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Old 18th Sep 2008, 09:57   #1 (permalink)
 
Join Date: Aug 2008
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737-800 Landing Speed

Technically interested passenger question:

Every time I fly in a 737-800 series the landing speed always seems to be much faster than I would expect with consequent heavier breaking on the runway. Is there a special reason for this. I get the impression that the 800 series has a lower coefficient of drag than earlier series as descending from cruise level also almost always seems to be done with airbrakes now.

Anybody throw any light on this?

Many thanks, Bruce
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Old 18th Sep 2008, 10:01   #2 (permalink)
 
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Wait till you land at City of Derry Airport in Ireland with Ryanair, you should try it for a laugh,,, BREAKING isnt the word for it...

lol

Not sure about speeds but always felt it was fast myself to.
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Old 18th Sep 2008, 10:13   #3 (permalink)
 
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From a Boeing manual:

Depending on weight:
140 klbs (63 ton) Flaps 30, 146 kt Vref
120 (54 ton)....................135 kt
100 (45 ton)....................123 kt

Usually a few kt's are added to the Vref as I understand it. (+5)?
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Old 18th Sep 2008, 12:13   #4 (permalink)
 
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Quote:
Usually a few kt's are added to the Vref as I understand it. (+5)?
It can be a lot more than a few knots - how about plus 20 knots above the Vref?

Boeing recommend add half the steady headwind component and all of the gust factor. While Boeing also say the half the steady HW component should be bled off approaching touch-down, in reality that rarely occurs with the result that a good proportion of touch-downs occur faster than they should. No problem with a long runway but a flight safety problem on a short wet runway especially if the additives cause an unintentional float.
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Old 18th Sep 2008, 12:14   #5 (permalink)
 
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So are those speeds faster than previous series?
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Old 18th Sep 2008, 12:29   #6 (permalink)
 
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Quote:
It can be a lot more than a few knots - how about plus 20 knots above the Vref?
Just out of interest, is that in place due to the extra tail strike risk??
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Old 18th Sep 2008, 12:43   #7 (permalink)
 
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Yes the speeds are a lot faster than the "older" series (300/400/500).
I fly the -800 & -900 and I have a theory that the approach speed is more a function of body angle than stall speed (the normal criteria that dictates approach speed). By approaching faster, the pitch attitude is flatter and there is less likelihood of a tailstrike during the flare.
I note that the -900ER's are fitted with a number of aerodynamic improvements (slots, slats & flaps) as well as an extra tail skid to prevent fuselage damage in the event of a tailstrike.
As I say, just a theory and I could be wrong!

See:-
The Boeing 737 Technical Site
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Old 18th Sep 2008, 15:55   #8 (permalink)
 
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As far as I know, Capt Chambo is correct; the Vref is artificially higher to decrease tail-strike risk.
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Old 18th Sep 2008, 23:16   #9 (permalink)
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Caveat - I have little specific NG background to speak of.

I have a theory that the approach speed is more a function of body angle

I would be extremely surprised if this were to be the case due to the marketing penalties for the OEM .. ?
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Old 19th Sep 2008, 01:28   #10 (permalink)
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Quote:
Yes the speeds are a lot faster than the "older" series (300/400/500).
The speeds quoted above are about 5 kts slower than for the 400 classic.
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Old 19th Sep 2008, 02:38   #11 (permalink)
 
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Some weeks ago I flew a 737-900 with a final approach speed of 169kt. Around max. landing weight, flaps 30, max. wind + gust additives. Needed to inform ATC in advance, or we would have gained on the preceding 777 that was doing 140kt.
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Old 19th Sep 2008, 02:45   #12 (permalink)
 
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Bloody hell!!! And its still a Cat C right?? Whats the Flap 30 limit speed on the -900? We might be getting them (or the -800) soon.

Regards
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Old 19th Sep 2008, 03:00   #13 (permalink)
 
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Max. landing weight for a -900 (not an ER) is about 66,000 kg. VREF30 for a landing weight of 65,000 kg is 151kt, and the total of wind, gust, shear, or ice formation additives may not exceed 20kt or flap placard speed minus 5kt. The flaps 30 limit speed is 175kt, so we were operating on the limit. Not every landing is like that, but a fully loaded -900 does land pretty fast in comparison with a lighty loaded classic.

And although the 737 is a cat C aircraft, we use cat D limits under such circumstances.

Last edited by xetroV; 19th Sep 2008 at 03:12.
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