THE AIRLINE PILOTS FORUM & RESOURCE

Takeoff Weight and Speeds

by K.Haroon: Last Updated on 24th December 2006

B737-300 Takeoff Performance and Calculations

This article covers the following:

1. Normal Take-Off Data Card Preparation

   1. Normal Take-Off

   2. Reduced Power Take-Off

   3. Improved Climb Take-Off

2. Anti-Skid Inoperative Take-Off

3. Slush / Standing Water Take-Off

4. Software for Automatic Calculations

1) NORMAL TAKE-OFF DATA CARD: Carry out the following steps ...

• Obtain the Maximum Allowable TOGW from Airport Analysis Chart

• For weight adjustments and corrections refer to the following tables:

  
  

  Falps 05	QNH Correction for each mb difference		PACK Correction REDUCE (Kg)
  	Above 1013 ADD (Kg)	Below 1013 REDUCE (Kg)
  Climb Limit	25	65	1300
  Field Length / Obstacle Limit	25	100	500
  Improved Climb Limit	25	90	---

  
  

  Falps 15	QNH Correction for each mb difference		PACK Correction REDUCE (Kg)
  	Above 1013 ADD (Kg)	Below 1013 REDUCE (Kg)
  Climb Limit	30	65	1300
  Field Length / Obstacle Limit	25	100	500
  Improved Climb Limit	25	80	---

  
  

• PMC Correction if any from FCOM PI 14.1

• Note down the Maximum Allowable TOGW Limit after applying the above corrections

• Compare the Actual Trim weight with Max TOGW calculated:

  1. If actual trim weight is equal to Max TOGW calculated, then carry out a Normal Take-off.

  2. If actual trim weight is less than the Max TOGW calculated, then carry out a Reduced Power Take-off.

  3. If actual trim weight is greater than the Max TOGW calculated, then carry out an Improved Climb Take-off.

a) Normal Take-Off:

• Obtain Normal N1 from FCOM PI 10.12 or PMC INOP N1 from FCOM PI 14.2

• Obtain Go Around N1 from FCOM PI 10.16

• Obtain V1, VR, V2 based on the Actual Trim weight (FCOM PI 10.1)

b) Reduced Power Take-Off:

• No reduced power take-off under the following conditions:

  - Contaminated runway (water, ice snow, slush)
  - In wind shear
  - If Anti-Skid is inoperative
  - Dont use assumed temperature reduced thrust with PMC OFF

• Apply Reverse Corrections to the Actual Trim Weight

  1. QNH Correction: Add if Subtracted earlier or Subtract if Added earlier

  2. Pack Correction: Add if Subtracted earlier

• Obtain Assumed Temperature from Airport Analyses Chart by selecting the Temperature against the Corrected Weight

• Obtain Reduced N1 from FCOM PI 10.13 and Go Around N1 from FCOM PI 10.16

• Obtain V1, VR, V2 based on the Actual Trim weight ( FCOM PI 10.1 )

c) Improved Climb Take-Off:

• No Improved Climb take-off under the following conditions:

  - If limited by field length
  - Slippery or contaminated runway (water, ice snow, slush)
  - If Anti-Skid is inoperative

• Take-Off will be with Packs on APU, so Pack correction not required

• If the Actual Trim weight is within the QNH corrected Climb Limit weight then obtain V speeds and N1 as for a normal take-off

• If the Actual Trim weight is more than the QNH corrected Climb Limit weight and less than the QNH corrected Improved Climb Limit weight, then go for Improved Climb Take-Off

• Obtain Normal N1 from FCOM PI 10.12 and Go Around N1 from FCOM PI 10.16

• For calculation of V Speeds, carry out the following steps:

  1. Calculate the difference between the Improved Climb Limit weight and the Climb Limit Weight. Call it (W)

  2. Calculte the difference between V Speeds of Improved Climb Limit weight and the Climb Limit Weight. Call it (V)

  3. Calculte the value of V speeds against one ton of weight and call it (Vt) e.g: If the difference between the weight limits (W) is 1800 Kg (i.e. 1800/1000 = 1.8 tons) and difference between the V speeds (V) is 10 knots, then value of a V speed per ton (Vt) would be V/W (i.e. 10/1.8 = 5.5)

