shaner82
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Why retract flaps on the ground?

Sun Jun 02, 2019 12:26 pm

I'm sure there's an obvious explanation, but I've always wondered why flaps are retracted after landing. They need to be extended again before takeoff, so why bother retracting them? There's been a few crashes over the years where pilots forgot to extend the flaps for takeoff, so why not leave them extended while on the ground? Even if a checklist requires them to be tested, they can be retracted and immediately extended again before taking off.
 
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SuseJ772
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 12:36 pm

Landing flaps are a different setting than takeoff settings. Takeoff is usually less so a retraction would have to take place anyways.

But the real reason is less probability of damage from FOD while taxing (with a low wing aircraft) and better visibility in small high wing aircraft.
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AirKevin
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 12:46 pm

One less thing for the ground crew to crash into if the flaps are retracted.
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citationjet
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 12:46 pm

Retracting the flaps (and leading edge slats) keeps them from getting damaged by ground equipment at the gate.
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jetskipper
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 12:47 pm

One, to avoid damage from ground vehicles. There are a few CRJ operators that reset to the flaps to a normal takeoff setting after landing because there is not enough clearance for ground vehicles to with that’s extended or retracted.

There are a few other exceptions as well. Some carriers will call for the flaps to be retracted to an intermediate setting (I.E. 15 degrees for Boeings) after landing on a runway contaminated with slush or snow. If the flaps are fully retracted with contaminants on the leading edges the tracks could be damaged.
 
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AirKevin
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 12:49 pm

As far as the mention of crashes as a result of forgetting to set flaps for take-off, that's what happens when you don't follow the checklist. Checklists are there for a reason. Leaving the flaps extended certainly wouldn't solve anything in this regard since the flap setting for take-off and landing generally aren't the same. On a 737, for instance, you could be taking off with flaps 5 and landing with flaps 30.
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N766UA
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:03 pm

Every takeoff is different and not every one requires the same flap setting. So, in order to figure out what setting you need, you’d need passenger counts, fuel, and bag numbers for your weight and balance. You don’t get those numbers until right before pushback, so how would you set the *next* flights flaps correctly if you don’t know those numbers? It may not even be your jet. Heck, the plane might not leave again for a day or 2!

That, plus the above reasons, is why. You’d actually be making it more complicated and, per your assertion, more dangerous.
Last edited by N766UA on Sun Jun 02, 2019 1:04 pm, edited 1 time in total.
 
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cathay747
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:04 pm

citationjet wrote:
Retracting the flaps (and leading edge slats) keeps them from getting damaged by ground equipment at the gate.


I have the opposite question from the OP and it's funny this thread came up because I've been wondering about this for some.

Your explanation above is of course the correct & obvious answer but...in many a YouTube trip-report video, I've seen lots of cases where on AA Airbus narrowbodies, particularly here at PHX, where the slats & flaps are not fully retracted after landing...looks like they're only brought up to the takeoff position. Why would that be in a place like PHX where there is no slush/snow/ice issue as mentioned by the poster above? I think I've seen it at DFW too.
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workhorse
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:05 pm

Another interesting question is why there is an inconsistency on when the flaps are retracted. Some pilots retract them immediately after leaving the runway while others (within the same airline) taxi with full flaps almost all the way to the gate. Shouldn't there be a checklist saying something like:

When leaving the runway:
- autobrake: off
- spoilers: down
- flaps: 0
- strobes: off
- contact ground
- ...

?
 
Cathay777300ER
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:13 pm

I would also say in some airports with longer taxi time it will save enough fuel to make it reasonable to retract the flaps.
 
paullam
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:19 pm

cathay747 wrote:
citationjet wrote:
Retracting the flaps (and leading edge slats) keeps them from getting damaged by ground equipment at the gate.


I have the opposite question from the OP and it's funny this thread came up because I've been wondering about this for some.

