Edited extract from the 737 FCTM re crosswind landings on a slippery runway.
Assume autobrakes previously selected.
Standard crosswind landing technique. If reverse thrust side component drifts the aircraft to the downwind side of the runway, correct back to the centreline, by reducing the reverse thrust to reverse idle and release the brakes.
This minimizes the reverse thrust side force component without the requirement to go through a full reverser actuation cycle and improve tyre cornering forces for re-alignment with the runway centreline.
Use rudder pedal steering and differential braking as required to prevent over correcting past the runway centreline. When established near the runway centreline, apply maximum braking and symmetrical reverse thrust to stop the aircraft.
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If it sounds real complicated well it is. It needs to be practiced several times in the simulator to become anywhere near safe. First of all, note the FCTM statement "reduce reverse thrust to reverse idle and release the brakes". From full reverse in the 737 to reverse idle of 23 percent N1 takes around 10 seconds of winding down. If you miss the idle detent and go straight through from full reverse to normal forward thrust idle detent, it is likely you will be around 50-60 percent N1 as the reverse levers are fully down. That means significant forward thrust just when you don't need it - especially on a slippery runway.
In fact, snapping the reverse thrust levers from full reverse straight to the forward stops could mean at least 60 percent N1 forward thrust still running down remains by the time the reverser panels have stowed. That can be positively dangerous on a short wet runway. It is often quite difficult to judge exactly the position of the reverse levers that will give you idle reverse. You need to practice that movement in the simulator. And you need to do it quickly - not a slow lowering of the reverse levers.
Now decide exactly how you will release the autobrakes at the same time as you are selecting reverse idle. This can be tricky. You have to do this quickly if you are sliding sideways. Read the FCTM advice step by step. If the autobrakes are armed and immediate braking takes place on touch down, then think about how you are going to quickly disarm the autobrakes. Don't put the speed brake down for obvious reasons even though this is one method of disarming the autobrakes.
Should you switch off the autobrake selector which will give you instant release? Or should you tramp on the manual brakes in the hope of disarming the autobrakes first go? The book says release the brakes not hit them harder to disengage them! How heavy should you squeeze the brake pedals in order to disarm the autobrake sytstem? You cannot afford to experiment with over-riding the autobrakes via manual pressure because it all depends how much pedal pressure you need. Remember you may be still sliding sideways.
It may be that the quickest, efficient and most certain way to disarm the autobrakes, is by simply switching them off. So that leaves you with no brakes at all for a couple of seconds and reverse winding down. Not a good situation to be in on a slippery runway but no choice if you stick to the FCTM advice on the subject.
With some nifty pedal work and now differential manual braking you get the thing straight down the runway albeit the crosswind is a problem. Now you select full reverse again while keeping in mind that from idle reverse of 23 percent N1 to full reverse N1 takes at least 6-8 seconds of winding up.
By now you are applying full manual braking as per the FCTM. If the aircraft starts sliding sideways again then go back to square one and start again.
What pilots need to get into their heads is it is imperative to get rid of the autobrakes if the aircraft starts going sideways under the influence of the sideways component of reverse and weather cocking into wind. This may be hard to accept but there it is in black and white in the Boeing 737 FCTM.
In my experience few simulator instructors set up this slippery runway crosswind scenario for practice. It takes real flying skill and needs to be practiced until perfect. Many new pilots to the 737 have their own handling problems with basic strong crosswinds on a dry runway - let alone the situation described above.
Just remember to brief the other pilot of how you intend to handle things.
Last edited by A37575; 22nd Jun 2011 at 14:37.