Fuel planning

[Spooky 2]

Has anyone ever seen or for that matter used the following technique for verifying adaquate fuel FAR Part 121 or similar flight plan?

Using the FIX page and average wind to provide preliminary wind calculation for FMC (may not be needed if you’re getting an ACARS wind uplink).

o

Load destination into FIX page

o

Note bearing from destination

o

Insert flight plan average wind at TOD point in FMC, using bearing or opposite of bearing as direction (depending on avg headwind or tailwind on FP)

o

TOD wind propagates back through FP; provides first-order check of FP fuel

o

Update with exact point winds as enroute time permits

[ImbracableCrunk]

Nope.

Update with exact point winds as enroute time permits

I have heard of people updating the enroute winds in the FMC along the way, but I've always wondered whether or not that was a waste of time.

[ant1]

From 737 OM:

Crew entries of forecast winds (or default 000°/000) are automatically biased with the actual wind computed by the FMC when within 100 NM of a cruise waypoint and within 2000 feet of a cruise altitude. Biased values are not displayed.

[BOAC]

but I've always wondered whether or not that was a waste of time.

- often it is, but occasionally with an Oceanic entry or other required ETA it should be used. Only other time I have used it is to cheer myself up when I'm battling a 200kt headwind at some part of the trip

99% of the rest of the time mean cruise wind inserted does the job beautifully.

[GlueBall]

I haven't seen anyone dabble with such minutiae. Unless there is a fuel leak, or one of the four engines has gone on vacation mid pacific, I'm satisfied with computer flight plan technology. Over the years the data has been extremely close to actual wind and fuel score, so that there was no need of constantly modifying FMS wind inputs and forever verifying adequate fuel by TOD.

[Checkboard]

On the 737, I've never seen the TOD wind propagate back - only the TOC wind propagate forward.

[BOAC]

That's the way I see it too. Mind you, we have no idea which a/c type the OQ was about and I can see NO point in using TOD wind which could be drastically different to average trip wind eg with a TOD tailwind you could easily be suckered into thinking you had enough when you had an average trip h/wind of 30kts!

I suspect someone has been playing 'spoof' on Spooky

[flyburg]

In my company we used the average wind as well. However, last year, due to the economic crisis there was a real push to drive the fuel usage back.
We got a couple of "memo's" on how to fly fuel efficient. One was indeed to use top of climb wind and then change the winds on the legs page whenever the winds changed by more than 10kts or 10 degrees.

I tend to do this whenever there is sufficient time in the preparation fase. I do think though, it's either the one or other option. Either you use the toc wind and adjust the winds on the legs page, or use avg winds.

If not it will screw up your times and fuel predictions.

I like the first option. Flying for a large carrier with thousands of flights a month, even a saving of a few kgs per flight makes a difference!

edit: I didn't read the initial question right. No sense in using the TOD wind. TOC allows the FMS to calculate the most efficient climb speed, however, since this entry propagates forward all predictions would be messed up. So you will have to adjust the speeds on the legs page whenever they differ from the TOC wind. TOD winds only help calculate the most efficient point of descent.

Actually, pretty basic stuff. TOC winds allow the FMS to calculate the most optimum climb speed, TOD allow the FMS to calculate the optimum TOD, winds enroute allow the FMS to calculate accurate predictions.Fill these in during preflight and you would get an accurate picture of fuel usage. Should be basic knowledge taught during ATP theory training and enhanced when reading the FCOM

[Checkboard]

One was indeed to use top of climb wind and then change the winds on the legs page whenever the winds changed by more than 10kts or 10 degrees.

I don't see how this saves fuel, as the planning is done, and the fuel loaded.

[flyburg]

Using TOC wind instead of average results in a optimum clb spd. This would save fuel (or for that matter more closely match the fpl figures)

[Checkboard]

Ah -makes sense now - late night post, sorry.