Your explanation above is of course the correct & obvious answer but...in many a YouTube trip-report video, I've seen lots of cases where on AA Airbus narrowbodies, particularly here at PHX, where the slats & flaps are not fully retracted after landing...looks like they're only brought up to the takeoff position. Why would that be in a place like PHX where there is no slush/snow/ice issue as mentioned by the poster above? I think I've seen it at DFW too.


You may look this one up. Airbus recommends leaving flaps at 1 at hot airports. It has to do with heat (obviously), I think it’s about fuel temperature or hydraulic fluid temperature. There are a couple of threads about that on this site.
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:22 pm

Cathay777300ER wrote:
I would also say in some airports with longer taxi time it will save enough fuel to make it reasonable to retract the flaps.


Gee, I like your screen-name! LOL

How does retracting slats/flaps on the ground save fuel? You've totally lost me on that comment. :?
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cathay747
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:23 pm

paullam wrote:
cathay747 wrote:
citationjet wrote:
Retracting the flaps (and leading edge slats) keeps them from getting damaged by ground equipment at the gate.


I have the opposite question from the OP and it's funny this thread came up because I've been wondering about this for some.

Your explanation above is of course the correct & obvious answer but...in many a YouTube trip-report video, I've seen lots of cases where on AA Airbus narrowbodies, particularly here at PHX, where the slats & flaps are not fully retracted after landing...looks like they're only brought up to the takeoff position. Why would that be in a place like PHX where there is no slush/snow/ice issue as mentioned by the poster above? I think I've seen it at DFW too.


You may look this one up. Airbus recommends leaving flaps at 1 at hot airports. It has to do with heat (obviously), I think it’s about fuel temperature or hydraulic fluid temperature. There are a couple of threads about that on this site.


Hey thanks! Such a quick answer, and it's logical. My case is closed.
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zeke
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:26 pm

paullam wrote:
cathay747 wrote:
citationjet wrote:
Retracting the flaps (and leading edge slats) keeps them from getting damaged by ground equipment at the gate.


I have the opposite question from the OP and it's funny this thread came up because I've been wondering about this for some.

Your explanation above is of course the correct & obvious answer but...in many a YouTube trip-report video, I've seen lots of cases where on AA Airbus narrowbodies, particularly here at PHX, where the slats & flaps are not fully retracted after landing...looks like they're only brought up to the takeoff position. Why would that be in a place like PHX where there is no slush/snow/ice issue as mentioned by the poster above? I think I've seen it at DFW too.


You may look this one up. Airbus recommends leaving flaps at 1 at hot airports. It has to do with heat (obviously), I think it’s about fuel temperature or hydraulic fluid temperature. There are a couple of threads about that on this site.


Close, it has to do with bleed air ducting being able to release heat
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:39 pm

workhorse wrote:
Another interesting question is why there is an inconsistency on when the flaps are retracted. Some pilots retract them immediately after leaving the runway while others (within the same airline) taxi with full flaps almost all the way to the gate. Shouldn't there be a checklist saying something like:

When leaving the runway:
- autobrake: off
- spoilers: down
- flaps: 0
- strobes: off
- contact ground
- ...

?


I can expand on this a bit further. In the CRJ, with our low ground clearance, during the winter snow and ice can build up on the underside of the flaps. If we retract them after landing, that snow/ice build up with be brought into the back side of the wing and crush metal. So we leave them down until they can be inspected and de-iced, if needed.

Other times, it’s just that we are busy. At simple airports, flaps come up immediately when exiting the runway, but sometimes when LaGuardia is in chaos and you’re exiting immediately onto a busy taxiway, you just have to prioritize.
 
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 1:53 pm

cathay747 wrote:
paullam wrote:
cathay747 wrote:

I have the opposite question from the OP and it's funny this thread came up because I've been wondering about this for some.

Your explanation above is of course the correct & obvious answer but...in many a YouTube trip-report video, I've seen lots of cases where on AA Airbus narrowbodies, particularly here at PHX, where the slats & flaps are not fully retracted after landing...looks like they're only brought up to the takeoff position. Why would that be in a place like PHX where there is no slush/snow/ice issue as mentioned by the poster above? I think I've seen it at DFW too.


