NATIONAL HARBOR, Md.--The 13 F-35As grounded late Friday could be out months as the Air Force and prime contractor Lockheed Martin [LMT] work toward finding a solution, according to a key Air Force officer.Air Combat Command chief Gen. Herbert "Hawk" Carlisle told reporters Tuesday the peeling and crumbling insulation in avionics cooling lines inside fuel tanks that forced the grounding was not a design or development issue, but instead the result of a faulty product provided by a subcontractor. He…