View Full Version : B738 - Flaps 40 vs Flaps 30 technique

Don Gato
4th Sep 2015, 03:07
To the B737 drivers on the forum: On the -800 do you change your landing/flare technique while landing with Flaps 40 as opposed to Flaps 30? Thanks for your feedback!!

4th Sep 2015, 03:35
Short answer - no.

Start reducing the power towards idle at approximately 30', aiming to reach idle at touchdown. Prevent the tendency for the nose to drop with elevator & then flare the aircraft at the appropriate point. Believe it or not, I usually flare immediately after the 10' auto callout is made (if it is working - or purely by visual reference if not), the callout backing up the visual picture.

Some have been taught that the A/C will 'fall out of the sky' if you don't carry power into the flare when using flap 40. It wont as long as you prevent the nose from dropping & then positively flare the aircraft. If you try to do a proper flare without taking the power off it will balloon. To avoid a balloon without taking the power off at the appropriate time, you will end up with a very flat landing (almost a 3 pointer) & also have the possibility of a long landing. I see it all the time.

Good luck with it.

de facto
4th Sep 2015, 05:27
The drag increase using 40 compared to 30 means the thrust needs to be pulled back a little slower.
The drag is about the same as with ailerons drag during a 30 kts crosswind.
Flare height slightly lower than flaps 30 for same conditions due to lower Speed.
Dont keep thrust in until too low before chopping it off, as many do,as it is not IF but when you will bounce it.
Landing is a visual maneuver,aim for aiming point until you see the runway rise then shift vision further while increasing pitch and reducing thrust.
If by the time your thrust is idle and you have not touched,release gently elevator force and the aircraft will settle.
Keeping thrust too high too long reduces or even cancels elevator control/feel.

Happy landings

4th Sep 2015, 13:01
Oakscape is right, no difference in technique.

The only difference of note is that the pitch attitude is slightly less and thus needs to be accounted for to avoid the 3-point landing.

4th Sep 2015, 20:13
The FCTM contains only one landing technique that is not stated above.

Check, close, hold.

Reduce rate of descent by pitching up slightly,simultaneously reduce thrust slowly so that it reaches the idle stop at touchdown. As the thrust reduces the nose will want to drop so you increase back pressure to HOLD the landing attitude.

You should maintain awareness of the descent rate and vary the thrust reduction accordingly. Be very careful however, you should avoid landing with thrust on, as doing so may inhibit the auto speed brake and perhaps lead to a bounce.

5th Sep 2015, 02:12
Yes. With F40 landings most guys reduce power slightly later. The net result is the landing attitude is almost set when the power reaches idle.

Higher power setting on final shows how much additional drag F40 have. The speed reduction/increasing sink rate associated caused by the thrust reduction with F40 makes it a tough combination to time correctly.

A fair amount of guys get humbled with F40 landings, especially when they're new in the airplane. Not that many get humbled with F30.

5th Sep 2015, 22:11
IGh - IMO the DEN and KIN examples don't fit into this discussion about F30 vs F40.

KIN was a F30 touchdown 4,100' past the threshold with standing water. Aimpoint/touchdown point was the issue.

The other was a high sink rate unstabilized approach. Avg sink rate the last 1,400' was 1,100 FPM. Average, to include roundout for landing. Autopilot turned off 5 seconds prior to impact...on a non-autoland landing.

With high, or higher drag configurations, power is reduced slightly later but still idle prior to touchdown. Yes, even the 727 was supposed to be landed at idle but guys had all sorts of strange beliefs and techniques.

Low, or lower, drag configurations require earlier power reductions. Some configurations could be as high as 300' above touchdown elevation.

Amadis of Gaul
5th Sep 2015, 22:21
Holly Green Hydraulic Pump, IGh is back!

Don Gato
5th Sep 2015, 23:35
Thanks for your replies! Interesting points and suggestions. I agree that in a F40 landing, thrust reduction timming is very important. It's also possible that a slightly lower flare is preferred. All in all, F40 landings seem a bit trickier!

