So WestJet almost puts one of their 737 in the water while landing at St-Maarten...
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G.Y.S. and others: no one has answered the question which others are asking, as to how they arrived in this predicament. That is very pertinent; was it a crew mess up, a system malfunction, an NPA training issue, a....etc.
Also, what stimulated the GA? It was VMC. Was it the EGPWS, was it the sudden awareness of the RA, was it losing sight of the runway, was it the sudden realisation they were going for a swim.
Were they visual at MDA and on profile? If so, and the a/c was in trim and stable (i.e. was the approach flown on automatics?) then doing nothing should have put the a/c closer to the correct spot than this.
So, what did they do to arrive in the wrong place and why was the GA so late. For the Canadian CAA to not investigate further to find these answers is almost a dereliction of duty to the rest of us and the pax.
Also, what stimulated the GA? It was VMC. Was it the EGPWS, was it the sudden awareness of the RA, was it losing sight of the runway, was it the sudden realisation they were going for a swim.
Were they visual at MDA and on profile? If so, and the a/c was in trim and stable (i.e. was the approach flown on automatics?) then doing nothing should have put the a/c closer to the correct spot than this.
So, what did they do to arrive in the wrong place and why was the GA so late. For the Canadian CAA to not investigate further to find these answers is almost a dereliction of duty to the rest of us and the pax.
RAT 5 I agree. It’s not about pillorying the crew, it’s about understanding what led them down the path they went so we can avoid repeating it. In a “just culture” we should be able to learn from others in a non-judgemental way, unless of course it was gross negligence or cowboy flying that got them there.
I’m at a loss (having flown a lot in the Tropics) to explain how the aircraft got to where it did without prior intervention. What guidance was being followed? Instrument? Visual? Mix of both? Neither? They obviously didn’t set out to crash but they were not far away from it, IMHO. Hopefully we may see a report at some time which may answer a few questions...
I’m at a loss (having flown a lot in the Tropics) to explain how the aircraft got to where it did without prior intervention. What guidance was being followed? Instrument? Visual? Mix of both? Neither? They obviously didn’t set out to crash but they were not far away from it, IMHO. Hopefully we may see a report at some time which may answer a few questions...
As I understand it, the TSB (the safety/accident investigation chaps) are investigating. The local CAA (enforcement) are not. That strikes me as the right call. Both I am sure will have seen the QAR record and it strikes me as precisely the right call that this will end up in a bulletin for us all to learn from.
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Rat, I believe people are questioning how they got to that point, but there is no information, certainly not from WJ. The WJ blog has been all over the place on the incident.
To be that close to CFIT or CFIW, that far out, multiple systems must have all been screaming at them. The ac is not that old, (even has the split scimitar winglets), so it should have all the bells and whistles...
Close to the water, a delay in the GA, then 40 minutes in hold? Why was that?
There we also lucky the was not the usual flotilla of boats out there on the flightpath, they were certainly at mainsail ht!
This has made news all over the World, so it should be reviewed, and sorted as to why and how this happened.
To be that close to CFIT or CFIW, that far out, multiple systems must have all been screaming at them. The ac is not that old, (even has the split scimitar winglets), so it should have all the bells and whistles...
Close to the water, a delay in the GA, then 40 minutes in hold? Why was that?
There we also lucky the was not the usual flotilla of boats out there on the flightpath, they were certainly at mainsail ht!
This has made news all over the World, so it should be reviewed, and sorted as to why and how this happened.
aterpster, re, "I don't share your confidence.", where do your doubts lie? Tx...
underfire, what "multiple systems" and "all the bells and whistles" do you have in mind that would be "screaming"? I'm not being flippant/sarcastic and am asking seriously, what warnings would you expect, and why? I am assuming you're a B737-800 pilot with training & knowledge to comment reliably. Thanks.
underfire, what "multiple systems" and "all the bells and whistles" do you have in mind that would be "screaming"? I'm not being flippant/sarcastic and am asking seriously, what warnings would you expect, and why? I am assuming you're a B737-800 pilot with training & knowledge to comment reliably. Thanks.
