I have seen a guy I used to fly with do this a few times in the Citation 650. (he was retired NWA and flew everything from the dc3 up to the 400) And I'll map it out for you because a few on here are getting their upwind confused with their downwind
Try to picture this in your head



Lets say you are landing rwy 35 and the wind is 280/21G31, now big crosswind coming off your left side, so which way will the nose be pointed? .......You're right! the left....Now the 650 was a squirrely pig in any wind and would dance all over even with the yaw damp So he kept about 5% more N1 on the LEFT throttle (which is upwind) and with the help of the rudder bias system would help keep the plane on centerline ..... His explanition was it kept the airplane a little more "stable" going down final. He still used the crab to 50ft or so and kicked it out , he just used a few more percent throttle to help centerline alingment and reduce the amount of crab angle down final.

 

Yes, in this situation, you would reduce the crab angle with the runway. However, in balancing the force vector diagram, you now have unbalanced forces on the aircraft and the aircraft WILL start to drift downwind. This is due to the horizontal component of the thrust from the downwind engine being reduced. When that horizontal component is reduced, you will have to increase your bank into the wind in order to prevent drifting off centerline and off the runway.

Now for landings on ice. I've never done it, only snow. I don't want to land on ice. However, it seems to me that if you are need to use differential thrust to stay on the runway during a landing, this is probably a situation that warrants a go-around and a landing when conditions don't require such cowboy tactics in order to make an airfield. Just my 2 cents.

This type of judgement and thinking a highly congtributing factor as to why Alaska leads the number of crashes and/or occupational pilot deaths (by 20%) over all other states combined.

 

Maybe it's the guys not adapting to the environment and using "cowboy tactics" who are going off the runways... I'm still here aren't I?

 

Wow ... you are missing the point. You shouldn't be landing in those types of conditions. It is called "poor judgement". Why would you risk your life and certificate for that?

Reading the comments in here reminds me of Lt Col Bud Holland and his famous crash. He knew it all and there wasn't one pilot who wasn't going to tell him that his flying was unsafe. YouTube - B-52 Bomber Crashes during Air Show

But, if you want to pin your career on using a technique which obviously, given the feedback from this forum, is controversial, then please go ahead.

Don't be surprised if you're slapped with a very hefty wrongful death law suit if you end up killing someone ... assuming you survive.

/rant

 

Comparing assem thrust for landing to what Bud did is a bit of a stretch. Your talking a gentlemen doing rolls in large bombers to someone giving a difference of thrust to reduce cross wind in a landing. A procedure that is certainly not unsafe in any way shape or form, just because it isn't practiced much anymore doesn't mean it unsafe.

Heck, like I mentioned earlier, many folks in here arguing against this have said in other threads that they would do a single engine go around. I am not claiming a single engine go around is a poor decision, but it certainly introduces far greater yawing tendencies then a 5-10 percent thrust difference.

Effective use of assem thrust can easily drop 10-15 knots out of any crosswind, it isn't used anymore because it isn't necessary in most cases, not because it is unsafe. I would love for some old multi tail dragger pilots to speak up a little more in here as that is the origin of assem thrust by my understanding. Landing crabbed isn't an option in that type of aircraft.

I have used it for a 20sG30s approach in a Seminole and it worked wonderfully, used between 200-400 RPM difference. It is no more unsafe than a simulated single engine approach, don't like the results, even throttles and off you go.

 

Threads like this is why I'm glad something being one pilot's technique doesn't make it another pilot's procedure...

 

Shdw, not picking on you, but I guess I have to spell it out. If you need differential power in order to stay on the runway or to reduce the effective crosswind component, then it is probably a runway that you shoudn't be landing on.

There are those that are arguing it is an effective tool to to land in high crosswinds on slippery surfaces ... and there are others suggesting it is a good technique to provide simulated additional rudder authority in order to reduce the crab angle (you). Apples and oranges. The same technique being applied to achieve completely different outcomes. One person using it to increase crab to stay on a runway, the other using it to align the nose with the runway.

In my previous threads, I stated why either scenario isn't a preferred.

But if you guys feel comfortable enough to continue applying this technique, by all means go ahead. Just be ready to explain why you landed on a runway that exceeded the flight control authority maximum crosswind limits.

 

Let me give another example that goes hand and hand IMO since they are both safe techniques. If you need reverse thrust to avoid sliding off the end of the runway than you probably shouldn't be landing there either. Like differential thrust, reverse thrusters are safe and used for this purpose. Do commuters really avoid going to runways just because it requires reverse thrust?

In the example that ce650 gave, who you quoted, the xwind component was about 18g27 (did it in my head with the lack of a wind chart so don't expect perfection). Is this considered too much? If not, what do you consider too much?



With all due respect, the member speaking of that was flying out of alaska, I would imagine he didn't have many other options. Of course with the exception of canceling all flights just because a pilot is scared to have a few extra pounds of thrust on one engine versus the other. Does this mean everyone should be using it to stay on the runway? Not at all, like he said, "it was extreme conditions."