6th Sep 2015, 10:13
I noted that several airlines SOP is F30... (mostly to save fuel when it was very expensive)

6th Sep 2015, 10:24
simultaneously reduce thrust slowly so that it reaches the idle stop at touchdown

That is not what my Boeing instructor pilot taught us. (he accompanied the crew on its trans-Pacific ferry flight). Quite the opposite in fact.
His advice was to simultaneously flare and close the thrust levers sharply against the idle stops. He said you don't want excess thrust once the flare is commenced especially as it takes time for the N1 to reduce from approach thrust present at the flare to idle N1. A slow reduction of thrust at the flare is counter-productive as it can extend the landing roll.

de facto
6th Sep 2015, 11:01
If you are planning to come at VREF and touch at 1000 feet then yes...however a normal landing is anywhere between 1000 and 2000 feet.
A technique to land on the 1000 marker (not 1100/1200 feet) may be irrelevant with a non limited runway and full house in the back.
Just my 2 cents.
I prefer flaps 40 landing except when gusty and strong headwinds.

6th Sep 2015, 11:25
It's an interesting point about the speed of thrust reduction. I was always taught (as per FCTM) to reduce slowly to reach idle on touchdown. I have flown with many guys that flare and then whack it against the stops.

Having watched the difference in these techniques I can say that there isn't all that much difference that I personally have witnessed, because as mentioned above it does take a small amount of time for the N1 to reduce. A lot of the guys I have watched that slowly close the thrust (like myself) actually close the thrust at approximately the same rate as the n1 reduces if sharply closing the thrust levers.

de facto
6th Sep 2015, 12:10
What happens when you flare?you are pitching up so lift increases...if lift increases and the thrust isnt reduced ..you are now floating.
As you pitch up,reduce the thrust commensurate with the pitch increase...give and take kind of.
Sensible no?

6th Sep 2015, 12:12
As underfire noted the reason for several carriers to opt for default F30: fuel.

It is worth noting the fuel different between F30 and F40, when configuring at 4nm, is only ~10kg!
Taken from the same rulebook, using 2nd detent reverse uses 40-70kg (depending on groundspeed at touchdown, auto brake selection and head/tailwind component).

When airlines use fuel as a reason for using F30, it is often not continuing the same argument preferring F40 with an idle reverse capability in favour of F30 with a reverse requirement for the same auto brake selection made.

6th Sep 2015, 12:44
All good arguments but i'll say this:

Do something suddenly in a jet and don't be surprised to get a rather sudden response !

You can be assertive / positive in your control / thrust inputs yet still be smooth and that is the response you will get.

de facto
6th Sep 2015, 16:02
You can be assertive / positive in your control / thrust inputs yet still be smooth and that is the response you will get.

Amen to that.

Pin Head
6th Sep 2015, 16:36
Just follow the FCtM and that will help.

I believe Boeing recommends F30 unless performance wise required.

Also I find, including myself that it will go on firmer. Again refer what the manual says, don't aim for a smooth landing.



Ps why not F40 in strong gusty conditions?

Amadis of Gaul
6th Sep 2015, 19:24
What happens when you flare?you are pitching up so lift increases...if lift increases and the thrust isnt reduced ..you are now floating.
As you pitch up,reduce the thrust commensurate with the pitch increase...give and take kind of.
Sensible no?

Kinda like bring married...

6th Sep 2015, 20:31
Ps why not F40 in strong gusty conditions?

Not taking increased roll rate with F40 into account, look at Vref vs. Vfe for F30 and F40 and you'll see.

6th Sep 2015, 22:31
Does anyone know how long a flare is in perfect conditions?
What I mean by that is, if you have a ROD of 750 fpm at 50ft while doing 150kts across the ground, and then conduct a perfect flare at 25ft, how many meters is it from 50 ft to touch down. The ROD obviously decreases as does the ground speed but only by a few knots. If my aim point is exactly 1000ft, and I conduct the perfect flare ( let's assume constant ground speed for simplicity of 150kts), where will I touch down? I would hazard a guess at about 1150ft, maybe 1200ft.
Interesting discussion. I find that by looking out the window I automatically vary the timing of my thrust reduction according to the rate of change I see out the window. Once in a while I find it necessary to keep thrust in until late in the piece, most of the time it is similar to a flap 30 landing.

