Originally Posted by Lemurian
Please compare the data on
1/- the mag heading
2/- the localiser
3/- the lateral acceleration
4/- the rudder - and brake - pedal inputs
5/- the ground speed, i.e. the deceleration.
It looks to me that the airplane started skidding as early as :30, some 20 degrees to the left.
That runway was indeed very slippery !.
Interesting observations. Here's my take on it.
1/ the magnetic heading:
It only deviates significantly in one direction (as opposed to just fluctuating in both directions in the time before) at :43, which is most likely where the aircraft started veering off the runway.
2/ the localizer:
Where exactly is the transmitter located? Any deviation from the localizer path would be bigger the closer you get towards it. And a slight deviation from the centreline would be shown exaggerated. I stand corrected on this one, if it turns out to be otherwise.
3/, 4/ rudder/brake pedals/accel-lat:
I think these are normal deviations we'd expect to see given a wet (but not slippery) runway, with asymmetric thrust, and the PF trying to keep the aicraft centered with the rudder, which interferes with the braking action.
5/ deceleration:
the deceleration is best seen directly at the accel-long graph. It is within the range I'd expect on wet surface with less-than-optimal downforce (high-lift devices extended, but no spoilers). Remember that deceleration force ("friction") is proportional to the downforce on the wheels. There is also no indication that anti-skid was inoperative. The brake pressure graph might shed light on that, but I think it is not among the released data. (And it would be difficult to interpret, since it is only sampled every 4s.)
Another remark is the control inputs . They are coming, later on the roll from the " wrong " side, i.e the F/O's. The left side stick was left pretty much neutral after touch-down.
Yes, I was wondering about that, too, but I have no idea what it might mean.
Bernd