744 Forum

Good morning,

as you all know, on the PERF INIT and VNAV CRZ pages a STEP SIZE can be entered. If ICAO is entered, flight level separation above FL290 used to be in 4000 feet steps.

I'm wondering ... is that still the default in the FMC, or has it changed to 2000 feet steps since the introduction of RVSM? But then, how should the FMC know whether it is currently in RVSM airspace or not?

I assume the FMC still uses the old rule. And when using RVSM, the crew has to enter 2000 in the STEP SIZE line manually.


Cheers,

|-|ardy

More likely, they don't enter STEP SIZE at all, as everything has been painstakingly planned ahead of time. I don't think (think, I am not a dispatcher or pilot) that pilots have much opportunity to make this kind of operational (step climb) decisions any more. They request and climb at predetermined waypoint X (unless something prevents them from doing it).

I hope I am wrong though.


Jeroen

Doesn't the FMC have the "RVSM" option? Haven't seen a 74 collegue in a long time, but from the moment I see one I'll ask. On the 737 we used to get a lot of FMC software updates, sometimes new functionalities would be included so maybe the 747 one has evolved as well. We had "RVSM" as the standard on our classic 737's, and on the 777 as well. We can select "ICAO", "RVSM", the step size in 100ft increments, or "0" if no steps are planned.

Dispatch provides a flight plan with step climbs but these are "estimates" based on estimate weights and winds. Sometimes dispatch doesn't even consider state regulations.

The way I use it is to keep "RVSM" initially, with an initial cruise flight level based on actual weight. Once levelled off, get a wind update from dispatch, have the FMC calculate step climbs and then put the step climbs on the legs page (/FL340S, /FL360S,...) and put the step size to 0 afterwards. If you don't put the 0 the FMC will continuously hope for a step climb and calculate fuel estimates accordingly.

I think there is more RVSM airspace being flown through than non-RVSM at the moment :-)

http://www.jasma.jp/pic_rvsm_plan_lrg_new.gif

Cheerz

Hi Hardy,

I checked with a friend flying the B744/8's for a major cargo airline.  Your hypothesis is correct.  Their standard is stil ICAO and if they fly RSVM its 2000ft.

But in practice (not really an SOP), they are mostly following the S/C from the flightplan, which has been calcullated by the dispatchers in function of head/tailwinds and etc.
In that case they are setting the S/C's in the LEGS page and in PREF INIT or VNAV CRZ 0 (zero), even in RVSM conditions.

Hope this help clarifying

B. Rgds
Michel

Thanks guys,

conclusion: in the 737 FMC (Smith's) one can enter thousands or hundreds or the words ICAO or RVSM. The 747 FMC (Honeywell) still allows thousands only or just the word ICAO.

And from the pic I conclude: The whole world is now RVSM. The last white space was Russia until late 2011.


Cheers,

|-|ardy

Quote from: Hardy Heinlinconclusion: in the 737 FMC (Smith's) one can enter thousands or hundreds or the words ICAO or RVSM. The 747 FMC (Honeywell) still allows thousands only or just the word ICAO.

Or it also allows 0 (zero) to be entered to indicate no further step climb.

Cheers

Jon Bunting

Hi Jon!

Or zero, yes.

While you're here ... can I ask you another one?

If I enter a step climb altitude in a CRZ LEG, say, 360S, is this an advice that I shall capture FL360 at that waypoint, or that I shall start climbing to FL360 at that waypoint?

I haven't found any manual that answers this particular "S" question. It's always the same text everywhere. Bulfer or Honeywell doesn't even mention the "S", if I'm not overlooking something.


Cheers,

|-|ardy

Morning Hardy,

Yes, just passing through checking on your progress ;-)

My understanding is that the FMC will take it that you are level at the new flight level from the waypoint which has the step climb inserted.I also understand that the FMC doesn't recognise if you don't actually do the climb or not, so if you are at FL340 with a step 360S inserted at the next waypoint but remain at FL340 past the waypoint the FMC still thinks that you've done the climb for it's fuel predictions.
You get around that by re inserting 340 into the VNAV crz alt window 1L to tell it you are still at FL340 ( the VNAV CRZ ALT will still actually show FL340 if you haven't climbed, but the FMC will be working with FL360 winds ) I hope I've explained that in an understandable way?

Do you have access to the Honeywell FMC manual? I presume you have but if not we have a copy on board I can search for anything else you may need on my next trip.

Cheers

Jon

Thanks, Jon!

So, whenever I enter a CRZ ALT in 1L, any existing S altitudes in the LEGS will be removed and reset to small font predictions?

As far as I see, there's a "circular" hierarchy:

- A STEP TO entry (big) in 1R overrides the FMC's next recommended step alt
- An S entry in a LEG overrides the STEP TO entry in CRZ 1R (font remains big)
- A CRZ ALT entry deletes all S entries in the LEGs (1R font gets small)

Yes, I have that manual, too.