You may look this one up. Airbus recommends leaving flaps at 1 at hot airports. It has to do with heat (obviously), I think it’s about fuel temperature or hydraulic fluid temperature. There are a couple of threads about that on this site.


Hey thanks! Such a quick answer, and it's logical. My case is closed.


It has to do with the bleed air, I believe specifically the anti ice system in the leading edge of the wing. The external temperature can cause a bleed air leak warning. So anytime field temperatures exceed a certain amount (IIRC 86°F) they recommend flaps set to 1 which helps the air circulate around that area.

I’ve seen flight crews forget to do this in PHX and tech ops has to come out and find a way to cool the sensor. Usually involves blowing preconditioned air into the bleed system.
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jfklganyc
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 2:14 pm

30C or higher for Flaps 1 on bus

Flaps always set to 0 after landing unless they are iced up

Modern planes have a TO CONFIG test before takeoff to check for Flaps, Trim, Spoilers etc to prevent crashes

Takeoff flaps are much lower setting than landing flaps

You retract flaps on the go around to a setting that allows extra lift/less drag in a critical phase of flight
Last edited by jfklganyc on Sun Jun 02, 2019 2:16 pm, edited 1 time in total.
 
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conaly
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 2:15 pm

The issue with Airbus on flaps 1 is afaik only valid for A320, A330, A340 and A380. On the A350 they fixed the "issue". I've noticed the extracted flaps a few years ago when I arrived in Kuala Lumpur on Lufthansa A343 and asked the flight crew afterwards about that. They explained something with air circulation and cooling issues. Last year I arrived in HND on LH A359 during very hot weather (around 37°C) and there they fully retracted the flaps after landing. The crew said, that this problem doesn't exist anymore on A350 as it has some venting holes in that slats (or something similar).
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Cathay777300ER
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 2:33 pm

cathay747 wrote:
Cathay777300ER wrote:
I would also say in some airports with longer taxi time it will save enough fuel to make it reasonable to retract the flaps.


Gee, I like your screen-name! LOL

How does retracting slats/flaps on the ground save fuel? You've totally lost me on that comment. :?


It's mainly about extra drag requiring more thrust from the engine. The affect of the extra drag might be negligible on short taxis but in larger airports with many start stop taxing it can account to enough fuel to make retracting the flaps make sense.
 
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 3:20 pm

Cathay777300ER wrote:
cathay747 wrote:
Cathay777300ER wrote:
I would also say in some airports with longer taxi time it will save enough fuel to make it reasonable to retract the flaps.


Gee, I like your screen-name! LOL

How does retracting slats/flaps on the ground save fuel? You've totally lost me on that comment. :?


It's mainly about extra drag requiring more thrust from the engine. The affect of the extra drag might be negligible on short taxis but in larger airports with many start stop taxing it can account to enough fuel to make retracting the flaps make sense.

Uh. What? There is no basis of fact on any of this, nice try though.
 
mandala499
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 3:26 pm

flight152 wrote:
Uh. What? There is no basis of fact on any of this, nice try though.

Maybe he taxies his jet in the middle of typhoons all the time. :)
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Starlionblue
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 4:05 pm

Cathay777300ER wrote:
cathay747 wrote:
Cathay777300ER wrote:
I would also say in some airports with longer taxi time it will save enough fuel to make it reasonable to retract the flaps.


Gee, I like your screen-name! LOL

How does retracting slats/flaps on the ground save fuel? You've totally lost me on that comment. :?


It's mainly about extra drag requiring more thrust from the engine. The affect of the extra drag might be negligible on short taxis but in larger airports with many start stop taxing it can account to enough fuel to make retracting the flaps make sense.


At taxi speeds, any extra drag would be practically non-existent.
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VirginFlyer
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 4:09 pm

mandala499 wrote:
flight152 wrote:
Uh. What? There is no basis of fact on any of this, nice try though.

Maybe he taxies his jet in the middle of typhoons all the time. :)

It does raise an interesting question though... if one were to taxy on a conveyor belt, what would be the ideal flap setting?

