Strange FMS info

[Markieboy]

Gentlemen,

Can anyone possibly shed light on this? I noticed in 2 weeks ago coming home from Shanghai.



Any help is welcome, thanks,

Mark

[Jimmy Do Little]

Are you asking about the "STEP SIZE?" If so, it's referring to a 4000 foot step climb increment, opposed to an "RVSM Size" of 2000 feet.

[Markieboy]

No, that isn't what I am referring to. Look at the "Step To" and the "Max" lines.

[Jimmy Do Little]

I think the "Step To" is refering to the next level "Step" (achievable at time of 2103UTC) where the max level is refering to the "Current" maximum. The Optimum being the "Current" optimum level. Otherwise, could also have been a cockup in the Cost Index figure.

I'm guessing that you were less than 3 hours into your flight when you saw this?

Disclaimer: Haven't flown a Boeing for a long time.

[Markieboy]

The point that I don't understand is that we have a MAX ALT of FL372 and the aircraft says that the next step climb (to FL390) is in only 68NM!

The FL390 step should be at least another 3 hours off. I checked CG, CI, Temp, everything. Perhaps just a temporary bug?

[Jimmy Do Little]

Okay. Knowing all that. A possible reason (Seen on Airbus a few times) was a grossly incorrect waypoint wind entry. Maybe for the waypoint immediatly proceeding or following where you're at "now", the wind was entered with a gross error ( or TROP altitude entry error). In the Airbus, that will effect max levels to some extent, often to a large extent.

Sorry, but my Boeing knowledge is really rusty. Otheriwse, just trying to share some ideas about it.

[Intruder]

No, that isn't what I am referring to. Look at the "Step To" and the "Max" lines.

Did you manually enter a Step Climb in the FMS at that waypoint?

[BOAC]

Even if so, there is no way 390 is available.

[IndAir967]

so what happened .. did u guys step climb to 390 ?

[Markieboy]

Of course not. We stayed at 10600m and dicked around with the FMS until it suddenly showed more "normal" values! Then the STEP TO line showed FL390 in about 1500NM.

[Jimmy Do Little]

Funny how quick people can divert from the topic.

Back to the issue, I'm thinking that a Tempurature or Wind entry at a specfic waypoint got messed up, especially since - as you said - it "...suddenly showed more "normal" values...".

Aside from that, a "Bug" in the software is a probable cause.

[Three Wire]

Depends on your version of software. If you go DCT TO a WPT and select ABEAM WPTS, the software deletes the temperature/temp line in the WPT data page. I have seen that screw up climb forecasts/CRZ availability. Blockpoint 14 supposedly fixes that.
And then you are honking along at M.856. Speed is life, but that drastically affects fuel consumption. The step function AFAIK, assumes ECON CLB/CRZ values.
Two possible reasons.

[Capn Bloggs]

Happens on the 717 all the time. Step now to FL370 when current Max is only FL355 (FMS input data correct). Yeh, right. Good thing the effo's got a brain. He wouldn't let me go up...

[arba]

hi Markieboy,
how come CRZ ALT FL348 ?
too bad there's no FMA display picture.

[Frankie_B]

They must be over Russian airspace. FL348 = 10600m.

[411A]

Well, I have to admit that I'm surprised at all this 'incorrect' FMS data, as these should be the latest and greatest wonderboxes...however, 37 years ago one rather advanced/automated wide-body airplane entered service, and when equipped with the Hamilton Sundstrand FMS units unfailingly (at least in my 29 years of operation) presented an accurate picture of the optimum desired cruising altitude, without the glitches mentioned earlier on this thread.
Let's see, it had inputs for...
pressure altitude
TAT/SAT
takeoff weight
actual fuel consumption
distance to destination
cruising mach number....

along with many others, and provided accurate step climb/optimum cruise altitude data, that was right on the money, every time.

The airplane was manufactured by Lockheed, and it is called the TriStar.
And yes, it still works as advertised, even today, for the few remaining operators of this truly remarkable airplane.

[showers]

The step to as one can see was in bold display,so the crew must have input fl390S on the legs page.Usually if the FMS is allowed to calculate the step climb it does not present it in bold display.

[FLCH]

The step to as one can see was in bold display,so the crew must have input fl390S on the legs page.Usually if the FMS is allowed to calculate the step climb it does not present it in bold display

I agree for what it's worth, 390S has been entered and it is telling you that you have 68 nm to go to a "forced" step.

OPT and Max show the current values for the weight.

Seen it when I get a particular crossing altitude for the tracks for which I did not really want, but got it anyway.

[Mister Geezer]

The airplane was manufactured by Lockheed, and it is called the TriStar. And yes, it still works as advertised, even today, for the few remaining operators of this truly remarkable airplane.

Yawn..... next!

[Capn Bloggs]

I don't think the FMS type in question has a LEGS page. The 390 step would have been inserted on INIT page 1. Had a waypoint been VERT REVved to be "AT" FL390 only 68nm ahead, the box surely should have said "no can do". I stand to be corrected though!