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Airbus A333
... During the daylight approach to Runway 24R in the presence of a thunderstorm just north of the airport, the crew was advised that the lighting on Runway 24R was out of service. This was the only runway in operation. During final approach, meteorological conditions changed from visual meteorological conditions to instrument meteorological conditions. On short final, during the approach to Runway 24R, using the instrument landing system, the aircraft entered a heavy rain shower and encountered a right crosswind exceeding 20 knots. The aircraft deviated from its path before touching down to the left of the runway centreline at 1234 Eastern Daylight Time. Following the landing, the left rear tire of the left main landing gear left the hard surface of the runway and travelled approximately 600 feet before regaining the runway. The aircraft returned to the centreline before taxiing to the terminal gate, where the passengers exited. Three runway edge lights were damaged. ...
Aviation Investigation Report A14Q0155 - Transportation Safety Board of Canada
EDIT: Following excerpt added with some bolding by me
3.1 Findings as to causes and contributing factors
During an approach in the presence of a thunderstorm, pilot-induced oscillation led to the aircraft being in a left bank as it crossed the runway threshold which, combined with a strong right crosswind, resulted in a rapid drift to the left very close to the ground.
Once the aircraft crossed the runway threshold, the intensity of the precipitation increased suddenly, such that the pilot flying (PF) had reduced visual references. Under these conditions, the PF did not detect the lateral movement of the aircraft in time to correct the drift before the outboard tires of the left bogie landed in the grass.
Given the absence of runway lighting in reduced visibility conditions, it was difficult for the pilot flying to detect the lateral movement of the aircraft over the runway and therefore to prevent the runway excursion.
A lateral wind shear generated by a downburst to the north of the runway suddenly increased the aircraft's drift to the left during the landing flare.
Runway 24R was not closed in instrument meteorological conditions, even though the runway lighting was not working. As a result, the runway was not equipped with the lights required to enable crews to clearly distinguish the lateral confines of the runway.
3.2 Findings as to risk
If airports are not equipped with a low-level wind shear alert system, crews landing there may not be aware of the presence of downbursts or microbursts, and therefore may be exposed to the risk of approach-and-landing accidents.
If a crew is unable to verify landing performance in heavy rain conditions involving a risk of hydroplaning, there is an increased risk of runway excursion.
If the "landing" response to the "minimum" calls reinforces the notion that landing is assured, there is a possibility that preparation for, and the decision to, go-around could be affected, increasing the risk of a landing incident or accident.
If the rain repellent system is unavailable or not used, there is an increased risk, in heavy rain conditions, that crews will lose the visual references necessary to avoid a runway excursion.
If a crew does not consider the consequences of multiple threats, there is a risk that pilots will continue a landing under conditions that are not favourable.
If the aircraft is drifting near the ground and pilots place the aircraft in low-energy landing regime, there is an increased risk of runway excursion.
If crews are not trained to retake the controls at very low altitudes or during the low-energy landing regime, there is a risk that, in the event of a problem, the pilot monitoring will not have time to identify the problem and take the appropriate measures.
If TC does not take action to develop the clear standards on avoiding thunderstorms during approach and landing called for in Recommendation A07-01, approaches in the presence of convective weather will continue, exposing aircraft to the multiple, unpredictable hazards associated with thunderstorms.
If occurrence sites are not preserved, there is a risk that evidence essential to identifying factors that contributed to an occurrence will be lost.
If dispatch is not aware of an aircraft communications, addressing and reporting system transmission failure, there is an increased risk that critical flight information is not received by the crew.
3.3 Other findings
... The runway excursion was not the result of a premature crab angle reduction manoeuvre, which is often associated with landing incidents in crosswind conditions.
Ignore history and history will repeat itself over and over again.
