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737-800 Landing Speed

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737-800 Landing Speed

Old 18th Sep 2008, 10:57
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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, 11:01
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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, 11:13
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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, 13:13
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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, 13:14
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So are those speeds faster than previous series?
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Old 18th Sep 2008, 13:29
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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, 13:43
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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, 16:55
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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 19th Sep 2008, 00:16
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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, 02:28
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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, 03:38
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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, 03:45
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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, 04:00
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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 04:12.
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Old 2nd Sep 2018, 11:45
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Originally Posted by WindSheer View Post
Just out of interest, is that in place due to the extra tail strike risk??
No. Only the touchdown speed (if too low) affects the probability of a tail strike or a hard landing, not the approach speed. As the guys said before, the adage of knots above Vref is a wind correction.
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Old 2nd Sep 2018, 11:51
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Does anyone have a correct manual (I say this because I've seen wrong data in some pdf articles where the vrefs for no LE/TE devices were abnormally low) with the stall speed (or Vref which is stall speed * 1.3) tables for zero flaps/slats? I've only seen correct Vref speeds for flaps between 15 and 40 vs weight, so in order to have a clue of the corresponding stall speeds, I simply divided the Vrefs to 1.3. Someone might say: why do you need stall speeds for no flaps/slats? Well, there have been occasions when cannot extend the flaps/slats from neutral (ex: flaps skew, asymmetry, other system failures), so you must land with no slats/flaps at all. I know for sure that there must be a table of stall speeds vs weight for flaps and slats retracted.

Regards,
Mav.
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Old 3rd Sep 2018, 22:00
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Vref=1.3xVso isn't a hard rule on the 737.

Also, there is a checklist for this situation. My QHR calls it "All Flaps Up Landing." Vapp=Vref40+55.
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Old 4th Sep 2018, 13:34
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The -800SFP2 has a landing speed set 7kts slower than normal. I see mto recall the -800 originally had the same landing speeds but it was re-scheduled +7kts fairly quickly after entering service due to, well, interesting tendencies to resemble a sack of potatoes....... Certainly the SFP2 landed a lot better if you were 7kts faster...
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Old 5th Sep 2018, 10:18
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Originally Posted by Capt Chambo View Post
Yes the speeds are a lot faster than the "older" series (300/400/500)
Compare the like-for-like models, not the heavier longer variants.
E.g.: -700 vs -300, -400 vs -800
You will find in general that the NG is a heavier aircraft than Classic [faster speed requirement] but has a better wing [lower speed requirement[, which more or less is won in favour of better wing, therefore slower approach speed, with comparable model used.
You [u]cannot compare the -300 (149Y) to the -800 (189Y) or even longer/heavier -900 (189Y) as the models, payload, and therefore landing weight, are completely incomparable.

Originally Posted by RVF750 View Post
The -800SFP2 has a landing speed set 7kts slower than normal.
Great addition to the NG line, enabling with same weight a lower speed and LDR, or increase payload on same LDR.
Similarly for departure, add payload for same TORA, or add range for same payload, or depart slightly slower making use of more ATM.
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Old 5th Sep 2018, 11:58
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Anything on offer now will feel pedestrian compared to what will be coming in the Max 10. The MTOW is 92T with the same wing so you can only imagine what an average Vref will be.
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Old 5th Sep 2018, 12:52
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Originally Posted by neville_nobody View Post
Anything on offer now will feel pedestrian compared to what will be coming in the Max 10. The MTOW is 92T with the same wing so you can only imagine what an average Vref will be.
I doubt to be honest. The A321 for example is not known for very high approach speeds, despite higher overall weights. Flap design (with multiple slots as on the A321) can make a difference. MTOW is not really an indicator here. The maximum landing weight needs to be known.

Last edited by Kakaru; 5th Sep 2018 at 13:02.
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