Cheers,

|-|ardy


By the way, if you have an altitude constraint in a SID/STAR/APP, and the altitude is predicted to be captured somewhere along a leg (not directly at the waypoint), then is there a green donut on the ND for that capture point? E.g. if I have 250/4000 on the leg to XY and the FMC predicts the capture will be 2 nm before XY, will the ND show something like O 250/4000 ... i.e. like a T/C or E/D, just not with "T/D", but with "250/4000"?

Hardy,

Your first 2 hierarchy points are correct yes.

The last point about entering a CRZ ALT deleting step climbs on the legs, I don't think that would happen no, it shouldn't delete anything entered in the legs page with regard step climbs.Entering a higher CRZ ALT than your present ALT at 1L on the VNAV CRZ page when in VNAV PATH may well switch you into VNAV ALT, I'll check that on the plane and get back to you Friday Morning.

If you have for example a step climb of 360S next to a waypoint on the legs page and climb up to FL360 prior to that waypoint, the 360S will still remain in bold font on the legs page.
If you are at FL340 and ATC wont let you climb at the way point which has 360S entered next to it the FMC will start using it's  FL360 wind/temp data from that passing that waypoint even though you haven't climbed.
In order to tell the FMC to keep using the data for your present FL 340 you need to manually enter 340 into 1L on the VNAV CRZ page.(which of course will already show FL340 anyway, but it still needs to be manually over written)
The honeywell manual explains  it a bit better than I can.

I think you can summarize it as follows:

Re-entering a cruise alt in VNAV CRZ 1L does not delete anything ahead of the current position, but kicks the FMC out of believing that you will any moment now climb to the planned step climb altitude posted at a waypoint already passed.

Should there be more step climbs planned ahead, they won't be touched. It is just the already passed planned step climb that is canceled.

Can you put step DOWN altitudes in a waypoint ahead of current position?


Jeroen

The Honeywell pilot's guide I have says that a CRZ ALT entry deletes HOLD constraints greater than the entered CRZ ALT; all other constraints not lower than the entered CRZ ALT are deleted.

However, an S altitude may not be considered a "constraint" here. So, the text remains vague.

Re FMC winds: Say, I have this in the LEGS:

FL390
FL390
FL410S
FL410
FL410

It's clear to me that the FMC will use FL390-winds for the first 2 wpts, then FL410-winds thereafter.

I can't imagine that re-entering the CRZ ALT will keep that FL410S entry and then apply FL390-winds for those FL410 wpts. I assume the FMC will always use the winds at the predicted altitudes.

In other words, I'd expect that the CRZ ALT re-entry will cause this:

FL390
FL390
FL390
FL390
FL390

And then it makes sense if these waypoints indeed use FL390-winds. But I may be wrong, of course.


Cheers,

|-|ardy

QuoteCan you put step DOWN altitudes in a waypoint ahead of current position?

Yes.

Hardy, your example looks correct after passing the FL410S waypoint the fmc will use FL410 wind data, unless you then enter FL390 into the CRZ ALT then as you say you'll get the FMC to continue using FL390 data. I only read that in the manual when I was bored one trip, it's not something many pilots would actually know about. Also you are quite correct an "S" altitude isn't considered a constraint, it wouldn't for example trigger an "unable next alt" scratchpad message if you put in a silly high number in there. (having said that, I'll have a play and see what happens eg FL650S !)

Jon

Take care that re-entering a cruise alt may happen AFTER passing the step climb altitude. There is nothing to delete then, but the FMC still assumes you will soon be at the (passed, not executed) step climb altitude.

Quote from: jonb(having said that, I'll have a play and see what happens eg FL650S !)

Theoretically, valid altitude entries range from -1000 to 45100 only.

Jon, when you're playing ... :-) -- also interesting would be if you can enter an S altitude below the active CRZ ALT. The books say you can. But it could be a misunderstanding.


Cheers,

|-|ardy

One small remark: I'm pretty sure a pilot entered step climb on the legs page is an indication that the step climb will be commenced at that waypoint, not that the airplane will reach the step altitude at that specific waypoint.

The way I understand is, the "FLXXXS" function on the legs page is a pilots tools to create the most accurate vertical profile during cruise and get the best fuel prediction for the arrival. Reasons for step climbs can be performance, but also expected ATC FL restrictions during cruise. Example would be that over certain countries certain flight levels are expected to be unavailable.  So step climbs can be higher or lower (ie certain flight levels not available) and are not treated as constraints by definition.

Cheerz

QuoteOne small remark: I'm pretty sure a pilot entered step climb on the legs page is an indication that the step climb will be commenced at that waypoint, not that the airplane will reach the step altitude at that specific waypoint.

Thanks Ief. A small remark, but a big step in the programming work :-)

What you're saying is what I originally expected to be true. But I have already programmed it as a capture waypoint and the algorithm for this is rather complicated because it includes reversal extrapolation. So, before I disable that part of the code in order to make it a climb start waypoint, I'd like to be 100% sure this is the correct way.

So, how sure are you on a scale from 0 to 100? :-)

99?


Cheers,

|-|ardy

Quote from: jonbMy understanding is that the FMC will take it that you are level at the new flight level from the waypoint which has the step climb inserted.I also understand that the FMC doesn't recognise if you don't actually do the climb or not, so if you are at FL340 with a step 360S inserted at the next waypoint but remain at FL340 past the waypoint the FMC still thinks that you've done the climb for it's fuel predictions.

