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RFields5421

unstable ils final approach

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i dont know how many have experienced this but i have observed that in fs2004 if i attempt to land a fully loaded fully fuelled 747 or a 777 the autopilot takes me on a very unstable decent with wild nose pitch up and downs worsening as i get closer to the runway, ending up in a crash on it. this does not happen in the case of 737 which maintains a constant pitch and decent rate. is there any physics behind this or is it a flaw in fs2004?does this happen in the real world too?

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>i dont know how many have experienced this but i have>observed that in fs2004 if i attempt to land a fully loaded>fully fuelled 747 or a 777 the autopilot takes me on a very>unstable decent with wild nose pitch up and downs worsening as>i get closer to the runway, ending up in a crash on it. this>does not happen in the case of 737 which maintains a constant>pitch and decent rate. is there any physics behind this or is>it a flaw in fs2004?>does this happen in the real world too?in real life generally the only problem AP's have is capturing "false" glide slopes. i have seen one captured and the AP violently shoved the nose down trying to follow this. nothing you can do but disconnect the AP and reset the FCP. the false glide slopes are usually caused by a/c blocking or partially blocking the antennae while they taxi (hence the ils hold short lines).

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Trying to land a Boeing at MTOW is not permissible in the real world so I wouldn't get too het up about the auto pilot not coping.How does the auto pilot manage if you reduce the aircraft weight to the maximum landing weight?

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Also, if you're going to try to land a "fully loaded and fueled" aircraft, a rarety in an airliner in real life, than you have to add a considerable amount of speed to your Vref. If you're flying an approach at a Vref for a lower weight than you are flying very near a stall, which will cause the nose to pitch down. Try increasing your approach speed.John M

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>> Trying to land a Boeing at MTOW is not permissible in the>real world so I wouldn't get too het up about the auto pilot>not coping.>How does the auto pilot manage if you reduce the aircraft>weight to the maximum landing weight?yes, you need to jettison about 280,000 lbs of gas. i am sure the airplane lands fine at MTOW, but expect to replace all the tires.here's the weights:http://www.boeing.com/commercial/airports/acaps/777rsec2.pdf

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>yes, you need to jettison about 280,000 lbs of gas. i am sure the airplane lands fine at MTOW, but expect to replace all the tires.:-eekWow! I just couldn't let this pass without comment. :-) Do you honestly think that 280,000 lbs of fuel is dumped just to save a few lousy tires?The maximum landing weight is a STRUCTURAL limitation designed to preserve the structural integrity of the aircraft. Exceed the max landing weight at your peril as you can expect to do some very nasty structural damage to the aircraft eg. Shear the wing gear fuse bolts Bend/crease the fuselage distort the airframe symmetry write off an aircraft :-lolCheers,Roger

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In the real world the only reason to make a MTOW landing would be a dire emergency.The squadron which was my first Navy squadron had a EP-3E make an almost MTOW landing at Mombasa (HKMO) back in the 90's.Things went to heck right after rotation on a hot night with a high density altitude.Losing two engines immediately, they correctly guessed contaminated fuel. With almost certainly no efficient rescue capability, they did a 180 even though they never got above 500 ft ASL.They came in heavy and very fast - touched down a little short of the runway and took a bit over 12,000 feet to get stopped since they burned the brakes off the bird. Only the APU was running by the time they stopped.Yes, the runway is only 11,000 feet long. That early touchdown about 150 feet from the paved overrun surface and no rain for several months saved them. The plane came to rest against the airport fence off the north end of the runway.Surprisingly, the bird is still flying for VQ-1, but it was an expensive repair and recertification.

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>>>yes, you need to jettison about 280,000 lbs of gas. i am sure>the airplane lands fine at MTOW, but expect to replace all the>tires.>:-eek>>Wow! I just couldn't let this pass without comment. :-)>> Do you honestly think that 280,000 lbs of fuel is dumped just>to save a few lousy tires?>>The maximum landing weight is a STRUCTURAL limitation designed>to preserve the structural integrity of the aircraft. Exceed>the max landing weight at your peril as you can expect to do>some very nasty structural damage to the aircraft >>eg. Shear the wing gear fuse bolts> Bend/crease the fuselage> distort the airframe symmetry>> write off an aircraft :-lol>>>>Cheers,>>Roger in an emergency who cares about your list? in the CRJ anything over MLW at less than 500fpm is a NON reportable / maintenance event. most modern aircraft these days can structurally handle such items. i think the idea is to safely allow an a/c to land in an emergency, obviously not normal operations.my $0.02 (discounted.... :) )