:duck:

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loranfair
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 4:17 pm

In the mid 70s I worked for the caterer at PVD, looking at what was going on the field as much as possible. As has been said, all the airline DC-9s, 727s, and BAC-111s had their flaps up by the time they turned off the runway. One day a USAF C-9 came in. He left his flaps and spoilers deployed all the way to the (then) Air National Guard ramp. I never figured out why.
 
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zeke
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 4:55 pm

conaly wrote:
The issue with Airbus on flaps 1 is afaik only valid for A320, A330, A340 and A380. On the A350 they fixed the "issue". I've noticed the extracted flaps a few years ago when I arrived in Kuala Lumpur on Lufthansa A343 and asked the flight crew afterwards about that. They explained something with air circulation and cooling issues. Last year I arrived in HND on LH A359 during very hot weather (around 37°C) and there they fully retracted the flaps after landing. The crew said, that this problem doesn't exist anymore on A350 as it has some venting holes in that slats (or something similar).


The issue has actually been fixed across the board, the practice is continued to retain commonality as most operators have a mixed fleet of new and old aircraft.

If an airline has all newish aircraft, or aircraft with the new sensors the procedure is not required for above 30 degrees, however the other requirements are retained.

A320 FCOM

FLAPS....................................................... ......................... RETRACT
Set the FLAPS lever to position 0.
If the approach was made in icing conditions, or if the runway was contaminated with slush or snow, do not retract the flaps and slats until after engine shutdown and after the ground crew has confirmed that flaps and slats are clear of obstructing ice.
On ground, hot weather conditions may cause overheating to be detected around the bleed ducts in the wings, resulting in “AIR L (R) WING LEAK” warnings. Such warnings may be avoided during transit by keeping the slats in Configuration 1 when the OAT is above 30 °C.
To avoid damage on the RTLU (Rudder Travel Limit Unit) mechanical stop, the SLATS/FLAPS should be retracted before all ADIRS are set to OFF simultaneously.
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conaly
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 5:16 pm

zeke wrote:
The issue has actually been fixed across the board, the practice is continued to retain commonality as most operators have a mixed fleet of new and old aircraft.

If an airline has all newish aircraft, or aircraft with the new sensors the procedure is not required for above 30 degrees, however the other requirements are retained.


Interesting, thanks for sharing this information. In the next four weeks I will have a few A330 and A350 flights to some hot regions (DEL, SIN, HND), will keep my eyes open what exactly will happen after landing and maybe ask the crews about that again.
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Scarebus34
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 7:04 pm

I mean, why do you put the gear up if you're just going to put it back down again?
 
stratclub
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 8:11 pm

Scarebus34 wrote:
I mean, why do you put the gear up if you're just going to put it back down again?

Job security for maintenance because of additional wear and tear on the landing gear. :biggrin:
 
stratclub
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 8:19 pm

VirginFlyer wrote:
mandala499 wrote:
flight152 wrote:
Uh. What? There is no basis of fact on any of this, nice try though.

Maybe he taxies his jet in the middle of typhoons all the time. :)

It does raise an interesting question though... if one were to taxy on a conveyor belt, what would be the ideal flap setting?

:duck:

V/F

I saw that episode of Myth Busters. Probably one of the most bogus "Myth" they ever wasted airtime on. For the proper flap setting, you would have to consult the abnormal operating procedures check list. Just a guess, but it would be the same flap setting you would use if you were backing into a mountain.
 
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VirginFlyer
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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 9:40 pm

stratclub wrote:
VirginFlyer wrote:
mandala499 wrote:
Maybe he taxies his jet in the middle of typhoons all the time. :)

It does raise an interesting question though... if one were to taxy on a conveyor belt, what would be the ideal flap setting?

:duck:

V/F

I saw that episode of Myth Busters. Probably one of the most bogus "Myth" they ever wasted airtime on. For the proper flap setting, you would have to consult the abnormal operating procedures check list. Just a guess, but it would be the same flap setting you would use if you were backing into a mountain.

