737NG PERF INIT page: CRZ WND?

[NGjockey]

To all the 737NG pilots:

Which wind should be programmed into the FMC PERF INIT page during pre-flight? The average wind along the total route, or the wind at the TOC?

That entry has a direct effect on the CLB speed calculation (punch in some trial winds on the ground and see how the calculated climb speed changes with different winds. The climb speed range on the 800 goes from 275 to 315 KIAS I believe), so I would guess that it also has an impact on the fuel consumption. The average wind along the route may differ significantly from the TOC wind though, so which one should it be?

According to Mr. Bulfer it's the TOC wind, but some (or many?) operators use the average wind.

I appreciate your inputs!

[eagerbeaver1]

Put TOC in then update via legs page for waypoints further along route.

[alexban]

According to FCOM 2, FMC preflight, that entry is for forecast cruise wind and optimises FCM calculations.
On the CL old manuals ( big,white ones - 07/94 pg 19.50.10) it says :
Cruise wind line: Entry of forecast true wind a top-of-climb helps optimize the FMC computation. If no entry is made, the FMC assumes 000/000.

The specification top-of climb went lost on the new books,hence the confusion.


we'll let the Boeing guys learn about this, and hopefully we'll have the corrected version asap.
bgds Alex

[Becker Junior]

I use the average cruise wind. I check the average cruise wind component at SITA flight plan, then in the legs page, I check the average heading and insert this heading (for head winds or 180 of this for tails) with the SITA component.

[justintime5]

Well as it's used to calculate the climb speed the best wind to use is the TC wind as it's the closest thing you have to the experienced wind during climb. If you put average cruise wind of a 2 hour flight you might find that the climb wind was a tail wind of 60Kts and have an average cruise wind of +30. The climb will be totaly wrong.

If in your flight plan you can find an average climb wind then use that.
On the cruise wind in the LEGS page use the flight plan winds.

[NGjockey]

@ alexban:

That's what I thought: If that wind in the PERF INIT page was named "TOC WND" instead of "CRZ WND" everything would make perfect sense to me. As was already mentioned here before, the wind at the TOC can sometimes differ significantely from the average wind, but from the information I have on this topic all that this insertion does is change the climb speed - the FMC wants to get the airplane up into a tailwind as quickly as possible and stay out of a headwind as long as possible in order to improve economy, depending on the cost index. That's also the only information on this specific question in Bill Bulfers FMC manual.

In fact, is there something like a FMC manual written by Boeing?

[737ngpilot]

I know on our property we use the average cruise wind, but as been pointed out, TOC wind would be more accurate, then update the wind on the legs page till TOD

[iflytb20]

As per our SOP, we enter the average wind in the CRZ WIND column and enter the actual winds for each Waypoint in the LEGS page.
The climb speed change is not much of a factor as our SOP speed schedule is ECON/300 whichever comes early

[justintime5]

I have been doing some reserch on this and back with some info from Boeing.

I have been told to understand this as a double use data imput. The design of these FMCs where done long ago and had to use as little steps as possible and have the least computation processes as possible. Since then we have been stuck with some design limitations but are solved in new models like B787.
In the early days where flights of the 737 where not that long and in the 757 and 767 wind predictions not that good a fast way to introduce a wind imput to the FMC was to insert an average wind in all the points of the route and this was the option. Climbs speeds at first would not vary at all and would not consider wind and only do so for CRZ and DES when using CI.
When oil price was no joke and companies staring to say that climb speed should be optimised climb speeds (about 200Kg savings possible) they started to take average wind and was almost right for short flights and basically an easy way to answer the clients needs.

Having powerfull CFP programs and very accurate winds the best option is to insert all CRZ and DES winds in LEGS and DES/FORCAST but renders the CRZ WIND usless for those phases. The idea now is to try and get a average climb wind from CFP and inster this ins CRZ WIND.

This is a thing we are trying with automatic wind loads via ACARS. The data input we will insert for that data field is going to be average climd wind. (hopefully)

What I do tell everyone is that inserting ALL your winds is very important. Many people don't insert DES winds and even though we all know that the recent VNAV updates are .... CRAP we have been doing trials and have found that a more accurate TOD point due to DES wind info being inserted can save an average of 50 - 100Kg. That is a lot of fuel ant the end of he day for a 300 fligh per day company. About 1.2 million €/year.
Good motivated and trainned crews can save easily 5 million €/year with precise fuel saving policies. That is what CEO and other narrow minded managers don't easilly understand.

Hope to not have said too many stupid things.

[framer]

Justin Time,
How has this worked out for your company?
My company uses the TOC wind but loking at our flight plans that is often quite a bit different from the average climb wind.
I'm interested to know if your company went through with inserting the average climb wind and what difference t made.
Framer

[Virtual738]

never mind.