Assymetrical Thrust proper tech in x-wind?
#21
Pulling power on a good engine certainly is a decrease in performance. And having an asymetrical spool up in case of a rejected landing isn't a good situation.
And as you have said, you don't stop the drift. That's one of the big dangers in crosswind landings is not killing he drift. Landing gear can only take so much side loading before they fail.
What's scary are pilots on here admitting they do this "technique" when it goes against the manufacturer's recommendations on crosswind landings. I definitely would have handed out an "epic fail" to someone had they done this while I was an aircraft examiner.
#22
Gets Weekends Off
Joined APC: Feb 2006
Position: B-737NG preferably in first class with a glass of champagne and caviar
Posts: 5,886
Boeing describes three crosswind landing techniques;
“…Three methods of crosswind landings are presented. They are in the touchdown in a crab, the de-crab technique (with removal of crab in the flare), and the side slip technique. Whenever a crab is maintained a crosswind approach, offset the flight deck on the upwind side of the centerline so the main gear touches down in the center of the runway.”
The upwind wing down technique will provide the least amount of torsion type stress to the landing gear as a whole.
While it may not be a specific manufacturers limitation, reducing thrust on the downwind side of the jet may have limiting performance due to go around performance and potential VMC situations from a balked landing at extremely low speeds when flaps are extended beyond the engine inoperative landing position.
Boeing has this to say about touchdown in a crab.
“…the greater amount of crab at touchdown, the larger the lateral deviation from the point of touchdown. For this reason, touchdown in a crab on condition is not recommended when landing on a dry runway in strong crosswinds.”
“…Three methods of crosswind landings are presented. They are in the touchdown in a crab, the de-crab technique (with removal of crab in the flare), and the side slip technique. Whenever a crab is maintained a crosswind approach, offset the flight deck on the upwind side of the centerline so the main gear touches down in the center of the runway.”
The upwind wing down technique will provide the least amount of torsion type stress to the landing gear as a whole.
While it may not be a specific manufacturers limitation, reducing thrust on the downwind side of the jet may have limiting performance due to go around performance and potential VMC situations from a balked landing at extremely low speeds when flaps are extended beyond the engine inoperative landing position.
Boeing has this to say about touchdown in a crab.
“…the greater amount of crab at touchdown, the larger the lateral deviation from the point of touchdown. For this reason, touchdown in a crab on condition is not recommended when landing on a dry runway in strong crosswinds.”
Last edited by captjns; 08-09-2009 at 01:23 AM.
#23
Gets Weekends Off
Joined APC: Feb 2006
Position: B-737NG preferably in first class with a glass of champagne and caviar
Posts: 5,886
What's scary are pilots on here admitting they do this "technique" when it goes against the manufacturer's recommendations on crosswind landings. I definitely would have handed out an "epic fail" to someone had they done this while I was an aircraft examiner.
Perhaps other crewmembers can provide information about other Boeings, and other manufacturer specific rather than airline specific such as Airbus, or Embraer.
With that being said, chapter section page contained within your airline's specific flight crew training manual would have to be provided to "Epic Failed" applicant/pilot.
Last edited by captjns; 08-09-2009 at 01:43 AM.
#24
LANDING MODE For the A320 Volumen 3 3.04.27. Pag 4
The system's landing mode gives the aircraft a stabilized flight path and makes a conventional flare and touchdown. It carries out the initial approach as this manual described earlier. At 50 feet, the system memorizes the attitude, usually 3° or 4° nose up. From 30 feet down, this value washes out over eight seconds to - 2°. The result is that the pilot has to exert a progressive pull to increase pitch gently in the flare. He should pull the thrust levers back at or above 20 feet, and the landing should occur without a long flare. Touchdown quality is better and more repeatable at fairly flat attitudes. An audible "RETARD" callout reminds the pilot if he has not pulled back the thrust levers when the aircraft has reached 20 feet.
Crosswind landings are conventional. The preferred technique is to use the rudder to align the aircraft with the runway heading, during the flare, while using lateral control to maintain the aircraft on the runway centerline (Refer to SOP 3.03.22). The lateral control mode does not change until the wheels are on the ground, so there is no discontinuity in the control laws. The aircraft tends to roll gently in the conventional sense as drift decreases, and the pilot may have to use some normal cross control to maintain roll attitude.
Even during an approach in considerable turbulence, the control system resists the disturbances quite well without pilot inputs. In fact, the pilot should try to limit his control inputs to those necessary to correct the flight path trajectory and leave the task of countering air disturbances to the flight control system.
