Originally Posted by
shdw
Differential thrust allows for a decreased degree in crab angle and I have not seen a single person here provide a legitimate reason as to this being unsafe. Just because the procedures, which are nothing more then recommendations and are in no way limitations for any aircraft, don't include this technique doesn't mean it is dangerous and shouldn't be done.
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YES YOU HAVE ... ME !!! I've said it only 4 times now. And let me explain it ONE more time. (If only I could draw a force vector diagram here).
You said earlier, you pull the DOWNwind engine. Yes, the crabangle is going to change (decrease). However, you just upset the once balanced horizontal force component vectors. And for every action, there is a reaction.
Here comes your reaction. Since you pulled power on the right engine, some of that thrust (pointing to the left) kept you on centerline. When you reduced it, the crab angle decreased, which means the engine thrust horizontal component that was pulling to the left of centerline, also decreased. The net effect is that you now start drifting. Since aircraft aren't designed to handle side loads, landing in a drift is not good.
Another reason why landing crabbed is bad. In every aircraft I've flown, TRs were only taken into account during aborts and abnormals. Normal landing distances were never predicated on TRs. Regardless, if you landed crabbed into the wind, and you pulled the TRs, you are in for a rude awakening. The thrust vector for the TRs in a crab is backwards pulling you DOWNWIND. And as such, causes you to slide off the runway downwind. That is why, in every aircraft I've flown with TRs, there was always a warning about closing the TRs if directional and/or drift control could not be maintained.
In the video you attached, those aircraft are being CERTIFIED at their MAXIMUM CRABBED LANDINGS ... some of which used a forward slip maneuver to align the nose just prior to touchdown. In case you didn't know this, Boeing publishes crabbed and uncrabbed crosswind limits for their aircraft. They also publish the max demonstrated and theoretical. Operaters can choose which numbers they want to use. But if they always land crabbed, they're going to go through tires and landing gear at a much much faster rate ($$$$$$$$$).
I'm not receptive to your technique because I think it is FLAWED. I'll agree, you are going to decrease your crab angle, but you're going to drift. So how do you counteract that? More wing down into the wind?