... During the daylight approach to Runway 24R in the presence of a thunderstorm just north of the airport, the crew was advised that the lighting on Runway 24R was out of service. This was the only runway in operation. During final approach, meteorological conditions changed from visual meteorological conditions to instrument meteorological conditions. On short final, during the approach to Runway 24R, using the instrument landing system, the aircraft entered a heavy rain shower and encountered a right crosswind exceeding 20 knots. The aircraft deviated from its path before touching down to the left of the runway centreline at 1234 Eastern Daylight Time. Following the landing, the left rear tire of the left main landing gear left the hard surface of the runway and travelled approximately 600 feet before regaining the runway. The aircraft returned to the centreline before taxiing to the terminal gate, where the passengers exited. Three runway edge lights were damaged. ...
Aviation Investigation Report A14Q0155 - Transportation Safety Board of Canada
EDIT: Following excerpt added with some bolding by me
3.1 Findings as to causes and contributing factors
During an approach in the presence of a thunderstorm, pilot-induced oscillation led to the aircraft being in a left bank as it crossed the runway threshold which, combined with a strong right crosswind, resulted in a rapid drift to the left very close to the ground.
Once the aircraft crossed the runway threshold, the intensity of the precipitation increased suddenly, such that the pilot flying (PF) had reduced visual references. Under these conditions, the PF did not detect the lateral movement of the aircraft in time to correct the drift before the outboard tires of the left bogie landed in the grass.
Given the absence of runway lighting in reduced visibility conditions, it was difficult for the pilot flying to detect the lateral movement of the aircraft over the runway and therefore to prevent the runway excursion.
A lateral wind shear generated by a downburst to the north of the runway suddenly increased the aircraft's drift to the left during the landing flare.
Runway 24R was not closed in instrument meteorological conditions, even though the runway lighting was not working. As a result, the runway was not equipped with the lights required to enable crews to clearly distinguish the lateral confines of the runway.
3.2 Findings as to risk
If airports are not equipped with a low-level wind shear alert system, crews landing there may not be aware of the presence of downbursts or microbursts, and therefore may be exposed to the risk of approach-and-landing accidents.
If a crew is unable to verify landing performance in heavy rain conditions involving a risk of hydroplaning, there is an increased risk of runway excursion.
If the "landing" response to the "minimum" calls reinforces the notion that landing is assured, there is a possibility that preparation for, and the decision to, go-around could be affected, increasing the risk of a landing incident or accident.
If the rain repellent system is unavailable or not used, there is an increased risk, in heavy rain conditions, that crews will lose the visual references necessary to avoid a runway excursion.
If a crew does not consider the consequences of multiple threats, there is a risk that pilots will continue a landing under conditions that are not favourable.
If the aircraft is drifting near the ground and pilots place the aircraft in low-energy landing regime, there is an increased risk of runway excursion.
If crews are not trained to retake the controls at very low altitudes or during the low-energy landing regime, there is a risk that, in the event of a problem, the pilot monitoring will not have time to identify the problem and take the appropriate measures.
If TC does not take action to develop the clear standards on avoiding thunderstorms during approach and landing called for in Recommendation A07-01, approaches in the presence of convective weather will continue, exposing aircraft to the multiple, unpredictable hazards associated with thunderstorms.
If occurrence sites are not preserved, there is a risk that evidence essential to identifying factors that contributed to an occurrence will be lost.
If dispatch is not aware of an aircraft communications, addressing and reporting system transmission failure, there is an increased risk that critical flight information is not received by the crew.
3.3 Other findings
... The runway excursion was not the result of a premature crab angle reduction manoeuvre, which is often associated with landing incidents in crosswind conditions.
Ignore history and history will repeat itself over and over again.
Last edited by alph2z; 29th Mar 2017 at 23:45.
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The ground prox/taws would have warned below glideslope, perhaps terrain closure rate, and too low...
