Unreliable FMC fuel calculation with gear extended
ECON cruise, LR cruise...
Join Date: Apr 2002
Location: MIRSI hold - give or take...
Age: 52
Posts: 568
Likes: 0
Received 0 Likes
on
0 Posts
yes
The FMC calculates fuel based on the parameters entered + the DB installed.
Since there is no "gear down" option in most DBs, it follows that the predicted fuel will be wrong when dispatching with the gear down. A quick Google of "Condor+Vienna" will lead you to a case in point
Some FMS OEMs have included a "measured" perfromance option that will use the previously achived SAR as the base for calculations, but this will generlly need to be pilot selected, since "predicted" performance (i.e. the DB values) is default on most FMS'.
Honestly...
The FMC calculates fuel based on the parameters entered + the DB installed.
Since there is no "gear down" option in most DBs, it follows that the predicted fuel will be wrong when dispatching with the gear down. A quick Google of "Condor+Vienna" will lead you to a case in point
Some FMS OEMs have included a "measured" perfromance option that will use the previously achived SAR as the base for calculations, but this will generlly need to be pilot selected, since "predicted" performance (i.e. the DB values) is default on most FMS'.
Honestly...
Join Date: Mar 2006
Location: Choroni, sometimes
Posts: 1,974
Likes: 0
Received 0 Likes
on
0 Posts
ECON cruise, LR cruise...
Join Date: Apr 2002
Location: MIRSI hold - give or take...
Age: 52
Posts: 568
Likes: 0
Received 0 Likes
on
0 Posts
hetfield,
Indeed it was - I stand corrected Classic bit of "knowing your aircraft", tho... or one should have thought that when the FMS came up with the same arrival fuel after the gear wouldn't come up as it had on the ground, a penny or two should have dropped.
But then again - there but for the grace of God...
Indeed it was - I stand corrected Classic bit of "knowing your aircraft", tho... or one should have thought that when the FMS came up with the same arrival fuel after the gear wouldn't come up as it had on the ground, a penny or two should have dropped.
But then again - there but for the grace of God...
Join Date: Jul 2007
Location: ***
Posts: 350
Likes: 0
Received 0 Likes
on
0 Posts
The CRJ I fly with a Collins FMS has a prompt to switch from "predicted" to "messured" mode wich will change the fuel calculation to where it calculates with the actual fuel flow. It won't take into account descent or climb, just use the present fuel flow to predict the arrival fuel.
Not a good tool for normal ops, but having something wrong with your configuration, it would serve as a good guess on where you might be able to go.
Nic
Not a good tool for normal ops, but having something wrong with your configuration, it would serve as a good guess on where you might be able to go.
Nic
Join Date: Jun 2010
Location: Brisbane, Australia
Posts: 304
Likes: 0
Received 0 Likes
on
0 Posts
Not again....
Look, I'm a Boeing man so know little about Airbus A310's, or any other ab,
but I CAN tell you this...after reading that report,
I can tell you it does not carry a Flight Engineer...
will they ever learn.....
ew73
Look, I'm a Boeing man so know little about Airbus A310's, or any other ab,
but I CAN tell you this...after reading that report,
I can tell you it does not carry a Flight Engineer...
will they ever learn.....
ew73
Join Date: Oct 2002
Location: In Frozen Chunks (Cloud Cuckoo Land)
Age: 17
Posts: 1,521
Likes: 0
Received 0 Likes
on
0 Posts
Having spoken to a couple of people who have done ferry flights with gear down, their opinion was that even the charts with gear extended in the performance manuals were incredibly inaccurate....ie they used significantly more fuel than they had expected.
Now thats only from a couple of people across 2 types of boeings, so it isnt a big sample, but it does make you wonder.
Now thats only from a couple of people across 2 types of boeings, so it isnt a big sample, but it does make you wonder.
Join Date: Mar 2006
Location: Choroni, sometimes
Posts: 1,974
Likes: 0
Received 0 Likes
on
0 Posts
Concerning the A310 Vienna accident, as far as I remember the FMC was really tricky there. The calculation to the next waypoint was correct, using actual FF. But afterwards the FMC assumes a retracted gear again. So from waypoint to waypoint the situation changed drastically.
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
really tricky
I just know there's a word for that - cannot recall it..............................
Join Date: Mar 2006
Location: Choroni, sometimes
Posts: 1,974
Likes: 0
Received 0 Likes
on
0 Posts
BOAC
All I wanted to point out is the technical background of the FMC.
(Assuming a clean ship after next waypoint).
To let these guys look like idiots is your business not mine.
All I wanted to point out is the technical background of the FMC.
(Assuming a clean ship after next waypoint).
To let these guys look like idiots is your business not mine.
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
I think 'fly744' got the answer to the 'technical' stuff in post#2?
It does not need my help to achieve what you describe, Hetfield - and it was not "these guys" it was "that guy". Lucky indeed only 28 were injured and all were not killed. My views on Computers in the cockpit and the safety of aviation are on record. He:
Ignored F/O's warnings
Appeared to 'trust' illogical fuel predictions
Ignored 'short of fuel' warning 1 hr before crashing
Was reported to be most senior H-L Captain - until
fly744 - you say you are a 744 Captain. I would recommend (I guess you would know anyway?)
a) listen to the F/O's views
b) when fuels start to depart from the expected, consider abandoning any gizmos like the FMC and revert to a straightforward 'how-goze-it' graph
c) if the gizmo then tells you you will run out of fuel, take note.
BTW - did we ever get a link to an English translation of the Austrian report and what happened in the court case against the Captain?
It does not need my help to achieve what you describe, Hetfield - and it was not "these guys" it was "that guy". Lucky indeed only 28 were injured and all were not killed. My views on Computers in the cockpit and the safety of aviation are on record. He:
Ignored F/O's warnings
Appeared to 'trust' illogical fuel predictions
Ignored 'short of fuel' warning 1 hr before crashing
Was reported to be most senior H-L Captain - until
fly744 - you say you are a 744 Captain. I would recommend (I guess you would know anyway?)
a) listen to the F/O's views
b) when fuels start to depart from the expected, consider abandoning any gizmos like the FMC and revert to a straightforward 'how-goze-it' graph
c) if the gizmo then tells you you will run out of fuel, take note.
BTW - did we ever get a link to an English translation of the Austrian report and what happened in the court case against the Captain?
Join Date: Aug 2005
Location: Too far from the equator
Posts: 745
Likes: 0
Received 0 Likes
on
0 Posts
Ferried a gear-down 737 from Borneo to KL a few years back . Apart from the incredible noise and unhelpful ATC ( Why you fly so slow ? gear down ? you wanna declare mayday ? ((Mentioned on FP under Rmks , waste of time )) what struck me was how very accurate the QRH Planning data was .
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
I think you will find that Block18 (remarks) do not normally make their way onto controllers' flight strips, and of course the absence of the customary 'kotakota' R/T background 'clackers' would have caused confusion to them.