B737-800 FLAP30 OR FLAP40 select and the main distinction

[yugviq]

Q:usually,i can select flaps30 for landing.But I hear that Some airlines (not mine) have a Flaps 40 policy for all landings. i think that why?
-------cat 3------slipply------short runway------.......
We use flaps 30,but it's not a must.We use flaps30 most of the time (>90% of the landings we do,I guess) so why useflap40( a not so trained configuration) in a cat 3 approach?

[Cough]

Flap 40 in Cat III conditions is to provide greater view over the nose (lower nose attitude) to give you a better chance of acquiring visual reference at DH.

As to not being familiar with the flap 40 landing, isn't the A/P doing it anyhow?

Cough

[IRRenewal]

Flap 40 = more drag = more fuel.

Flap 40 = better forward visibility.

Flap 40 = shorter LDR.

Use it when you have to, otherwise don't bother.

[galdian]

All the previous true, another great factor is there's some 7kts difference in Vref 30 and 40 and at high gross weights that extra speed at touchdown equates to a noticeable (and at times scary) amount of extra runway especially when compared to the classic.

The other time it should/must be used without question (unless you have an obscene amount of runway available) is when you have any tailwind component.
I know of a few guys who have gone about as far as you can go, without becoming a statistic and from which others can (hopefully) learn, by using F30 when operational considerations should have mandated F40.

[Jinkster]

Have a look at your brake cooling schedule for a short turnaround - Flap 40 - less wear on brakes, and keeping the brakes cooler!

Also, greater view over the nose during Cat II or III as someone else said!

[Flexi]

Observed also, that 90% of landings are accomplished using F30.

The difference in fuel consumption can almost be neglected. I read something in the range of ~15kg/approach. On the other hand, additional noise is created by drag and 8-10% more power with F40...

As mentioned before, in low visibility ops (esp. when flying manually CAT I down to minimum) it becomes much more easier with F40, also better landing performance therefore strongly recommended on CONT. or short and wet RWYs by giving you additional safety margin...

I personally think that both very heavy A/C and very light ones can be better controlled using F40...

F30 can be more desirable in gusty condititions with high Target-Speeds to avoid reaching placard speed for F40(158kts in the classics) and therefore to activate the reliefvalve retracting flaps to 30°...

[BandH]

I agree with the 7 kts but also bear in mind that you also have a higher thrust setting at the TH with F40 (especially at high gross weights). Combine this with a lower nose attitude and you can see that judging the flare is going to be more difficult. There is also a longer spool down time at F40 which in turn means the very real possibility of float (we all know this is an 800 trait!!). So your choice, take the extra 7 knots or just go for F30. Personally I think in poor viz it is the way to go, otherwise it is overkill and makes very little difference to improving landing performance....horses for courses:ok:

[Callsign Kilo]

I agree with BandH. F40 makes the flare a little harder to judge, especially at night. Can induce that tendency to float a little (-800), which can be a right barsteward if you have a slight tailwind and therefore removes the benefits of a F40 landing in the first place. I am relatively new to type, so it's a problem I am overcoming. I find my landings using F30 are much better as I find it easier to judge the flare (plus the shorter spool down period), however it doesn't stop me from selecting F40 for performance reasons.

[cirr737]

F30 also standard landing in my company (classic 737s)

Personally I prefer F40 - don't know why but I find it easier to land.

[fireflybob]

Boeing originally used to say that F40 has better "speed stability"

[Becker Junior]

My companies SOP demands FLAP 40 on all landings. In adiction to all reasons above, they are afraid of tail strikes upon landing.

[Callsign Kilo]

Out of interest, what is your company policy when the wind is gusting on approach? Flap 40 often isn't managable due to 'blowback' from 40 to 30. Requires an immediate go around with my bunch. I believe this is laid down in the FCTM as well, but cannot be certain??

[Mach E Avelli]

The blowback feature is there to protect the structure in just such a situation and transient blowback in gusty condiions should be no reason to go around. Unless the appoach gets unstable as a result, that is.....

[FCS Explorer]

concerning flap load relief from 40 to 30: at least 30 is a "allowed" landing flap setting while if you are on 25 (due to load relief from 30) you basically are NOT in landing config.
on a gusty day where speed is hard to control there will also be little discussion about not having set Vref30 etc pp
but after some years flying the 738 to windy destinations i never had a case where 40 was set and landing was 30. also keep in mind the risk of flaps going back to 40 during speed decrease in flare.

when i started on the 73G/738 i preffered 30. didn't like difference in handling and visual segment. felt like to entirely different planes.
NOW i only do 40's. except that one runway where our company recommends 30 in the one landing direction due to tricky wind conditions during flare.

for me 40 is more practical on short or wet runways. also makes more sense. you don't want to be fast for landing, you want to be slow. landing means decreasing speed and altitude to zero, no need for those extra 7 knots.
by the way the idea of flying faster just to get less body attitude on landing is another example of poor engineering, nothing else. the 737 got a lot bigger since 1968, but rarely better.

and one more thing: drag with f40 is so high that it practically doesn't FLOAT when your app was on speed and you cut the power. especially with winglets and flaps30 that thing floats like hell.

[Bushed]

The company i work for flies the 600/700/800. For most landings in the 600 and 700, flap 30 seems to be the preferred flap setting. Cat III requires flap 40. With the 800, i prefer to use flap 40 as it gives a landing attitude that most closely resembles that of the 600/700.

[A37575]

There is also a longer spool down time at F40 which in turn means the very real possibility of float
The float is caused by poor pilot landing technique - not the fact Flap 40 is used. The longer spool down time is a distinct advantage when using reverse thrust as the engines will have already been a relatively higher N1 and reverse comes in more quickly and we all know that reverse is more efficient at high speed (don't we?).