757/767 FMS Fuel / ETA Disappear
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Join Date: Mar 2004
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757/767 FMS Fuel / ETA Disappear
Hi All,
Sorry to ask a question without a huge amount of detail, but I was wondering if anyone has come across the following.
A couple of times, when entering data into the 757/767 FMC (CRZ parameters, or perhaps the arrival, or DES parameters or something), I make a change which causes the destination ETA and Fuel Arr to go missing on PROG 1 (in the way they do when it's having a think about a RTE mod). On further inspection it seems that at some point along the route - normally at a seemingly random waypoint - the ETA and Fuel calcs stop, and this carries forward to the end of the route.
I can't remember exactly what I do to get it back to normal (the answer is basically 'fiddle') but things like changing some of the hard heights / speeds / routes towards the end normally do the trick.
My assumption is that it's something to do with the particular descent I have put in - some combination of height and speed at a particular waypoint, or some level / speed being outside a range - but I would just be interested to know if anyone had a concrete reason.
Many thanks in advance for any thoughts,
NW3
Sorry to ask a question without a huge amount of detail, but I was wondering if anyone has come across the following.
A couple of times, when entering data into the 757/767 FMC (CRZ parameters, or perhaps the arrival, or DES parameters or something), I make a change which causes the destination ETA and Fuel Arr to go missing on PROG 1 (in the way they do when it's having a think about a RTE mod). On further inspection it seems that at some point along the route - normally at a seemingly random waypoint - the ETA and Fuel calcs stop, and this carries forward to the end of the route.
I can't remember exactly what I do to get it back to normal (the answer is basically 'fiddle') but things like changing some of the hard heights / speeds / routes towards the end normally do the trick.
My assumption is that it's something to do with the particular descent I have put in - some combination of height and speed at a particular waypoint, or some level / speed being outside a range - but I would just be interested to know if anyone had a concrete reason.
Many thanks in advance for any thoughts,
NW3
Join Date: May 2005
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well it happened to me (not on a B757/767) but the point is as follows..
when you enter an altitude in a waypoint which is not logical to the subsequence wayponts the "Fuel / ETA" Disappear.
E.G:
you enter a STAR whose defautl values are (speed/altitude):
WP A 250/8000
WP B 250/5000
WP C 180/2500
.
.
and you enter in the scratchpad
WP B 250/15000
then the FMS blanks the ETA/FUEL
I think thats the problem
try it and tell me
when you enter an altitude in a waypoint which is not logical to the subsequence wayponts the "Fuel / ETA" Disappear.
E.G:
you enter a STAR whose defautl values are (speed/altitude):
WP A 250/8000
WP B 250/5000
WP C 180/2500
.
.
and you enter in the scratchpad
WP B 250/15000
then the FMS blanks the ETA/FUEL
I think thats the problem
try it and tell me
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Sounds good - will give it a go next time LHR starts getting busy 
Thanks!
NW3
PS N_S_R - I thought of that, and it didn't seem to be the problem. Great minds, and all that, though.
Thanks!
NW3
PS N_S_R - I thought of that, and it didn't seem to be the problem. Great minds, and all that, though.
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It can sometimes occur when the FMC thinks it cannot make the programmed FL. Try putting in a lower cruise ALT, or ,preferrably, stick in a higher cruise mach no ( 0.82 ) and then speed intervene until the weight reduces. The Fuel and ETA should magically reappear.
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Steve757, you're dead right. But you can type in normal cruise mach (.8 or .81) without selecting anything in the speed window and you'll still get your estimated fuel and ETA for destination.
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On a similar vein - if you are a long way above or below Optimum FL, I've seen the fuel and ETA's blank - same sort of thing I guess- too far outside its calculation performance envelope.
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On a similar vein - if you are a long way above or below Optimum FL, I've seen the fuel and ETA's blank - same sort of thing I guess- too far outside its calculation performance envelope.
Does that mean you've run out of fuel?
Does that mean you've run out of fuel?
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Does that mean you've run out of fuel?
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757/767 fuel/eta predictions
I have seen this a few times on the 767 going across the pond and flying way above optimum due to ATC etc..the fuel and eta's disappear.
This is due as several peple have suggested already to it beng outside of its performance parameters and usually only occurs with a variable cruise speed set in the fmc ie ECON or LRC. if you intervene at your desired econ/lrc speed as commanded and enter that speed in the fmc it will recalculate everything as it now has a constant speed to work from.
It does not ean however you are going to run out of fuel.
As for the descent profile situation. I hven't come across that one yet, come t thik of it i cant think when i have ever wanted to be 10000' above a star hard height either..
This is due as several peple have suggested already to it beng outside of its performance parameters and usually only occurs with a variable cruise speed set in the fmc ie ECON or LRC. if you intervene at your desired econ/lrc speed as commanded and enter that speed in the fmc it will recalculate everything as it now has a constant speed to work from.
It does not ean however you are going to run out of fuel.
As for the descent profile situation. I hven't come across that one yet, come t thik of it i cant think when i have ever wanted to be 10000' above a star hard height either..
