FAQ
What does “Max extra fuel allowed” actually mean?
It’s the additional fuel you can load on top of your current plan without exceeding the most restrictive weight limit.
The tool compares three candidates:
A: MTOW − OW
B: MLW + Trip − OW
C: MTW − Taxi − OW
The smallest governs; subtracting the current payload (Pax × W + Cargo) yields the extra fuel you can carry.
Why is the number red / negative?
A negative value means you are already above a limiting weight.
To recover margin, reduce fuel (block/taxi), decrease payload (pax/cargo), or revise assumptions.
What do the “Limited by MTOW / MLW / MTW” tags mean?
They indicate which constraint currently governs the calculation:
• MTOW/RTOW — Maximum Take-off Weight / Regulated Take off Weight
• MLW/RLW — Maximum Landing Weight / Regulated Landing Weight
• MTW — Maximum Taxi Weight
What are OW, ZFW, TOF, and LOAD?
TOF = Block − Taxi
OW = OEW + TOF
LOAD = Pax × Pax-Weight + Cargo
ZFW = OEW + LOAD
Which weights should I enter in the Aircraft Profile?
Use your current operational limits:
OEW (APS), MZFW, MTOW/RTOW, MLW/RLW, MTW.
If regulated limits are lower than structural, enter the regulated values.
Can I edit the default aircraft constants?
Yes.
APS, MZFW, MTOW, MLW, and MTW are editable and persist per selected profile (737-800 or 737 - 8200, or CUSTOM).
The Reset button restores factory defaults for the active profile and clears operational inputs.
How does the 1% MLW protection work?
When enabled, MLW is reduced by 1% inside candidate B (MLW + Trip − OW).
This margin accounts for shortcuts or lower actual trip burn.
A separate protected New Block Fuel is shown.
It is strongly suggested to use a 1% protection.
What happens if I change Taxi fuel?
Taxi affects TOF = Block − Taxi.
Lower Taxi increases TOF and OW, potentially tightening MTOW/MTW margins and changing the governing tag.
Why is Pax weight set to 84 kg and how do I change it?
84 kg is the default per-pax assumption.
Tick allow change to enter a different average passenger weight that matches your operation or season.
Are the units fixed?
Yes.
Inputs and outputs are in kilograms (kg) and passengers (pax).
What does “New Block Fuel with MAX fuel allowed” show?
Your current Block plus the computed extra (which may be negative).
It is the Block value that places you right at the governing limit under current assumptions.
Will this tool update company or regulatory data automatically?
No.
It does not fetch or sync operational data. Always cross-check with your approved performance tools, W&B, SOPs, and current company documents.
Why do I see the red message “Trip fuel can't be > block”?
This appears when Trip fuel exceeds Block fuel.
The calculation is stopped, results show “—”, and you must correct the inputs before the tool can compute a valid top-up.
Why do I see “—” instead of a number in Max extra fuel or New Block Fuel?
There are two reasons:
• One or more required fields have not been entered yet (Block, Taxi, Trip, Pax).
• If 1% MLW protection is enabled, the unprotected values are intentionally hidden. Only the protected numbers are displayed in the dedicated rows.
What is the “Derived Weights” section for?
It shows the diagnostic data behind the calculation:
• Candidate limits A, B, C
• TOF, OW, LOAD, ZFW
It is optional and purely informational. The calculation works the same whether collapsed or expanded.
Is this tool an operational authority?
No.
It is for informational and educational use only. Company SOPs, manuals, and official communications always take precedence. Refer to the on-page disclaimer.