I was more thinking the classic tech/ops thread from 2005: viewtopic.php?f=5&t=747177

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Re: Why retract flaps on the ground?

Sun Jun 02, 2019 10:31 pm

VirginFlyer wrote:
mandala499 wrote:
flight152 wrote:
Uh. What? There is no basis of fact on any of this, nice try though.

Maybe he taxies his jet in the middle of typhoons all the time. :)

It does raise an interesting question though... if one were to taxy on a conveyor belt, what would be the ideal flap setting?

:duck:

V/F

The ideal flap configuration in that situation would be "barn door" because you wouldn't want to let all the pigeons out.
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zanl188
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Re: Why retract flaps on the ground?

Mon Jun 03, 2019 1:44 am

Flaps up recommended after landing on some aircraft to kill lift and add weight to wheels - enhances braking.
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GalaxyFlyer
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Re: Why retract flaps on the ground?

Mon Jun 03, 2019 3:18 am

zanl188 wrote:
Flaps up recommended after landing on some aircraft to kill lift and add weight to wheels - enhances braking.


Maybe in a Cessna 172, but I know of no Part 25 plane where retracting the flaps during the roll out is procedure. Additionally, changing configuration during roll out is a recipe for disaster—the idea was done away with when pilots mixed up the flaps with the gear.


Gf
 
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zeke
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Re: Why retract flaps on the ground?

Mon Jun 03, 2019 3:53 am

Maybe a twin otter, seen some interesting techniques on them. Not sure if all of them were endorsed by the manufacturer.
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fr8mech
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Re: Why retract flaps on the ground?

Mon Jun 03, 2019 11:01 am

zanl188 wrote:
Flaps up recommended after landing on some aircraft to kill lift and add weight to wheels - enhances braking.


Ummm, no. That would be spoilers.
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N766UA
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Re: Why retract flaps on the ground?

Mon Jun 03, 2019 3:41 pm

zanl188 wrote:
Flaps up recommended after landing on some aircraft to kill lift and add weight to wheels - enhances braking.


That’s basically a tribal knowlege-style technique/rumor that some C172 instructors propagate and is absolutely not true, accurate, taught or practiced for any aircraft larger than 3,000 pounds. Honestly I’d even argue that it’s BS for small GA airplanes too, but I digress...
 
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cathay747
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Re: Why retract flaps on the ground?

Mon Jun 03, 2019 10:50 pm

Starlionblue wrote:
Cathay777300ER wrote:
cathay747 wrote:

Gee, I like your screen-name! LOL

How does retracting slats/flaps on the ground save fuel? You've totally lost me on that comment. :?


It's mainly about extra drag requiring more thrust from the engine. The affect of the extra drag might be negligible on short taxis but in larger airports with many start stop taxing it can account to enough fuel to make retracting the flaps make sense.


At taxi speeds, any extra drag would be practically non-existent.


There is NO aerodynamic "drag" at taxi speeds. There are no aerodynamic forces acting on ANYTHING at taxi speeds, period. I would be most curious to know where on EARTH Cathay777300ER is getting this notion. The only "drag" on a taxiing jet, if you want to call it that, would be friction from the tires on the pavement induced by gravity & weight. Good God in heaven!
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Starlionblue
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Re: Why retract flaps on the ground?

Mon Jun 03, 2019 11:12 pm

It would be inaccurate to say there is no aerodynamic drag at taxi speed. You're moving an object through the air, after all. It's just so little drag as to be insignificant.
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AbigailWT
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Re: Why retract flaps on the ground?

Tue Jun 04, 2019 3:05 am

cathay747 wrote:

There is NO aerodynamic "drag" at taxi speeds. There are no aerodynamic forces acting on ANYTHING at taxi speeds



You're kidding..... right? *crosses fingers*
 
N766UA
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Re: Why retract flaps on the ground?

