather, you must do the circle following valleys 2 miles wide under peaks level with FMS waypoints and get home in very VFR/N trying to mantain no less than 1000ft AGL (no radar control, no AFIS, no Information service, nobody flying there, you're alone).
Doing this it's usefull to have a EGPWS to tell you throught PFD and MFD (primary and multifunction displays) the pattern of the valley you must follow with FMS routing overlay on it.
Of course you alwais had GPS and done the trip around dozen of times maybe with 3000mt VIS and overcast with no moon with the stick on the very go-to line; now with EGPWS things are more easy, less triky: if the ship overruns a turn or turns lazy getting too close to obstacle the system shouts "WARNING, TERRAIN" in your helmet.
Alwais think things can get worse if you follow valleys at too low altitude, where GPS link can fail because of terrain obstruction.
In this case will have EGPWS also failed and if you don't see you are toasted.

I have no experience in overwater flying with 139 and his EGPWS but I think it would be as great as in mountains.

maeroda

[SASless]

Every Sectional Map has big two digit numbers in each grid square that denotes the safety height for that grid.....when was the last time the average pilot looked at them while in during a pre-takeoff brief....much less in flight at night?

Anything that sets off "Martha" in your ear is an improvement even if she sometimes gives spurious warnings.

Famous last words of a pilot in South America heard on the CVR tape following an altitude alert was "Shut Up Bitch!".....quickly followed by sounds of impact that killed all aboard the flight.

[JimL]

Maeroda,

I have no experience in overwater flying with 139 and his EGPWS but I think it would be as great as in mountains.

I am amazed that you can make such a statement - on what logic do you base this conclusion?

As has been pointed out in another post recently, the obstacle environment offshore is only partially mapped - that makes the 'E' portion of the EGPWS somewhat suspect. The 'GPWS' modes are based upon the six classic fixed wing modes (yes, modified for helicopters, but still based upon the climb, descent and landing modes of the aeroplane).

For onshore work, the enhanced mode of the EGPWS has great potential; for offshore work, we await the real-time obstacle detection that Honeywell have promised us. For all helicopter flying, we welcome the increases in the size of the market because that might lead to additional work to provide realistic classic modes.

Jim

[maeroda]

Hello Jim, nice to meet you.

I don't have any overwater experience with EGPWS, all I did at night on sea as co-pilot was something similar to ship-radar approaches, eye on radar-altimeter and CRM.

My opinion about EGPWS offshore capacity was based on logic: it is good on land (upon subject to emprovements to fit it to helicopter model), it may be good also on sea.
Understand you have different opinion based on specific experience and I do agree with you.

Maybe I should have write "..in overwater flying......I hope it would be as great as in mountains.", rather of "....I think......."

Sorry, maybe my writted lenguage is not as clear as it should be, I'm not mother thouge.

Maeroda

[anjouan]

A Dangerous Distraction Offshore

As Troglo says it's just a darned annoyance in most helicopters with useless 'Tail Too Low' warnings or 'Warning Terrain' if you lower the nose more than a few degrees when accelerating to Vtoss during take off. As it's not possible for offshore obstacles to be updated by the user and Honeywell seem incapable of producing a daily or weekly update which could be downloaded for users who could send in updated moving obstacle requirements, it's also pretty useless in the offshore environment. Many pilots I know just pull the CB to shut it up as it constantly distracts their attention during crucial phases of flight

I completely agree with JimL that until such time as Honeywell can produce a proper helicopter-specific EGPWS, capable of daily or weekly updates electronically by the user, it's an expensive waste of fuel or payload at best and a dangerous distraction at worst

[JimL]

Hi maeroda,

Now you have made me feel really mean spirited.

Jim

[Faffner shim]

Sasless - I don't know if your maps are the same as mine but our 2 digit numbers are a Maximum Elevation Figure - not a safety height

[SASless]

Perhaps I could have been more precise but what I meant is if you look at the chart at some time in your flight prior to getting to the grid square in question.....the large blue two digit number will indicate the highest elevation/obstacle height given as MSL and one can immediately arrive at a "safe" altitude to fly.

I suppose we could throw in comments about the difference between mountainous and non-mountainous terrain and how the "safe" height above each vary from the other.

