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clayton4115

loss of speed on approach

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hi alli seem to get stall warning and loss of speed on my final approach into an airport, i know i am not too heavy with about 15% fuel my landing speed is about 137 kts flap 30, but on approach when i dial down to say 140 kts and flap 20 i get stick shaker sound and the AP cancels the GS and then the LOC lights up.am i doing the approach wrong? am i too slow on the approach too far out?this is the 747Xthanks

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I assume A/T is maintaining 140KIAS.I also assume you have selected the flaps and Vref from the approach page in the FMC, and it has put Vref and the flap marks on the speed tape.I must also assume that you're not slowing below the flap mark for 30 until the flaps are in position.Given these assumptions, a stick shaker is surprising. "Too far out" is hard to judge cause you didn't mention how far out you were. You should be in landing configuration established on approach at 1000 agl, and it's common to be very close to that (say within one notch of flaps) at the FAF.Where are you intercepting GS?


Dan Downs KCRP

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hi Dan thanks for your reply now to the repliesI assume A/T is maintaining 140KIAS. (YES)I also assume you have selected the flaps and Vref from the approach page in the FMC, and it has put Vref and the flap marks on the speed tape. (YES)I must also assume that you're not slowing below the flap mark for 30 until the flaps are in position. (I dont know, how do i verify)Given these assumptions, a stick shaker is surprising. "Too far out" is hard to judge cause you didn't mention how far out you were. You should be in landing configuration established on approach at 1000 agl, and it's common to be very close to that (say within one notch of flaps) at the FAF. ( I am about 10NM - 15NM out and reducing fast from 180kts)Where are you intercepting GS? (LOC first then GS second)

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when you say A/T maintaining 140 kts, well the plane is coming down to that speed from say 180 kts and im going through the process of extending flaps to get there at 140 kts.

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Clayton,Dan said it all really. I think perhaps you're reducing speed below the minimum safe speed for your CURRENT flap extension before they finish extending.As Dan says, typically landing configuration at 1,000 AGL (above ground level). On my approaches I'm fully configured at 1,000AGL and maintain 160knots till 4 miles from the threshold (often done in reality to maintain separation). After passing 4 miles I reduce to my VRef plus whatever I feel is appropriate (5 - 10) depending on weather, other conditions etc, before I land. At 135knots vref speed, 140 - 145 isn't going to be a problem, you'll have plenty of runway to slow down gently on.You should get no stick shaker at all on approach, make sure you manage the decelleration correctly. Use the speed tape markers as guides, they'll indicate if you're going too slow (yellow, red zones).CheersCraigPS - One more thing, remember flaps take some time to extend, initially they extend more slowly. Simply pulling the lever doesn't mean they are actually extended to flaps 1/5/10/20/25/30 at that point. You need to keep an eye on the EICAS flaps display to ensure you're safe to continue reducing.


Craig Read, EGLL

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Clayton,Are you sure your entered ZFW in the FMC is what the aircraft and payload actually weighs? This is what all other data is based on. If this is wrong you can get the behaviour you are describing.If you, on the other hand, isn't entering the ZFW manually I am at a loss.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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thanks guys, yes i am using the PMDG payload data and then pressing the ZFW LSK which automatically feeds in data to the FMC.I think i may not be waiting long enough before i proceed to extend the flaps the next level and way to slow, i am already dirty and on REF Speed too far out i think, even before the OM.I will try these tips on my next flight.

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Clayton:Here's my procedure (as a complete amateur driver, of course) given a typical landing weight of 530,000 lbs, (my ZFW is generally set permanently at 500K, with typical landing fuel of 30k--your 15% fuel sounds a bit excessive)1. Pre-approach, I start by extending flaps 1 at 10 knots above the 'UP' indicator on the PFD. That's usually around IAS 220-230.2. I make sure that I go to the NEXT flap setting as I slide past the next green flap marker on the PFD. So, if I am doing IAS 190, slowing to IAS 180 and I see the '5' marker at, say, IAS 185, I go to flaps 10 so I am actually at flaps 10 by IAS 180. This keeps my pitch a little lower and helps with control generally.3. When levelling off for the GS which I normally intercept at 2500 or 3000 AGL after at least 1 minute of level flight, I slow down to around IAS 170-175 and as the GS diamonds start descending to 1 dot above interception on the PFD (and/or ND), I slow to 170, go to flaps 20 and dump the gear at the same time. If I do this, it reduces my pitch somewhat and gets me stable for the remaining flap dump to 25 or 30 after GS interception.4. Once I intercept the GS, I reduce IAS to Vref+5 within about 30 seconds and after twirling the MCP SPD knob down to such a speed, I go to flaps 25 (or 30) depending on which flap speed I've elected to accept for touchdown.In sum, I am never in the landing config with my touchdown Vref until about 5-6nm away from the field. If you are in the landing config too early, at your flap Vref, and you're not even sliding down the glideslope, you risk having an excessively steep pitch and experiencing control problems. I may have screwed up with the FMC, the APU, the generators, and everything else in my years with this Queen, but I have never once stalled on approach or had a poor approach using the technique I summarize above for you, for which I thank the developers and the pros on this forum!Hope this helps.Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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hi Jonathanthanks for your valuable input, just one question with the FLAP settings on the PFD, am i blind or something because what i do is thisi am slowing down to say 200kts from 250 kts and then around 220 i see the UP in the PFD, once i pass the UP i call for Flap 1 which i manually do by pressing F5, then i dont see the next setting on the PFD till i actually press again F5 and call for the next Flap Setting (1)i.e the next flap setting doesnt show up on the PDF till i press for it.is this correct?

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Clayton:I shall check on my Queen PFD later today when I fire up FS.Meantime, as you slow down and approach "UP" on the PFD, go to Flaps 1 at roughly 10 knots BEFORE you pass UP. The practice is to go to the flap setting BEFORE hitting the indicated flap speed.More a bit later.Cheers,JS


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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On checking right now, seems NEXT flap speed does not show beyond the flap position you're currently at. So, if you're slowing to "UP" and throw out flaps 1, then "1" appears on the tape -- but NOT "5". The figure "5" appears when you go to flaps 5 -- which you go to as you are slowing down and sliding past the "1" to your next approach speed.Flaps crank out and down slowly (long moments) so reduce to your next speed and then throw out the flaps but generally I am ahead of the speed by one flap setting most of the time (i.e., I am at flaps 10 by the time I hit "5" on the PFD speedtape, even if my MCP speed or VNAV speed is set to the flaps 5 speed) to keep pitch stable and manageable all the way down. Be ahead of the plane all the way down and you'll be fine.The margin for flaps deployment is fairly huge on the Queen, especially the initial flap settings. The limit for flaps 1 is IAS 280 and for flaps 5 it's 250 or so, so as you descend for approach your speeds are already way below those max limits and you can afford to be one flap setting ahead.Hope this is clear. Post again if not.Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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Clayton:Any better luck or progress with your approaches? If you can post results, that would be great. Thanks!Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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hi JonathanYes! what i have been doing was landing on FLAP 30 with the corresponding speed from the FMC, now i am landing at Flap 25 which makes the speed about 5-8 kts higher at landing, i have also followed your advise and am i now putting the next flap position well before the flap advisory on the PFD tape. i have not had any stall warnings for the past two landings which i have done, one into Manchester on Rwy 06L and the other last night from the cross the pond event into Boston, runway 27.Thanks for your help, it does sound promising.

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Excellent, Clayton, well done! Keep up the good work. Most of all, keep up your SPEED to match the flap settings!Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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