submitted calculations to establish the ultimate structural strength. Other prototypes will undergo other systems tests until the satisfaction of the regulators. With all ground tests completed, prototypes are made ready for flight tests. The flight tests are flown by specially approved flight test pilots who will fly the prototypes to establish the ultimate flight limits which should be within the airworthiness rules. If a long range airliner is tested, the flight tests may cover the whole world. Tests may also cover different environments - high and low altitude, freezing and hot climates, and so on, to confirm correct performance throughout the aircraft's design envelope. In parallel with aircraft testing, the applicant firm also draws up maintenance program to support continuous airworthiness after approval of the design. The program is drawn with inputs from tests results and also from initial customers' engineering departments. The proposed maintenance program is submitted to the regulators for comment and approval. After successful completion of ground and flight tests, along with an approved maintenance program, the prototype is approved, and the firm is granted the TC for the prototype (as understood that it should include all furnished equipment for its intended role). The legal term for the firm is now the "type certificate holder". Subsequently, the prototype now serves as a template for serial aircraft production and the aircraft rolling out of the factory should be identical to the prototype within the frames outlined in a TC data sheet, and each given a serial number (a "series aircraft"). Continuing airworthiness Aircraft maintenance As the aircraft enters into service, it is subject to operational wear and tear which may cause performance degradations. The set of processes by which an aircraft, engine, propeller or part complies with the applicable airworthiness requirements and remains in a condition for safe operation throughout its operating life called continuing airworthiness. A maintenance program is issued by the aircraft operator and approved by the regulatory authority of the state of registry to maintain the airworthiness of the aircraft of the type owned by the operator. Maintenance tasks outlined in the maintenance program have to be scheduled and timely accomplished in order for the airworthiness certificate of their aircraft to remain valid. Other continuing airworthiness activities include additional tasks associated with the maintenance program and design changes to be accomplished via: Airworthiness directives (ADs) Service bulletins (SBs) Airworthiness directives Sometimes during service, the aircraft