737-800 approach speeds

[ottoboy 0]

Hi!Boeing suggests following formula for 737NG-series to be used during approaches until runway threshold:"Vref + 5kn + 1/2 steady wind + full gusts"When using above formula with -800 plus 40 degree flaps on landing during high headwind components we get sort of a mess. The aircraft likes to pitch down, between 2.5-5 degrees as the engines are screaming at 70-85% N1. During such situations you have to fly below the calculated Vapp, in some situations speeds equal to or even below Vref. With other NG-series the formula works all fine, not with -800 (at least with 40 degree flaps, which is reguired in some cases in order to accomplish the braking safely)How do you handle such situations? Just fly the approach in Vref, with normal pitch and engine power, or fly with the Vapp-speed with nose down and high throttle?

[Guest Boeing Skunk Works]

Leave the flaps at 30

[downscc 1,327]

Please sign your posts to this forum.Flaps 40 is not used very often. High headwinds will always shallow your descent rate so the corresponding increase in power is expected. I don't understand your rationale for 40 flaps (safe braking?). Try Flaps 30Also, the "Vref + 5kn + 1/2 steady wind + full gusts" you quote just doesn't look right. I guess that is because I live where the average steady winds are about 20-30 kts on any afternoon. EDIT: Up to 20 kts correction... per target speed definition in AOM.

[onurksn 1]

Hi Otto (?)To add to what has been written above, normally I go for 30 Flaps approaches unless a short runway or autoland is involved. What you are experiencing is due to a high final approach speed with too much drag. Those additionnal flaps are creating lift at that speed so the aircraft has to pitch down to sink. As far as I know 40 Flaps aren't normally used in gusty and strong winds anyway.Happy landingsEDIT: Some airlines favor 40 flap approaches as company policy some don't.

[ottoboy 0]

Please sign your posts to this forum.Flaps 40 is not used very often. High headwinds will always shallow your descent rate so the corresponding increase in power is expected. I don't understand your rationale for 40 flaps (safe braking?). Try Flaps 30Also, the "Vref + 5kn + 1/2 steady wind + full gusts" you quote just doesn't look right. I guess that is because I live where the average steady winds are about 20-30 kts on any afternoon. EDIT: Up to 20 kts correction... per target speed definition in AOM.

Yees, sorry about that. Will do in the future. And also forgot to mention the max wind-correction-limits.Okay, thanks from this info. Is there some good rule when to use flaps 40 and when to not?And btw, do you have some hard facts about your claim that flap 40 landing is not usual? IRL-pilot comments would be appreciated ;)- Otto -

[Jack C 8]

Yees, sorry about that. Will do in the future. And also forgot to mention the max wind-correction-limits.Okay, thanks from this info. Is there some good rule when to use flaps 40 and when to not?And btw, do you have some hard facts about your claim that flap 40 landing is not usual? IRL-pilot comments would be appreciated ;)- Otto -

Hey Otto. I fly the 737-600/700/800's. We rarely use 40 flaps. Yes of course use it for a short field by all means. Also it is a requirement to use flaps 40 for a CAT 3 autoland. I will use flaps 40 every now and then for no reason except for the fact I don't want to lose touch with how you flare with flaps 40. The flare is a bit diffeent since your nose is inherently more down with flaps 40.Jack

[ottoboy 0]

Hi Jack!Appreciate your comment. I have also noticed (though in the simulator :D) that in my opinion the -800 is easier to flare down with flaps30 than with 40. I haven't flown so much with -800 (I fly at SAS VA, mostly with -600, as well as -800's and some rare flights on -700) that I could roughly estimate how much we spend runway with different flap-configurations. SAS uses only 30 degree and 40 degree flaps with 737's, no 25 in normal situations. Do you have some rough airspeed limits which you would like to go with when selecting the flap-configuration from INIT REF?- Otto -

[Jack C 8]

Hi Jack!Appreciate your comment. I have also noticed (though in the simulator :D) that in my opinion the -800 is easier to flare down with flaps30 than with 40. I haven't flown so much with -800 (I fly at SAS VA, mostly with -600, as well as -800's and some rare flights on -700) that I could roughly estimate how much we spend runway with different flap-configurations. SAS uses only 30 degree and 40 degree flaps with 737's, no 25 in normal situations. Do you have some rough airspeed limits which you would like to go with when selecting the flap-configuration from INIT REF?- Otto -

Hi again Otto. Generally for me a flaps 30 is a smoother landing. Not to say a flaps 40 wouldnt be smoother its just that 95% of my landings are with flpas 30 and thats what I am used to. The Boeing rule "half the wind speed and all the gust added to your approach speed (which is REF+5 knots). So a REF of 130 would have an approach speed of 135. Now with the wind correction there is to be a MAX of 20 knots applied. Example: If winds are 20 knots gusting to 40 you would take half the wind speed which is 10 and all the gust which is 20. Added together obviously 30 BUT we use a max 20 added to the approach speed.Jack

[Guest Boeing Skunk Works]

The TWA and US Air POH both state the 30 flaps were the normal limit for flap operation unless performing a short field approach or for obstical clearance.Before retiring the 727 many airlines put a physical stop on the flap gate to limit the flaps to 30

[ExNusquam 11]

I would fly the approach at Vtarget. I had a similar situation at MDW earlier today in the -700, winds were 020@18G27, so 1/2 + Gust Factor came out to 18 kts, and the approach speed was 143 with flaps 40. I flared a little as I crossed the threshold, and touched down firmly. I find that is is usually best to not flare as much when you have the extra speed, to avoid floating in the ground effect.

[ottoboy 0]

Okay, thanks to you all of you guys, this helped ;)- Otto -

[Jack C 8]

I would fly the approach at Vtarget. I had a similar situation at MDW earlier today in the -700, winds were 020@18G27, so 1/2 + Gust Factor came out to 18 kts, and the approach speed was 143 with flaps 40. I flared a little as I crossed the threshold, and touched down firmly. I find that is is usually best to not flare as much when you have the extra speed, to avoid floating in the ground effect.

Don't use flaps 40 in gusts. In the beginning of th eflare you should be at target speed already. In your case 125. Don't start the flare at 143. The extra 18 knots in your case is for the approach and slowly bleed of the extra 18 knots so you start the flare at target.

[ExNusquam 11]

Don't use flaps 40 in gusts. In the beginning of th eflare you should be at target speed already. In your case 125. Don't start the flare at 143. The extra 18 knots in your case is for the approach and slowly bleed of the extra 18 knots so you start the flare at target.

Under normal circumstances, I would have used flaps 30, but I was landing at MDW, and the runways are less than 6000 ft from the threshold.

[downscc 1,327]

Under normal circumstances, I would have used flaps 30, but I was landing at MDW, and the runways are less than 6000 ft from the threshold.

I don't have Flap30 landing tables, but the Flap40 table has a max minimum runway length of 6000 ft for about 150,000lbs gross landing weight for the -700... I'm sure Flaps30 will work unless you are heavy and the surface is not dry. The 17/35 at KCRP is about the same and they operate here all day.

[dave_paige 11]

I don't have Flap30 landing tables, but the Flap40 table has a max minimum runway length of 6000 ft for about 150,000lbs gross landing weight for the -700... I'm sure Flaps30 will work unless you are heavy and the surface is not dry. The 17/35 at KCRP is about the same and they operate here all day.

Keep in mind, though, that the max landing weight for the 737-700 is 128,000 lbs.