Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

B738 - Flaps 40 vs Flaps 30 technique

Tech Log The very best in practical technical discussion on the web

B738 - Flaps 40 vs Flaps 30 technique

Old 4th Sep 2015, 02:07
  #1 (permalink)  
Thread Starter
 
Join Date: Nov 2011
Location: America
Posts: 33
Likes: 0
Received 0 Likes on 0 Posts
B738 - Flaps 40 vs Flaps 30 technique

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!!
Don Gato is offline  
Old 4th Sep 2015, 02:35
  #2 (permalink)  
 
Join Date: May 2007
Location: Western Pacific
Posts: 721
Likes: 0
Received 0 Likes on 0 Posts
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.
Oakape is offline  
Old 4th Sep 2015, 04:27
  #3 (permalink)  
 
Join Date: Apr 2010
Location: Home soon
Posts: 0
Likes: 0
Received 0 Likes on 0 Posts
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
de facto is offline  
Old 4th Sep 2015, 12:01
  #4 (permalink)  
 
Join Date: Jan 2000
Location: FL410
Posts: 860
Likes: 0
Received 0 Likes on 0 Posts
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.
Skyjob is offline  
Old 4th Sep 2015, 19:13
  #5 (permalink)  
 
Join Date: Mar 2005
Location: My house
Posts: 1,339
Likes: 0
Received 0 Likes on 0 Posts
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.
nick14 is offline  
Old 5th Sep 2015, 01:12
  #6 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 2,205
Likes: 0
Received 0 Likes on 0 Posts
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.
misd-agin is offline  
Old 5th Sep 2015, 21:11
  #7 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 2,205
Likes: 0
Received 0 Likes on 0 Posts
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.
misd-agin is offline  
Old 5th Sep 2015, 21:21
  #8 (permalink)  
 
Join Date: Jun 2014
Location: Village of Santo Poco
Posts: 869
Likes: 0
Received 0 Likes on 0 Posts
Holly Green Hydraulic Pump, IGh is back!
Amadis of Gaul is offline  
Old 5th Sep 2015, 22:35
  #9 (permalink)  
Thread Starter
 
Join Date: Nov 2011
Location: America
Posts: 33
Likes: 0
Received 0 Likes on 0 Posts
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!
Don Gato is offline  
Old 6th Sep 2015, 09:13
  #10 (permalink)  
 
Join Date: Aug 2013
Location: PA
Age: 59
Posts: 30
Likes: 0
Received 0 Likes on 0 Posts
I noted that several airlines SOP is F30... (mostly to save fuel when it was very expensive)
underfire is offline  
Old 6th Sep 2015, 09:24
  #11 (permalink)  
 
Join Date: Jun 2000
Location: Australia
Posts: 4,188
Likes: 0
Received 14 Likes on 5 Posts
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.
Centaurus is offline  
Old 6th Sep 2015, 10:01
  #12 (permalink)  
 
Join Date: Apr 2010
Location: Home soon
Posts: 0
Likes: 0
Received 0 Likes on 0 Posts
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.
de facto is offline  
Old 6th Sep 2015, 10:25
  #13 (permalink)  
 
Join Date: Mar 2013
Location: EU
Posts: 497
Likes: 0
Received 0 Likes on 0 Posts
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.
OhNoCB is offline  
Old 6th Sep 2015, 11:10
  #14 (permalink)  
 
Join Date: Apr 2010
Location: Home soon
Posts: 0
Likes: 0
Received 0 Likes on 0 Posts
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?
de facto is offline  
Old 6th Sep 2015, 11:12
  #15 (permalink)  
 
Join Date: Jan 2000
Location: FL410
Posts: 860
Likes: 0
Received 0 Likes on 0 Posts
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.
Skyjob is offline  
Old 6th Sep 2015, 11:44
  #16 (permalink)  
 
Join Date: Apr 2004
Location: Planet Earth
Posts: 2,087
Likes: 0
Received 8 Likes on 7 Posts
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.
stilton is offline  
Old 6th Sep 2015, 15:02
  #17 (permalink)  
 
Join Date: Apr 2010
Location: Home soon
Posts: 0
Likes: 0
Received 0 Likes on 0 Posts
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.
de facto is offline  
Old 6th Sep 2015, 15:36
  #18 (permalink)  
 
Join Date: Oct 1999
Posts: 1,050
Likes: 0
Received 0 Likes on 0 Posts
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.

Regards

Pin

Ps why not F40 in strong gusty conditions?
Pin Head is offline  
Old 6th Sep 2015, 18:24
  #19 (permalink)  
 
Join Date: Jun 2014
Location: Village of Santo Poco
Posts: 869
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by de facto
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...
Amadis of Gaul is offline  
Old 6th Sep 2015, 19:31
  #20 (permalink)  
 
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 1,230
Likes: 0
Received 0 Likes on 0 Posts
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.
FlyingStone is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.