Flight monitoring - in-flight replanning and fuel monitoring
Flight monitoring - in-flight replanning and fuel monitoring tests ongoing fuel and route checks. You must compare actual fuel with planned, identify trends early and replan before a reserve is breached.
Monitoring rules
- At each checkpoint compare fuel remaining with the OFP; fuel used alone is not enough.
- Calculate the deviation and trend, then project to destination and alternate.
- Minimum fuel means land as soon as practicable; emergency fuel means declare mayday.
- Replanning can change route, altitude, speed, alternate or destination; update fuel and ATC.
Worked example
At a checkpoint, planned remaining fuel is 5,000 kg and actual remaining is 4,600 kg, a 400 kg deviation. Required fuel to destination plus final reserve is 4,200 kg, so current margin is 400 kg. If the trend is 100 kg/h extra burn over 3 h, add 300 kg; margin falls to 100 kg. If the trend is 200 kg/h, projected shortfall is 200 kg, so divert or reduce burn now.
Traps
Comparing fuel used rather than fuel remaining hides a starting-fuel error. Do not spend final reserve during normal replanning. Average burn without trend can miss a developing leak or higher-than-forecast headwind. Do not delay a minimum-fuel declaration until the reserve is already gone.