Depending on how they dropped, descent rate near terrain
Warning for closure rate
The altitude annunciator would have been giving them the periodic, and the 50 foot..There is altitude callouts in 10 foot increments, they certainly heard the 100 foot increments, but that is custom set, so not certain how often altitude was annunciated, but I bet they had 50 foot called.
The is Boeing, so the system uses a 500'ROC at FAF, and tapers down, (AB is 400' ROC at FAF) so they would not have had the required obstacle clearance and it would warn of imminent ground contact...
They would have the forward looking capability, based on the FAF, threshold location, thus the predicted flightpath, and this would have been yet another warning, more than 2 dots below flightpath.
It would have given a premature descent alert when that far below flightpath.
IF windshear had occurred, that would have been another warning.
EDIT: approach over water, there is supposed to be an additional obstacle area added for the transient boat traffic, unclear if this is added to their database.
Depending on how they dropped, descent rate near terrain
Warning for closure rate
The altitude annunciator would have been giving them the periodic, and the 50 foot..There is altitude callouts in 10 foot increments, they certainly heard the 100 foot increments, but that is custom set, so not certain how often altitude was annunciated, but I bet they had 50 foot called.
The is Boeing, so the system uses a 500'ROC at FAF, and tapers down, (AB is 400' ROC at FAF) so they would not have had the required obstacle clearance and it would warn of imminent ground contact...
They would have the forward looking capability, based on the FAF, threshold location, thus the predicted flightpath, and this would have been yet another warning, more than 2 dots below flightpath.
It would have given a premature descent alert when that far below flightpath.
IF windshear had occurred, that would have been another warning.
EDIT: approach over water, there is supposed to be an additional obstacle area added for the transient boat traffic, unclear if this is added to their database.
Last edited by underfire; 30th Mar 2017 at 01:51.
aterpster;
Thanks...figured something like that [-(
I've used the FR24 data to plot the first & second approach paths, much like someone has done earlier in this thread, but a 3deg descent path (red line, from the threshold, out) is drawn in, and 150' added to all FR altitudes as per an earlier discussion on altimetry & ADS-B.
The flight path may appear a bit lower than it was because the aircraft was slightly left of the inbound course after MAPON, and Google Earth takes such perspective into account, as many here would probably understand.
The steady altitude during the hold also indicated "2450". Adding 150' to that gives 2600ft which is the MHA for the hold and for all inbounds so it seems reasonable to do so.
150' appears too much at the lowest point of the first approach; I think the airplane was less than a hundred feet above the water at lowest point but the investigation will provide that information - that level of fine-tuning for a baro correction is too much for FR24.
Anyway, here are some trial results...nothing scientific about it at all:
Second approach:
Thanks...figured something like that [-(
I've used the FR24 data to plot the first & second approach paths, much like someone has done earlier in this thread, but a 3deg descent path (red line, from the threshold, out) is drawn in, and 150' added to all FR altitudes as per an earlier discussion on altimetry & ADS-B.
The flight path may appear a bit lower than it was because the aircraft was slightly left of the inbound course after MAPON, and Google Earth takes such perspective into account, as many here would probably understand.
The steady altitude during the hold also indicated "2450". Adding 150' to that gives 2600ft which is the MHA for the hold and for all inbounds so it seems reasonable to do so.
150' appears too much at the lowest point of the first approach; I think the airplane was less than a hundred feet above the water at lowest point but the investigation will provide that information - that level of fine-tuning for a baro correction is too much for FR24.
Anyway, here are some trial results...nothing scientific about it at all:
Second approach:
Last edited by PJ2; 30th Mar 2017 at 03:33.
underfire;
Well, interesting. We'll see if any of those warnings were active any time during the approach. As aterpster states, age-old failure to maintain minimum until in the slot. Lion Air, UPS @ Birmingham come to mind, (and I believe there were no warnings in the UPS accident).
Well, interesting. We'll see if any of those warnings were active any time during the approach. As aterpster states, age-old failure to maintain minimum until in the slot. Lion Air, UPS @ Birmingham come to mind, (and I believe there were no warnings in the UPS accident).