Jon, by "next" waypoint do you mean the active waypoint? Are the two waypoints quoted in blue the same in your statement? If so, I don't understand the logic. I assume if the active waypoint is sequenced out (removed from the LEGS), the constraint of this sequenced waypoint will no longer restrict the flight plan, and the FMC computed optimum step profile will be displayed again, starting at the current aircraft altitude.


Cheers,

|-|ardy

I guess if you're programming it, it can't be 99, but has to be 100% :-). I've send an e-mail to a 744 collegue and waiting for the answer.

Although it is perfectly possible, it would be a strange functionality difference between 2 Boeing airplanes (777 vs 747). But I don't know anything about different FMC versions and software they use,... 777 is 100% sure: /FL360S is start of the step climb at the specified waypoint. Boeing has a strange way of thinking here because in the manuals they actually call it an "insert as an altitude constraint and the letter S" :-).

Hi. Sorry have been away for a while.

We still fly around with the older FMC (memory capacity of around 800kb..... yes you read that right kb !!)

We have to upload the winds manually and tend to do just one column from the flightplan. i.e. the one you intend to fly.

As you know, if you upload the winds manually and there is a step climb, there is no facility to alter the FL's in the wind page for subsequent waypoints.

i.e. initial cruise is at FL320. and you put a level 320 (for the wind) in the windpage for that waypoint, it will be there for all other waypoints. Therefor the FMC calculated optimum stepclimbs are not always very acurate.

We tend to stick with the Flightplan stepclimb calculations, rather than the optimum calculations from the FMC.

In our flightplan we get the winds for 4 FL's for each waypoint, (i.e. 4 columns... e.g. FL280, FL320, FL360, FL380) with the 3rd column being the level you are planned at for that waypoint.

There doesn't seem to be a set guidance in the difference between levels published on the winds page. (i.e. sometimes its 2000ft sometimes 4000 and other times 5000ft.

As an example at

                             260     280    300    350
AAAAA  300 M39 30080 30079 30078 30090
BBBBB  300 M39 30073 30072 30071 30086
                         260    280     320    350
CCCCC   320 M44 30064 30062 30063 29071
DDDDD  320 M44 30065 30063 30063 29069
                             280     310     340    390
EEEEE   340 M49 29067  29064 30060 29067

really sorry for the formating.. can't get the levels to show above the winds to show correct columns, but hopefully you get the drift

So at waypoint AAAAA you get the temp (= FL300 temp -39 (M39)) for that planned cruise level (which then goes into the winds page for that waypoint).

And the winds at AAAAA are given for the levels FL260, FL280, FL300, FL350

So entering the winds for EEEEE are then going to be a problem if in the FMC you have entered all the FL's (260, 280, 300 & 350), because now at EEEEE you want (280, 310,340 & 390)
               
And to get a more accurate fuel prediction (becaus that's what you're trying to achieve by doing all this) what we do is:

Enter the wind (and dont update the FL)for the actual FL that you are planning to fly for each waypoint from the flightplan. (i.e. the 3rd column) and accept that the level given for that wind waypoint is not correct.

So in the FMC it would look like:

WPT AAAAA
300.... 300/78
300/-39

WPT BBBBB
300.... 300/71
300/-39

WPT CCCCC
300.... 300/63 even though you are planning to fly at FL320 here
320/-44

so the accurate FL in the temp section.

What we then do is put the accurate Stepclimbs in the legs page
i.e. CCCCC...... 0.85/320S

and then go to the VNAV page and put the Stepclimb to 0 !!

This way you get an accurate fuel prediction for landing.... = the most important information you want..

What has happened in the past is that someone got say FL280 for the atlantic crossing i.s.o. say FL360, but didn't set the VNAV stepclimb to 0. The FMC then still assumes optimum stepclimbs and the fuel prediction is a LOT more optimistic..

Hope all of this makes sense

Yes, it makes sense. Thank you, Autopilot :-)

Somewhat off-topic, and something I've wondered about for years.

As is well-known, the jet stream at cruise altitudes can be as fast as 247 mph (per Wikipedia), and may be as thick as about 3 miles.  It seems to me that the earlier autopilots for sure couldn't be programmed to accurately handle such rapid transitions as an aircraft at cruise speed traversed such winds.

Do most or all autopilots compensate reasonably accurately for such high-speed winds and for such rapid variation with altitude and spatial location?  An aircraft flying at say 600 mph with 250 mph winds seems like a severe aerobatic challenge, unsuitable for airliners!

Modern autopilots (i.e. 737 classic, 744 and newer) cope with jetstreams just fine.

A jetstream is classified as a windspeed of 80kts (I believe) or more (fastest I've seen is 200 kts).

The core of a Jet as you said can be 3 miles ( roughly 18000ft) high (or more). but many more miles wide (sometimes 100's) and can obviously be 1000's of miles long.

The wind doesn't generally go from say 30 kts to 150 kts within seconds... It is a very gradual proces.

