Definition
A flexible, fuel-resistant compound applied to the inside seams and joints of an aircraft fuel tank to prevent leaks. In integral fuel tanks (where part of the wing or fuselage structure itself forms the tank), the sealant is what actually keeps fuel from seeping through rivet lines, panel joints, and access ports. Over time, sealant can age, crack, or shrink, leading to fuel weeps and stains on the underside of the wing.
Plain English
A rubbery sealing compound smeared inside the fuel tank to stop fuel leaking out through joints and seams. When it gets old or damaged, fuel can start seeping through and leave stains on the wing.
Context Anchor
Seen in fuel system discussions, aircraft maintenance records, and during preflight when checking for fuel stains, fuel odor, or signs of leakage around a tank area.
Why Pilots Care
Unsealed tanks can leak fuel, creating fire risk, reducing range, or causing engine failure; proper sealant application is essential for airworthiness.
Analogy
It is somewhat like caulk around a bathtub, but made for aircraft fuel tanks and fuel exposure instead of household water.
Intuition Check
Do not think of tank sealant as ordinary glue or a quick patch. In aviation, it means an approved fuel-resistant material used to seal parts of the aircraft fuel tank system.
Example Sentence 1
During preflight, the pilot noticed a blue stain running aft from a wing seam and suspected the tank sealant was beginning to fail.
Example Sentence 2
During the annual inspection, the IA checked the condition of the tank sealant around the fuel sender units for signs of cracking or fuel seepage.