Customs duty exemption for airport navigational and communication equipment imports, subject to DGCA certification for modernization. Limits customs treatment for navigational, communication, air traffic control and landing equipment imported for airport modernisation by capping basic customs duty at 25% ad valorem and exempting such goods from the additional duty under section 3 of the Customs Tariff Act, subject to a clearance stage certificate from the Director General of Civil Aviation confirming requirement for modernisation and recommending the exemption.