Derotation is conventional. The pilot releases the back pressure he was holding for the flare and the nose wheel comes down nicely.
Pitch trim then resets to zero.
YouTube - American Airlines b757-200 landing in Toncontin , MHTG
The system's landing mode gives the aircraft a stabilized flight path and makes a conventional flare and touchdown. It carries out the initial approach as this manual described earlier. At 50 feet, the system memorizes the attitude, usually 3° or 4° nose up. From 30 feet down, this value washes out over eight seconds to - 2°. The result is that the pilot has to exert a progressive pull to increase pitch gently in the flare. He should pull the thrust levers back at or above 20 feet, and the landing should occur without a long flare. Touchdown quality is better and more repeatable at fairly flat attitudes. An audible "RETARD" callout reminds the pilot if he has not pulled back the thrust levers when the aircraft has reached 20 feet.
Crosswind landings are conventional. The preferred technique is to use the rudder to align the aircraft with the runway heading, during the flare, while using lateral control to maintain the aircraft on the runway centerline (Refer to SOP 3.03.22). The lateral control mode does not change until the wheels are on the ground, so there is no discontinuity in the control laws. The aircraft tends to roll gently in the conventional sense as drift decreases, and the pilot may have to use some normal cross control to maintain roll attitude.
Even during an approach in considerable turbulence, the control system resists the disturbances quite well without pilot inputs. In fact, the pilot should try to limit his control inputs to those necessary to correct the flight path trajectory and leave the task of countering air disturbances to the flight control system.
Derotation is conventional. The pilot releases the back pressure he was holding for the flare and the nose wheel comes down nicely.
Pitch trim then resets to zero.
YouTube - American Airlines b757-200 landing in Toncontin , MHTG
#26
Remember, this is done at the last minute. Until then you are flying the crab all the way down. The maneuver is a transition from the crab, into the dipped wing/asymmetrical thrust, into the landing.
Not an issue in the B1900 in this scenario.
My impression is that you flew KD10s in the military and then went to a major airline. The B1900 is a whole different animal. I can understand why it sounds crazy and does not make much sense. Once you fly one, you'll understand.
#27
Gets Weekends Off
Joined APC: Apr 2007
Posts: 867
Just to be clear, the technique is to lead the power reduction with the upwind engine as you apply opposite rudder so that when the mains touch, the down wind engine is carry more torque? Typically what is the torque spit?
#28
Line Holder
Joined APC: May 2008
Posts: 25
It is my understanding that the asymmetrical-thrust crosswind technique is useful for reducing the amount of rudder required to keep the longitudinal axis aligned with the runway. (You still need to bank to correct for any drift.) If you have the rudder effectiveness available, I don't see how using this technique is practically useful (unless, of course, you're landing in a situation where the rudder is not able to keep the aircraft aligned, but if that were true I bet the bank required to correct for drift would be dangerously excessive). Either with asymmetrical-thrust or the forward-slip, you're still slipping the aircraft. Assuming this, then, why is it even considered as pragmatically useful?
#29
Question for the masses: Is the use of assymetrical thrust a valid technique for control about the vertical axis in a crosswind in any jet, large-light? Go...
For the record, I am of the school that it is not but flew with someone who swore by it and looked at me as if I were crazy for not subscribing to it. Not that I am an expert, but this is something I've never seen taught and I'm sure there are aerodynamic consequences that make it unadvisable. However, I havn't yet put much thought into it so I thought I'd lob it out there.
For the record, I am of the school that it is not but flew with someone who swore by it and looked at me as if I were crazy for not subscribing to it. Not that I am an expert, but this is something I've never seen taught and I'm sure there are aerodynamic consequences that make it unadvisable. However, I havn't yet put much thought into it so I thought I'd lob it out there.
I cant even believe some of the stuff I am reading here.......WOW!!!
If the xwind is that bad to make you think the only way to get the aircraft on the ground is to use assymetrical thrust it is definately time to talk about going somewhere else. I have flown biz jets as small as a citation, and airliners up to an A320, and several sizes in between, and I have never even considered this technique. As some have posted, the best, most comfortable, and safest method is to hold the crab to the flare then kick it out just before touchdown.
#30
The torque split is dependent on the wind. I found that if the required torque differential was significant, that the adverse effects of said maneuver were not worth the rewards. It was more of an addition to the crosswind landing than the majority actions of the crosswind landing.
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