Aircraft Sealant

1 . A sealant comprising expanded polytetrafluoroethylene having a coating comprising an active hydraulic fluid repellent component and an indicator, said sealant having a first uncompressed state and a second compressed state, wherein said sealant is repellent to hydraulic fluid in both said first uncompressed state and said second compressed state.

2 . A sealant as defined in claim 1 wherein said active hydraulic fluid repellent component is polyperfluoromethacrylate.

3 . A sealant as defined in claim 1 wherein said indicator is a fluorescent indicator.

4 . A sealant as defined in claim 1 wherein said expanded polytetrafluoroethylene is imbibed with silicone.

5 . A sealant as defined in claim 1 wherein said sealant has surfaces and edges and all of said surfaces and edges are repellent to hydraulic fluid in both said first uncompressed state and said second compressed state.

6 . An apparatus comprising a first aircraft panel, a second aircraft panel joined to said first aircraft panel at a joint, and a sealant as defined in claim 1 disposed at said joint.

7 . A method of producing an aircraft sealant comprising the steps of providing an expanded polytetrafluoroethylene substrate, preparing a solution of polyperfluoromethacrylate in a solvent combined with a fluorescent indicator in a cosolvent different from said solvent, coating said substrate with said solution, and heat-drying said substrate and solution coating.

8 . A method as defined in claim 6 wherein said solvent is hydrofluoroether and said cosolvent is methylene chloride.

9 . A coating system comprising two organic solvents with differing polarity, an active component and an indicator adapted to provide homogeneous coating on nodes and fibrils of expanded PTFE.

10 . A coating system as described in claim 9 wherein said active component comprises a hydraulic fluid repellent and said indicator is a fluorescent indicator.