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Guest bf109hartmann

PMDG747 strong X-wind autoland?

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Descriptions from real Boeing747-441 operations manual about A/P landing in crosswind:---------------------------------------------------------------------Runway Alignment and Asymmetric Thrust CompensationAFDS controls the rudder during multiple A/P approaches to compensate forcrosswind landings and engine-out asymmetric thrust conditions. With LAND 2 or LAND 3 annunciated, A/P control of the rudder is active.For crosswinds requiring more than 10 degrees of crab angle, runway alignmentoccurs at 500 feet AGL. A sideslip of 5 degrees is established to reduce the crabangle. This configuration is maintained until touchdown. The airplane lands withthe upwind wing low.---------------------------------------------------------------------PMDG747 was the only addon i know can perform runway alignment or decrab maneuver during A/P landing, but i found that pilot can handle the rudder manually but ailerons still under A/P's control, and if crosswind is greater than 20kt(within the autoland limitiation 24kt) the aircraft will be blew to the downwind grassland with A/P engaging, Is it PMDG's bug or it really happens in real world?

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"but i found that pilot can handle the rudder manually but ailerons still under A/P's control,"Is this in a 744 pilot's handbook somewhere... or is this something you thought of yourself?I can't imagine anyone using manual input on the controls during an autolanding. It may result in the A/P disengaging at critical time.Cheers.Q>

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"Is this in a 744 pilot's handbook somewhere... or is this something you thought of yourself?"neitheri've practiced many times(20+) to land PMDG747 in 24kt crosswind with A/P engaged and i can input rudder manually, only rudder, and A/P still engaging! if you didn't interfere A/P landing, the plane will deviate >50ft to runway centerline even blown to the grassland weird isn't it?

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Doing something you're not supposed to do is even weirder :(The autopilot has a certain tolerance to manual input. If the autopilot is trying to do one thing and you are trying to do another, no doubt you will confuse it... or at best, it will try not to smash the engine pods onto the ground or put in extremes of crab angle for the landing. I'm really not surprised that the PMDG 744 would would veer off the runway.You're asking what a real aircraft would do when obviously no one would try to do it in reality. I really don't understand the point of the exercise. If you want to fly manually, disengage the A/P.Cheers.Q>

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but i consulted some real world pilots and a 767 pilot says A/P landing "performed flawlessly, maintaining the runway centreline was not an issue", i reckon in big crab or sideslip angle, but the aircraft really did it automatically.so i was doubted if there's something wrong with PMDG747's A/P landing logic :)

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and a key maneuver PMDG747'A/P didn't apply:-------------------------------------------------------------"A sideslip of 5 degrees is established to reduce the crabangle. This configuration is maintained until touchdown."-------------------------------------------------------------PMDG747 starts to veer off the localizer after decrab begins and didn't compensate the deviation anymore :(

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The PMDG text may simplify what actually happens...According to my 744 notes...."If the crab angle is greater than 5 degrees, the decrab function starts at 500' and a maximum of 5 degrees crab is removed. If the crab angle is less than 5 degrees, the decrab functions starts at 200' and all of the crab angle is removed."Of course, the behaviour of the sim may be due to other factors.... Check previous postings for runway misalignments, add-on scenery causing problems, have database problems, etc.My _767_ notes describe decrab in the following manner (and it appears quite different to the 744):"For crosswinds of 12kts or less, the resulting crab angle is allowed to remain.During crosswinds greater than 12kts up to the maximum of 25kts, the crab angle is maintained at 5 degrees through rudder and limited aileron. The combined command results in a forward slip. Above 25 knots the crab angle is allowed to build from 5 degrees."At high crosswinds, the 744 seems to decrab only 5 degrees.... the 767 seems to decrab until the crab angle IS 5 degrees (up to a limit of 25kts crosswind). I'm surprised that the two aircraft behave so different. Perhaps one manual author has interpreted the actually operation of the autopilot incorrectly?Cheers.Q>

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my 744 manual:---------------------------------------------------------------------For crosswinds requiring more than 10 degrees of crab angle, runway alignmentoccurs at 500 feet AGL. A sideslip of 5 degrees is established to reduce the crabangle. This configuration is maintained until touchdown. The airplane lands withthe upwind wing low.For crosswinds requiring a crab angle of between 5 and 10 degrees, an initialalignment occurs at 500 feet AGL, followed by a second alignment at 200 feetAGL. The initial alignment initiates a sideslip to reduce the crab angle to 5degrees. This configuration is maintained to 200 feet AGL, where a secondsideslip alignment increases the sideslip to further reduce the touchdown crabangle.For crosswinds requiring a crab angle of less than 5 degrees, runway alignmentoccurs at 200 feet AGL, where a sideslip is introduced to align the airplane withthe runway.---------------------------------------------------------------------several differeces with your 744 notes:)and are similar to 767I tested PMDG747 in KSFO 28R CATIII, KSEA 34R CATI, both are default scenaryHave been tested PMDG747 A/P landing again and again in 24kt crosswind but I was confused that A/P landing performs perfect accidently and randomly! maybe probability<1/20. She removed 5 degrees crab angle then moderate sideslip angle applied and her touchdown exactly happened on the centerline. but she drifted with winds without proper decrab or sideslip at most time:-hangi don't know what happened

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