Descent Calculation Problem

[thrillsandchills]

I'm flying along the POWDR8 which is the STAR into KDEN. So lets assume for the sake of conversation, I'm approaching HBU.(Blue Mesa) at the beginning of the STAR.The TOD (according to my calculations - see the spreadsheet) is 37.5 nm from POWDR. So far so good.

Now lets advance the time line. We're at POWDR, and have descended to FL190 and are complying with the speed restrictions of 250kts.

So, here's my predicament, I've just crossed POWDR. I thinking, by the time I get to SLOPE I'm thinking I should be down to 8,000 ft. So, at the end of the day, I need to lose 11 thousand ft. in 36.4 nm.36.4 being the distance between POWDR & SLOPE. 8,000 ft. would be a nice altitude to have on the edge of the ILS feather. By the time I get to CORDE the altitude drops to 7,000 ft.(and you pick up the G/S.)

Here's the thing. (Please correct me if my "approach" to this wrong.) I thought by the time I get to SLOPE, I should be at 140 - 150 knots. My spreadsheet says, (that I made) I need to start my "final approach" (for lack of a better word,) to get down to ILS altitude, 44nm out, after you take into account the speed adjustment of 110kts. (250 - 110 = 140) My formula said, a descent rate of 840 ft/m, would be appropriate, if I had the 44 miles, which I don't; at least not theoretically.

Also is 3ooo fpm excessive in the descent?

Thanks in Advance,


Thrills And Chills

LINK TO POWDR8

[aerofoto - HJG Admin]

I'm not familiar with the approach to which you you're refer .... BUT .... if flying at 31,000 FT .... then you really want to start down (TOD) no later than around 90 miles DME from your destination airport .... at the very latest.

Technically speaking .... "IN FS" .... one should also reduce ones airspeed to leass than 300 KIAS prior to starting down too, or, the simulation is likely to gain up speed (pick up too much airspeed) on the way down and which will, likely, "mess up" ones descent profile.

I generally start down at no more than 2000 FPM .... having already reduced my airspeed to less that 300 KIAS prior to commencing my descent.

One should, really, aim at being around 10,000 FT by 30 mile DME prior to ones destination airport.

250 KTS below 10,000 FT is, essentially, a traffic flow airspeed restriction (as I understand) around busy airports and/or relatively congested patterns.

Within the approach pattern at some less busy and/or less congested .... airports/airspace there may be no airspeed restriction at all. At AKL/NZAA .... "in the past" .... some aircraft have been known to have enter the pattern, at some times during the day, or night, at in excess of 300 KTS

A 3000 FPM ROD is practiceable in FS, but, most simulations probably won't like it as a sustained descent rate all the way down. If using the AT system to cotrol airspeed such a descent rate may also cause the AT system to constantly cycle engine power "up" and "down" throughout the descent .... and which is an "FS" based imposition.

Again .... "IN FS" .... 100 to 90 DME, 2000 FPM ROD, less than 300 KTS prior to descent, and almost idle engine thrust throughout most of the descent .... will/should keep one "out of trouble".

All the same .... "IN FS" .... one may/will still need to monitor the progress of ones descent rate, and altitude, in conjunction with distance to run .... and be prepared to adjust ones descent rate, if necessary, in order to arrive at around 10,000 FT prior to ones destination airport.

If one's relying upon an FS ATC add-on (adventure) program for auto-genrated instruction etc .... then .... just bear-in-mind that such programs aren't always reliable, or even authentic, in their instructions/caculations .... SO .... one, at all times, needs to/should be thinking ahead and adjuting appropriately where/if necessary

The likes of VATSIM .... I can't really speak for

That's about all I can tell you

Mark C
AKL/NZ

[thrillsandchills]

Thanks Mark, for the help.

By "approach," I meant to say "way of doing things."

Would you (or anyone else) know how to negotiate waypoint crossings with NO speed restrictions in FS?

I'm presuming you'd slow down to 250, then descend; then return to (approx) 280 285 IAS...(which is where you were before)

Thrills and Chills...

[aerofoto - HJG Admin]

I need to start my "final approach" (for lack of a better word,) to get down to ILS altitude, 44nm out

"IN FS" .... one simply can't get onto any ILS from 44 miles out.

15 miles DME .... is around the average (20 mile DME nomaslly the absolute maximum) .... "IN FS" .... or .... FS will have a habbit of missing/stuffing-up such an approach to landing completely

Or, in my somewhat distracted state (lots of interruptions today), am I missing something basic that you're really trying to ask/check here ? ....

I think there's potential/a danger for people to often get too/so focussed on real world procedures .... at the expense of what actually works well/best within any FS environment.

