((a)) ** Procedure for revocation** In the event of repeated willful violations of any of the provisions of this chapter by the grantee, the Board may revoke the grant after four months’ notice to the grantee and affording it an opportunity to be heard. The testimony taken before the Board shall be reduced to writing and filed in the records of the Board together with the decision reached thereon.

((b)) ** Attendance of witnesses and production of evidence** In the conduct of any proceeding under this section for the revocation of a grant the Board may compel the attendance of witnesses and the giving of testimony and the production of documentary evidence, and for such purpose may invoke the aid of the district courts of the United States.

((c)) ** Nature of order of revocation; appeal** An order under the provisions of this section revoking the grant issued by the Board shall be final and conclusive, unless within ninety days after its service the grantee appeals to the court of appeals for the circuit in which the zone is located by filing with the clerk of said court a written petition praying that the order of the Board be set aside. Such order shall be stayed pending the disposition of appellate proceedings by the court. The clerk of the court in which such a petition is filed shall immediately cause a copy thereof to be delivered to the Board and it shall thereupon file in the court the record in the proceedings held before it under this section, as provided in . The testimony and evidence taken or submitted before the Board, duly certified and filed as a part of the record, shall be considered by the court as the evidence in the case.section 2112 of title 28