As long as it happens gradually nothing changes to the forces on the airplane, it still flies the same True Airspeed (or TAS) it's just the groundspeed that changes.

So if the TAS is 450 kts in no wind conditions then the groundspeed is also 450kts.

If the wind gradually ramps up to say a 150kt headwind, then the groundspeed goes down to 300 kts. (airspeed = TAS stays the same...)

TAS (wel IAS actually, but lets not complicate things) has to stay the same because, as you said the maximum force on the airplane is limited by Vmo / Mmo (Max operating speed / Max operating Mach).

And also the stall speed.

So the forces on the airplane are (initially) purely from the speed of the air over the airframe and wings.

So a steady increase in wind doesn't cause any upsets.

What sometimes does happen is that the change aren't as gradually as one would like and this causes turbulence due to wind gusts. This turbulence then causes the g-forces to increase and that obviously affects the structure of the airframe.

However I reckon a pilot would probably only ever see severe (and I mean proper severe turbulence, not heavy moderate...) turbulence once or twice in his / her entire career (30 years?).

Short anwer is that in 99% of the jetstream cases the autopilot does just fine. In those 1% (probably much less) where you might encounter proper severe, there might be issues with the autopilot disconnecting.

I've flown with a collegue who once lost 4500ft in severe turbulence and one other who lost 6000ft. These cases however are more rare than an engine failure, so nothing to worry about.

Quote from: Hardy Heinlin

Quote from: jonbMy understanding is that the FMC will take it that you are level at the new flight level from the waypoint which has the step climb inserted.I also understand that the FMC doesn't recognise if you don't actually do the climb or not, so if you are at FL340 with a step 360S inserted at the next waypoint but remain at FL340 past the waypoint the FMC still thinks that you've done the climb for it's fuel predictions.

Jon, by "next" waypoint do you mean the active waypoint? Are the two waypoints quoted in blue the same in your statement? If so, I don't understand the logic. I assume if the active waypoint is sequenced out (removed from the LEGS), the constraint of this sequenced waypoint will no longer restrict the flight plan, and the FMC computed optimum step profile will be displayed again, starting at the current aircraft altitude.


Cheers,



|-|ardy

Hardy,

Yes, I was referring to the same waypoint.Wether you climb or not at an inserted S climb the FMC will think that you have for the purpose of it's wind calculations, and there will be a "step to FLxxx now" message top right on VNAV.
As you know the S altitude entries are just for performance predictions rather than creating a VNAV profile. You tell the FMC you haven't climbed by reinserting your present cruise FL in 1L, this will remove the "step to FLxxx now" from the top right.
That should be in the honeywell manual somewhere, operationally most pilots won't be aware of these more intricate workings of the FMC as not a great deal of attention is given to the FMC generated arrival fuel, the computer flight plan is used for that. The FMC generated figure comes into it's own when operating in a terminal area when it is more accurate and "live".
I had a play at putting in a S step climb FL at the next waypoint which was way above the present max alt, it simply brings up a "step to FLxxx avail at xxxxz/xxxxnm" message top right on VNAV if there is sufficient flight time remaining , otherwise the message would be a "FLxxx unavailable "
The instant climb to a S climb waypoint altitude I mentioned in an earlier post was actually the way our computer flight plan software used to calculate it, and not in fact the FMC so please disregard that statement, sorry for the miss information on that one.

Re the question on autopilots in strong winds, higher altitudes in jetstreams are generally OK  as you have a larger tolerance of error allowed in track and height tracking.It's the transition of wind speeds, getting into and out of jetstreams  where you get the turbulence, I've been sat in 200kt tailwinds and it's been perfectly smooth. It's when lower down and it's coupled to an ILS it can start to pitch up and down quite badly especially in thermal or windshear conditions.

Hi Jon,

all clear now. Thank you!

Just one cosmetical question:

Quoteotherwise the message would be a "FLxxx unavailable "

My current PSX Alpha version displays the word "NONE" in 2R if a FL is unavailable, not the word UNAVAILABLE (haven't seen this in the manuals). I assume you're referring to the associated scratchpad messsage.

...

Re jetstreams. Here's a drawing I made a couple of years ago, while developing the jet stream model for PSX. The source of this principle is from a Jeppesen book called "Aviation Weather".

(http://aerowinx.com/assets/pics/idealJetStream.jpg)

CAT = Clear Air Turbulence.


Cheers,

|-|ardy

Yes quite right Hardy, none, not ..unavailable. Another prime example of why pilots are no good at this sort of thing, I've been staring at that FMC for the last 16 years but still can't tell you what the correct wording is! Best sticking with the manuals.

Jon

Confirmed by 744 guy: FL360S in legs page means step climb is supposed to start at the waypoint.

