TOD or average winds into FMC?

[Vagabondo 23]

 

 

where did you see that the CRZ WIND entry is for T/C? In the descent, given the higher probability of altitude constraints with a fixed airport location at which you should be at 0 AGL, wind would play a large role. In climbing, however, wind would not play a role at all in calculating a best climb speed. The best econ speed would be the one that uses the least amount of fuel with the best rate of climb.

You are correct with regard to best climb speed (MAX RATE or Vy), this is approximately clean speed + 50, and would contribute the lowest possible trip fuel burn (all other things being equal).

 

I am assuming that your mention of "best econ speed" is a reference to ECON speed which is the only FMC speed that uses the CRZ WIND input. ECON speed is the lowest cost determined by the operator according to their chosen cost index (CI) taking into account airframe time, fuel and possibly even schedule. Therefore "best econ" becomes a tautology and ECON speed (for all relevant phases of flight) is slower with a tailwind and faster in a headwind to best balance those vs over time compromises expressed through the CI.

 

I got the extra information from the Bulfer FMC Users Guide. Also the FCTM has this to say on ECON speeds:

 

 

For ECON climb, the speed is a function of gross weight (predicted weight at top of climb),
predicted top of climb wind, predicted top of climb temperature deviation from
ISA, and cost index.

[scandinavian13 5,192]

 

 

Also the FCTM has this to say on ECON speeds:

 

Awesome - thanks!

[krisyyz 1]

The FCOM merely says: Following on from some additional reading it seems the CRZ WIND entry is for the ToC wind for the entered CRZ ALT. Its purpose is to define the best econ speed in the climb starting with zero wind on the ground and linearly interpolating to the CRZ ALT. The LEG, RTE DATA pages are for entering forecast leg winds for predictions and smoothing against actual cruise wind. A general and unwritten rule of thumb is to enter a wind for a leg if it differs by more than 10kts or 10º of the previous entry.

 

I fly with some guys who like to enter the average wind and leave it at that. Not my preferred method, but if there is a difference it is subtle.

 

Yeah, the Embraer leads me to believe that it was a shorter flight and that the two would be similar enough not to matter (cruise average would be similar to T/C).

 

What concerns me about all of the video evidence of things is that people in simming rarely ever fact check.  How many times have we seen the 250/10 "rule" come up and people just repeat it because the last guy said it?

 

I'm not necessarily disagreeing with you, it's just nice to have a specific official reference from an FCOM or other manufacturer-specific source.

 

 

So if you are doing a short flight, let's say less than 500nm, entering the TOC wind as the CRZ wind on the PERF INIT page is sufficient.  However, if you are doing a longer sector, entering the average wind component would be the best approach? 

 

I recently flew KDEN-CYYZ in a B738,  I had to change altitudes several times due to CBs and winds variations. I updated the winds on the LEGs page to match the new winds aloft (based on AS2012 flight log) and my ETE was still off by about 20minutes.  Is that the correct procedure?

 

Thanks,

 

Kristof

[scandinavian13 5,192]

 

 

Is that the correct procedure?

 

According to Vagabondo (and his reference to the FCOM), the correct procedure is to enter the T/C wind in that position.  I, personally, always entered the average, assuming the FMC was using it for its cruise calculations.

[Vagabondo 23]

 

 

So if you are doing a short flight, let's say less than 500nm, entering the TOC wind as the CRZ wind on the PERF INIT page is sufficient. However, if you are doing a longer sector, entering the average wind component would be the best approach?

I would say that regardless of the trip length the ToC wind should be entered as the CRZ WIND in PERF INIT and the LEGS, RTE DATA pages updated with the forcast winds where the differ significantly from the ToC. Then the FMC can calculate the most efficient speeds for each leg with the most accurate ETA and arrival fuel.

 

If you were to enter an average wind in PERF INIT and leave it at that, I reckon the FMC would calculate speeds based on that wind, any significant difference in enroute wind from the forecast could affect all the predictions.

 

That's my opinion, but any overall loss or gain over a number of flights is probably immeasurable and would thus remain conjecture :(

[FirstOfficera320 1]

Hi,

 

This is what we use on the Airbus A320.

 

• at the first waypoint in cruise, insert wind DIR/VEL, and temperature at the initial CRZ FL.
• at next waypoint where wind differs by 30° or 30 kts and temperature by 5°.

This can be entered on the ground or in cruise (to keep you busy). Also before the flight check the DTG with the CFP.

 

Have a nice flight

[krisyyz 1]

I would say that regardless of the trip length the ToC wind should be entered as the CRZ WIND in PERF INIT and the LEGS, RTE DATA pages updated with the forcast winds where the differ significantly from the ToC. Then the FMC can calculate the most efficient speeds for each leg with the most accurate ETA and arrival fuel.

 

If you were to enter an average wind in PERF INIT and leave it at that, I reckon the FMC would calculate speeds based on that wind, any significant difference in enroute wind from the forecast could affect all the predictions.

 

That's my opinion, but any overall loss or gain over a number of flights is probably immeasurable and would thus remain conjecture :(

 

 

I actually watched some JustPlanes videos last night, the pilots did enter the ToC wind in the PERF INIT page.

 

Thanks for all the input everybody!

 

Kristof

[hopskip 253]

Because as we all know, there's no wind at FL350.

 

oh wait, Jetstreams happen at FL350 and can exceed 100kts wind speed.

 

S turns can be managed by turning off (clear air) turbulence effects. Clouds still make turbulence if you want to. Up/Down drafts can still work fine. Gusts are ok.

 

Wind Smoothing is good so you don't get 50+ knot changes in wind velocity in 1 second as you cross the 'border' between one weather reporting area and another.

 

Good weather = Weather program like ActiveSky with Winds aloft enabled and FSUICP smoothing the wind-shifts. FSX Turbulence effects disabled. (cloud turbulence effects dialled down a bit from maximum but still present).

[pcubine 143]

 

 

Good weather = Weather program like ActiveSky with Winds aloft enabled and FSUICP smoothing the wind-shifts. FSX Turbulence effects disabled. (cloud turbulence effects dialled down a bit from maximum but still present).

 

Trent

 

Look at the first post of this thread http://forum.avsim.net/topic/387061-activesky-2012-settings-what-i-am-using-now-with-ngx/. This works for me for the NGX, 744, and MD-11.

 

Michael Cubine