Airbus "TERRAIN…TERRAIN" & "TOO LOW, TERRAIN"
Micro, 
Aerocat et al. Alternative action for alerts might be plausible, but any situation where the alert or warning questions your judgement does not warrant further use of judgement.
A favourite reference Celebrating TAWS ‘Saves’: But lessons still to be learnt.
Note all of the incidents, but particularly # 7, re the crew’s judgement of flying level or re-establishing a safe approach path.
framer, I recall a simulator trial at an operators conference where pilots were expecting a Pull Up warning; the purpose was to evaluate differences in procedure application and timing. The scenario was at min effective timing for the equipment – no pre alerting (yes it can happen, see incident #8)
Half of the pilots did not survive the encounter. The deviance was divided equally between a late/slow reaction or less attitude/speed trade than required/available.
Aerocat et al. Alternative action for alerts might be plausible, but any situation where the alert or warning questions your judgement does not warrant further use of judgement.
A favourite reference Celebrating TAWS ‘Saves’: But lessons still to be learnt.
Note all of the incidents, but particularly # 7, re the crew’s judgement of flying level or re-establishing a safe approach path.
framer, I recall a simulator trial at an operators conference where pilots were expecting a Pull Up warning; the purpose was to evaluate differences in procedure application and timing. The scenario was at min effective timing for the equipment – no pre alerting (yes it can happen, see incident #8)
Half of the pilots did not survive the encounter. The deviance was divided equally between a late/slow reaction or less attitude/speed trade than required/available.
Just because you get a callout, doesn't mean you have lost SA and shouldn't continue using judgment. If the problem is obvious and you can fix it, then fix it, if not, go around. A glide slope callout at 1200 AGL should get the response "correcting", not "going around". Not that the latter is wrong, just unnecessary on an otherwise stable approach. Likewise a glide slope callout in the flare when landing on a runway with a displaced threshold can be ignored under some circumstances.
Terrain callouts can also be momentary blips in an otherwise good approach. A visual approach into an airfield with high terrain can sometimes trigger EGPWS callouts that aren't "spurious" but are just indicators of minor transgressions.
Terrain callouts can also be momentary blips in an otherwise good approach. A visual approach into an airfield with high terrain can sometimes trigger EGPWS callouts that aren't "spurious" but are just indicators of minor transgressions.
Join Date: Mar 2000
Location: Australia
Posts: 811
Likes: 0
Received 0 Likes
on
0 Posts
AerocatS2A, given that GPWS Mode 5 (Glideslope) 1- only works below 1000' AGL and 2- would indicate LOW on approach, both your examples demonstrate the importance of not assuming you haven't lost SA!
Aerocat, I disagree with the view of knowing or not knowing the state of awareness. A significant aspect in many accidents is surprise; a situation which was not anticipated, or an outcome which does not match actions or intent. IMHO any EGPWS alert would more likely fall into this category; if you are surprised, then act.
There may be ‘obvious’ situations where a small correction will apply, providing the alert (the situation) was expected. Being able to anticipate an event is part of awareness; thus a callout – “we may get an alert because” imparts knowledge because the situation is sufficiently understood and to a degree is being managed; situation awareness – being able to project ahead.
Calls after the event have little meaning other than to cover embarrassment.
If anticipation is absent, then so might general situation awareness; what then is the value of judgement.
(GS alerts are also inhibited below xx ft according to system/instalation)
There may be ‘obvious’ situations where a small correction will apply, providing the alert (the situation) was expected. Being able to anticipate an event is part of awareness; thus a callout – “we may get an alert because” imparts knowledge because the situation is sufficiently understood and to a degree is being managed; situation awareness – being able to project ahead.
Calls after the event have little meaning other than to cover embarrassment.
If anticipation is absent, then so might general situation awareness; what then is the value of judgement.
(GS alerts are also inhibited below xx ft according to system/instalation)
Thread Starter
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
The "AVOID TERRAIN" and the "PULL UP" alerts are straightforward: pull up for your life.
"SINK RATE" and "DON'T SINK" are straightforward, too: correct it if you don't want to get in trouble.
"TOO LOW GEAR" and "TOO LOW FLAPS" are straightforward as well: go around
"GLIDE SLOPE" is straighforward, too: correct, or ignore if intentional
"TERRAIN AHEAD" is relatively simple. Adjust flight path by stopping descent, starting a climb and/or turning as necessary to avoid terrain as shown on the ND.
But the ones that seems ambiguous to me are "TERRAIN-TERRAIN" (excessive terrain closure rate) and "TOO LOW TERRAIN" (unsafe terrain clearance when not in landing configuration) : Adjust the flight path, or initiate go around
May I choose? Based on what?
It sounds quite serious to me. If I am in IMC or in a dark night, I'll go around unless there is specific information of that airport giving false alerts.
A "TOO LOW TERRAIN" alert comes if you are flying at 250 kt or more and below 1,000 RA without being configured for landing (that's not good). If you are flying at 170 or so, it will come at about 300 RA and not configured yet (that's bad)
It is a very serious one, which I will regard as genuine unless I can see with my own eyes.