7th Sep 2015, 14:33
Slamming the thrust levers closed does nothing.

How long does N1 take to reduce.....

7th Sep 2015, 15:12
Real men slam the throttles, or advance them, faster than the engines can respond.

It's especially entertaining on the application of takeoff thrust if one engine doesn't accelerate. One engine lagging the command thrust sector? Push the throttle farther forward?!?! That explains the skid marks you see when holding in position. They start on the centerline and have a nice curve towards the side of the runway before skidding back towards the centerline.

Amadis of Gaul
7th Sep 2015, 15:31
Real men slam the throttles, or advance them, faster than the engines can respond.

I have somewhat of an annoying habit of slamming them into full reverse. I think it started during OE when just popping them into idle reverse proved trickier than expected. So, I learned to rip them all the way back, then adjust.

7th Sep 2015, 19:36
Most commonly I see pilots leaving the thrust in longer then slamming the levers closed. The only thing it leads to is a float as the N1 reduces at the same rate as if they had followed the manufacturers landing technique (you know the people that built and certified the aircraft).

Then again, people do what they want despite what Boeing recommend and our instructors teach.

7th Sep 2015, 20:18
Do we really need to discuss how to flare F30 vs F40? Can we not just assume that everyone here knows how to do it? Every landing is different; weight, wind, gusts, thermals..

7th Sep 2015, 20:32
Real men slam the throttles, or advance them, faster than the engines can respond.

Especially from full reverse directly to forward idle, followed by heavy braking when the aicraft begins to accelerate on landing roll :ugh:

7th Sep 2015, 20:52
172: finally, a modicum of common sense. Every time is different. It is not a manoeuvre that can be fitted into the modern day trained monkey philosophy. Thank gawd there is still a moment that can still can be an assessment of competence & understanding. It is a moment, on any aircraft, that a certain finesse & dexterity is required. You either have it or you don't. Perhaps you can learn it, but those who want to do it by numbers ain't gonna get it.
Every a/c is different, every day/runway is different. You have to adjust and cope & control the beast.

7th Sep 2015, 20:57
As a last resort, if you can't accept or don't receive ADEQUATE INSTRUCTION, neither from your company's training captains nor from their approved SOPs, try watching the autoland doing it, make a note of what it does and go imitate the "box".

It's quite humbling to see how well Mr Boeings autoland performs, even to a time-expired old geezer like me! :)

7th Sep 2015, 21:26
I would get a bit twitchy if the f/o began raising the nose at 50ft like the auto pilot does. Maybe tell your mate before you try to emulate that one :)

7th Sep 2015, 23:00
Of course every landing is different. Talk about stating the obvious! The thing is, you need a reference point to start from when learning a maneuver & this is what most here believed the original poster was seeking.

8th Sep 2015, 00:32
Of course every landing is different. But they're not night and day different. Everyone agrees that no flaps are a lot different than F30 or F40 landings. Why? Speed, sink rate, and drag.

F30's ARE different than F40 landings. Like the difference between no flap and F30/F40 landings? No, of course not. But a F40 landing is not the same as a F30 landing.

Does it take some sort of crazy type of techniques, like guys used to say the 727 needed? Of course not. But an awareness that you're using a lot more thrust, so the plane will be quicker to slow and generate an increased sink rate if pitch control is less than ideal, might be worth telling a newbie.

8th Sep 2015, 09:21
Some landings my ass tells me to start pulling at 50 ft and leave the thrust in until I feel the rate of descent has been broken, even until touch down. Other days when the LW is 48 tonnes and that 10 kts TW magically disappears at 100 ft I merely give it a nudge at 10 ft.

The FCTM works well in the perfect world (and in the sim), but otherwise it's a seat of the pants maneuver.

With that said, I trust you all here to be able to land a 737 whether you are book type or not.

8th Sep 2015, 10:25
You are right about the 727 mdg, loads of bs techniques on that aircraft.

It could be landed quite normally with a normal flare and idle thrust despite adamant opinions that could not be done.

I saw more long landings on that aircraft than any other type as Pilots were just terrified to take the power off.

10th Sep 2015, 05:22
Let us be careful here, loco`s will turn the technique into a SOP.