B744 GPWS Sink Rate trigger?
Joined: Dec 2003
Posts: 147
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From: South of Watford
Should NOT happen at 3.3 degrees, BOM 28 is about that slope...never had any problem there.
(even at close to max landing weight with slight tailwind and F25 when tankering)
(even at close to max landing weight with slight tailwind and F25 when tankering)
Last edited by Sir Richard; 4th July 2007 at 18:25. Reason: additional info
Joined: Aug 2000
Posts: 324
Likes: 1
From: Hindhead, UK
Have a look at this site. It has all the parameters for GPWS. It's a 727 site, but basic GPWS i believe has the same parameters for all types.
GPWS
At 2500' RA you need almost 5000fm to get a SINK RATE, at 1000'RA you need over 2000fpm
T'bug
GPWS
At 2500' RA you need almost 5000fm to get a SINK RATE, at 1000'RA you need over 2000fpm
T'bug
Joined: Jun 2001
Posts: 215
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From: Above 30,000 ft
It's not so much about GS angle than about sink rate. ACN rw 14 at max LWT on 744 can quite easily trigger the GPWS sink rate warning. At Vapp ~ 165 KIAS, the sink rate required to stay on the glide is about 900 fpm. Approx 300ft agl, there's quite often an updraft which can start to get you a little high if you're not anticipating it. At that point if the sink rate is increased, you easily exceed 1000 fpm & often get the sink rate alert too.
Thread Starter
Joined: Mar 2001
Posts: 317
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It does seem from that graph (thanks Thunderbug) <500 the warning is on a sliding scale from 1500ft/min to 1000ft/min at 50ft ....
The reason I ask is that my colleague called 'sink rate' to me when I was at 300ft having been pitched down to around 0deg in rising air with 3 whites/ 2 reds whilst on a visual approach ..
I guess my ROD was around 900-1000ft/min ... I normally check a bit at 100-50ft in these circumstances and flare normally at 30ft ...
I know at some airports, like Prestick's 3.3deg slope or Tiblisi's 3.5 deg 'sink rate' warnings at heavey weights / high Vref's are not uncommon.
The reason I ask is that my colleague called 'sink rate' to me when I was at 300ft having been pitched down to around 0deg in rising air with 3 whites/ 2 reds whilst on a visual approach ..
I guess my ROD was around 900-1000ft/min ... I normally check a bit at 100-50ft in these circumstances and flare normally at 30ft ...
I know at some airports, like Prestick's 3.3deg slope or Tiblisi's 3.5 deg 'sink rate' warnings at heavey weights / high Vref's are not uncommon.
Junior trash
Joined: Nov 1999
Posts: 1,025
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From: UK
Dont know who you work for but we have an SOP call on 744 from the PNF if ROD is 1000fpm or more in the latter stages of the approach. Its not to do with the GPWS. 1000fpm over the threshold is quite tricky to recover from without either burying it of wasting runway.
Edited to say, Think we work for same bunch, check out standard calls in the Flying Manual. Your Oppo was probably being a little nervy.
Edited to say, Think we work for same bunch, check out standard calls in the Flying Manual. Your Oppo was probably being a little nervy.
Last edited by Hotel Mode; 5th July 2007 at 10:38.
Thread Starter
Joined: Mar 2001
Posts: 317
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With a Vref at Max Landing weight of 160Kt plus say 10Kt wind correction, giving 170Kts ... say the wind is all accross, 5xGS = ROD on a 3deg slope ... so ROD would be around 850ft/min ...
So it's would not be unreasonable to see on occasions 1000ft/min correcting for rising air, going slightly into the whites etc ...
I've always felt, even on the 744, looking out at 50ft a rapid ROD can be easily seen and recovered from so long as one doesnt wait to flare at 30ft!
Also in these scenarios delaying closing the throttles helps ...
Anyway ... thats my 2cents worth ...