Enjoy the code deleting :-)

Done. Thanks :-)

I was wondering whether my prediction algorithm -- I mean the code that calculates the small font altitudes -- should, at the S, start a normal climb, or rather jump directly to the target altitude. If the leg is long after the S, it makes no difference. But if you have some short legs after the S, it could look like this:

3 NM .874/FL350
3 NM .874/FL390S
3 NM .874/FL361
3 NM .874/FL372
3 NM .874/FL390
3 NM .874/FL390

... or like this:

3 NM .874/FL350
3 NM .874/FL390S
3 NM .874/FL390
3 NM .874/FL390
3 NM .874/FL390
3 NM .874/FL390

...

By the way, speaking of autothrottles ...

When VNAV starts a cruise descent, the A/T mode goes to THR, reducing the power until approx -1200 fpm is reached, then changes to HOLD.

How long does it take from THR to HOLD? How smooth is it? My current model takes more than 20 seconds. Is this way too long? In general, PSX is a looooot smoother than PS1. Also on the LNAV axis. But in that THR to HOLD timing I may be exaggerating? It's all for pax comfort! :-)


Cheers,

|-|ardy

Does the A/T really control to a target V/S (so it must measure, correct, measure, correct, until satisfied)?

Or does it look up the throttle change from current to target setting from a table, guesstimating the setting for the target V/S, move there, and go to HOLD?


Jeroen

There is a V/S control by A/T when in FLCH SPD and when the distance to go is less than 4000 feet (at mode engagement). In that case the level change is flown in 2 minutes. (e.g. 2000 fpm for a 4000 feet change, or 500 fpm for a 1000 feet change).

In VNAV CRZ DES the A/T gradually reduces the thrust until -1200 fpm is reached, while the elevators keep the selected airspeed. Then it goes to HOLD. The -1200 fpm are just an approximate target. It may change when the air gets denser or the airspeed changes. The pilot can adjust the thrust when in HOLD mode.

In a well trimmed aircraft, be it a Cessna or a 747, you don't have to do much on the elevators when you want to change the altitude. Just reduce the thrust a bit and let the nose go down.


|-|ardy

Ok, so for VNAV (CRZ) DES is does not just set a presumed correct thrust and then go HOLD?

J

Bulfer/Gifford writes "it initially uses a predicted thrust". I don't know if "predicted" means "by database" or "by live detecting". In any case, I find it pretty easy to have the FMC detect the required thrust by smoothly retarding the throttles (also nice for the pax) -- and then HOLD it and use this held thrust as a "predicted" value until altitude capture.


|-|

Hardy,

That slow throttle reduction from THR to HOLD is deliberately programmed to be smooth and slow to reduce thermal shock of the engines after being at cruise power for hours.
We were taught not to manually override the throttle servos during this programmed thrust reduction. I wouldn't know if the timing and rate is different for different engine types though.
I can get you a timing for the GE if you want, but not going near an aeroplane for about 2 weeks now  :) , on leave, time for motorbikes instead !

Quote from: jonbI can get you a timing for the GE if you want, ...

Would be nice, yes, thanks!

Do you think, from memory, it takes about half a minute? Just approx. Not a whole minute, but not just 5 seconds either?


Happy ride on the bike!

|-|ardy

As we all know, when the MCP ALT bug is moved, the selected value may appear as a scratchpad message (which may update the FMC CRZ ALT by pushing the MCP knob).

Does anybody know when this "MCP-to-scratchpad" feature is enabled? Apparantly, it's disabled when on the ground. I guess it's enabled only when VNAV is engaged (or when  400 feet above runway). I'm sure it's also disabled when VNAV DES is active.


Cheers,

|-|ardy


P.S.: I think the following criteria are involved also: The new selected MCP altitude appears in the scratchpad only if it's ...

... higher than the current FMC CRZ ALT and VNAV phase is CLB
... higher or lower than the current FMC CRZ ALT and VNAV phase is CRZ*

* and not within 200 nm from T/D

I'll try and film it on my phone or at least time it, but from getting the FMA IDLE the thrust leavers retarding to idle, then getting HOLD on the FMA is probably around 15 seconds at most.

Quote from: Hardy Heinlin

Quote from: jonbI can get you a timing for the GE if you want, ...

Would be nice, yes, thanks!

Do you think, from memory, it takes about half a minute? Just approx. Not a whole minute, but not just 5 seconds either?


Happy ride on the bike!

|-|ardy

From FMA "IDLE" to "HOLD" takes exactly 26 seconds, or it has done on the 2 times I've timed it. I'll try and get some more observations.

Exquisite, thanks :-)


|-|

Hi guys,

I just created this account for 3 things :

1) thanks for the wonderful program
2) thanks for all the info about step climbs (I'm in the process of writing a tutorial about step climbs for my VA)
3) add a little something from the 777 FMS pilot's guide I own about whether 350S is the starting or ending point of the step climb.
Here is a little graph about planned step climbs from this official honeywell manual :
(http://img600.imageshack.us/img600/1002/777step.jpg)

The red line is mine, but as you can see, it seems to suggest that the planned step is ENDING at the waypoint, not starting. I'm sure there's an explanation and IefCooreman's assertion is true, but it's quite funny honeywell themselves are confused about this. And don't forget it is a 777 manual, so it might be different from 747. But it's strange enough to raise a doubt.

