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convair880mfan
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Flap movement always in stages?

Tue Jul 13, 2021 9:59 pm

I am wondering whether flaps on jetliners must always be moved in stages?

I have seen videos taken by passengers from inside jetliners where it appears that flaps move to intermediate positions without first stopping at initial settings. For example, in one video it appears that a landing 747-400 goes to flaps 10 from clean without stopping. There doesn't appear to be any editing involved but perhaps I am mistaken.

To airline pilots here, can you lower and raise flaps without stopping at intermediate settings? Sorry if this is a lame question.
 
GalaxyFlyer
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Re: Flap movement always in stages?

Tue Jul 13, 2021 11:38 pm

If your speed is low enough (weight light enough) to not exceed the flap speed limit, sure. Usually, they’re moved in increments.
 
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Starlionblue
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Re: Flap movement always in stages?

Wed Jul 14, 2021 8:24 am

SOP dictates going through the steps. Also, flap levers have gates so you can't move directly from some settings to others.

You don't always pass through all the stages. For example, on the A330 and A350, you retract from three to one on takeoff and go around. Also, if you're at Flaps One on takeoff and go around, you can get auto flap retraction, which is sort of an automatic "half stage".
 
CosmicCruiser
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Re: Flap movement always in stages?

Wed Jul 14, 2021 12:26 pm

Not to mention with every flap change there's trim changes and possibly airspeed changes.
 
e38
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Re: Flap movement always in stages?

Wed Jul 14, 2021 6:03 pm

convair880mfan wrote:
I am wondering whether flaps on jetliners must always be moved in stages?

To airline pilots here, can you lower and raise flaps without stopping at intermediate settings?


convair880mfan, with reference to your first question, "I am wondering whether flaps on jetliners must always be moved in stages?"

No, not necessarily, but there are some considerations . . .

First, on most aircraft, there are maximum airspeeds for various flap settings and pilots are required to honor those limitations. As an example, on the Airbus A320, the maximum airspeeds for flap extension are as follows:
Flaps 1: 230 KIAS
Flaps 1 + F: 215 KIAS
Flaps 2: 200 KIAS
Flaps 3: 185 KIAS
Flaps Full: 177 KIAS

These speeds are generally fixed.

In addition, there are minimum airspeeds with each flap setting that you should not go below without selecting the next increment of flap. These speeds generally vary depending on aircraft gross weight. Again, on the A320, as an example, these speeds are referenced using green dot airspeed, S speed, and F speed.

Next, you normally don't want unnecessary drag, so most pilots will try to maintain clean configuration until such time as air traffic control requests a speed slower than required for the configuration, or in the absence of ATC direction, until such time as necessary to begin configuring for the approach and landing in order to maintain stabilized approach criteria.

To answer your first question about selecting the flaps in stages. No, you don't HAVE to as long as you maintain airspeed within the required parameters, but it is in most operators procedures to do so and provides for better stability and pacing. (As another example, in the DC9-30, during approach it was acceptable to select either slats extend flaps 5 or slats extend flaps 15--bypassing the flaps 5 setting. Both were acceptable and it usually depended on where you were in the pattern, position and altitude).

As an example for takeoff, again A320, if you takeoff using Flaps 2, you would have to wait until the airspeed is above F speed before selecting Flaps 1; then wait until airspeed is above S speed before calling for Flaps up. It is done in increments. However, if you takeoff using Flaps 3, it is permitted to go straight to Flaps 1 when above F speed; although it is also permitted to go from Flaps 3 to Flaps 2; then from Flaps 2 to Flaps 1, then from Flaps 1 to Flaps Up. But, to select a lower flap setting prematurely could result in the aircraft approaching a stall condition.

With regard to your second question, "can you lower and raise flaps without stopping at intermediate settings?" On certain aircraft, YES, but why would you do that? (our A320 aircraft do not have flap gates on the levers; theoretically you could move them from full up to full down and vice versa if you wanted to do so).
CosmicCruiser (Reply # 4) above brought up a good point about trim. Each increment of flap setting is going to require a certain amount of trim. Bypassing increments will result in an increased need for trim. You previously asked about flap settings on the Boeing 707. I cannot speak for the 707, but on the KC-135, it is possible that some the older generation autopilots would not have been able to keep up with the trim requirement if you bypassed flap increments, and to trim manually would have required an almost constant activation of the trim motor while the flaps were in transit. In that aircraft, to run the trim continuously increased the potential for a runaway trim situation. Just another reason to lower and raise the flaps in increments.