I totally agree with Safetypee. If I disregard a GPWS is because I can see terrain with my own eyes or if there is reports of nuisance alerts. I will never disregard a GPWS alert in IMC or night because I am convinced I have been doing everything OK so far and there is no reason for an alert.
"SINK RATE" and "DON'T SINK" are straightforward, too: correct it if you don't want to get in trouble.
"TOO LOW GEAR" and "TOO LOW FLAPS" are straightforward as well: go around
"GLIDE SLOPE" is straighforward, too: correct, or ignore if intentional
"TERRAIN AHEAD" is relatively simple. Adjust flight path by stopping descent, starting a climb and/or turning as necessary to avoid terrain as shown on the ND.
But the ones that seems ambiguous to me are "TERRAIN-TERRAIN" (excessive terrain closure rate) and "TOO LOW TERRAIN" (unsafe terrain clearance when not in landing configuration) : Adjust the flight path, or initiate go around
May I choose? Based on what?
A After “TERRAIN” has sounded twice, the warning switches to “PULL UP”, and is continually repeated until the aircraft leaves the warning envelope. In addition, the PULL UP lights come on.
A "TOO LOW TERRAIN" alert comes if you are flying at 250 kt or more and below 1,000 RA without being configured for landing (that's not good). If you are flying at 170 or so, it will come at about 300 RA and not configured yet (that's bad)
It is a very serious one, which I will regard as genuine unless I can see with my own eyes.
I totally agree with Safetypee. If I disregard a GPWS is because I can see terrain with my own eyes or if there is reports of nuisance alerts. I will never disregard a GPWS alert in IMC or night because I am convinced I have been doing everything OK so far and there is no reason for an alert.
Last edited by Microburst2002; 5th Aug 2014 at 19:27. Reason: typos
Lancer, 1 was a bad example. 2 has happened to me when following an ILS down to a circling minima for a straight in approach to a runway with a displaced threshold. The final 400' or so of the approach (visual on temporary PAPIS) was way above the normal glide slope which should not normally cause a callout, however, in the flare the glide slope signal fluctuated a bit and the indicator briefly went from full fly down to full fly up and back. It caused a glide slope callout. Was it a surprise? Yes. Had we lost SA? No. Should we have gone around? No definitely not. In my opinion, if your immediate response to a callout is "why did it do that?" Then you've lost SA, on the other hand if it is immediately obvious what has happened then it is no different than a support call from the PNF.
Microburst, you never disregard a GPWS alert. It went off for a reason. If you know why it went off and you can fix it, then fix it. If you don't know why it went off or you can't fix it then then get out of there. Very simple.
Join Date: Sep 1998
Location: wherever
Age: 55
Posts: 1,616
Likes: 0
Received 0 Likes
on
0 Posts
M202
Is there no Terrain clearance floor in the system you are describing?
If there is then all bets are off at 700RA where you will get a "Too Low Terrain" or similar regardless of configuration unless you are approaching a runway.
Is there no Terrain clearance floor in the system you are describing?
If there is then all bets are off at 700RA where you will get a "Too Low Terrain" or similar regardless of configuration unless you are approaching a runway.
Thread Starter
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
Yes, I haven't checked the heights and conditions for the TCF of the EGPWS, but If I recall correctly they are really "conservative" in the sense that if you are really at that height in that place you have made something really wrong.
Aerocat2sA said it well
That, for me, is a go around unless visually I can determine I'm OK every time I hear TERRAI TERRAIN or TOO LOW TERRAIN
Aerocat2sA said it well
Microburst, you never disregard a GPWS alert. It went off for a reason. If you know why it went off and you can fix it, then fix it. If you don't know why it went off or you can't fix it then then get out of there
Join Date: Jun 1999
Location: Queensland
Posts: 408
Likes: 0
Received 0 Likes
on
0 Posts
TOO LOW FLAP important consideration
TOO LOW FLAP is not simply restricted to final approach with the final landing flap not yet set.
With only approach flap set but otherwise in the landing config, it is possible to get this callout with steeply rising terrain, more so with normally expected higher downwind groundspeed during circle to land. Less steeply rising terrain could still be a great danger, but there may be no TOO LOW FLAP callout due to reduced rad alt ROD. Most other GPWS callouts are inhibited because of the aircraft configuration.
Check ALL the conditions that can give this callout.
There are many cues in aviation for immediate action. There is a good case for immediate action in this case.
The most modern GPWS may have addressed this.
With only approach flap set but otherwise in the landing config, it is possible to get this callout with steeply rising terrain, more so with normally expected higher downwind groundspeed during circle to land. Less steeply rising terrain could still be a great danger, but there may be no TOO LOW FLAP callout due to reduced rad alt ROD. Most other GPWS callouts are inhibited because of the aircraft configuration.
Check ALL the conditions that can give this callout.
There are many cues in aviation for immediate action. There is a good case for immediate action in this case.
The most modern GPWS may have addressed this.
Thread Starter
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
Black hole noted, Safetypee!
I have to add, then, that I will only disregard one of those alerts if I am in daylight VMC CAVOK.
The PULL UP alerts are never ever to be disregarded, of course.
