What decides SOP flap setting?

[OBK!]

Just a general query that's bugging me...How do you go about choosing flap settings for example in a 767/757? (:O ). I noticed that most airlines use a default flap setting of 5 in the 767, but BA (being unique as they are) use 15...why? I also noticed a lot of operators use flap 15 for default in the 757...howcome 15 instead of 5? What are the deciding factors?

Thanks
obk

[ETOPS]

In BA we have a nifty peice of kit called CARD (don't ask me what it stands for). Before take off you send an ACARS message to the performance computer in head office specifying departure airfield/runway and all the met details together with estimated RTOW. A few minutes later you get the reply which shows optimum flap setting, assumed temperature for derate and Max take-off weight. The system appends the relevant performance notes including emergency turns and multiple runway requests are available. It also brews a nice cup of tea!

The performance assumptions are based on maximum engine derate for extended engine life and thus if any tailwind is present Flap 15 will be offered.........

[Dan Winterland]

On the 747, you have a choice of flap 10 or 20 for take-off. My previous operator only used flap 20, only providing the tables for 20. My current operator gives us both sets of tables and lets us make the decision. We chose the setting gives us the best RTOW. Where there are obstacles or a high density altitude, flap 10 generally wins.

[OBK!]

I don't understand? Why would Flap 10 give you the better RTOW? Surely flap 20 would give you more lift...getting you off the runway quicker for a given weight, therfore enabling you to carry moreweight with flap 20?

:confused:

[Frosty Hoar]

In cases where take off is obstacle limited,(mountain at end of runway for instance) less flap will improve climb performance and use the available runway length to achieve this with a higher speed at rotation.On some aircraft in our fleet, e.g A310 flap 0 is often the optimum setting on take off.

Where for example runway length is the most limiting factor , more flap is used to get the aircraft rotated at a lower speed in less distance, in which case flap 20 might be relevant, but a degraded climb performance will result.

[BAe 146-100]

Hi,

On the A300 when they take off with flap 0 do they deploy the leading edge instead?

Regards :)
BAe 146-100

[Frosty Hoar]

Normal setting slat 15 flap 0

rgds FH

[411A]

When SV operated TriStars (their first widebody aircraft), they used exclusively flap 18 for take off, most other operators using 10 (the TW guys didn't like it, but did as they were told).

The reason was quite simple...lower Vspeeds resulted in lower tyre speeds, and to the best of my knowledge, never had a tread separation on the L10, at least up to 1990.

[Georgeablelovehowindia]

BAe146-100 you bet they deploy the leading edges, it wouldn't fly otherwise! This configuration led to the incident where, as they turned onto the runway for takeoff, a passengering crew member (non A300 rated) sprang from his seat and rushed towards the flightdeck yelling 'Flaps, you idiots, Flaps!!' Huge embarrassment, of course, when it was explained to him, but what would you have done in the circumstances? With the knowledge of the above, I've flown as passenger on the A300 and it is most disconcerting to start the takeoff roll with no trailing edge flaps set, especially if you can't see the leading edges from your seat ... (However, any attempt to set takeoff thrust would cause an extremely loud warning to come from the Takeoff Configuration Warning - or whatever Airbus call it.)

Oh, and in case anyone 'thinks on', I wasn't the crew member in that incident. :rolleyes:

[mustafagander]

Selecting t/o flaps is a compromise. If you are given a choice by your airline and/or manufacturer, in general terms, shorter runways need more flap, but you lose in 2nd segment climbout.

More flap gets you into the air at lower speeds allowing lower tyre speeds among other things, but you will have a lower climb gradient in the 2nd segment.

A lesser flap setting OTOH means higher tyre speeds and needs longer runways, but (usually) results in improved 2nd segment climb gradient. Sometimes you can crib a bit by using more flaps and a bit of "overspeed" to improve the 2nd segment.

Overspeed is increasing the certified V speeds by a margin to improve 2nd segment. It works when the V2 speed is on the "back of the drag curve", meaning less energy is required to fly a few knots faster. Naturally it costs runway length to accelerate to the higher speeds.

My mob use (on the B747s) F20 where possible and F10 when it enables a higher TOW or greater engine reduced thrust.

[dusk2dawn]

External considerations could also be applied : Study of optimisation procedures for decreasing the impact of noise around airports (http://www.nlr.nl/public/hosted-sites/sourdine/)

[Row 12F]

Since this is about flaps, perhaps someone can comment on this.

On 29th April at around 18:20, leaving Heathrow and passing the west end of 27L on M25, I saw a Cathay Pacific 744 take off with what appeared to be full flaps. I assume this from the amount of sky that could be seen between the large flap extensions and the wing. The wind was quite strong and very gusty but it still surprised me. He was following the same path as many others previously taking off. Perhaps he was going around but as others were landing on 27R and taking off on 27L, that might have been just as unusual.

Any comments? Is it ever necessary to take off with large amounts of flap?

[Rynopilot]

Air Canada has a similar system to BA. Before take-off data is sent via ACARS to the performance computer. Take-off performance data is sent back to the aircraft in the form of a WAT chart (Weight Limitations Chart). This only applies to ACARS equipped aircraft.

Flaps 20 is normally selected for rough or contaminated runways as it ruduces tire wear.

Normal flap selection priority for the 767:

-200
1. Flaps 5 Reduced Thrust Packs ON
2. Flaps 5 Full Thrust Packs ON
3. Flaps 5 Full Thrust Packs OFF
4. Flaps 1 Full Thrust Packs OFF
5. Flaps 20 Full Thrust Packs ON

-300
1. Flaps 5 Reduced Thrust Packs ON
2. Flaps 5 Full Thrust Packs ON
3. Flaps 5 Full Thrust Packs OFF
4. Flaps 20 Full Thrust Packs ON
5. Flaps 20 Full Thrust Packs OFF

Best Regards,

[BAe 146-100]

Hi,

On the Fokker 100 they mostly use Flap 0 on takeoff.

Regards
BAe 146-100

http://www.zap16.com/images/ph-ezn.jpg

[JetDriverWannabe]

I would just like the ask are there any cost implications of using different flaps settings ?

Would using a excessively high flap setting incease ?
A: Drag
-Extra Drag means extra fuel burn
-Extra Drag means extra aerodynamic stress

B: Noise
-Noise created by higher flap settings will increase disturbance to people living near the airport.


Wouldn't the above have influence of SOP as well?

[Dan Winterland]

Yes. Less flaps equals less noise. Since my last post, my airline has suggested that we use the lower setting at an airport where we have just received a couple of noise violations.