Aquaplaning and autobrake question

[AeroSpark]

I flew into Bournemouth last night on a Thomson 738. Weather was absolutely rubbish, heavy rain and strong winds. We didn't break cloud until we were virtually over the airfield boundary. When we touched down it felt like we aquaplaned for a couple of seconds, and the brakes/reversers certainly took normal than longer to be applied. Cue lots of sharp intakes of breath and many a clenched bum cheek! When the brakes did come on they went on hard and I'm pretty sure we used more than reverse idle.
My question is (and I'm assuming autobrake was used) what triggers the autobrake? I guess they wouldn't work in an aquaplane as that would only make it worse?

By the way if anyone operated TOM877 yesterday, or knows someone who did, great job and thanks!:ok:

[parkfell]

And what does aqua planing "for a couple of seconds" feel like. ? How do you know?
You would want a firm touchdown to ensure that the wheels spin up, and AUTOBRAKE would then activate. Mandatory to use it.
Probably max reverse would be used as the prescribed AUTOBRAKE decel rate (setting 3 or max?) cannot be certain in really wet conditions.

[Denti]

Autobrake is mandatory? Surely another children of the magenta SOP. In the OEM SOPs it is recommendet to use autobrake, but not mandatory. Max manual braking is actually better according to the performance software and with well trained pilots that are still allowed to land without auto brake whenever they want to.

[AeroSpark]

And what does aqua planing "for a couple of seconds" feel like. ? How do you know?

We didn't touch down as firmly as I would have expected on a (very) wet runway. There was a strange noise from underneath for a couple of seconds and the aircraft didn't start to decelerate until after the noise had stopped, and you could feel and see we were moving across the runway. I don't know what aquaplaning feels like in anything other than a car, and I'm sure to the guys up front it was a pretty standard arrival, however to me in the back it didn't feel normal hence why I asked the question.

[vapilot2004]

Autobrake refers to the system that automatically applies brake pressure to obtain a target rate of deceleration. It can be switched in or out as required by SOP or at the pilot's discretion. Air/ground relays/logic and thrust lever position determines when the system will activate, if switched on. It will not activate until the wheels 'spin up', indicating to the computer via sensors that they are on terra firma and the tires have traction.

Anti-skid refers to a system that enhances braking action, particularly on wet or slippery tarmac, and when high brake pressures are applied for rapid deceleration. Anti-skid rapidly cycles brake pressure to the wheel or wheels, allowing the tires to maintain traction near the limits of adhesion. A rapid decrease in wheel speed, as measured by sensors at the wheel, activates the system. On some newer aircraft, a wheel's speed is not only compared temporally against itself, but also to other wheels on the aircraft.

[parkfell]

Denti
It was mandatory (if "S") for us (SOP)as it got the process of braking started. Where is the harm in that? Max manual braking would indeed give better stopping distance. Probably a precautionary approach when landing distances are marginal. Take Aberdeen (ABZ) as an example in a -800.......
I agree with you that with 3000m+ available, it would not be an issue not to use it.
I didn't write the SOPs !

AeroSpark
I wonder if you had a strong crosswind as well?

Va...2004
I was unaware that thrust lever position was a factor in activating it?

[vapilot2004]

Max manual braking, or using the MAX Autobrakes (or sometimes even level 3) can be uncomfortable for the folks in the back. A setting of 2 or above, without the benefit of above-idle reverse thrust can cause high brake temps and wear, the degree to which depends on landing weight.

[AeroSpark]

vapilot - thanks for the informative reply

parkfell - very possibly, it was a very wet/windy evening but I don't know which direction