I don't fly using any FS generated ATC programs/adventures .... and nor do I fly on VATSIM either .... SO .... the airspace around any virtual airport is "my own" .... in that there's nobody else there sharing it with me, so, I can more-0r-less "do as I please".

Personally .... I like to fly a long approach to landing rather than a short one (especially in the case of any AP controlled ILS/GS coupled auto-approach to landing) .... simply because that's what seems to work "BEST" in FS .... in that it gives any simulation more time (by way of its constant manouvering during early stages) to become established, and stable, on any AP controlled ILS/GS coupled approach to landing.

As I enter any downwind legue "ahead of any approach" (prior to turning to the base league) I generally slow down toward around 215 KTS in level flight and with around 5,000 FT of seperaqtion between me and the virtual tierra firma/ground below me .... with at least 2-3 knotches of flap selected prior to 215 KTS being (depending on the virtual aircraft type though) extended by this stage .... and normally exactly parallel to my intended RWY approach heading and with at least 10 to 12 mile DME sepsration/distance from it also.

At between 17 to 18 miles DME I then commence my 90* (degree) turn towards the base legue prior to the final 90* (degree) turn towards the intended final approach to landing heading .... slowing down to around 200 KTS in the process .... and possibly extending a third knotch of flap also.

Once established on the base legue .... and at a 90* (degrees) intercepting heading to my planned final ILS/GS aided RWY approach heading .... I then activate the AP "APR" mode in order to enable the simulation to "auto-intercept" the ILS/GS aided approach to landing once it's detected.

As soon as the simulation detects the ILS/GS aided RWY heading .... and commences its auto-turn toward it .... I then reduce airspeed toward 180 KTS .... then extend the thrird knoth of flap and further reduce airspeed toward 170 to 165 KTS just prior to becomming established on the ILS/GS indications.

Once established "OH THE ILS/GS" .... during any AP controlled ILS/GS coupled auto-approach to landing .... I fly my approaches to the actual landing pretty much on on the basis of "feel" .... or rather .... how everything looks in terms of the simulations allignment with the ILS/GS indiactions, its pitch attitude, and airspeed .... and then extend the landing gear and more flap accordingly .... as well as further manipulating my approach to landing airspeed down towards 145 to 140 to 138 (which aids keeping the pitch attitude about right) .... again depending on the virtual aircraft type being flown.

I've taught/recommended this particular procedure to a lot of folk here on this forum/within the HJG FS community, and most, appear, to have found it a highly successful one .... despite my acute 90* intecept of any ILS "from a distance" from the base legue and which HJG simulation seem to be able to fly (if properly managed) without any difficulties at all.

The only other thing I can really add to this/my recommended procedure is ....

No such approach to landing should ever be attempted (in the interest of success) with anthing in excess of 20 to 25% (30% at the very most) total fuel remaining .... or .... "FS" simply "WILL NOT" be able to fly the approach very well at all.

"THAT'S THE WAY" I've been doing it (recommending it be done) .... for many years past

I don't think there's anything more I can really add here.

Mark C
AKL/NZ

[Falcon]

"Personally .... I like to fly a long approach to landing rather than a short one (especially in the case of any AP controlled ILS/GS coupled auto-approach to landing) .... simply because that's what seems to work "BEST" in FS .... in that it gives any simulation more time (by way of its constant manouvering during early stages) to become established, and stable, on any AP controlled ILS/GS coupled approach to landing." by Mark C.



In real life a longer approach is preferred to obtain a stablized approach and landing. I can't speak for what is happening in the real world regarding STARS, but years ago, one would start a published star, and get vectored out of it anyway, many times.
Falcon

[aerofoto - HJG Admin]

to obtain a stablized approach and landing

YEP .... that's precisely what I was on about/why I always recommend a longer (up to 18 miles DME), rather than a shorter (less than 10 miles DME), approach whenever performing an AP controlled ILS/GS coupled auto-approach to landing .... "IN FS"

Even during the very best ILS/GS intercepts, in FS, the simulation will always tend to "weave left and right", in slowly decreasing increments, as it tries to acquire the beam (it also does this when acquiring a VOR navigation beam too) and endeavours to stabilize on it. During an a long approach .... as I've always recomended .... the first several miles DME will always/typically result in such "weaving" prior to becoming stabilizing on the beam .... but .... so long as ones airspeed is good/right, and both the flaps and gear extended appropriately too, then the simulation will/should become perfectly stabilised on the ILS/GS indications by around 12 miles DME (10 miles DME at the very least) prior to landing .... enabling one to then concentrate on properly flying the remainder of the apprach to landing in advance of actually landing.

