I have had a quick read of it and the Airbus document is remarkably similar to the B737's FCTM.
In both cases they explain how in a X-wind situation, reverse thrust can be resolved into (basically) two vectors, the one we are interested for the purposes of this discussion is the "side force" component.
From the Boeing 737NG FCTM. (The Airbus document requires very similar techniques)
....... 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 downwind side of the runway. Also, high braking forces reduce the capability of the tires to corner.
To correct back to the centerline, release the brakes and reduce reverse thrust to reverse idle. Releasing the brakes increases the tire-cornering capability and contributes to maintaining or regaining directional control. Setting reverse idle reduces the reverse thrust side force component without the requirement to go through a full reverser actuation cycle. Use rudder pedal steering and differential braking as required, to prevent over correcting past the runway centerline. When directional control is regained and the airplane is correcting toward the runway centerline, apply maximum braking and symmetrical reverse thrust to stop the airplane.
Neither manufacturer mentions using asymmetric reverse thrust.
safetypee wrote:-
So from the gist of the discussion above, when / how would single reverse be used?
Personally I would not; and to avoid the ‘but if you really had too’ argument, there are few if any such situations which could not be covered by a pre departure decision. No go for crosswind on a 'dry' take off (RTO) – the Captain judges the value, and a 'dry' crosswind or wet/ contaminated runway for landing (EU operators may, in addition have to consider landing distance if reverse is credited on contaminated runways).
Entirely your call as to whether or not you use a single reverser. The B737 allows dispatch with only one operational reverser, provided performance considerations are met. Having done a "couple of dozen" landings in various versions of the 737 (-100/200/600 excepted) in my experience it is a non-event.
The MEL covers pre departure issues; what if there was an en route failure, is there similar operational advice in the QRH or is the issue entirely ‘operational’?
Again 737 specific. There is no checklist for a reverse thrust failure whilst in flight. From a performance point of view adjustments to your landing distance, based on the number of serviceable reversers, are covered in the QRH/PI.
As ever operate your aeroplane in accordance with your company's SOPs