This excerpt from a usually reliable source explains how those numbers are derived.

All sectionals and terminal charts contain Maximum Elevation figures in each latitude and longitude box. They are stated in thousands and hundreds of feet above mean sea level (MSL). They represent the highest obstacle (towers, terrain, antennas etc.) within the box, with usually a 100 ft. error allowance added, and then rounded up to the next 100 ft. level.

In reality, what I should have said is one could look at the map and deduce those altitudes that would pose a danger to safe flight.

Perhaps someone can explain how to compute actual altitude vice indicated altitude so we can all be completely safe out there.

[Mars]

The efficacy of EGPWS for offshore operations was discussed before. Here is an extract from a previous post:

http://www.pprune.org/forums/showthr...88#post2970788

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-ŕ-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

[[email protected]]

Sasless - in UK the MEFs depend on whether the highest obstruction in the section is terrain or an obstruction (mast or other) - if it is terrain then a
300' correction is added and then rounded up to the nearest 100; if it is an obstruction then it is just rounded up to the nearest 100.

It has nothing to do with increasing Safety Altitude over mountainous terrain.

[SASless]

Mars,

The article you referenced has one flaw that stands out to me. It states landings are a deceleration maneuver to a "zero groundspeed".

It is not all that unusual to land on moving decks such as Seismic Boats, Rigs under tow, and other moving vessels.

[JimL]

SASless - if I might take the opportunity to answer,

Thanks to Mars for reminding us; it was not an article but something that I wrote in response to the discussions in the S92 thread about 18 months ago.

As far as the speed goes; yes the decks are sometime moving. The difference of approach speed/manoeuvre to the classic modes might not be apparent when comparing aircraft IFR procedures onshore, but is when considering flights offshore.

The original reason for the quoted post was to postulate that, for offshore operations, the EGPWS algorithm would benefit from being modified. Not only does the Enhanced mode need the presence of real-time sensors - to address the dynamic obstacle environment - the protection envelope provided by the six classic modes also needs to be redefined.

Because of the less complex operating conditions (some elements of which are described in the bullet points), and because we already have terabytes of data describing offshore operations (from the HOMP/FDA programs), the provision of definition of a safe offshore operating envelope would not be impossible to achieve.

An extremely worthwhile research project that would not cost a great deal of money or time to conduct (providing the data is made available - as I'm sure it would). The provision of a safe operating envelope might have also mitigated for the Cormorant Alpha accident, which appeared to be caused by the helicopter being put into an unsafe regime whilst turning downwind in strong winds.

Jim

[SASless]

JimL,

I did not mean to sound critical....but was wanting to highlight helicopters sometimes do not achieve zero groundspeed during landings which would be yet another difference to the fixed wing model.

[maeroda]

EGPWS shot

hello.
this was in a tipical mission "around the circle" on mountain SAR in Italian Alps, daylight near sunset, +2000mt vis, two pilots with 139 ship.
Pic was following the go-to line with hands on.
This is the view from the inside.

[maeroda]

And this is the view of the outside.
After a while it started deteriorating a lot more than it was suposed to be at halfway to destination.
IMHO in that flight EGPWS has been helpfull to fly more confortable in marginal weather, say in VMC.
As all you know for sure IMC under peacks is forbidden!

[JimL]

Now why is maeroda's story making me feel uncomfortable?

What ever happened to the caption that that said navigation was not to be predicated upon the EGPWS? Has the Honeywell policy changed?

Jim

[SASless]

That is an excellent comparison of what the view outside looks like compared to the cockpit display.

Perhaps JimL, in days of old, we would were out there doing the deal without any aids beyond the MK I eyeball. That made me "uneasy" then and still does.

I see the electronic eyes"" adding to the pilot's situational awareness and provides an additional source of information upon which to make a decision to carry on or turn around.

I sure wish I had similarly equipped aircraft when I was trundling around the mountains in Winter....it gets awfully hard to judge height looking out the windows sometimes.

Excellent photos Maeroda!

[sunnywa]

Maeroda,

What a great set of photos to show the system at work. It would certainly help the pilot with his SA and when to turn back.

Flying through those mountains at night VFR, I tips my hat to you as it would certainly get my heart rate up. Another thing to help you would be NVG.

Ciao