PMDG 747X Porpoising

[Guest chrut]

I use ECON descent speed until 40 nm out or below 10,000, which is normal. At 10,000 you should be no closer than 40 nm anyway, since this yields 250 ft/nm (to sea level). The key point is to slow down within 40nm.

Yes, how do you do this? Speed inv, altering ECON SPD, manually entering every WPT in LEGS page to set 250 SPD, alter 250/10000 VNAV SPD/RES (and/or TRANS)? Sorry for nagging but I find this topic very interesting as I'm trying to perfect my own technique.

[downscc 1,327]

Depends. In the 737/747 I start using MCP SPD and V/S for descent/speed control below FL180. In the MD11 it depends on the arrival. If it doesn't have a speed constraint in the STAR I will either add one or start using FCP SPEED, usually the STAR constraints are all the MD11 with it's superior PROF verses the VNAV in the Boeings.

[Guest chrut]

Depends. In the 737/747 I start using MCP SPD and V/S for descent/speed control below FL180. In the MD11 it depends on the arrival. If it doesn't have a speed constraint in the STAR I will either add one or start using FCP SPEED, usually the STAR constraints are all the MD11 with it's superior PROF verses the VNAV in the Boeings.

Okay, but when switching from VNAV/PROF to anything else in a CDA approach totally messes up the profile and then it isn't really a CDA anymore? CDA approaches that I fly requires P-RNAV, which are suppose to "automatically determine aircraft desired flight path by a series of waypoints held in a database". Isn't the desired profile/path to be "selected" by the civil aviation authority (like FAA) in the country and just flown automatically by the P-RNAV equiped aircraft (using profile mode in order to be as close to the desired descent path)?Naturally, I'm a bit confused. Can you please explain further?

[downscc 1,327]

Are we talking about descents prior to the final approach or the final approach itself?Isn't a constant descent approach a technique rather than a type of approach such as RNP, RNAV LPV, etc? (I think P-RNAV is the European equivalent of the US RNP)I thought your problem was descending from 10000 to the approach, once on the approach fly the technique and type of approach you wish and/or are cleared for by ATC. I have limited my recommendations to before IAF/FAF. Re-reading your comments, I see you referred to a CDA STAR. I've never run into one of those... got an example?The FAA RNP approaches have the altitudes included in the approach procedure used by the FMS and in this case yes, you want to be in the VNAV/PROF mode. Agreed.

[Guest chrut]

Are we talking about descents prior to the final approach or the final approach itself?Isn't a constant descent approach a technique rather than a type of approach such as RNP, RNAV LPV, etc? (I think P-RNAV is the European equivalent of the US RNP)I thought your problem was descending from 10000 to the approach, once on the approach fly the technique and type of approach you wish and/or are cleared for by ATC. I have limited my recommendations to before IAF/FAF. Re-reading your comments, I see you referred to a CDA STAR. I've never run into one of those... got an example?The FAA RNP approaches have the altitudes included in the approach procedure used by the FMS and in this case yes, you want to be in the VNAV/PROF mode. Agreed.

Ah, misunderstanding. Yeah, I was talking about Continuous Descent Approach (CDA) STARS or Optimized Profile Descent (OPD) STARS (like the ones used at London Heathrow Airport, Stockholm-Arlanda Airport and Los Angeles International Airport).

[downscc 1,327]

Which ones at EGLL are OPD?At KLAX, I suppose the CIVET arrival could be thought of as a CDA STAR, never heard it put that way. I notice they bracket the altitude constraints and my custom sidstar has the calculated crossing altitude to maintain a reasonably constant descent rate, but the STAR isn't designed for RNP use. On this STAR, I let the MD11 do it's majic all the way from DAG VOR to rollout but in the 747 I use MCP SPD and VS using the descent rate to approximately following the verticle deviation indicator that appears on the ND. But, I never considered this a special kind of arrival except KLAX is one of the few US locations that have different legs to each one of the parallel runways on the STAR.