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PJ2,
Interesting flightpath profile information, which program are you using? Are you just plotting the .kml file from FR?
I thought that the ADSB showed 0 altitude when the ac was on final (per earlier posts)
What is the lowest altitude that you are showing,is this the 150' add that you used?
Note that there is a 50' TCH on the flightpath, not a direct line to TCH 0.
So you know, ADSB data reports altitude in 25 foot increments, and has latency factors in the system, to which there is about an 8 second delay.
It is notoriously inaccurate in reporting altitude on final approach due to the descent rate and kalman reporting latencies, especially if there is rapid descent, a turn or crosswinds.
Interesting flightpath profile information, which program are you using? Are you just plotting the .kml file from FR?
I thought that the ADSB showed 0 altitude when the ac was on final (per earlier posts)
What is the lowest altitude that you are showing,is this the 150' add that you used?
Note that there is a 50' TCH on the flightpath, not a direct line to TCH 0.
So you know, ADSB data reports altitude in 25 foot increments, and has latency factors in the system, to which there is about an 8 second delay.
It is notoriously inaccurate in reporting altitude on final approach due to the descent rate and kalman reporting latencies, especially if there is rapid descent, a turn or crosswinds.
Last edited by underfire; 30th Mar 2017 at 05:25.
I suspect that where a non-corrected ADS-B altitude becomes negative (i.e. in this case at the points where the actual height was less than 150'), FR24 dumbly substitutes null/0 values, so those can't be trusted.
So you know, ADSB data reports altitude in 25 foot increments, and has latency factors in the system, to which there is about an 8 second delay.
It is notoriously inaccurate in reporting altitude on final approach due to the descent rate and kalman reporting latencies, especially if there is rapid descent, a turn or crosswinds.
It is notoriously inaccurate in reporting altitude on final approach due to the descent rate and kalman reporting latencies, especially if there is rapid descent, a turn or crosswinds.
Where did you get the idea that there is a delay of anything like 8 seconds (not that we're particularly interested in absolute time values in this instance) ? Where is the data being buffered in the meantime ?
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Other than the 25' granularity, altitude reported by ADS-B should be as accurate (subject to adjustment for QNH) and timely as your altimeter, given that both are coming from the same source and subject to the same errors.
Where did you get the idea that there is a delay of anything like 8 seconds (not that we're particularly interested in absolute time values in this instance) ? Where is the data being buffered in the meantime ?
8 seconds is what is typically used in the latency calcs, and the information is buffered in the INS. (the net has significant papers on latency issues with GPS and aircraft)
Each low band sat signal takes about 3 seconds to receive, (and in realty, it may be 5 seconds with correction) with multiple sats required, it takes a while to receive all of them, process them.
The kalman filter, tracks the data, determines the ac location where it was, and interpolates the data to where the ac actually is. That calculation has a latency of about 8 seconds. Within that 8 seconds, if there are changes to the horizontal flightpath, such as a turn, or even crosswinds, or vertically with descent, the data will not be accurate.
After all of that, the ac systems uses a lookup feature from the internal database for altitude. Depending on the manufacturer, that methodology is vastly different. That is then compared with the rad alt and baro data, and viola, that is your altitude as reported. (ohhh the algorithms) You want it to figure out the descent profile, in a turn, (a 3d spiral) using a lookup feature to an internal database with an 8 second delay? oh yea.
The descent on final approach, again based on 8 seconds latency, will not be accurate at all, even with continuous descent. Too much happens in 8 seconds for the ADSB data to be accurate, ie how much has the ac descended in 8 seconds based on an 8 second delay with 25 foot reporting....
The data transmitted through ADSB is far different that what you have on the ac, in both reporting and granularity.
Last edited by underfire; 30th Mar 2017 at 12:19.
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Underfire, an impressive list of warnings. Obviously the crew must have ignored all of them.
