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Guest wisborg

Descend in B747

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Hi all,I have a small problem while descending in the B747. At the top of descend I'm usually at FL370 to FL390. Using Radar Contact I will first be asked to descend to FL350 where I'll be transfered to another controller. So I set the MCP to 35000 and press 'Descend Now' in the FMC. Now everything works fine, I'll be descending at 1250 ft/minute, since I'm below the optimal descend path.However, once I'm transfered to the next controller and asked to descend to e.g. FL240, then my problem occurs. I'm setting the MCP to the new assigned altitude, but it seems that VNAV refuses to go below FL350 before it intercepts the descend path.Anyone who knows how to convince the autopilote to continue the slow descend? Of course I can set the V/S (and indeed that's what I'm doing for the time being), but I would be nicer to stay in VNAV mode.Another question related to the descend. In the legs page it's possible to assign a speed and altitude to a waypoint (e.g. I know that I will have to cross 40 nm from the airport at either FL110@250kts or FL120 depending on whether it's a near- or far-sided approach). I have no problem entering these restrictions when I know both the speed and altitude, however during the approach I would like to slow down the plane gradually (else it'll stay at 240 kts until just before the runway), but I would like to let the plane take care of the descend path by itself. Is there anyway to enter a speed restriction in the legs page without altering the target altitude, or will I have to change the speed restriction parameter on the descend page succesively as the descend progresses?/ Jesper

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If you are within 50 miles of your TOD point and you press the Descend Now LSK, you will descend about at ~1250 fpm for a bit then level off. The FMC will then maintain that altitude until it catches up with "path." Then a normal VNAV PATH descent will begin. A real life 744 pilot was the first one to find this and describe it as 'non-real-life' behavior a while back. Normal ops should be a gradual ROD until Vnav Path is captured. Then a normal Vnav Path descent will initiate. It's a bug. Right now in the sim, VS, FLCH (or reset to a lower Vnav cruise alt) are your options. Search for the PMDG forum post. It

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Sam,If you are within 50 miles of your TOD point and you press the Descend Now LSK, you will descend about at ~1250 fpm for a bit then level off. This is true but also if you press DES NOW regardless of 50> < you will enter descent mode, DES NOW's only limitation is being in CRZ.A real life 744 pilot was the first one to find this and describe it as 'non-real-life' behavior a while back. Normal ops should be a gradual ROD until Vnav Path is captured. The "issue" has been an abrupt initial descent. In reality, the descent is not a "stated" AOM ref i.e. 1250-1000 FPM as you state. Actual descent while 'shallow' in this situation (early Descent) should not have been determined by a set figure but by performance data for the aircraft. This has been delt with as you know.Jes,So I set the MCP to 35000 and press 'Descend Now' in the FMC. Now everything works fine, I'll be descending at 1250 ft/minute, since I'm below the optimal descend path. If you are within 50 NM from TOD then you are doing it one way that is correct. What you need to do after you are at FL350 and are cleared to a new altitutde is to reset the MCP to the new clearance and press the altitude KNOB on the MCP. The aircraft will now descend to the new altitude. One thing to keep in mind here, the 'shallow' descent rate only applies when you are in an early descent and will terminate AT the capture of the original path. It is not practical to use V/S. You are limited only to altitude by ATC not by ROD. One other thing, if you are further than 50 NM from TOD you can still keep the aircraft in CRZ MODE even if you need to descend to a lower altitude. ATC clears you to FL350 from FL390, you are 100 NM from TOD, simply dial in FL350 into the MCP altitude window and press the ALTITUDE KNOB, the aircraft will perform a CRZ DESCent to the new altitude while retaining CRZ with TOD still to come................Randy J. Smith................A PROUD MEMBER OF THE PMDG BETA TEAM[h4]Evolution is a process that results in heritable changes in a population spread over many generations[/h4]

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Try this test flight. Stabilize in Vnav cruise. This is what I'm seeing. First reset MCP to a lower alt. Then LSK Vnav

