Ground collision avoidance system - what's its name?

[themoffster]

Hi, what is the name of the system (just overall, not model names or anything) of the system that shouts "Terrain, Terrain" if you are flying into a hillside?

Obviously none of you will have heard this when flying into a hillside and still be around to post on here, but you get my point ;)

Cheers!

[DOVES]

On board of each and every commercial aircraft there's a system which, among other functions has the one you are referring to.
Its name is: GPWS=
Ground Proximity Warning System
BRDS
DOVE

[themoffster]

That's the fella, thanks!

[Old Smokey]

DOVES, you beat me my a microsecond to reply. Indeed, GPWS = Ground Proximaty Warning System.

To remark upon a quote from themoffster, - " Obviously none of you will have heard this when flying into a hillside and still be around to post on here"

Actually, there's a lot of us still around after hearing this warning, and responding to it. There IS sufficient time to carry out terrain avoidance techniques if acted upon promptly. Sadly, the last words on many Cockpit Voice Recorders are "It's just a warning", for those who didn't.

Fly Safe, heed the warnings,

Old Smokey

[PTH needs tarmac]

themoffster

As an add on to Old Smokey's comment I think I can provide an example of when a "false" GPWS warning can be experienced from my old local of Leeds Bradford Airport.

The final approach to RWY 14 at LBA is initially over the Wharfe valley. At approximately 2-3 nm from touchdown the valley makes a turn and the valley side/ridge, known locally as the Chevin, rises rapidly from the valley floor.

I suspect the GPWS system detects the start of the slope and calculates that IF the hillside continues to rise at the current angle/rate then the aircraft will collide with the ground should it continue on its present course. Therefore a GPWS alert is sounded.

As the aircraft gets closer to the Chevin the top of the slope is accurately detected, GPWS recalculates that the aircraft will pass safely above the peak of the hill and the alert is cancelled.

The LBA approach information for 14 therefore I understand includes a note that spurious GPWS warnings may be experienced at around 2 nm from touchdown and can be ignored PROVIDED that the approach is correctly located on the glideslope.

I freely admit I am not an expert on the internal working of the GWPS and I would welcome any comments from those more qualified but I thought this may serve as an example of when GPWS warnings might be heard during normal operations.

PTH

[alf5071h]

PTH needs tarmac, many of the problems with the ‘old’ GPWS were resolved by modification or by using an interface with FMS. The example at Leeds (similar to MCT 24 base leg) could be eliminated by desensitising the GPWS alerts based on the aircraft’s position, but this obviously requires a good position sensor (approved FMS).

All pilots should have been taught to fly with the concept that there are no ‘false or spurious’ GPWS warnings. In the very rare event of an unwarranted alert, the cause may only have been discernable from the FDR and location analysis after Pulling Up and surviving a most probable CFIT accident.

All large commercial aircraft should now be fitted with the Enhanced GPWS (EGPWS), which does not suffer any of these problems; there are no false or spurious warnings with this system … provided operators obtain regular software updates, fit the add-on obstacle mode, and refresh the terrain and obstacle databases regularly.

The details of how EGPWS works can be found at egpws.com, look under operations – pilot’s guide’s. The operation of the older GPWS was similar to the Enhanced GPWS modes 1-6.
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Unless specifically authorized everything else is forbidden.

[PTH needs tarmac]

alf

Thanks for that extra information. I had a feeling that EGPWS resolved these problems associated with older models in the period after they were first introduced. I was trying to cite an example where pilots could have experienced a GPWS warning without facing a mountain at close range.

In the case of LBA the Chevin is still the cause of the non-standard glideslope angle on 14.

cheers

PTH

[Ka8 Flyer]

"which does not suffer any of these problems; there are no false or spurious warnings with this system …"

Well I'd say that depends on how accurate your position info is! Assuming you have GPS sensors, I agree, you should not recieve nuissance warnings.
But on aircraft with no GPS installed (some 737NG's for example) do have EGPWS installed and after long flights you might get a nuissance warning!

[alf5071h]

Ka8 Flyer, you are correct in stating that ‘it depends on how accurate your position info is’, but most FMS are sufficiently accurate when operating in DME/DME mode. This of course assumes that you have good DME coverage.
Aircraft and FMS manufactures should provide advice on the FMS/NAV position accuracy requirements. I believe that some Airbus FMS degrade gracefully with the loss of DME and use blended IRS up to a point where the FMS provides a warning when the accuracy is insufficient for EGPWS (terrain) use. Also in early Boeing installations the FAA stipulated specific locations / airfields where the EGPWS Terrain mode should be switched off due to the lack of DME; modes 1-6 still work as they are independent of location.