I have to add, then, that I will only disregard one of those alerts if I am in daylight VMC CAVOK.
The PULL UP alerts are never ever to be disregarded, of course.
Roger that Micro, but note this photo for further thought:-
Retrieved from just below a hilltop (1,120ft), where previously a crew, flying day VMC above cloud, had confirmed their location by a geographic feature (having often flown the route), then descended into cloud. Mistakenly the locating hilltop identification was in error by 8nm ...
- and the QNH was 1013/2992.
That picture was on my office wall for many years; probably make a good screen-saver now.
Also lookup the CFIT accident at Sao Jorge (Azores) 11 Dec 1999 – misidentified an Island, turned and descended into cloud and into another island cliff face.
No Exceptions … If-then-Do.
Retrieved from just below a hilltop (1,120ft), where previously a crew, flying day VMC above cloud, had confirmed their location by a geographic feature (having often flown the route), then descended into cloud. Mistakenly the locating hilltop identification was in error by 8nm ...
- and the QNH was 1013/2992.
That picture was on my office wall for many years; probably make a good screen-saver now.
Also lookup the CFIT accident at Sao Jorge (Azores) 11 Dec 1999 – misidentified an Island, turned and descended into cloud and into another island cliff face.
No Exceptions … If-then-Do.
Thread Starter
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
Hmmm, scary...
But if there are clouds it is not CAVOK. In a CAVOK daylight (not twilight or anything, plain daylight and you can see the beautiful landscape, the runway and its surroundings, and terrain features and obstacles, and PAPI showing on slope… And always referring to the TERRAIN TERRAIN or TOO LOW TERRAIN only (no pull up alerts) wouldn't you continue?
but I see those are a lot of conditions. In that case it would be worth at least leveling off, if there is no subsequent pull up alert, nor further alerts, and all those conditions are met (specially the on slope PAPI) you might continue. If the alerts continue, a go around if probably the best even if everything seems Ok, since I might be nicely approaching the wrong runway…
Damn, I see it is better just to always trust the voice!
But if there are clouds it is not CAVOK. In a CAVOK daylight (not twilight or anything, plain daylight and you can see the beautiful landscape, the runway and its surroundings, and terrain features and obstacles, and PAPI showing on slope… And always referring to the TERRAIN TERRAIN or TOO LOW TERRAIN only (no pull up alerts) wouldn't you continue?
but I see those are a lot of conditions. In that case it would be worth at least leveling off, if there is no subsequent pull up alert, nor further alerts, and all those conditions are met (specially the on slope PAPI) you might continue. If the alerts continue, a go around if probably the best even if everything seems Ok, since I might be nicely approaching the wrong runway…
Damn, I see it is better just to always trust the voice!
Micro, the discussions in your thread have been most valuable, if only to identify the complexities that the industry tends to introduce to apparently simple aspects of safety.
Operations pre GPWS, allocated significant attention to avoiding the threat of CFIT, but there were few ‘detector’ systems and no drills.
With GPWS there was a simple drill:- IF “Whoop Whoop Pull Up”, THEN pull up. This was a memory item which added to an increasing number of operating memory drills.
EGPWS introduced more alerting levels and a range of warning prefixes. Whilst it could be argued that the prefixes helped to understand the situation, the drill should always be the same, and should not be delayed by re-evaluation or context dependant modifiers, but perhaps the drill is not always published in a simple manner.
The prefixes might help understand the situation after the event, but this analysis should only be conducted when a safe operating situation has been assured – and checked.
EGPWS is by far the most significant contributor to flight safety in recent years; it evolved from a simple concept, requiring additional features to counter the ingenuity of human error – particularly thinking that the situation is understood.
The industry should take care in not to overcomplicate operational use, nor use systems in ways other than designed, but unfortunately emerging pressures from reduced training / experience and a litigious social environment require more checklists and published explanation, which unfortunately often become the rule, whereas the intent was to provide guidance because not every situation can be foreseen, particularly when it involves the human.
Operations pre GPWS, allocated significant attention to avoiding the threat of CFIT, but there were few ‘detector’ systems and no drills.
With GPWS there was a simple drill:- IF “Whoop Whoop Pull Up”, THEN pull up. This was a memory item which added to an increasing number of operating memory drills.
EGPWS introduced more alerting levels and a range of warning prefixes. Whilst it could be argued that the prefixes helped to understand the situation, the drill should always be the same, and should not be delayed by re-evaluation or context dependant modifiers, but perhaps the drill is not always published in a simple manner.
The prefixes might help understand the situation after the event, but this analysis should only be conducted when a safe operating situation has been assured – and checked.
EGPWS is by far the most significant contributor to flight safety in recent years; it evolved from a simple concept, requiring additional features to counter the ingenuity of human error – particularly thinking that the situation is understood.
The industry should take care in not to overcomplicate operational use, nor use systems in ways other than designed, but unfortunately emerging pressures from reduced training / experience and a litigious social environment require more checklists and published explanation, which unfortunately often become the rule, whereas the intent was to provide guidance because not every situation can be foreseen, particularly when it involves the human.