I am by no means a real world liner pilot (just some sunday vfr flying) but thought it could interest you guys. And I'll be most interested to read from real world pilots/honeywell-Boeing engineers on this.

Also, following your questions about steps-down, here is what the same manual says :

"If the last step is a step down, that step is maintained until the descent profile is intersected"

Seems indeed to suggest that they are perfectly possible. Same line in the 747-400 FMS Pilot's guide.

Eagerly waiting for PSX's release
Cheers

Welcome aboard, Manumanu.

Quote from: Manumanu"If the last step is a step down, that step is maintained until the descent profile is intersected"

Yep, this feature is also implemented in PSX.

Quote from: Manumanu3) add a little something from the 777 FMS pilot's guide I own about whether 350S is the starting or ending point of the step climb.
Here is a little graph about planned step climbs from this official honeywell manual :



The red line is mine, but as you can see, it seems to suggest that the planned step is ENDING at the waypoint, not starting. I'm sure there's an explanation and IefCooreman's assertion is true, but it's quite funny honeywell themselves are confused about this. And don't forget it is a 777 manual, so it might be different from 747.

Interesting. Just to confirm: In this printed example, is N61W030 a waypoint in the LEGS with FL390S entered by the crew, -- or an FMC generated phantom waypoint not occuring in the LEGS?


Cheers,

|-|ardy

Hi Hardy,
many thanks for the warm welcome.

N61W030 is a crew-entered waypoint in the LEGS page :

(http://img827.imageshack.us/img827/6246/777step3.jpg)

I finally managed to dig out my 1996 old 747-400 FMS Pilot's Guide (yeah quite old I know but that's all I've got :) )

and page 3.4-4 reads :

QuoteIf there are planned steps on the LEGS page, predicted values assume step climbs are made at the planned STEP AT points.

Then pages 3.4-24 and 25 gives us an interesting -imho- info :

QuoteA planned step point is made on the RTE LEGS page by entering the step altitude followed by "S" adjacent to the desired step point. The flight scenario requires a step climb to FL350 at FITES, so adjacent to FITES the pilot would enter /FL350S.
[...]
The FMC calculates a step climb from FL310 to FL350 on the KLAX to YSSY flight at a point 41NM prior to FITES. A second step climb is calculated from FL350 to FL390 at a point 120NM prior to 26S158.

(my bold emphasis)

then almost the same diagram as the 777 :

(http://img72.imageshack.us/img72/418/747step.jpg)

But the interesting info in my humble opinion is the line saying that after entering FL350S next to FITES... "The FMC calculates a step climb... 41NM prior to FITES". Which would mean that even when you enter a XXXS planned step climb in the LEGS page, the FMC calculates a S/C point in order to reach the new cruise altitude at the specified waypoint.

Hope this helps (although I can't help having the feeling it just complicates things. Sorry.) So don't delete your code just yet ;)

I'll try and ask an Air France 747 FO (OPL as we call them in France) friend of mine about this.

Cheers

Emmanuel

PS : a little hello to Steve B. who taught me so much about the 744 and this place :)

Well, that sounds convincing.

QuoteIf there are planned steps on the LEGS page, predicted values assume step climbs are made at the planned STEP AT points.

I've read this sentence before; the question was whether "are made" means "are started" or "are completed".

In the Honeywell book I bought I couldn't find the other stuff you quoted. Your manual is obviously more detailed. Edit: Found it now. I'm so blind.

I guess I'll have to re-activate my previous step-to model ...


Cheers,

|-|ardy

Or ... were there any changes in the FMC software recently? Here's an opposite statement again :-)

Quote from: IefCooremanI guess if you're programming it, it can't be 99, but has to be 100% :-). I've send an e-mail to a 744 collegue and waiting for the answer.

Although it is perfectly possible, it would be a strange functionality difference between 2 Boeing airplanes (777 vs 747). But I don't know anything about different FMC versions and software they use,... 777 is 100% sure: /FL360S is start of the step climb at the specified waypoint. Boeing has a strange way of thinking here because in the manuals they actually call it an "insert as an altitude constraint and the letter S" :-).

Quote from: Manumanu

Sigh. I have doubts again :-)

Now that I've found these pages in my manual as well, looking at the whole context, this STEP TO before FITES doesn't seem to be an S altitude based step but an FMC suggested step. Also, the step in that image seems to end 10 or 20 nm before FITES.


|-|

Sorry  :oops: I knew I would just be adding doubts more than solving the problem.

Quotethis STEP TO before FITES doesn't seem to be an S altitude based step but an FMC suggested step.

The only thing that's weird is the sentence above :

Quoteadjacent to FITES the pilot would enter /FL350S

which seems to suggest it's a crew-entered step.

As soon as I have the answer from my friend I'll let you know.

No need to sorry :-) I think you're right.

I was confused again when I re-read in my manual what you already quoted: "The FMC calculates a step climb from FL310 to FL350 on the KLAX to YSSY flight at a point 41NM prior to FITES."

By "the FMC calculates a step climb" I was suspecting the text doesn't refer to a crew entered step climb.

Ief, if you read this, do you remember what your source was? My Honeywell manual is from 1996.


