krisyyz
Topic Author
Posts: 1271
Joined: Thu Nov 25, 2004 11:04 pm

Cruise Wind Vs. ToC Wind In CDU

Tue May 28, 2013 1:34 am

Hello,

The 737's PERF INIT page calls for a CRZ WND entry, do most airlines use the average wind component or the top-of-climb wind?

Would a pilot ever leave the CRZ WND section blank and manually enter the winds for each waypoint on the legs page instead?

Thanks,

KrisYYZ
 
Woodreau
Posts: 1334
Joined: Mon Sep 24, 2001 6:44 am

RE: Cruise Wind Vs. ToC Wind In CDU

Tue May 28, 2013 3:49 am

I'm not sure about the 737, but in my aircraft if you enter leg winds, it overrides what you enter in crz winds. When you enter the crz wind it populates that wind info in each leg of the cruise portion of the flight plan.

It's just an entry to help the FMS determine ETAs and compute vnav climbs and descents. It uses a blended solution for winds. At your current location it uses actual winds and as you get further down the flight plan it weights the leg winds/ crz winds more heavily.

A few pilots put in leg winds for each leg, but most pilots I fly with just put in the crz winds and I just choose the strongest headwind or the lightest tailwind that I can find on the flight plan to make the FMS give me the worst case performance.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
CosmicCruiser
Posts: 2055
Joined: Tue Feb 22, 2005 3:01 am

RE: Cruise Wind Vs. ToC Wind In CDU

Tue May 28, 2013 1:55 pm

The FMS I flew required the headwind wind/tail wind component to be inited but then we would up load the forecast winds for about 4 or 5 altitudes on longer flights to add more accuracy . There would be no reason to just leave it blank, it won't hurt anything. If you add the forecast winds manually or uploaded that will override the cruise component. I believe I remember correctly that the FMS is also looking at actual winds as well.
 
User avatar
glen
Posts: 296
Joined: Thu Jun 30, 2005 4:43 pm

RE: Cruise Wind Vs. ToC Wind In CDU

Tue May 28, 2013 4:08 pm

On short haul (A320) flights we are/were usually happy with the average head- or tailwind component which we entered at FMS initialization.

On longhaul flights this gives you a good estimate for the ETA at the beginning of the flight, but not for enroute estimates. Once you pass zones with different wind components, the ETA becomes unreliable as well. In order to have better enroute estimates as well as a reliable ETA, we were entering average wind for legs - each about one hour length (MD11, A330/340).
A few years ago we started entering wind data for all enroute waypoints with a considerable change in wind direction and/or speed at four different levels. This enables the FMS to calculate a optimum level not only depending on weight but also on different wind at different levels. This helped to save fuel by flying more on optimum levels but was quite a bunch of data which had to be entered.

Quoting CosmicCruiser (Reply 2):
but then we would up load the forecast winds for about 4 or 5 altitudes on longer flights to add more accuracy

Luckily we have this feature now as well.
"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
 
CosmicCruiser
Posts: 2055
Joined: Tue Feb 22, 2005 3:01 am

RE: Cruise Wind Vs. ToC Wind In CDU

Tue May 28, 2013 10:26 pm

Quoting glen (Reply 3):
Luckily we have this feature now as well.

Yeah, amazing how much faster it is!!

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