Certainly no "glideslope" warning, there is no glideslope (ILS) in St Maarten!
Also no "terrain" warning (terrain closure); within a defined area around the airport (not sure how big that exactly is, but I guess they were to close) you don't get those; otherwise you could never land
For a "sink rate" you would need around 1000FPM at low altitude, doesn't look like it on the video..
And a "windshear" warning would warrant an aggressive maneuver; the go around looks very gentle too me. Doen's look like this one either..
The "minimums" call is at 500' (or 700'), that awareness call had already passed..
They should have had the 100' Radio alt call though. Perhaps that was the trigger for them. At about 100' you should see the threshold disappearing under the nose; I guess they had a lot of water instead.. Suddenly that creepy feeling comes up...
Last edited by golfyankeesierra; 30th Mar 2017 at 18:58.
After all of that, the ac systems uses a lookup feature from the internal database for altitude. Depending on the manufacturer, that methodology is vastly different. That is then compared with the rad alt and baro data, and viola, that is your altitude as reported. (ohhh the algorithms) You want it to figure out the descent profile, in a turn, (a 3d spiral) using a lookup feature to an internal database with an 8 second delay? oh yea.
No satellites or databases involved, just a bit of aneroid magic.
You can easily verify that if you visit your local airport with an ADS-B receiver and watch aircraft taking off. You will see the altitude readout changing within a second or so of the wheels leaving the runway.
Not that any of this is relevant to the WestJet - we know the data that it sent, we know the QNH correction factor, so unless you're suggesting that the positional and altitude data were out-of-sync with each other then we can be pretty confident that the flightpath plots we've seen represent what actually happened.
underfire;
I created the images using the basic FR24 kml data in Google Earth (free version), with modifications as described in my post.
Method:
You can right-click-copy each/any of the FR24 waypoints and paste the text into Notepad to see both lat-long & altitude, which follows right after the lat-long data.
You can also create sloping lines to simulate descent paths by modifying the height (in meters), at one end of the line thus created. A slope can be calculated using trig functions. For the 3° descent path on the SXM10 I created a line from the runway threshold extended to a point 10NM out and saved it in Google Earth so it appeared in the Places list on the left side of the map. I right-click-copied that line and pasted the text into Notepad. I calculated the height of the line (ASL) using trig:
tan (3°) x d = h, or, 0.052407 x 60000 = 3144.46ft, or 958.4m ASL.
In Notepad, I changed the line's end height of 0m to 958m then Selected-All and pasted the changed kml over top of the original one in the Places list, (it actually gets inserted just below the waypoint over which you paste).
Because GE defaults to "Clamped to Ground" when drawing any lines, I right-clicked on the line to get the drop-down menu, and selected "Properties > Altitude". I selected "Absolute" which releases it from "clamped" and becomes a slope from a height of 3144ft (the correct height 10NM out on a 3° slope) to about 12', the height of the SXM airport. To be precise one could add that 12' (4m) in and program the end of the line to 962m, but none of this is that accurate, as discussed elsewhere. It takes a little experimentation and intuition.
To be clear, I concur with other posters regarding "no warnings" at that stage of flight. I believe that if you flew these aircraft you'd know that and the fact that GPWS glide slope warnings do not monitor RNAV approaches. As stated, we'll see what the investigation says; I think there are some interesting theories here.
I created the images using the basic FR24 kml data in Google Earth (free version), with modifications as described in my post.
Method:
You can right-click-copy each/any of the FR24 waypoints and paste the text into Notepad to see both lat-long & altitude, which follows right after the lat-long data.
You can also create sloping lines to simulate descent paths by modifying the height (in meters), at one end of the line thus created. A slope can be calculated using trig functions. For the 3° descent path on the SXM10 I created a line from the runway threshold extended to a point 10NM out and saved it in Google Earth so it appeared in the Places list on the left side of the map. I right-click-copied that line and pasted the text into Notepad. I calculated the height of the line (ASL) using trig:
tan (3°) x d = h, or, 0.052407 x 60000 = 3144.46ft, or 958.4m ASL.
