View Full Version : Strange FMS info
Markieboy
3rd Aug 2009, 12:47
Gentlemen,
Can anyone possibly shed light on this? I noticed in 2 weeks ago coming home from Shanghai.
http://i22.photobucket.com/albums/b345/JesusChrist1000/photo.jpg
Any help is welcome, thanks,
Mark
Jimmy Do Little
3rd Aug 2009, 13:01
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
3rd Aug 2009, 13:20
No, that isn't what I am referring to. Look at the "Step To" and the "Max" lines.
Jimmy Do Little
3rd Aug 2009, 13:30
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
3rd Aug 2009, 13:37
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
3rd Aug 2009, 13:43
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
3rd Aug 2009, 15:13
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?
Even if so, there is no way 390 is available.
IndAir967
3rd Aug 2009, 16:22
so what happened .. did u guys step climb to 390 ?
Markieboy
3rd Aug 2009, 18:32
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
4th Aug 2009, 06:33
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
4th Aug 2009, 08:09
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
4th Aug 2009, 08:28
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...:ok:
hi Markieboy,
how come CRZ ALT FL348 ?
too bad there's no FMA display picture.
Frankie_B
4th Aug 2009, 15:28
They must be over Russian airspace. FL348 = 10600m.
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
5th Aug 2009, 00:23
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.:ok:
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. :uhoh:
Mister Geezer
5th Aug 2009, 01:58
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
5th Aug 2009, 02:03
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!
Brain Potter
5th Aug 2009, 16:14
If Markieboy's current type given by his profile is correct (B744) then this FMC certainly does have a LEGS page. I would agree with the other posters that F390S has been entered against a waypoint on that page, and the FMC is being forced up at a position that is 68nm away.
I never flew this type on metric flight levels, and am willing to be corrected, but with FL348 (ie FL10600m) entered as the CRZ level and the step setting to ICAO (ie 4000') would the FMC not plan for the next level to be F388? If this assumption is correct, the explanation that FL390S has been entered manually has even more credence.
Markieboy, did you clear this step by re-entering the CRZ level after you had passed the waypoint that is 68nm away on this picture? I seem to remember that sometimes an unwanted manual step won't clear from the 'Step-to' field after the associated waypoint has been passed even by entering Step 0. The solution was to hold the present altitude, dial a lower one into the MCP, push the button, redial the current altitude and push the button again.
rubik101
5th Aug 2009, 16:40
411A, the beloved Tristar was a mighty machine for sure.
Did you know; if you have the intellegence and the time to calculate the antipodean position and enter it as a waypoint, line select it to the top at L1, and as you get directly overhead the opposite point, execute 'direct to' the screen shows about 125 Zeros. Try it some time!
p.s. disconnect LNAV before you try it!
ad-astra
6th Aug 2009, 21:32
Mr Google has already thought of that :D:D
antipodr - Find the other side of the world! (http://www.antipodr.com/?addr=&x=177&y=17)
411A, the beloved Tristar was a mighty machine for sure.
Ha! It still is, make no mistake.:ok:
Now, as to inapproporiate FMS inputs, yes, quite correct, however....the FD crew really has to try to positively screw-up.
Other aircraft?
Yup, I fully expect so.
Capt Claret
7th Aug 2009, 07:32
I fly the B717 with Bloggs, in fact he taught me some of what I know.
It is not at all uncommon to see the Honeywell FMS in the 717 show a step climb to a higher level is possible in a short distance, yet the MaxFL is thousands of feet below the same level.
On one occasion, I foolishly commenced a climb because OPT & Max were indicated to be achievable, and as soon as the climb was commenced, both Opt & Max indicated below the level on climb to! :eek:
Markieboy
8th Aug 2009, 20:38
Wow, a 5 day LAX and all this has been posted! Sorry, I should have checked in earlier.
Type is indeed 744. I will check next week wednesday as I am off to Shanghai again. I know many guys use the LEGS page to enter an expected step, I normally don't which is probably why I was confused by this.
FL348 is indeed 10600m, Russian airspace. And Mach .856 is ECON with CI150 which is our normal cruise CI, with delays being flown at CI400.
Many thanks everybody,
Mark