I hope that helps answer some of your questions. YES, you can bypass certain flaps settings on certain aircraft, but NO, it is not generally done in normal operations, depending on the aircraft.

e38
 
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Florianopolis
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Re: Flap movement always in stages?

Thu Jul 15, 2021 2:39 am

This is slightly off-topic, but on the bus if you put the flap lever in 1, the actual position of the flaps and slats depends on if the airplane thinks you're taking off or landing?
 
Snuffaluffagus
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Re: Flap movement always in stages?

Thu Jul 15, 2021 3:10 am

Florianopolis wrote:
This is slightly off-topic, but on the bus if you put the flap lever in 1, the actual position of the flaps and slats depends on if the airplane thinks you're taking off or landing?


Yes, if you're on the ground and select flaps 1, you'll get slats and flaps. In the air, you'll get slats only when you initially select flaps 1 from flaps up. If you're going from flaps 3 to flaps 1, you'll have both flaps and slats when selecting flaps 1.
 
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Starlionblue
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Re: Flap movement always in stages?

Thu Jul 15, 2021 3:10 am

Florianopolis wrote:
This is slightly off-topic, but on the bus if you put the flap lever in 1, the actual position of the flaps and slats depends on if the airplane thinks you're taking off or landing?


Sorta. It depends on whether you are above or below auto-retract speed. The flap movement speeds on takeoff and approach are normally a bit different, so in effect it makes a difference whether you are approaching or departing. For example, you might not retract to clean until 230 knots when departing. However, on approach, you might not select flaps 1 until you're under 210 knots.


On the A330, with the lever in Flaps 1, you get either 1 or 1+F. On takeoff it will initially be 1+F (slats 16 degrees, flaps 8, ailerons 5). If you haven't cleaned up by 200 knots, you get autoretract, resulting in 1 (slats 16 degrees, flaps 0, ailerons 0). On approach, if you're over 215 knots, you get 1. If you're under, you get 1+F.

Flap load relief means you technically also have two flap positions in each of of lever positions 2 and 3.

The A350 has similar logic but adds spoiler droop to close the gap to the flaps. And the autoretract speeds are different.
 
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Florianopolis
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Re: Flap movement always in stages?

Thu Jul 15, 2021 9:12 pm

Starlionblue wrote:

Sorta. It depends on whether you are above or below auto-retract speed. The flap movement speeds on takeoff and approach are normally a bit different, so in effect it makes a difference whether you are approaching or departing. For example, you might not retract to clean until 230 knots when departing. However, on approach, you might not select flaps 1 until you're under 210 knots.


On the A330, with the lever in Flaps 1, you get either 1 or 1+F. On takeoff it will initially be 1+F (slats 16 degrees, flaps 8, ailerons 5). If you haven't cleaned up by 200 knots, you get autoretract, resulting in 1 (slats 16 degrees, flaps 0, ailerons 0). On approach, if you're over 215 knots, you get 1. If you're under, you get 1+F.

Flap load relief means you technically also have two flap positions in each of of lever positions 2 and 3.

The A350 has similar logic but adds spoiler droop to close the gap to the flaps. And the autoretract speeds are different.


Would you ever intentionally accelerate through the auto-retract speed on a climb out? Say you wanted to keep the slats out until you were going faster, just leave the handle in 1 and let the airplane bring in the flaps?
 
e38
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Re: Flap movement always in stages?

Thu Jul 15, 2021 9:33 pm

Florianopolis wrote:
Would you ever intentionally accelerate through the auto-retract speed on a climb out? Say you wanted to keep the slats out until you were going faster, just leave the handle in 1 and let the airplane bring in the flaps?


Florianopolis, in general, on the Airbus A320 series, we normally don't intentionally allow the airspeed to increase to the point where the auto-retract system kicks in, but sometimes, particularly on the A321 since it is a heavier aircraft, it does.

During climb out, we are more focused on the various flap retract airspeeds--F speed and S speed--and sometimes the S speed is high enough that flap auto-retract activates to protect the flight controls. In those cases, we attempt to retract the flaps as quickly as possible once the aircraft is above the appropriate airspeed.