  4. Calculate the difference between the Climb Limit Weight and the actual takeoff weight. Call it (A). This is the weight which is above the limit e.g. assume it to be 3000 Kg i.e. 3 tons

  5. Apply the correction per ton above the Climb Limit Weight. If you are 3 tons above your limit (i.e. A=3 tons, step 4) and value of V speed per ton is 5.5 (i.e. Vt=5.5, step 3) then the Final V Speed Value (call it Vf) to be added to the Climb Limit V speeds would be A x Vt i.e. Vf will be 3 x 5.5 = 16.5

  6. Add 16.5 (calculated from step 5) to Climb Limit V1, VR and V2 for obtaining the Improved Climb V1, VR and V2 speeds

Note: According to a PIA bulletin, Takeoff Gross Weight Analysis holds good if QNH for departure field is 1013 mb. If QNH is other than ISA then Climb Limit speeds for corrected weight should be obtained from FCOM.

2) ANTI-SKID INOPERATIVE TAKE-OFF:

Considerations:

• No wet or contaminated surface take-off

• No high elevation take-offs (like Skardu)

• Both Thrust Reversers have to be serviceable

• Full power take-off

• No Improved Climb techniques

Weight Adjustment for take-off:

1. Reduce the QNH/Pack corrected field length/obstacle limited weight by 7000 Kg (FCOM PI 16.4) to get the limit weight

   Note: Apply pack correction only when not restricted by payload.

   
   

2. Check other weight limitations to select the minimum weight for take-off:

   1. Climb limited weight [QNH/Pack corrected]

   2. Landing limited weight [max landing weight 51709 + trip fuel]

   3. Zero fuel limited weight [max zero fuel weight 48307 + (block-taxi fuel)]

   4. Allowable Landing Field Length Limit weight (Vol.3 FPPM, 1.3.5 or relevant)

N1 Values:

• Obtain Take-Off N1 from FCOM PI 10.12 and Go Around N1 from FCOM PI 10.16

V Speeds:

• Obtain V1 (from FCOM PI 10.1) based on "Corrected Field Length Limit Weight" (Step 1 of Weight Adjustment above)

• Adjust this V1, from Anti-skid Inoperative V1 adjustment chart (FCOM PI 16.4)

• Obtain V1, VR and V2 based on Trim weight from FCOM PI 10.1

• Final V1 will be the minimum of the two obtained above

• If V1 is less than VMCG then set V1=VMCG if dry Accelerate Stop Distance (adjusted for wind and slope) exceeds 7900 feet

3) SLUSH / STANDING WATER TAKE-OFF:

Considerations:

• Full Power take-off

• Power on brakes 70% N1 for 30 seconds

• Thrust Reversers Available

• Select the longest runway for take-off

Weight Adjustment for take-off:

1. Adjust field length/obstacle limited weight from FCOM PI 10.5 and apply QNH correction

2. Check other weight limitations to select the minimum weight for take-off:

   1. VMCG limited weight from FCOM PI 10.5

   2. Climb limited weight [QNH corrected]

   3. Landing limited weight [max landing weight 51709 + trip fuel]

   4. Zero fuel limited weight [max zero fuel weight 48307 + (block-taxi fuel)]

N1 Values:

• Obtain Take-Off N1 from FCOM PI 10.12 and Go Around N1 from FCOM PI 10.16

V Speeds:

• Obtain V1, VR and V2 from the Actual Trim weight

• Adjust V1 from FCOM PI 10.6

4) SOFTWARE for AUTOMATIC CALCULATIONS:

This software, made in Microsoft Excell, helps in preparing the take-off data card. It calculates the maximum takeoff weght, weight limits for a normal take-off, reduced power take-off, V speeds incase of an improved climb take-off, antiskid inoperative calculations and calculations for takeoff on a wet runway.

This software (as an excell file optimized for Galaxy Tab 10.1) can be used in the cockpit for reducing the mathematical workload and errors. However please note that This is Not a Certified Software and I have developed it for my personal use and convenience.

Click Here to Download

Incase you encounter a problem in downloading. Right click on the above link and select "Save Target As"

Was this document helpful? Click here to Answer!

---

Disclaimer: "B737-300 Takeoff Performance and Calculations" are personal notes of the author that do not sanction any pilot to violate his Company's Standard Operating Procedures, Aircraft Manuals or Manufacturer's Recommendations.