Cheers,

|-|ardy

Quote from: IefCooremanConfirmed by 744 guy: FL360S in legs page means step climb is supposed to start at the waypoint.

I'm lost :-)

What is right, the book or the observation?

Ief and your 744 guy: Are your source the aircraft or a manual?

We all know, manuals are wrong sometimes.


Cheers,

|-|ardy

The life of the FMC programmer, interesting :-).

My personal _777_ source is the 777 FCOM, but don't ask me what FMC version or software provider we use... The airplanes are brand new, max 18 months old, we even discovered dreamliner flight display functionalities so these things do evolve in time. Our 747-400's are max 5 years old.

The FCOM states literally:

A legs page inserted step climb like "XXX/FL350S" indicates: "the FMC assumes the step climb starts at the waypoint. Accomplish the step climb at the waypoint with the steps described in the cruise climb".

My 747 source: no idea what reference he used. We run into eachother because we have layovers in the same hotel together fairly often, but since I'm having a vacation now, it might take a while before I see him.

I'm still having difficulties accepting the FMC would internally assume a step climb before the waypoint. Ie: an every-day-real-life example is the initial NAT track cruising level. We are cruising FL330, inbound to our oceanic entry point. We might ask for a slightly higher level (say FL350) than optimum for our initial oceanic clearance only to prevent being stuck all the way at a lower level (step climbs along the way end quite often end up "unable due traffic"). If we get FL350 as our initial level, it is a requirement to be AT the entry point AT FL350. And this is the only example where we don't use FL350S for that particular reason: it is a step climb that starts at the waypoint, and we need a step climb that ends at the waypoint. So we have to estimate the start of our climb ourselves.

Now actually I'm lying, we do put ie .83/FL350S at our entry point, but only to have more correct fuel estimates than without, and to remind us of the entry level we are required to be at (local ATC often doesn't know our oceanic clearance).

I'll try to experiment a bit once back in the air, and see if I can catch me a 747 instructor :-).

Hi IefCooreman

Do you have a specific page in your 777 FCOM so that I can check in my several editions and revisions ?
edit : found it page 11.42.22 (2006 edition, I'll have a look in a more recent edition but no really important) in the Flight Management, Navigation / FMC Cuise chapter.

In order to have a more "practical" reference, I asked to 2 777 FO, and one 747 FO at Air France and 1 777 FO and 1 747 CPT at BA. I didn't want to start writing the answers before having them all or at least a few of them, but since things are moving, let's go :)

So far I only had one answer (I only sent my emails yesterday) from a 777 AF guy and it was pretty clear : a step climb is considered as any altitude constraint, meaning the plane will plan to BE at the new altitude at the waypoint the altitude is associated to. Therefore planning a climb BEFORE said waypoint, hence the little green circle with S/C written next to it BEFORE the waypoint.

I'll come back as soon as I get more answers from my sources.

PS : For the moment, I'm trying to check in all my documents if in FLCH mode, the 747-400 does as the 777 and tries to reach the new altitude within 125 seconds. It's in part 22 of the 777 AMM but not in the 747 AMM...

Found in my copy of Cathay Pacific Cargo 747-8 SOPs (dated 31st of October 2011):

QuoteStep Climb
Step climbs must be entered as a Planned Step on the LEGS page. Once a Planned Step is entered, the CRZ page shows predictions to reach the altitude at the Planned Step point or after it if the Planned Step altitude cannot be attained by the waypoint.

Seems pretty clear here to : "predictions to reach the altitude at the Planned Step point". But it's 747-8 :/

edit : Found in the 787 FCOM, the exact same line as the 777 FCOM :

QuotePlanned Step Climb
When a step climb is planned to start at a waypoint, the data can be entered on the RTE LEGS page. The FMC performance predictions assume the airplane will start the climb at the identified waypoint.[...] Enter the cruise altitude as an altitude constraint and the letter S. The FMC assumes the step climb starts at the waypoint. Accomplish the step climb at the waypoint with the steps described in cruise climb.

One step further, one step backwards. Sorry  :?

Or is the word "start" possibly meaning something else ?  :?

All right, got some time to chat with my sources. Some even took pictures for me during their last flight.
There was a misunderstanding between me and one of my 777 sources so we cleared things up and the conclusion goes in the same way as what IefCooreman wrote earlier : in the 777 when you enter a step climb (not an altitude constraint) in the LEGS page as "FLxxxS" the FMS plans for you to START climbing AT the waypoint. So when the waypoint is sequenced, you are still at the old cruise altitude and only start climbing AFTER passing the waypoint. The little green circle labelled "S/C" is situated ON the waypoint.

Here are two pictures to illustrate :

(http://imageshack.us/a/img29/8784/777step1.jpg)

(http://imageshack.us/a/img62/6365/777step2.jpg)

In this situation they have entered a step to FL320 (oceanic entry point) at SIVIR and you can clearly see the S/C ON the waypoint.

Ok this is still 777 but things are getting clearer. I'm expecting news from my 747 sources shortly but I don't see why it should be otherwise.

Interesting. Thanks.