[Guest chrut]

Which ones at EGLL are OPD?At KLAX, I suppose the CIVET arrival could be thought of as a CDA STAR, never heard it put that way. I notice they bracket the altitude constraints and my custom sidstar has the calculated crossing altitude to maintain a reasonably constant descent rate, but the STAR isn't designed for RNP use. On this STAR, I let the MD11 do it's majic all the way from DAG VOR to rollout but in the 747 I use MCP SPD and VS using the descent rate to approximately following the verticle deviation indicator that appears on the ND. But, I never considered this a special kind of arrival except KLAX is one of the few US locations that have different legs to each one of the parallel runways on the STAR.

Here, I found a CDA-approach. You can see that there are alt. constraints all the way to FAF (so that VNAV can calculate ILDE/HOLD approach I think). Here the goal is to make an IDLE thrust approach all the way down to final approach.

[downscc 1,327]

Hey, I need to try this one soon. Thanks.Okay, the instructions to pilot request a constant descent from 10000 to FAP at 2500 but none of the altitude constraints are hard constraints (they are at or above). The MD11 should pull this off quite easily but in the 737/747 I would definitely not use VNAV but the MCP SPD and V/S as discussed earlier. I notice the constraints allow a descent angle of about 250 ft/nm, just as a point of interest.

[michal 44]

Here the goal is to make an IDLE thrust approach all the way down to final approach.

Complete idle though full duration of this CDA is simply not achievable in real life (as Boeing's study indicates). The goal is to eliminate or reduce number of "step downs" - when engines have to rev up.

[Guest chrut]

Complete idle though full duration of this CDA is simply not achievable in real life (as Boeing's study indicates). The goal is to eliminate or reduce number of "step downs" - when engines have to rev up.

EDITED: Oh, I'm not saying that it should be COMPLETE IDLE. It's the goal. I read in the docs you suggested above, how for example a sudden tailwind can make the autothrottle to become active. And as I said before, from own experience in replies above, that the occasional "autothrottle intervention" is NOT the problem. But the main goal is to have IDLE thrust as long as possible all the way down (even to the threshold, but that depends from airport to airport). That's what I have a problem with.

[michal 44]

Hmmm.... can you point me to that study, would be great to study.

Mentioned above ....

[downscc 1,327]

But the main goal is to have IDLE thrust as long as possible all the way down (even to the threshold, but that depends from airport to airport). That's what I have a problem with

You won't be able to with only 250ft/nm, or you would have to solve differential equations in your head to start a just the right airspeed and let it bleed off to 2500. Like I said, the procedure only requests a constant descent, not that it is required. Rule number one is to fly the airplane.

[Guest chrut]

Hey, I need to try this one soon. Thanks.Okay, the instructions to pilot request a constant descent from 10000 to FAP at 2500 but none of the altitude constraints are hard constraints (they are at or above). The MD11 should pull this off quite easily but in the 737/747 I would definitely not use VNAV but the MCP SPD and V/S as discussed earlier. I notice the constraints allow a descent angle of about 250 ft/nm, just as a point of interest.

I think you're suppose to use VNAV, because I think these P-RNAV approaches requires you to do that unless told otherwise by ATC. For example, look at the docs suggested by michal above for Louisville International Airport. Here the pilot procedure for the CDA is explained for a boeing 767:

2. Pilot ProcedurePilot procedures were developed based on the speed and altitudeconstraints determined in Sec. IV.B.1. The CDA pilot procedureused both the lateral navigation (LNAV) and vertical navigation(VNAV) modes of the FMS.

And below the conventional approach pilot procedure is described:

The conventional approach pilot procedureused the LNAV and either the vertical speed mode or theflight level change mode to follow ATC commands.

Source

You won't be able to with only 250ft/nm, or you would have to solve differential equations in your head to start a just the right airspeed and let it bleed off to 2500. Like I said, the procedure only requests a constant descent, not that it is required. Rule number one is to fly the airplane.

Yes, safety always comes first, hence the request. But I believe it's possible and done in Sweden.

The Green Approach is the result of GE Aviation’s Systems participation in Europe’s NUP2+ project, in which select 737 aircraft in Sweden were allowed to employ GE’s Flight Management System (FMS) to fly the aircraft at idle thrust from cruise through landing. The FMS’ reliable performance and predictability gave Air Traffic Management authorities the confidence they needed to approve the new approach in Europe for 737s equipped with GE’s FMS.