Trust me

It's perhaps needless to say, but, realworld aircraft systems are pretty decisive in regard to captures of the like of ILG/GS and VOR beams, so, you don't see such weaving (from my past experience as a jumpseat rider aboard a variety of airliner types .... when I could sstill do that before 9/11) .... at least not to the extent that it's experienced within FS at least

Mark C
AKL/NZ

[Falcon]

Exactly Mark! The thing is, I always relate to the equipment we had in the late 1960's early 70's, and depending on the A/P in General Aviation a/c, you might get a wandering ship trying to lock on! Business Jets were much better, of course many more dollars worth in costs also. Even a hands on approach, whether it was IFR or VFR, the longer approach was preferred to stablize the final. Of course the FAA at that time wanted us to teach an approach to final close enough that if the engine quit, the A/C would make the runway. However most Instructors I knew kind of ignored that idea. Flying B-17's as Fire Suppression would teach you to stabilze the approach.
Falcon

[Mike Monce - HJG]

I've flown that STAR many times (I grew up in Denver). The key is to recognize that all your IAF's state FL200, so you need to be down at that altitude by then. Mark flies a bit differently from me, but what works for me is to start down at about 1700fpm, maintaining 270kts IAS at about 130nm out from the final destination. I think you'll find that if you do this and then also maintain that descent rate the STAR is fairly easy....it's designed to keep the aircraft above the continental divide and then drop into Denver.

Note HBU is about 108nm from DEN, so by starting down at about 140nm out you should be on track for the STAR upon reaching HBU. From powdr to slope is 21 nm so getting down from 14000 to 8000 should not be a problem. The real planning from there is going to be what runway you are landing on. If landing 8 or 7, then you may have to speed up the descent in order to drop in over the front range and then line up on the glide slope. For all the other runways take your time, you've got plenty of room

Mike

[walterleo]

Hi:

As we dont have PAX in FS we need not think about ears popping and complaints about that. But not all airliners come down the same way: The real B 727 or the real DC-10 were known to come down like a "load of briks" when asked for, the real DC-8 and B 737 and the FS-9 DC-8 need much more distance. The real Tu-114 as a Turboprop had this published emergency let down:

11000-8000 m: Mach 0,79-0,82 40-45 m/sec descent rate (8000-9000 ft/min descent!)
8000-6000 m 610-635 km/h 25-30 m/sec
6000 - 3000 m 20-25 m/sec
Below 3000 m 480-500 km/h
Done in that way you will reach 4500 m in 4,5 minutes.

But this was a turboprop without airbrakes but 4 enormous (6m+) propellers going into beta-range. Angry letters to aeroflot managment are not known...

In real life existed also the trick of making 360 for slowing down and descending I have experienced that twice as PAX in real even at final approach to LOWW.

Dont know if AVSIM would accept a that.

Kind regards

Walter

P.S.: "My" FS-9 adaption of the Samdim Tu-114 can do that also.

[thrillsandchills]

Thanks guys for all the replies. Very informative.

Thrills and Chills

[walterleo]

I dont want to breath life into an already dead thread.

But even jets without airbrakes like the Tu-104 could come down quickly:

Here from the original TU-104 handbook:

m D. rate RPM MACH IAS TAS time distance Fuel burned kg
10000 10 4050 0,75 - 810 15-50 187 680
90000 10 4020 0,75 - 820 14-10 164 630
8400 10 4000 0,75 - 827 13-10 150 595
7800 10 3980 0,75 - 835 12-10 136 555
7200 10 3950 0,75 - 842 11-10 122 515
6600 10 3920 0,75 - 849 10-10 108 470
6000 10 3900 0,75 - 856 9-10 94 410
5000 10 3850 - 600 753 7-30 72 320
4000 10 3700 - 500 600 5-50 53 255
3000 10 3700 - 500 570 4-10 37 190
2000 10 3670 - 500 540 2-30 22 120
1000 10 3600 - 500 512 0-50 7 45
500 - - - - - 0-00 0 0

As usual in Russian Aviation all numbers are metric:
From 10.000 m (FL 330) you reduce to 4050 RPM Mach 0,75 and start the descent with a rate of -2000 ft/min while descending you reduce power till 3600 RPM from 5000 m down keep 600 km/h from 4000 m 500 km/h. Done that way you will reach 0 m in 187 km in 15:50 minutes and with 680 kg of fuel burned.

The emergency descent was still faster:



Mach 0,83-0,85 Descent Rate: -23 to -25 m/sec with gear up, Descent Rate -32 to -35 m/sec with gear down
Below 6000 m 740 to 750 km/h.
Below 5000 m apply normal procedures.