QuoteOk this is still 777 but things are getting clearer. I'm expecting news from my 747 sources shortly but I don't see why it should be otherwise.

I believe the 744 is different and that the stuff you quoted from the 744 manual is correct. There are quite a few differences between the 777 and 744 EFIS/FMC. To name just one (it's also on the photos): In the 744 FMC, you can't enter Mach speeds in the LEGS, in fact you can't enter a speed at all in a 744 cruise leg. That .848 on that 777 photo would be in small font on a 744 FMC. Also, the 744 ND doesn't show speeds in the route DATA, only altitude and time.

(Unless there was a major software update recently.)


Cheers,

|-|ardy

I'm on the phone with one of my 747 sources at the moment. Plenty of info coming in as soon as the call's over.

First a little picture from the 747-400 :

(http://img233.imageshack.us/img233/6306/step747400.jpg)

Then a few info before getting more :

my buddy 747-400 FO at AF never uses the "S" in the legs page. Some of his colleagues only use step size and climb when the FMC tells them to, some others use their OCTAVE (now LIDO) CFPL to climb only when the flight plan says, but he prefers using a step size (2000 or 1000 if on a NAT track) and every time the FMC tells him to climb, he compares to the CFPL to see how winds are compared to planned ones. If winds are close to planned winds (which may be quite old as their system updates winds only twice a day. Although it's going to change soon to 4 times a day) he then climbs when his CFPL tells him to. Otherwise he looks at the wind trade charts to estimate when it would be better to climb between the FMC suggestion and the CFPL suggestion.

It will also depend on Cargo or passenger flight (they do both at AF 747) and turbulence : if previous aircraft tell them on 123.45 that it is turbulent they will stay lower longer (provided fuel permits) to avoid getting to close to the margin, and if not turbulent go higher earlier. During cargo flights obviously comfort is of less importance.

So no definitive answer for now. He just came back from Cairo and only got my message now so couldn't take any pictures. He's off to Kuweit on next monday and has promised to take a film for us. Should settle the matter.

Cheers everybody

Emmanuel

Another 747-400 one showing clearly the S/C ON the waypoint (or is it because the scale is max 640 ?) :

(http://img853.imageshack.us/img853/9475/step7474002.jpg)

QuoteAnother one showing clearly the S/C ON the waypoint

Clearly, indeed.

Quote(or is it because the scale is max 640 ?)

I don't think so. Even if the green donut were only 5 nm from the white star center, the offset of the donut would be clearly visible.


Cheers,

|-|ardy

May we conclude that the designers of the S/C function had a strategic fuel planning feature in mind, not a tactical feature that can be used to comply to ATC clearances?

It makes some sense. If it were to be used tactically, it should work by popping up RESET MCP ALT so you can ask ATC for clearance ahead of time, and when you get clearance, dial the altitude up and sit there until the FMS decides to climb (or descend). Does it? If not, better stay with just for fuel planning, where climb point does not matter too much.

A S/C is not an altitude constraint.


Jeroen

That has been my conclusion through the past 20 years until I got confused recently.

I think, at the moment, -- 13 NOV 2012, 1300z --, Honeywell needs to correct the text in the 744 FMS Pilot's Guide.


|-|ardy

It can not be tactical because it's not ATC's job and they don't have the tools for it. Even when you send a flightplan with step climbs in it at specified waypoints, all the cruise FL's are subject to "requested by pilot on the spot and approved by local controller if possible" and hence the definition of a step climb cannot be a constraint (which is the other way around: ico no news you have to comply with it).

It is informative only, a "suggestion" from the FMC for you to play with. The fact that it is written like a constraint in the FMC confuses a lot of people apparently.

There are differences between 777 and 747 FMC's (from what I've seen jumpseating on 744's). 777 has extra functionalities. The most interesting here is the "recommended" cruise FL next to opt and max, which includes winds from the legs data page into calculations. So if dispatch is kind enough to beam the correct ones up to your FMC, it will tell you all you need to know :-). Besides that, it's faster, has a bigger memory and is multi-color! And it's more silent... oh well... the whole 777 is :-)

Final word on this : the manual planned step entered in the LEGS page in the 747-400 FMC means the climb STARTS at the waypoint it is associate with (photo taken a few days ago but didn't have time to post here before today) :

(http://img15.imageshack.us/img15/7061/20121126220520.jpg)

Here we were cruising at FL310, we entered the "FL390S" planned step, and before EXECuting the FMS automatically updates the following planned altitudes and we see that he plans the next altitude below FL390, hence climb STARTING at the waypoint which is associated to the constraint.
Same as the 777 in the end.

Sorry I haven't been able to come back earlier on this.

Cheers

Clear as crystal.

Very nice. Thank you!


Cheers,

|-|ardy

It's getting closer ...

Quote from: Manumanu

|-|

Wow ! Fantastic !

The line between reality and simulation is very thin ....  ;)
Congratulations Harry.
B. Rgds
Michel

Very cute!

Btw., whats that "Flaps 15 Pref." sticker doing there? Preference for a faster
landing to save the flaps-extension mechanism for the next service interval?  :?