ATM procedure, the choice of the V speeds

[cmcjma]

I shall appreciate any comments on this, regarding the way to use Boeing Runway Takeoff analysis.
Sorry, it is a bit long…

In order to get the V speed for takeoff, the Boeing Runway Takeoff analysis says:
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Follow steps 1-7

1. Obtain TOW (Take-off Weight) for OAT (Outside Air Temperature) wind component, flap setting and % MAC if other than standard, using the wet or dry runway take-off data (TPC) from RTOLW B 737. This weight will be determined by the most limiting of the climb, obstacle, runway, tire or brake energy limit weight. Interpolate between temperatures and winds if required.

2. If required calculated corrections for QNH pressure, anti ice and winds if required. The sum of the total corrections will be either a positive or negative total correction, i.e. a total correction that will need to be added or subtracted in the performance calculations.

3. Add or subtract the sum of the total correction obtained in step 2 to the TOW for OAT obtained in step 1 to obtained a regulated TOW. The regulated TOW obtained must not be higher than the maximum structural take-off weight; if this is the case then the regulated TOW is the maximum structural take-off weight of the particular aircraft.

4. Obtain actual TOW from load sheet and if it is at or below the regulated TOW obtained in step 3 an assumed temperature reduced thrust take-off may be considered.

5. Reverse the sum of the total corrections obtained in step 2 and apply this figure to the actual TOW obtained in step 4 to generate an Assumed TOW. If the total correction calculated in step 2 was negative (-), you would now add this correction to Actual TOW, if the total correction was positive (+) you would subtract the correction from the Actual TOW. If no corrections are required in step 2 Assumed TOW will equal the Actual TOW for the purpose of calculating the maximum Assumed Temperature and you would use the Actual TOW to calculate the maximum Assumed Temperature.

6. Enter the TPC with the Assumed TOW or Actual TOW to find the maximum temperature at which this weight becomes limiting. This temperature is the maximum ‘Assumed Temperature’ that can be considered for use.

7. Enter TPC with the Actual TOW to determine V speeds.
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Up to these last days, this procedure was quite clear for me. Very recently, some pilots explained to me during the step 6 above, the assume temperature chosen is the lowest of Maximum climb limit weight AND the Maximum takeoff weight (limited for whatever), usually the climb weight when the weights may be different.

But the V speed chosen are always those related to the Maximum takeoff weight (not the climb weight) even though the temperature is related to the climb weight.


I think there are different interpretations.

The step 1 clearly mention the most limiting weight between Climb and Takeoff. But the step 6 does not mention we have again to choose between Climb and Takeoff… Thus for me no need to select le lowest of the 2 in step 6…

Any comment is welcome.
Thank you in advance

[de facto]

Hi there,

I didnt read all your explanation but im pretty sure what is your issue here,you need to know 2 facts:

1)To find your ASSUMED TEMP:you need to ADD all the regulated perf to your ACTUAL takeoff weight.(IE actual take off weight is 63T,add QNH correction(90kgs/mb BELOW standard),add anti ice weight restriction if required(300kgs) etc to get your REGULATED TAKEOFF WEIGHT.(this regulated weight must be below your max structural take off weight,climb and runway weight limited weights).

With this weight you will first look in the CLIMB column where the CLIMB weight is equal or more to your REGULATED MASS.
Then you move to the right and see if your Regulated Take off Mass is less than the RUNWAY LIMITED MASS(BRAKES,Runway lengh....),
If your Regulated take off mass is less than both columns(Climb,Runway)then you can use the Associated Assumed temp and the Vspeeds associated with it.

2)If you are not allowed to use Assumed(strong crosswind,windshear,contaminated...) then you need to check for the ACTUAL OAT,your Actual Mass is less than both climb and runway limited weights(these weights must be DECREASED by the QNH/Anti ice restrictions).
If your ACTUAL MASS is less than those, you are therefore not limited and you can use the speeds on the FCOM,CDU to get your VSPEEDS.
V1 will be balanced field V1,so that your accelerate distance will be the same as your stop distance.
You can have an idea of how much runway will remain in case of a VEF reject at V1 by knowing by how much your Actual mass is below the Runway limit weight for the actual OAT.

Hope that helps,

[cmcjma]

De facto,
Sorry, but you do not bring an answer to my question.

The points 1 to 7 are a copy and paste of the Boeing manual part.

My question is at the end of the post.

Thank you

[de facto]

Pretty sure i did...
If u use assum,use the speeds in tje runway limited column as long as your assum cirrect take off weight is below the climb and runway limit.
No assum,use speeds for Actual takeoff weight.