Kind regards

Walter

[Deleted]

An interesting take on this thread is that I find it difficult to accurately replicate a B767 descent because the ATC treat it like it is any other aircraft. Flying a reduced descent rate often means a too high approach as happened when I flew a B764 from Atlanta to Manchester and ended up at 6,000ft on finals. The only way I have found of changing this is to initiate a high rate of descent at altitude and reduce this at low level. The problem is then not allowing air speed to build up beyond what the real world aircraft would do. In this respect, the B767 is quite a poor performer compared to Airbus a/c (except the A300-B4) and Boeings beyond the B727, and is somewhere between modern airliners and oldies like the B707. ATC seems to understand the rates of descent in the CFG files so I wonder if someone has got the (Posky) B767s wrong. Incidentally, ATC does not moan about low descent rates over quite a wide range but they seem to ask B767s to come down a bit late within the sim. I am talking about FS9 BTW so I wonder if anyone has experienced anything similar in FSX (my system will not take FSX so no upgrade for the time being ).

[Mike Monce - HJG]

If by "ATC" you mean the default ATC that comes with MSFS, then that's the problem. The ATC in FS in very bad at descent and approach. Try a second party ATC such as Radar Contact, otherwise ignore the FS ATC and do your descent as Mark and I have indicated.

Mike

[aerofoto - HJG Admin]

A good rule of thumb .... and one that I use at least .... is ....

Reduce airspeed to less than 300 KTS whilst still in level cruise and "prior to commencing any descent" .... THEN .... start down at around no more than 2000 FPM, and from around 100 miles (DME) from the nearest NAV aid associated with ones destination airport (landing at airports with a higher geographic altitudes .... like Bogota, La Paz, and Ciudad de Mexico in particular .... will require starting down from a little closer .... and .... foe some aircraft types a decent from much further our is necessary/adviseable too) .... THEN .... further reduce engine thrust to just above (what I interpret being) the flight idle setting once established in the descent.

A fair way into the descent it may become necessary to even resuce engine thrust, possibly all the way back to idle and/or reduced ones descent rate too. I generally "feel my way down" based on altitude, airspeed, and distance to run .... and then adjust my descent rate (primarily) in order to control airspeed. and which nearly always sees me passing through 10,000 FT (or there-abouts) at around 30 miles (DME) from my destination airport. This sort practice generally takes care of/keeps any potential airspeed control related issues under control .... right throughout the descent

Planning .... and awareness of what can happen before it starts happening are essentuial too .... otherwise .... FS "WILL" tend to gather airspeed on the way down .... and which can/"WILL" be translated into an irritation or 2 once nearing ones virtual approach to landing pattern.

I remember a DC8 PFE explaining to me how these aircraft, in particular, will "go down fast", but, not "slow down fast" .... and the obvious importance of good "PLANNING" and "MONITORING"

As Walter (I think it was) recently said earlier within this (or maybe another) thread .... "no 2 aircraft types really descend in the same way", but, whilst descent procedures can usually be favourably manipulated, through manual input/control, in the case of most virtual aircraft .... and to produce a more desired result, I think FS (itself) often doesn't/can't respect such realities .... any more than it's own built-in or maybe other add-on ATC programs can/do either .... particularly in respect of procedures applicable to different aircraft types in order for "THE GAME" to then be able promote a much more authentic flight/aviation experience.

That's just my 50 cent take on some of what's been recently raised here .... "IF" one gets what I mean

Mark C
AKL/NZ

[Deleted]

Jul 10, 2014 21:59:14 GMT aerofoto - HJG Admin said:

A fair way into the descent it may become necessary to even resuce engine thrust, possibly all the way back to idle and/or reduced ones descent rate too. I generally "feel my way down" based on altitude, airspeed, and distance to run .... and then adjust my descent rate (primarily) in order to control airspeed. and which nearly always sees me passing through 10,000 FT (or there-abouts) at around 30 miles (DME) from my destination airport. This sort practice generally takes care of/keeps any potential airspeed control related issues under control .... right throughout the descent

Mark C
AKL/NZ

Good tip Mark. I watch a lot of approaches into Manchester from where I live and all are around 10,000ft or lower within 30 miles. The other point that I have not quoted here is the onset of descent from cruising altitude because a true long distance flight will involve climbing higher than the flight plan allows for (if reality is the aim). For example, if you set a B747 for a cruise at 41,000ft then ATC will send the flight up there from the concrete. In reality, 41,000ft would not be achieved until well into the flight when fuel has been burned off and weight reduced. One thing I have noticed is that the default ATC always seems to calculate descent on the basis of the original flightplan so to file a plan at a lower altitude (necessary to achieve reality) means some planning is definitely required at some distance from the airport.