Reverse thrust on slippery runways with crosswind
 

This is a subject rarely covered during type rating training. My 1982 outdated B737 Pilot Training Manual has this to say on the subject:
As the airplane starts to weathervane into the wind, the reverse thrust side force component adds to the crosswind component and drifts the airplane to the downside of the runway. Main gear tire cornering forces available to counteract this drift will be at a minimum when the anti-skid system is operating at maximum braking effectiveness for existing conditions.

To correct back to the centreline, reduce reverse thrust to idle and release the brakes. This will minimize the reverse side force component without the requirement to go through a full reverser actuating cycle, and provide the total tire cornering forces for re-alignment with the runway centreline. Use rudder, steering and differential braking, as required to prevent over correcting past the runway centreline. When established near the runway centreline, apply maximum braking and reverse thrust to stop the airplane.

Reduced braking effectiveness due to anti-skid cycling on one side may cause the airplane to veer toward one side of the runway. Corrective action for this is to release pressure on both brakes, then use the rudder and differential braking as required.. When the airplane is again headed towards the centre of the runway, apply reverse thrust and steady brake pressure to develop maximum braking. Reducing pressure to rapid cycling brakes increases directional control capability.

The following represent maximum crosswind component guidelines: Runway condition Wet, no standing water Max crosswind component 15 to 23 knots. Runway condition Icy, slush or standing water Maximum crosswind component 5-13 knots.

Comment: Some operators mandate auto brakes are be used on all runways, regardless of runway length or condition. Thus, landing on a slippery runway with a crosswind where the aircraft is likely to weathervane into the wind, pilots would understandably be reluctant to release the autobrakes if weathervaning occurs. However, the brakes must be released as well as reverse thrust to idle if directional control difficulties are experienced and the aircraft must get back to the centreline in order to allow full reverse thrust and maximum manual braking to be used. The whole procedure requires good handling skills from pilots who may rarely have encountered such a combination of events.

If the aircraft is weathervaning and the pilot has to simultaneously get out of autobraking as well as reducing what may have been maximum reverse thrust down to reverse idle, he needs to be careful not to inadvertently go past reverse idle to forward thrust while all the time looking outside at the runway. I am not familiar with latest aircraft where autobraking can be re-established on the landing roll once it has been turned off, but establishing maximum manual braking once the airaft is re-aligned on centreline and full reverse thrust is applied is clearly a priority

Which brings me to simulator training for such an eventuality. While I have personally practiced the manoeuvre in the simulator, it was difficult to know the veracity of the simulator, particularly early models. I do know from experience that it takes good handling skills to cope with crosswind landings on slippery runways. I firmly believe the manoevre should be taught during type rating training. Comments invited.

Ok, I’ll dive in. First the concern of going from reverse thrust to anything above idle is non existent with little experience because you’d have to deliberately move the thrust levers forward. Reverse is a pull, and stowing is a downward motion, not forward motion and the interlocks prevent forward motion for a second or more.

Second, I know the reverse side force component is what can take the aircraft off but I’ve found that in the CFM engines (vs JT-8) the component is just not that strong.

"When required, differential braking must be applied by completely releasing the pedal on the
side that is opposite to the expected direction of the turn. This is because, on a slippery runway,
the same braking effect may be produced by a full or half-deflection of the pedal". FCTM A320

In the 737 case with regard to releasing the brakes during weathervaning caused by crosswind and reverse thrust vector. The quickest method of releasing the brakes under these conditions is to switch off the autobrakes. This is because releasing them by manual braking may only cause more trouble because you are depressing both brake pedals i.e. increasing brake pressure. Also it is sometimes difficult to know how much foot pressure is needed to disengage the autobrake system.