In Notepad, I changed the line's end height of 0m to 958m then Selected-All and pasted the changed kml over top of the original one in the Places list, (it actually gets inserted just below the waypoint over which you paste).
Because GE defaults to "Clamped to Ground" when drawing any lines, I right-clicked on the line to get the drop-down menu, and selected "Properties > Altitude". I selected "Absolute" which releases it from "clamped" and becomes a slope from a height of 3144ft (the correct height 10NM out on a 3° slope) to about 12', the height of the SXM airport. To be precise one could add that 12' (4m) in and program the end of the line to 962m, but none of this is that accurate, as discussed elsewhere. It takes a little experimentation and intuition.
To be clear, I concur with other posters regarding "no warnings" at that stage of flight. I believe that if you flew these aircraft you'd know that and the fact that GPWS glide slope warnings do not monitor RNAV approaches. As stated, we'll see what the investigation says; I think there are some interesting theories here.
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Agree Bloggs, don't think there would be a lot of warnings at all.
Certainly no "glideslope" warning, there is no glideslope (ILS) in St Maarten!
Also no "terrain" warning (terrain closure); within a defined area around the airport (not sure how big that exactly is, but I guess they were to close) you don't get those; otherwise you could never land
For a "sink rate" you would need around 1000FPM at low altitude, doesn't look like it on the video..
And a "windshear" warning would warrant an aggressive maneuver; the go around looks very gentle too me. Doen's look like this one either..
The "minimums" call is at 500' (or 700'), that awareness call had already passed..
They should have had the 100' Radio alt call though. Perhaps that was the trigger for them. At about 100' you should see the threshold disappearing under the nose; I guess they had a lot of water instead.. Suddenly that creepy feeling comes up...
Certainly no "glideslope" warning, there is no glideslope (ILS) in St Maarten!
Also no "terrain" warning (terrain closure); within a defined area around the airport (not sure how big that exactly is, but I guess they were to close) you don't get those; otherwise you could never land
For a "sink rate" you would need around 1000FPM at low altitude, doesn't look like it on the video..
And a "windshear" warning would warrant an aggressive maneuver; the go around looks very gentle too me. Doen's look like this one either..
The "minimums" call is at 500' (or 700'), that awareness call had already passed..
They should have had the 100' Radio alt call though. Perhaps that was the trigger for them. At about 100' you should see the threshold disappearing under the nose; I guess they had a lot of water instead.. Suddenly that creepy feeling comes up...
ADSB usually broadcasts both baro and geometric altitude. Because of all of the issues with baro, many automated ATC systems use geometric.
There were claims early on from WJ about a rapid descent, hence a possible windshear warning, and we dont see videos as to how far out they were that low, hence the other warning that may have occurred for terrain closure....
the question was how many warnings could there be, and that is a list of possible ones.
This ac should be EGPWS, which does use the terrain clearance floor and terrain awareness, based on the information of terrain and obstacles in the database.The EGPWS uses a geometric altitude that blends improved pressure altitude calculations, GPS altitude, radio altimeter, and terrain and runway information to eliminate the reliance on human data input. The look ahead feature uses a 60 second timeframe, so being that far out and that low, the 60 second look ahead would have picked that up.
They were pretty far out when the videos and images were taken, so it is likley that obstacle clearance protection was not met.
Last edited by underfire; 30th Mar 2017 at 21:59.
Originally Posted by Undefire
I did not say they had all of these, but depending on what was going on, these are the warnings.
May I suggest that if you don't know, then either don't say or write a clear disclaimer that you are hypothesising. I would wager there are plenty of readers on here who don't know, and reading your missives will give them the wrong ideas, especially since what you wrote above about warnings is largely irrelevant to this incident.
Originally Posted by Underfire
They were pretty far out when the videos and images were taken, so it is likley that obstacle clearance protection was not met.