ATPL Theory

Routine Fuel Monitoring

Routine Fuel Monitoring (Student Pilot Version)

Why Fuel Monitoring Matters

Fuel planning before flight is only an estimate. Once airborne, it’s your job to check that the airplane is actually using fuel as expected and that you’ll land with safe reserves.

When to Check Fuel

  • Check fuel at each waypoint, or
  • If waypoints are far apart, check every 30 minutes
  • Long flights over water or remote areas need extra attention

Simple Fuel Checks

  1. Compare actual fuel remaining with what you planned

    • Small differences are normal
    • Big differences must be explained

  2. Leak check (basic):

    • Fuel remaining + fuel used ≈ fuel at start
    • This helps find leaks but does not guarantee safe reserves

Why Fuel Is Rarely Exact

Fuel predictions can be off because:

  • Weight changes (more or less passengers/baggage)
  • Lower cruise altitude than planned
  • Climb delays or restrictions
  • Stronger headwinds or weaker tailwinds

Small errors early can turn into big problems later if not noticed.

Finite vs Progressive Errors (Easy Way to Remember)

  • Finite errors happen once (e.g. heavier weight, climb delay) → Situation stabilizes after cruise
  • Progressive errors continue to get worse (e.g. strong headwind) → Fuel situation keeps degrading over time

Contingency Fuel

Extra fuel is carried to cover:

  • Wind errors
  • ATC delays
  • Small planning mistakes

It is not unlimited—keep monitoring.

Abnormal Configurations

Fuel burn increases greatly if:

  • Landing gear is down
  • Flaps, slats, or spoilers are extended
  • An engine is inoperative (multi-engine aircraft)

In these cases:

  • Fuel predictions may be unreliable
  • A diversion may be required

Important Rule

The airplane (or FMS) helps, but YOU are responsible for fuel monitoring and decisions.

Key Takeaway

Check fuel early, check it often, and act before it becomes critical.