Ahmad et al. Figure 2. Blockchain for aircraft MRO operations and its health assessment. In the aviation industry, the manufacturer registers every manufactured component and spare part on the blockchain. The traceability of the timestamped transactions on the blockchain can be used by the MRO service providers to access the full operational history, aircraft components configuration, and spare parts provenance. The MRO service provider safeguards the aircraft against the accidents by providing scheduled and unscheduled maintenance services to aircraft components. The maintenance logbook on the blockchain ledger records the following: 1) identifier of malfunction component; 2) total repairing cost; 3) schedule for next repairing; 4) repairing date and time; 5) health condition of the repaired component; 6) estimate of life competency of the component. Blockchain-based smart contracts can assist MRO and aircraft operators to automate the scheduling of maintenance services of aircraft. The maintenance interval of MARCH 2021 aircraft components varies depending on the types of operations and their operating environment [9], [16], [19], [20]. Figure 2 presents smart contracts based operations flow among stakeholders in the aviation industry to provide MRO services to an aircraft. SECURING IDENTITY MANAGEMENT AND AIR TICKETING The centralized systems are insecure as the identity of an individual can be forged and used to perform fraudulent activities. Identity management refers to the technologies to identify, authenticate, and authorize entities to access certain services [9], [21]. The access requests of the entities are granted after a successful authentication check to transact on the blockchain. The immutability of records on the blockchain assures that the credentials about a registered entity cannot be tampered. Blockchain technology can tokenize the traditional electronic and paper-based ticketing to minimize the chances of tickets forging. The traceability of immutable tickets' sale and purchase records on the blockchain ledger IEEE A&E SYSTEMS MAGAZINE 7