The majority here are against it for, as I can see thus far, no legitimate reason, instead we get this, "just don't do it." Well for your information and everyone else's here, "just don't do it," is not a valid or legit reason.



These are two unrelated statements smashed into one. Additional rudder authority would be nice for a forward slip to land, in a crab you don't need rudder. It is either for additional rudder authority OR to reduce the crab angle, depending on the type of approach profile one chooses to fly.

I avoid the argument for additional rudder authority because in my opinion the idea of a "forward slip to land" died with the birth of the nose wheel. Crab the aircraft in and then stomp the rudder to straighten out in the flare, if you land a little crabbed, big deal. The idea of forward slip is rooted in old ideas that were necessary in the days where tric gear ruled the airways.

Differential thrust is used throughout the entire landing to reduce crab and make it easier to maintain centerline. It is done by increasing the power on the downwind engine, this means in a left to right crosswind the right engine would be at a higher power setting. It can be done on short final, but there is absolutely no reason not to set it up sooner to reduce the workload on short final. IMO and what I did when I used this, you should set it up early so you have nothing to do but sit back and reap the benefits of what will seem like a less windy approach.

Here is how it is done now, and rightfully so: 777 max cross wind demo - Google Videos



Unrelated Ranting

For anyone curious, the reason taildraggers required a forward slip and a wing low touch down was because landing straight/true was required to avoid ground loop. A tail dragger has the CG behind the main landing gear resulting in negative direction stability on the ground. This means that once that tail starts to wander if you don't stop it it will go until you flip, generally a matter of seconds, less if you land crabbed.

In a tric aircraft the CG is on or in front of the mains, the result is positive directional stability. This means if you land in a crab and do nothing the aircraft will straighten itself out. What does this all mean? Wing low landings are not required in any way shape or form for any aircraft with a nose wheel. They look cool, but wind isn't going to "get under your wing" and flip you, that isn't what a ground loop is and that was never the intention of a forward slip/wing low landing.

 

"I avoid the argument for additional rudder authority because in my opinion the idea of a "forward slip to land" died with the birth of the nose wheel. Crab the aircraft in and then stomp the rudder to straighten out in the flare, if you land a little crabbed, big deal. The idea of forward slip is rooted in old ideas that were necessary in the days where tric gear ruled the airways.

Differential thrust is used throughout the entire landing to reduce crab and make it easier to maintain centerline. It is done by increasing the power on the downwind engine, this means in a left to right crosswind the right engine would be at a higher power setting. It can be done on short final, but there is absolutely no reason not to set it up sooner to reduce the workload on short final. IMO and what I did when I used this, you should set it up early so you have nothing to do but sit back and reap the benefits of what will seem like a less windy approach.

Here is how it is done now, and rightfully so: 777 max cross wind demo - Google Videos"
shdw








Wrong, forward slip is used as a valid method in large jets, whether applied prior or during the flare. Autoland systems drive the aircraft into a forward slip well prior to the flare, there is a reason for this and it has to do with controllability. Landing in a partial crab is also approved for many jets. I have never seen differential power recommended in any large jet flight manual as a landing technique or approved policy. I have used it in the DC-3 and other light prop driven aircraft.
If you think a large jet "will straighten itself out" after landing in a crab or partial crab, you are in for a surprise. Rudder will be required. You may want to watch that video again.

Finally, I would be happy to read any Boeing or other factory guidance you have that endorses the shdw method. This statement is also incorrect: "Wing low landings are not required in any way shape or form for any aircraft with a nose wheel. They look cool, but wind isn't going to "get under your wing" and flip you, that isn't what a ground loop is and that was never the intention of a forward slip/wing low landing." Not sure where you are getting this stuff, but it is wrong in so many ways I have to guess you are just making it up as you go. It isn't going to "flip" you, but a wing low forward slip is a valid and recommended technique in every jet flight manual I have ever seen.

 

I meant to post this video: YouTube - Scary Landings in High Crosswind

As a clear view demonstration that while forward slip may be accepted it is rarely used in high crosswinds. It also shows that wing low isn't required as every aircraft in this video uses the crabbed method for landing.


Here is what I said, "in my opinion the idea of a 'forward slip to land.'" I didn't realize an opinion could be wrong.

Furthermore, I did not claim it was not a valid method, I said it was not required, meaning not necessary as you can see in the next quote.



I refer you to my previous response to things like this, "Well for your information and everyone else's here, 'just don't do it,' is not a valid or legit reason." Please explain what scenario where a wing low landing is required because as the video I posted demonstrates, a crab approach is sufficient in any scenario I have found.

I never claimed it wasn't valid, only put out there that it isn't required. A crabbed approach, in my opinion, provides all necessary control to safely land any aircraft.

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.



I would love to take credit for coming up with this ingenious method of approach style to reduce pilot workload, I however can not. But like you, I would love it if someone would show me and everyone else here a valid reason why differential thrust for landing should not be done. It is an aerodynamically safe maneuver for which I have never read an accident report stating, "differential thrust," as a cause.