Luftfahrer
Topic Author
Posts: 976
Joined: Sun Mar 15, 2009 11:27 am

Fuel Consumption/Flight Managment System

Thu Feb 25, 2010 5:29 pm

I just finished reading this article:

http://www.spiegel.de/international/world/0,1518,679980,00.html

This quote made me curious:

Quote:
It's only by means of a trick that the captain can reach Paris with more than the legal minimum reserves of kerosene that must be in the plane's tanks upon arrival in the French capital. A loophole allows him to enter Bordeaux -- which lies several hundred kilometers closer than Paris -- as the fictitious destination for his fuel calculations.

To be honest, I've never head of this practice. Is it a common one? Can anybode be more precise what is meant by 'loophole' here? Basically knowing how a FMGS works through flightsim, I wondered how the pilot would enter this into the MCDU. My assumption: Origin would be SBGL (GIG), destination LFBD (BOD), and alternate destination LFPG (CDG). I am almost certain the remaining fuel for both DEST and ALTN DEST is displayed on the Airbus -- so enroute, getting closer to the actual destination (Paris-CDG), the pilots will see if they have enough fuel to continue there or if they have to go for an unplanned stop at Bordeaux (or Lisbon). This is only my theory, I'd appreciate any insight how it works in reality. Thanks!

[Edited 2010-02-25 09:53:54]
'He resembled a pilot, which to a seaman is trustworthiness personified.' Joseph Conrad
 
Fabo
Posts: 1150
Joined: Tue Aug 16, 2005 1:30 am

RE: Fuel Consumption/Flight Managment System

Thu Feb 25, 2010 6:15 pm

The loophole is not within aircraft systems, but within rules. You need to have a specific amount of fuel left after you land. That means, you have to fill it on top of the fuel calculated for the trip. This would include alternate fuel, holding fuel, maybe taxi fuel etc. Thing is, calculations would not allow for sufficient amount of fuel upon arrival to Paris. Therefore the fuel would be calculated to Bordeaux, and sufficient extra fuel added (plus some more I guess, so better chances). If upon arrival to France, or other suitable place on your flightplan, you can declare suitable amount of fuel to get to Paris from your position, you can re-plan your flight direct to Paris. This can be achieved via better fuel flow, direct routings, more favourable winds, or other ways you can not officially count with when planning the fuel in your departure point.

(alhtough I have no idea how that would be relevant to AF447)

[Edited 2010-02-25 10:15:51]
The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
 
Luftfahrer
Topic Author
Posts: 976
Joined: Sun Mar 15, 2009 11:27 am

RE: Fuel Consumption/Flight Managment System

Thu Feb 25, 2010 6:34 pm

Quoting Fabo (Reply 1):

Hi, thanks for the explanations. I've known about the regulations, though. Sorry if this wasn't clear in my initial post.
I'm more concerned with the technical aspects (i.e., how the MCDU would programmed), therefore I interpreted the loophole as something related to the aircraft's system.

Quoting Fabo (Reply 1):
(alhtough I have no idea how that would be relevant to AF447)

It isn't, just spotted it this very article and thought I'd bring it up...
'He resembled a pilot, which to a seaman is trustworthiness personified.' Joseph Conrad
 
User avatar
BALandorLivery
Posts: 313
Joined: Mon Jan 17, 2005 7:54 pm

RE: Fuel Consumption/Flight Managment System

Thu Feb 25, 2010 6:34 pm

It happens more often than you might think.

If for some reason you cannot reach your destination with the legal requirement at the planning stage then it is acceptable to nominate a closer airport as your destination. If you burn less than anticipated enroute or if there will be more than minimum reserve AFTER you divert then you can 'divert' to the airport you originally wanted to fly to.

A more common practice than the one above is the en-route alternate.
Here you dispatch with 3% contingency fuel instead of 5% and nominte an alternate airfield en-route (before your destination)
Upon passing a specific waypoint nominated in the flight plan you check to see if you have enough fuel to continue to your destination (plus alternate and final reserve fuel).
If you don't you divert to your en-route alternate for a top up.
if you do then you carry on knowing you still have enough to divert from your original destination if you still have to.

The second method is preferred because you land at your original airport with ALT and FINAL RESERVE fuel.
The first method means you land at your original airport with only FINAL RESERVE

You can ask questions about the airmanship of such decisions but they do happen although not on a regular basis.

Don't forget that these things can be monitored by the authorities and they will not allow an operation that is consistantly marginal.
 
Luftfahrer
Topic Author
Posts: 976
Joined: Sun Mar 15, 2009 11:27 am

RE: Fuel Consumption/Flight Managment System

Thu Feb 25, 2010 6:55 pm

Thanks for the detailed depiction of this kind of operation. Very well understood now.

Quoting BALandorLivery (Reply 3):
nominate a closer airport as your destination
Quoting BALandorLivery (Reply 3):
you can 'divert' to the airport you originally wanted to fly to.

That's what I had originally suspected.
'He resembled a pilot, which to a seaman is trustworthiness personified.' Joseph Conrad
 
roseflyer
Posts: 9606
Joined: Fri Feb 13, 2004 9:34 am

RE: Fuel Consumption/Flight Managment System

Fri Feb 26, 2010 3:01 pm

Is GIG-CDG pushing the A330 range? I thought that a route like that without strong winds should be manageable.
If you have never designed an airplane part before, let the real designers do the work!
 
User avatar
BALandorLivery
Posts: 313
Joined: Mon Jan 17, 2005 7:54 pm

RE: Fuel Consumption/Flight Managment System

Fri Feb 26, 2010 3:04 pm

In an A332....

NO
 
CosmicCruiser
Posts: 2049
Joined: Tue Feb 22, 2005 3:01 am

RE: Fuel Consumption/Flight Managment System

Fri Feb 26, 2010 3:33 pm

It's called a re-release flight plan if no one has yet posted it. Int'l you must have 10% of the flight plan time added in fuel. You can see that on a long flight that's a lot of gas. So if you have a closer destination you can have less fuel and when you reach a certain point the co. will re-release you to you real dest if you have a predetermined amt of fuel remaining using a "new" 10% of reserve that's from the re-release point to dest.You program your "real" destination in the FMS. It knows only that you're going to your dest. We will get re-released anytime within a 2 hr window prior to the re-release point. Of course weather would be a consideration in that using a close by alt can be an issue if your dest wx sucks. ATC does not know or care about your re-release point or airport. You are filed to your dest. It's usually not a matter of not being able to make your dest but more the ability to carry less fuel which means burn less fuel as well. I've never seen filing to an "alt" arpt then "diverting" to dest. Maybe some co. do but we don't.
 
flyinTLow
Posts: 459
Joined: Tue Oct 12, 2004 10:40 pm

RE: Fuel Consumption/Flight Managment System

Fri Feb 26, 2010 10:03 pm

I've learned that as a Reclearance Flightplan. Not only done for weightcritical flights, but sometimes also for fuel savings  

German Wikipedia about this:

http://de.wikipedia.org/wiki/Reclearance

Cheers
- When dreams take flight, follow them -
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Fuel Consumption/Flight Managment System

Sat Feb 27, 2010 5:25 am

Quoting CosmicCruiser (Reply 7):
Int'l you must have 10%

FAA regulations only, others use 5% or other variable.
Re-clearance/re-release flight plans have been in use for over thirty years...nothing now.

Who is online

Users browsing this forum: qfflyer and 9 guests