Tue Jun 04, 2019 3:28 am

cathay747 wrote:
Starlionblue wrote:
Cathay777300ER wrote:

It's mainly about extra drag requiring more thrust from the engine. The affect of the extra drag might be negligible on short taxis but in larger airports with many start stop taxing it can account to enough fuel to make retracting the flaps make sense.


At taxi speeds, any extra drag would be practically non-existent.


There is NO aerodynamic "drag" at taxi speeds. There are no aerodynamic forces acting on ANYTHING at taxi speeds, period. I would be most curious to know where on EARTH Cathay777300ER is getting this notion. The only "drag" on a taxiing jet, if you want to call it that, would be friction from the tires on the pavement induced by gravity & weight. Good God in heaven!


LOL please let this be sarcasm?

Of COURSE fully extended flaps create drag at taxi speeds. It’s just, relative to a 50, 100, or 300,000 pound aircraft, insignificant and, referencing the OP’s post, irrelevant.
 
VSMUT
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Re: Why retract flaps on the ground?

Tue Jun 04, 2019 6:53 am

Taxiing in with flaps extended used to be a signal to ATC that you had been hijacked, at least in some places. Not really a thing any more, but I've still flown with old (mostly Russian) captains who insisted that it was still to be taken seriously.

I'm guessing there are 2-3 reasons:

    It keeps birds, insects and FOD out of the wing cavities if the aircraft is parked for a longer period.

    For light aircraft, having flaps extended could make enough of a difference to make a plane lift off in a gust of wind or backblast from a preceding aircraft. I'm guessing this is just a matter of habit that has hung on from the early days of flight. It makes no reason that we have to retract them for this reason once leaving the runway, but already set them just at pushback prior to takeoff.

    Lastly and most relevant to low winged aircraft, it reduces the risk of collisions between ground vehicles and the trailing edge. 737, 777 and MD-11 flaps extend very far down to the ground.


workhorse wrote:
Another interesting question is why there is an inconsistency on when the flaps are retracted. Some pilots retract them immediately after leaving the runway while others (within the same airline) taxi with full flaps almost all the way to the gate. Shouldn't there be a checklist saying something like:

When leaving the runway:
- autobrake: off
- spoilers: down
- flaps: 0
- strobes: off
- contact ground
- ...

?


Is that inconsistency something you have noticed within one airline on one type?

BTW, I think it is a non-issue in which order they do it. Navigating the aircraft safely on the ground comes first, that may mean spending time on radio calls, checking the taxi-charts and looking outside first. It won't be the checklist that mandates the order anyway, since (I assume on most types) do it as a memory item first, then check the checklist after.


N766UA wrote:
Every takeoff is different and not every one requires the same flap setting.


Not for all aircraft. ATRs always use one setting for takeoff and we still retract flaps. Isn't the A321 also limited to only the flaps 2 setting for takeoff?
 
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Starlionblue
Posts: 19268
Joined: Fri Feb 27, 2004 9:54 pm

Re: Why retract flaps on the ground?

Tue Jun 04, 2019 6:57 am

workhorse wrote:
Another interesting question is why there is an inconsistency on when the flaps are retracted. Some pilots retract them immediately after leaving the runway while others (within the same airline) taxi with full flaps almost all the way to the gate. Shouldn't there be a checklist saying something like:

When leaving the runway:
- autobrake: off
- spoilers: down
- flaps: 0
- strobes: off
- contact ground
- ...

?


Not a checklist. It's a flow. And the exact order that stuff is done depends. It might be very busy on the ground, or the pilots are unfamiliar. Better to pay attention to the taxi than immediately start cleaning the plane up.

AFAIK on most airliners, autobrake comes off if you tap the brakes, so you don't need to do that. Strobes would come off when leaving the runway.

Contact ground. The rest of the after landing flow can wait until there is time. Once all is done, time for the after landing checklist.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Max Q
Posts: 7483
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Re: Why retract flaps on the ground?