I'm not sure that answered your question, but generally, no, we don't intentionally leave the slats out until going faster. Once we are at or above S speed, it is generally safe to call for "Flaps up." I would have to say that many times pilots are not even aware that flap auto-retract initiated because they are focused on other aspects of the departure.

e38
 
N353SK
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Re: Flap movement always in stages?

Thu Jul 15, 2021 9:39 pm

Florianopolis wrote:
This is slightly off-topic, but on the bus if you put the flap lever in 1, the actual position of the flaps and slats depends on if the airplane thinks you're taking off or landing?


Here is the official Airbus "logic diagram" of what happens when when the flap lever is moved between 0, 1, and 2 based on airspeed. Good luck deciphering it :mrgreen:

Image
 
N1120A
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Re: Flap movement always in stages?

Thu Jul 15, 2021 11:56 pm

Even light airplanes can have differing flap speed limitations, or advisory limits on going between stages based on stress
 
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Florianopolis
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Re: Flap movement always in stages?

Fri Jul 16, 2021 12:26 am

e38 wrote:
Florianopolis, in general, on the Airbus A320 series, we normally don't intentionally allow the airspeed to increase to the point where the auto-retract system kicks in, but sometimes, particularly on the A321 since it is a heavier aircraft, it does.

During climb out, we are more focused on the various flap retract airspeeds--F speed and S speed--and sometimes the S speed is high enough that flap auto-retract activates to protect the flight controls. In those cases, we attempt to retract the flaps as quickly as possible once the aircraft is above the appropriate airspeed.

I'm not sure that answered your question, but generally, no, we don't intentionally leave the slats out until going faster. Once we are at or above S speed, it is generally safe to call for "Flaps up." I would have to say that many times pilots are not even aware that flap auto-retract initiated because they are focused on other aspects of the departure.

e38


That makes sense. I guess I was asking, is it an expected and normal part of operating the airplane that it may happen, sometimes. Sounds like it is.

Thank you all for the responses.
 
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Starlionblue
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Re: Flap movement always in stages?

Fri Jul 16, 2021 1:57 am

Florianopolis wrote:
Starlionblue wrote:

Sorta. It depends on whether you are above or below auto-retract speed. The flap movement speeds on takeoff and approach are normally a bit different, so in effect it makes a difference whether you are approaching or departing. For example, you might not retract to clean until 230 knots when departing. However, on approach, you might not select flaps 1 until you're under 210 knots.


On the A330, with the lever in Flaps 1, you get either 1 or 1+F. On takeoff it will initially be 1+F (slats 16 degrees, flaps 8, ailerons 5). If you haven't cleaned up by 200 knots, you get autoretract, resulting in 1 (slats 16 degrees, flaps 0, ailerons 0). On approach, if you're over 215 knots, you get 1. If you're under, you get 1+F.

Flap load relief means you technically also have two flap positions in each of of lever positions 2 and 3.

The A350 has similar logic but adds spoiler droop to close the gap to the flaps. And the autoretract speeds are different.


Would you ever intentionally accelerate through the auto-retract speed on a climb out? Say you wanted to keep the slats out until you were going faster, just leave the handle in 1 and let the airplane bring in the flaps?


It is quite normal to accelerate through auto-retract on the A330 and A350. Example: Departing with green dot speed (minimum clean) 228 knots with a SID speed restriction of 220. You'd accelerate to 220 and stay there until you're past the restriction (or cleared higher speed). You would get autoretract at 200 (A350 auto-retract speeds are different but the same logic applies).

Auto-retract would normally be included in the briefing so everyone is on the same page.
 
113312
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Re: Flap movement always in stages?

Sat Jul 17, 2021 6:13 pm

It depends upon the aircraft type and if you are speaking of ground or flight operation. For example, on the old 727, you could select Flaps 15 for departure while taxiing out so long as you confirmed that both inboard and outboard sets reached 15 degrees and all of the LED segments indicated GREEN. (NW had a blue light instead). However inflight, retraction and extension would be on a speed schedule: 2, 5, 15 extending and 5, 2, and UP on retracting. Flaps 25 or 30 would be selected usually after landing gear extension.

On most Douglas jets, Flaps are retracted in flight first and then Slats. For extension, Slats first and then flaps extended in increments.

The DC-8 series did not have slats but did have wing slots. They opened when the wing flaps were selected to extend to any position and would close as the wing flaps were through the last degrees of retraction. (I recall less than 8 degrees)

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