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A350 flap/slat operations

Fri Dec 24, 2021 12:30 am

I flew the A350 (SAS) for the first time a few months back, and when rewatching the videos that I recorded, I noticed that it seems as if the flaps and slats operate independently. I noticed this in several occasions, on the ground and in flight, the slats would first activate and then the flaps would follow after a few seconds. Also, on some occasions only the flaps would move while the slats remained in place, and rather interestingly, on my first flight (SE-RSA) after landing, the flaps and slats finished retracting simultaneously, while on my second flight (SE-RSB) the flaps took much longer to fully retract than the slats. Anyone know why this might be?
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Re: A350 flap/slat operations

Fri Dec 24, 2021 3:40 am

They do operate independently. They aren't mechanically linked.

There are also position variations with the same lever position, for example, flaps 1 and 1+F. Flaps 1 only extends the slats to the first position, while flaps 1+F also extends the flaps to the first position. Flaps 3 also has two positions depending on whether you are taking off or approaching.

The logic on the A330 is similar.

At a guess, after landing the PMs might have moved the lever slightly differently. If you move it first to 1 and then to 0 in steps, the flaps have more time to move. But that's just a guess.
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Re: A350 flap/slat operations

Mon Dec 27, 2021 1:13 am

studentlife, it may be helpful if you understand the sequence in which the flaps and slats operate.

The information following is applicable to the Airbus A320 series (A319/320/321). It may be different on the Airbus A350 aircraft on which you flew, but at least this will give you an understanding of the extension logic on the A320 series.

The flaps and slats are controlled by the same lever, annotated "Flaps," and there are five positions: 0, 1, 2, 3, and Full.

Obviously, at position Flaps 0, the flaps and slats are fully retracted. At my company, the terminology for that position is "Flaps Up."

Inflight (I emphasize this because the sequence is slightly different if on the ground):

Flaps 1: The slats extend to 18 degrees; the flaps remain at 0 degrees (retracted).

Flaps 2: The slats further extend from 18 degrees to 22 degrees. Once the slats have reached 22 degrees, THEN the flaps extend to 15 degrees.

Flaps 3: The slats remain at 22 degrees. The flaps further extend from 15 degrees to 20 degrees.

studentlife wrote:
the slats would first activate and then the flaps would follow after a few seconds. Also, on some occasions only the flaps would move while the slats remained in place

Based on your observation, these two flaps selections may be what you saw--slat activation followed by flap extension (Flaps 2) and flap extension while slats remain stationary (Flaps 3).

Flaps Full: The slats further extend from 22 degrees to 27 degrees and flaps further extend from 20 degrees to 35 degrees.

Here is the summary for slats/flaps (degrees) - Inflight

Flaps 0: 0/0
Flaps 1: 18/0
Flaps 2: 22/15
Flaps 3: 22/20
Flaps Full: 27/35

Note: the degree values may be slightly different for A321 aircraft and for A319/A320 equipped with IAE V2500 engine.

This may help explain what you observed.

When seated aft of the wing on the A320 series, the first observation of flap movement is actually the selection of Flaps 2.

studentlife, I am not able to answer your question regarding the difference in retraction sequence following landing. On some aircraft, if the landing was accomplished on a runway with ice/snow or if ice accumulation is suspected on the airframe (approach and landing in icing conditions), the slats/flaps are left either in the fully extended position or partially retracted to a specified position to prevent damage to flaps/slat components should they have ice accumulation. However, this does not seem to be the issue in the two retraction sequences you observed on the Airbus A350.


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