FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationMedium
A line technician draws a fuel sample from the aircraft's fuel strainer sump and adds a chemical water-detecting capsule to the sample. The capsule immediately changes color, confirming the presence of water in the fuel. What should the technician do next?
- AAdd fuel system icing inhibitor (FSII) to the tank and release the aircraft for flight
- BContinue draining fuel from the sumps and rechecking samples until no water or contamination is detected
- CAdd a small amount of isopropyl alcohol directly to the fuel tank to disperse the water
- DDisregard the result since a color change is a normal indication for all aviation fuels
Show answer & explanationAnswer & explanation
Correct answer: B. Continue draining fuel from the sumps and rechecking samples until no water or contamination is detected
When water is detected in a fuel sample, the technician must continue sumping the tanks and strainer, rechecking each sample, until clean, uncontaminated fuel is obtained before the aircraft is considered airworthy for fueling release. Simply adding chemicals or ignoring the result does not remove existing contamination.
Why the other options are wrong
- A. FSII is added by the fuel supplier before fueling, not as a remedy for water already found in a sample.
- C. Adding alcohol to disperse water in the tank is not an approved corrective procedure for contamination found during preflight.
- D. A color change indicates contamination and should never be disregarded.
Fuel Water Contamination Check
A preflight/maintenance check using sumping and chemical water-detecting capsules or paste to verify fuel is free of water and sediment before flight.
- Water settles at low points due to higher density than fuel
- Chemical capsules/paste change color when water is present
- Draining continues until samples are clean
Memory trick: Color change = 'red flag' — keep draining until the sample runs clean.