So it's would not be unreasonable to see on occasions 1000ft/min correcting for rising air, going slightly into the whites etc ...
I've always felt, even on the 744, looking out at 50ft a rapid ROD can be easily seen and recovered from so long as one doesnt wait to flare at 30ft!
Also in these scenarios delaying closing the throttles helps ...
Anyway ... thats my 2cents worth ...
Junior trash
Joined: Nov 1999
Posts: 1,025
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From: UK
I quite agree. Esp on steep slopes like CPT or recovering from a VOR 22L into JFK onto the Papis. However it is only a call and i see no requirement about correcting if its necessary. Think its just for awareness as high sink rates develop quite easily.
Joined: Jan 2007
Posts: 30
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From: Virtually anywhere!
From the EGPWS handbook. Mode 1 chapter.
Draw a line on a graph from 0ft RA/500 ft/min descent to 2500ft RA/4250 ft/min descent. Breaching this line will trigger "Sinkrate".
The "Pull Up" line is parallel to it for the bottom 250 ft and diverges from there up.
Two other considerations if a valid glideslope signal is recieved the boundary is adjusted to desensitize the alerts (doesnt say by how much though!) also EGPWS offers a "Steep Approach" option for given aircraft types which alter the above to allow steeper than normal approaches and I dont know if this will be the case for you 744!
Hope this helps
Draw a line on a graph from 0ft RA/500 ft/min descent to 2500ft RA/4250 ft/min descent. Breaching this line will trigger "Sinkrate".
The "Pull Up" line is parallel to it for the bottom 250 ft and diverges from there up.
Two other considerations if a valid glideslope signal is recieved the boundary is adjusted to desensitize the alerts (doesnt say by how much though!) also EGPWS offers a "Steep Approach" option for given aircraft types which alter the above to allow steeper than normal approaches and I dont know if this will be the case for you 744!
Hope this helps
Joined: Dec 2003
Posts: 36
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From: Virginia, USA
I've been flying the 744 F for 9 years and have yet to receive a "sink rate" callout even with numerous landings in Prestwick, VOR JFK 22L, Mexico City, Bogota, Quito, and Campinas. This despite most landing weights at max allowable 302.0 thousand kilos (except Quito) and 163 knots approach speed. Yet on almost every simulator ride someone gets a "sink rate" callout on almost every non precision approach flown in the "dive and drive" method. Some checkrides have been busted on more than two sinkrate callouts on a non precision approach, despite visual conditions.
Joined: Jan 2007
Posts: 30
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From: Virtually anywhere!
Bigiron
Yep it may well not be 74 specific, its the Allied Signal EGPWS handbook which covers some of the sims I work on here, none of which are 74's! we have from bizjet up to 772 here! So I may well be wrong! Its possible that the figures you give are the desnsitized option but I would be speculating as I have no solid data!
Be interested to know that though!
Yep it may well not be 74 specific, its the Allied Signal EGPWS handbook which covers some of the sims I work on here, none of which are 74's! we have from bizjet up to 772 here! So I may well be wrong! Its possible that the figures you give are the desnsitized option but I would be speculating as I have no solid data!
Be interested to know that though!
Top Dog
Joined: May 2000
Posts: 2,098
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From: Close to FACT
Empty 744F/min fuel.
FL450.
Approx 100nm out of TLV over Med. No-one lets you down until TLV speaks to you. Being an -F its ok to go down 6-7000fpm without screaming pax selling their story to the Daily Whatever.
I have seen GPWS inhibit (by F/O's left knee) being pushed.
Edit: Just studied the graph above properly - so no big deal.
FL450.
Approx 100nm out of TLV over Med. No-one lets you down until TLV speaks to you. Being an -F its ok to go down 6-7000fpm without screaming pax selling their story to the Daily Whatever.
I have seen GPWS inhibit (by F/O's left knee) being pushed.
Edit: Just studied the graph above properly - so no big deal.