SourceEdit: The last one is actually called Advanced CDA (A-CDA).Edit2: Here's some more information about CDA in Germany:

While, during a standard landing, the flaps open, the engine starts, the driver accelerates and then decelerates, and the aircraft loses altitude by step, the CDA is, as its name suggests, continues. It starts at a cruising altitude of about 35,000 feet (11 km). The engines operate on empty and the plane loses altitude until the runway.

SourceEdit3: From Swedish Civil Aviation

A green approach means that an aircraft descends continuously from its cruising altitude to the runway. By descending continuously, the aircraft requires almost no engine thrust, thereby saving fuel and reducing emissions. [...] Green approaches also mean a reduction of noise in the immediate vicinity of the airport, since pilots do not need to accelerate their engines at low altitudes.

SourceJust a reminder, I'm a newbie so I can be totally wrong here.

[michal 44]

But I believe it's possible and done in Sweden.

Found this comment a bit odd. I don't think Sweden holds any "secret" to perfect CDA STAR procedures. A "glossy" airport brochure or from a regulatory body is just that - it doesn't tell you anything how close to technical perfection the execution of their CDA is. The same aircraft that fly CDA in Stockholm do it at other airports, Louisville among them. I agree here with Dan - we should not make a religion out of this approach - the pilot is supposed to use whatever tools in his arsenal to fly it safely and effectively but I also agree that VNAV is probably the recommended mode to be in.

I think you're suppose to use VNAV, because I think these P-RNAV approaches requires you to do that unless told otherwise by ATC.

ATC clearly has no knowledge or expertise to verify whether pilot uses VNAV or something else so in my opinion this sentence misunderstands the role of ATC. There could be however some regulatory requirements about flying such CDAs in VNAV but I even doubt that, most likely they are part of airlines SOP. As Dan pointed out your altitude restrictions during such CDAs are almost always at-or-above giving the pilot fair amount of latitude how to fly it vertically. I think we should not confuse CDAs with RNPs which are different beasts and there significant precision is indeed required (these are RNAV based final approach instrument procedures).

[Guest chrut]

Found this comment a bit odd. I don't think Sweden holds any "secret" to perfect CDA STAR procedures. A "glossy" airport brochure or from a regulatory body is just that - it doesn't tell you anything how close to technical perfection the execution of their CDA is. The same aircraft that fly CDA in Stockholm do it at other airports, Louisville among them. I agree here with Dan - we should not make a religion out of this approach - the pilot is supposed to use whatever tools in his arsenal to fly it safely and effectively but I also agree that VNAV is probably the recommended mode to be in.ATC clearly has no knowledge or expertise to verify whether pilot uses VNAV or something else so in my opinion this sentence misunderstands the role of ATC. There could be however some regulatory requirements about flying such CDAs in VNAV but I even doubt that, most likely they are part of airlines SOP. As Dan pointed out your altitude restrictions during such CDAs are almost always at-or-above giving the pilot fair amount of latitude how to fly it vertically. I think we should not confuse CDAs with RNPs which are different beasts and there significant precision is indeed required (these are RNAV based final approach instrument procedures).

Sweden is the first country to my knowledge that have successfully used A-CDA (while other countries have used ordinary CDA) in off-peak sessions, meaning "no thrust" from CRZ to final. I don't know anything about any secrets or perfect CDA STAR procedures. But I do know that they are experiential and new. Keep in mind that CDA STARS in Sweden, shown above, are P-RNAV (based upon RNAV). Special requirements are needed to fly these kind of approaches (what the requirements are, I don't know).Regarding ATC role, where did you get the idea to even discuss if ATC should "verify whether pilot uses VNAV"? If you got it from reading my replies, than you must have misunderstood - for that I'm sorry. What I mean by "unless told by ATC" is that if the approach changes, like if it goes from a P-RNAV approach to let say vectors. Then it's better to proceed with a conventional pilot procedure, described above. The pilot is always responsible and decides how the plane is to be flown, not ATC. "There could be however some regulatory requirements about flying such CDAs in VNAV but I even doubt that". I think this is what we need to know for sure and that knowledge is beyond me. VNAV capability could very well be an option. I'll try to find out!