The solution is to use GPS, preferably the optional receiver within the EGPWS box itself.

Re your ‘and after long flights you might get a nuisance warning’; the arguments about there being no ‘nuisance’ warnings still apply, you must first pulling up and then subsequently determine the nature of the alert. If you do not pull up then there is every possibility that you will never know that it was not a nuisance warning.

EGPWS does not suffer from problem situations like PTH needs tarmac quoted, as the terrain look-ahead function alerts the crew well in advanced of the old GPWS modes.
The terrain mode is a most valuable safety feature and although the navigational inputs / terrain database accuracy (resolution) are not accurate enough for navigation, at least one display should always be on to provide terrain awareness when below MSA for both take off and landing.

[cormacshaw]

Ground collision avoidance system - what's its name?
Pilot?




... I'll get my coat.

[safetypee]

cormacshaw, make sure your coat is at least 2 inch armour plate; most often it’s the pilot’s who make the mistakes, EGPWS enables them to recover from the impending danger.

If the relevance of your post is reflected in the design of your simulators, as indicated by the inaccuracies in the 146/RJ flight deck (your referenced web page), then we can safely ignore your remark.

[cormacshaw]

If the relevance of your post is reflected in the design of your simulators, as indicated by the inaccuracies in the 146/RJ flight deck (your referenced web page), then we can safely ignore your remark.
Ah give me a break :rolleyes:, I was obviously only making a off-the-cuff joke. My post was obviously not a serious answer and I only posted it after the correct answer to the initial query had been given so that it could be "safely ignored" as such.
I post only occasionally here, use my real name and link to, as you found, my hobby website so you know where I am coming from. On the rare occasion that I make a post on a topic that could be interpretted as coming from a person with relevant qualifications, authority or experience that I do not have, I state so explicitly.

BTW, yes the 146 model on my site has many inaccuracies. It was one of my first attempts from a few years ago. Later efforts are better but still have inaccuracies, some my fault, some a result of the sim's limitations - part of the fun of this design hobby is trying to improve on your previous efforts.

[MyData]

Eyeball Mk I for me I'm afraid. I'm student PPL out of LBA. Just last Sunday I was joining R14 on left base incoming from Harrogate.

Didn't switch to QFE and used QNH (as have done on R27, R32 previously), and my own perception of height. Blimey, the Chevin can really screw your view so when I crossed over the ridge I was a tad (OK, a lot) too low and had to climb back to get height for an good approach.

It will be QFE from now on and going by the altimeter for circuit height rather than my 'perception' - the joys of learning by experience.

All this on top of the previous week's landing on R27 with warnings of windshear which did materialise. LBA - a great place to learn the fine art of landing ;-)

[End_of_Descent]

alf5071h,

basically, I agree with you that with EGPWS spurious warnings should not occur as frequently as with the old GPWS systems. Nevertheless, there are still traps and false warnings may occur.

example 1: when a new airport opens and the EGPWS runway database is not updated in time, false warnings may occur due to the missing 'terrain clearance floor'. Thus, spurious warnings may triggered approach the threshold of a new runway which is missing in the database. Although this is usually NOTAMed, this happened when LGAV opened, I was told.

example 2:
'but most FMS are sufficiently accurate when operating in DME/DME mode' ... true, but occasionally you may operate in VOR/DME mode and it has already happened that a faulty VOR caused a serious map shift in an (non-GPS) A320, also affecting the EGPWS. The airplane almost collided with terrain because the alert came much too late. Full report here:
http://www.aviationtoday.com/sia/20040201.htm

Hence, even with EGPWS you may have spurious warnings and you may have cases where the alert might not sound when necessary.

EoD

[john_tullamarine]

We are missing a significant point here, I think, chaps. All these very useful devices are still "aids to pilot navigation".

While the various systems' warnings can alert a pilot to a loss of SA, the basic defence still remains planning and crew SA.

In a manner analogous to the situation of the pilot who fails to maintain a reasonable level of stick and rudder skills in this increasingly automated world, he/she who blindly trusts to electronic wizardry sets up the potential for embarrassment .....

All systems can fail or do strange things if the code cutters didn't foresee every permutation ... mix up an unfortunate combination of failure and inattention and the result may be undesirable and, sometimes, catastrophic ....