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This is a known issue and has been discussed many times on this forum. It is not an issue anymore but that is all I am going to say................Randy J. Smith................A PROUD MEMBER OF THE PMDG BETA TEAM[h4]Evolution is a process that results in heritable changes in a population spread over many generations[/h4]

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>> If you are within 50 NM from TOD then you are doing it>one way that is correct. What you need to do after you are at>FL350 and are cleared to a new altitutde is to reset the MCP>to the new clearance and press the altitude KNOB on the>MCP. The aircraft will now descend to the new altitude. One>thing to keep in mind here, the 'shallow' descent rate only>applies when you are in an early descent and will terminate>AT the capture of the original path. It is not>practical to use V/S. You are limited only to altitude by ATC>not by ROD.This is exactly what I'm doing, however the plane refuses to descend below the initial altitude (it does descend all the way to that altitude though)./ Jesper

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Have you considered looking a being a pilot? I'm aware of some contract talks going on that will have a top 747 captain well over 300K/year. Sounds like you'd have no problem at all handling the real deal. The FMC is one of the toughest parts.What are you getting with the DEC NOW command from the initial '< 50 miles before TOD' Vnav cruise? Can you describe it? Does the airplane level off prior to a VNAV ALT or path capture? If it does, that's probably a bug. For me, the buggy deceleration happens in level flight after this early (and undesired) level off event. So if you are getting this problematic underspeed event too, I assume you are leveling off somewhere during your Descend Now ride. Where? What's it doing? It seems the beta testers might not be picking this up.

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>Hi all,>>I have a small problem while descending in the B747. At the>top of descend I'm usually at FL370 to FL390. Using Radar>Contact I will first be asked to descend to FL350 where I'll>be transfered to another controller. So I set the MCP to 35000>and press 'Descend Now' in the FMC. Now everything works fine,>I'll be descending at 1250 ft/minute, since I'm below the>optimal descend path.>>However, once I'm transfered to the next controller and asked>to descend to e.g. FL240, then my problem occurs. I'm setting>the MCP to the new assigned altitude, but it seems that VNAV>refuses to go below FL350 before it intercepts the descend>path.Jesper,From a RC4 perspective, I'd like to point out that when you are given the initial descent from cruise, if you have comms, you can request a Pilots Discretion descent. It is option 3 (PD). If approved, you can delay your start down until you reach the FMC-calculated TOD.-michael

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>Have you considered looking a being a pilot? I'm aware of>some contract talks going on that will have a top 747 captain>well over 300K/year. Sounds like you'd have no problem at all>handling the real deal. The FMC is one of the toughest parts.>I'll take that as a compliment - however I think I'm a bit too old to take that path, and I'm not sure the passengers would like my hand flown landings ;-)>What are you getting with the DEC NOW command from the initial>'< 50 miles before TOD' Vnav cruise? Can you describe it? Does>the airplane level off prior to a VNAV ALT or path capture? If>it does, that's probably a bug. >>For me, the buggy deceleration happens in level flight after>this early (and undesired) level off event. So if you are>getting this problematic underspeed event too, I assume you>are leveling off somewhere during your Descend Now ride.>Where? What's it doing? It seems the beta testers might not be>picking this up.Sorry, my initial describtion seems to be wrong. I tested it again yesterday, and it probably behaved closer to your describtion than mine, although I intervened before the descend came to a complete halt. At that time I was around 1200 feet below the cruize altitude descending around a couple of hundred feet a minute./ Jesper

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>From a RC4 perspective, I'd like to point out that when you>are given the initial descent from cruise, if you have comms,>you can request a Pilots Discretion descent. It is option 3>(PD). If approved, you can delay your start down until you>reach the FMC-calculated TOD.Thanks. I'm aware of this, and I also sometimes take advantage of it. However at other times I let the copilot have the comms the whole way - just for the sake of variation./ Jesper

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