Fuel tank leaks are classified into four groups, slow seep, seeps, heavy seeps, and running leaks, as il-lustrated below.
Any of the above mentioned leaks occurring in. areas around integral wing fuel tanks are not regarded dangerous if fuel is not actually dripping from the tank structure, and leak area is adequately ventilated. In manly instances, adequate temporary leak repair methods will bring excessive leaks within limits established by the permissible leakage classifica-tion, and may be employed at line maintenance stations. Running leaks on the top skins of tank areas, which permit fuel to run under the wing-to-nacelle fillets and similar areas, must be temporarily or perma-nently repaired. Running leaks that have progressed to the drip point must be re-paired. The principle concern in the dripping leak from open areas of the bottom skin is loss of fuel on the ground, which con-stitutes a fire hazard.