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Comparing a CRJ to a B-777, for example, is like comparing apples to oranges...or in this case, apples to watermelons when it comes to weights. The way I read it the difference between MTOW and MLW for a CRJ 900 is roughly 6300#, where the B-777 has a difference of 200,000#. Even with a stronger landing gear I would think that you would do considerable more damage to the Boeing when landing at MTOW. Just a matter of physics.Unless you cannot maintain altitude it's best to jetison, or burn off as much fuel as you can to get to MLW, especially in heavy aircraft. Just like trying to takeoff at a weight over MTOW, landing above the MLW will not guarentee a safe result.I am in agreement with you that in a true dire emergency to heck with the numbers and do what you got'ta do.John M

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>Comparing a CRJ to a B-777, for example, is like comparing>apples to oranges...or in this case, apples to watermelons>when it comes to weights. The way I read it the difference>between MTOW and MLW for a CRJ 900 is roughly 6300#, where the>B-777 has a difference of 200,000#. Even with a stronger>landing gear I would think that you would do considerable more>damage to the Boeing when landing at MTOW. Just a matter of>physics.>Unless you cannot maintain altitude it's best to jetison, or>burn off as much fuel as you can to get to MLW, especially in>heavy aircraft. Just like trying to takeoff at a weight over>MTOW, landing above the MLW will not guarentee a safe result.>I am in agreement with you that in a true dire emergency to>heck with the numbers and do what you got'ta do.>>John Mmost landings touch down at very little feet per minute vertical rate. if it can stand the stress of a MTOW takeoff in a crosswind (or by that measure a MTOW abort right at V1), by golly it can stand a smooth MTOW landing. its not comparing a CRJ to a 777, but rather design limits governed by the applicable FAR's.i am sure the testing of the aircraft involves landings above MLW. anybody in the know?

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>>most landings touch down at very little feet per minute>vertical rate. if it can stand the stress of a MTOW takeoff in>a crosswind (or by that measure a MTOW abort right at V1), by>golly it can stand a smooth MTOW landing. its not comparing a>CRJ to a 777, but rather design limits governed by the>applicable FAR's.>>i am sure the testing of the aircraft involves landings above>MLW. anybody in the know?I'm not in the know about testing landings above MLW, but also I wonder if they do actual flight tests to determine MTOW, or is it engineers crunching the numbers of all the parameters involved for a takeoff. I guess in the pre-computer era there must have been some "trial and error" type testing of both MTOW and MLW.For example how did they find out that an aircraft can takeoff if slightly over MTOW, but will not climb once out of ground effect.John M

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>I'm not in the know about testing landings above MLW, but also>I wonder if they do actual flight tests to determine MTOW, or>is it engineers crunching the numbers of all the parameters>involved for a takeoff. I guess in the pre-computer era there>must have been some "trial and error" type testing of both>MTOW and MLW.>>For example how did they find out that an aircraft can takeoff>if slightly over MTOW, but will not climb once out of ground>effect.sometimes, as in the CRJ 700's case, it is as simple as a scope clause. the CRJ 700 MTOW is 75,000#. it is that way due to a scope clause that the original buyer was under.obviously a 777 would not be subject to scope clauses, but i would imagine the numbers are dumbed down a little bit for error and legal protection.i know a few test pilots for hawker beechcraft. i'll see what they have to say about this.

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Today it's mostly math and number crunching. If people didn't truely understand the physics of flight, there would not be simulators worth a danged.Some of the stuff published on the A380 before the first airframe was completed showed most of those parameters and expectations.There was also lot of number crunching even back in the 40's, but there were also a lot of tests - which is why test pilots were, and still are, such heros.Ever see the landing test video of the DC-9 where the back end of the aircraft was broken off?Of course you well know that the numbers are only for certain conditions - add humidity, add temperature, add varying degrees of rain and runway adhesion......

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The FS2004 B744 reference document says at maximum weight you should be landing the B744 at 188 KIAS and you cannot use more than flaps 25.For the B777 - 157 KIAS - flaps 30Are you going slower than those speeds, have more flap?

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