Tue Jun 04, 2019 7:11 am

On the 727 we retracted flaps from 30 to 25 degrees immediately after touchdown to assist with weight on the wheels


This was the function of the PM, in fact the PF call out after touchdown was ‘speedbrake, flaps 25’



This does not really fit with the philosophy of leaving the configuration unchanged until clear of the runway but it was our, approved procedure
The best contribution to safety is a competent Pilot.


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workhorse
Posts: 614
Joined: Sun Jul 10, 2005 11:35 pm

Re: Why retract flaps on the ground?

Tue Jun 04, 2019 2:50 pm

cathay747 wrote:
There is NO aerodynamic "drag" at taxi speeds. There are no aerodynamic forces acting on ANYTHING at taxi speeds, period. I would be most curious to know where on EARTH Cathay777300ER is getting this notion. The only "drag" on a taxiing jet, if you want to call it that, would be friction from the tires on the pavement induced by gravity & weight. Good God in heaven!


Well, I, for one, remember well that windy day in HKG when our 340-300 was quite perceptibly "jumping" on its wheels while being stopped on a taxiway with flaps 0. And, by the way, the pilots waited until we were on the runway to set flaps to takeoff position.
 
e38
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Joined: Sun May 04, 2008 10:09 pm

Re: Why retract flaps on the ground?

Tue Jun 04, 2019 3:58 pm

Quoting VSMUT (Reply # 41), "Isn't the A321 also limited to only the flaps 2 setting for takeoff?"

No, at the company at which I work, on the A321, we use Flaps 1, 2, or 3 for takeoff depending on conditions.

e38
 
Tristarsteve
Posts: 3585
Joined: Tue Nov 22, 2005 11:04 pm

Re: Why retract flaps on the ground?

Tue Jun 04, 2019 6:12 pm

At ARN the fuel supply company will not drive their dispensers under the wing if the flaps/slats are not up.
 
workhorse
Posts: 614
Joined: Sun Jul 10, 2005 11:35 pm

Re: Why retract flaps on the ground?

Tue Jun 04, 2019 9:26 pm

VSMUT wrote:
Is that inconsistency something you have noticed within one airline on one type?


Yep. And even one flight. For example, there was a year when I flew the same ORY-NCE on Tuesdays and NCE-ORY on Fridays every week on EZY so overall I have cumulated more than 40 of them. The flap retraction occurred at different moments.

It was especially visible because all other things on EZY are so standardized: for example, I could set my watch (if I had one) using the timings of the PAs at the gate before the flight departure. Always the same phrasing in the same order at the same number of minutes before the departure time. During the flight too, the captain would make the typical PA's ("ladies and gentlemen, we are flying at XXXXX feet, blah blah blah", "ladies and gentlemen, we are starting our descent to NNN") always when passing the same waypoints.

Only the flap retraction time was different from flight to flight. :)
 
TSS
Posts: 3117
Joined: Fri Dec 29, 2006 3:52 pm

Re: Why retract flaps on the ground?

Tue Jun 04, 2019 11:34 pm

Starlionblue wrote:
It would be inaccurate to say there is no aerodynamic drag at taxi speed. You're moving an object through the air, after all. It's just so little drag as to be insignificant.

Exactly. As I understand it aerodynamic drag makes little difference up to about 40 mph and then increases exponentially after that. Technically aero drag is increasing exponentially below 40 mph as well, but "almost none" squared still ain't much and 40 mph seems to be the point at which it becomes a factor that must be accounted for.
Able to kill active threads stone dead with a single post!
 
BravoOne
Posts: 3356
Joined: Fri Apr 12, 2013 2:27 pm

Re: Why retract flaps on the ground?

Tue Jun 04, 2019 11:38 pm

Amazing 47 responses to a simple question from the OP. No wonder airlines are trying to dumb down initial training.
 
Yikes!
Posts: 333
Joined: Sat Oct 13, 2001 4:51 pm

Re: Why retract flaps on the ground?

Wed Jun 05, 2019 3:53 am

AirKevin wrote:
One less thing for the ground crew to crash into if the flaps are retracted.


Precisely. Flaps damaged by impact of ground crew typically are more expensive to repair than trailing edges of flaps retracted.

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