Turbulence and crosswind techniques in FBW Airbuses
As a retired ex-A320 driver (1988 - 2001), I've just come upon this interesting thread. Unfortunately, the link to the full set of pics is no longer applicable (?). So I'm stuck with the well-chosen three on Post#8.
Certainly looks like a late and sensible go-around, in what we can see (post#25) was roughly an on-limits crosswind (Posts#13 and #17); hence the lack of de-crab prior to touchdown, as has been said.
Having been there many times, I agree with the posts re. turbulence and wind shear at BIO, particularly the rotor effects on approach to R/W 12.
The wing-drop immediately after the brief touchdown may have been partly caused by the reaction as the tyres momentarily gripped the runway, yawing the aeroplane to the left. It may seem obvious, but this sudden roll would have required side-stick to correct, even on a FBW Airbus.
It is true that, with the AP disengaged, neutral side-stick on the A320 family normally gives zero roll-rate. Deflecting the stick to left or right commands a rate of roll (proportional to the deflection). In the event of a sudden side gust or yaw, however, the A/C rolls rather like any other. Once it has been rolled, say, 15 degrees to the left, it will stay there unless the pilot uses side-stick to pick the wing up (effectively by calling for a roll-rate to the right).
The difference from a traditional A/C is: once you have achieved the desired bank angle (zero, in this case), you remove pressure from the side-stick, whereupon the FBW will stop the A/C rolling (probably using a momentary bit of left aileron).
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Although the pictures are of a go-around, there has been some discussion on crosswind landing technique, and how this relates to the FBW Airbuses. Can I offer my two-pennies' worth?
Re. Post#37, in my day Flap 3 (which was also the G/A setting) was also recommended for landings in gusty conditions on the A320. Trouble was, we rarely had a chance to try it out for 'manual' landings on a nice day, to get used to the higher pitch and lower thrust setting. [With the excellent GS-MINI system normally averting the need for increased thrust as the IAS tumbled, the thrust over the threshold could be quite low.] There was also some handling difference in the control laws (I can't remember what), maybe because Flap 3 is one of the approved take-off settings.
I notice ray cosmic's Boeing quote (Post#38), permitting landing without de-crab. Don't remember this on the A320, and it feels dreadful when done unintentionally. [Am I right in saying that the main gear on the B737 has some ability to castor? After they have turned on to a straight taxiway, they often seem to be crabbing along.]
For the landing, side-slip (crossed-controls) technique has been demonstrated to work well, but is not an approved method. The most obvious reason is that, in a limiting crosswind, pod-scrape on the A320 is possible, particularly at higher pitch angles.
The recommended technique in my day was to de-crab before touchdown, avoiding use of aileron unless and until the aeroplane rolled. In my experience, however, the A/C invariably rolled as a result of the de-crab. Accordingly, I always pre-empted this by using a moderate amount of into-wind roll-demand in opposition to the rudder. At completion of de-crab, rudder and stick were centralised.
This technique often led to the up-wind gear touching down first, followed immediately by the down-wind gear, whether or not the roll demand was removed. With both wheels firmly on the ground, it was my practice to reintroduce into-wind aileron until about 80 knots.
By the way, on crosswind take-offs it helped to anticipate the all-too-commonly-seen wing drop, during rotation, in a similar fashion.
All this seemed to work well, but the obligation to teach only SOPs prevented me from recommending it to my co-pilots...
So, what are you FBW-Airbus pilots doing in 2008?