Originally Posted by
TheChitterneFlyer
Speaking as an ex RAF Flt Eng who flew the Hercules for many years I have never seen, nor heard, of any requirement to use asymmetric thrust for anything other than a 3-engine T/O (ferry flight).
My question to you would be, have you ever operated off of wet ice in winds strong enough to push the airplane sideways?
At a previous employer, we operated 3 times a week into one airport where it was completely common during winter to have a direct crosswind of 30+ knots. This runway was also mostly ice in the wintertime. It wasn't uncommon the gusts to exceed the max demonstrated crosswind component of the airplane I was flying (This was the DC-6, not the L382, but the principle is the same) So, you can either land with full rudder applied, hoping you don't get a last minute gust beyond your ability to control, or you can carry a little more power on your upwind engines into the flare leaving you a little reserve rudder authority. I normally chose the latter. When your runway is slippery ice, your challenges aren't over when you touch down, you still have to keep the airplane pointed down the runway as your rudder authority diminishes with your airspeed, and you have to get stopped, and nosewheel steering and brakes aren't a whole lot of help. So, you work with what you've got. Keeping a little power on the upwind engines helps with the directional control but is counterproductive to getting stopped. On the DC-6, the reverse lockout system required that the throttles were all lined up at the idle stop before they could be pulled into reverse. In the time it takes to bring the throttles to idle, pull the “Martin Bar” which opens the reverse gate (normally done by the engineer) and pull the throttles into the reverse range, 2 things will happen: 1) the airplane weathercocks into the wind and 2) the airplane starts drifting toward the downwind edge of the runway. If at that point, you bring the throttles evenly into reverse, the reverse thrust, in addition to slowing you, will also push you faster toward the downwind edge of the runway. I could draw a little vector diagram of why that happens, or you could take my word, having been there more than a few times that it does happen. The solution is using asymmetric reverse thrust to steer the plane and stop the sideways drift. Now, I don't know if this rises to the level of a “requirement” in your view, but I'm relatively certain that there was more than one occasion where I would have wound up parked off the edge of the runway, had I only used the throttles together as a single unit.
Granted, probably none of this is applicable to jets, but as noted earlier the original question was not specific to jets.