Fuel contamination: testing, drains & prevention
Fuel contamination = water or solid sediment in fuel.
- Water is the main contaminant.
- Water is heavier than fuel: settles at tank bottom.
Clear and bright test:
- Before every flight, drain a sample from the lowest point of the fuel system into a clear glass jar.
- Clear and bright (uncontaminated) fuel shows:
- No cloudiness.
- No water or sediment on bottom or sides.
- Visible brilliance and sparkle in light.
| Sample shows | Means |
|---|---|
| Cloudy or hazy | Usually suspended water; can be fine dirt |
| Clear layer separating at bottom | Water settled out |
- Water-finding paste also detects free water.
- Water suspected anywhere: keep draining and checking until proven clear.
- Lab analysis = only positive proof if doubt exists.
- Drain water before flight. Do not fly until proven clear (TC AIM AIR 1.3.2, 1.3.3).
Drains (both every flight):
| Drain | Notes | Cite |
|---|---|---|
| Strainer | - | TC AIM AIR 1.3.3; TP 1102 |
| Tank sumps | Water can remain in tank after strainer drain runs clean; only sump drains remove it | PHAK ch.7; TC AIM AIR 1.3.3; TP 1102 |
- Water in strainer sump: more in tanks probable. Drain tanks until none shows. Never take off until all water and contaminants removed (PHAK ch.7).
- Water can flow into carburetor and stop engine.
Causes of contamination accidents (PHAK ch.7):
- Inadequate preflight inspection
- Servicing from small tanks or drums
- Storing with partially filled tanks
- Lack of maintenance
Prevention:
- Avoid refuelling from cans and drums: drums often hold condensation and rust flakes (TP 1102).
- Fill tanks after each flight, or after day's last flight: stops tank condensation (PHAK ch.7).
Chamois skin: does not always decontaminate fuel.
| Chamois | Filters water? | Ref |
|---|---|---|
| Worn | No | PHAK ch.7 |
| New, water-wet or damp | No | PHAK ch.7 |
| Most imitation | No | PHAK ch.7 |
| Dry, genuine strainer | Resists water | TP 1102 |
Trap: cloudy fuel not always water, but fails clear-and-bright and must be investigated, never waved off as "probably fine." Worn, water-wet or imitation chamois does not filter water.
References
- TC AIM AIR 1.3.2
- TC AIM AIR 1.3.3
- PHAK ch.7
- TP 1102 Ch.3 Engine Handling