Science Fair Project Encyclopedia
A Type Certificate (sometimes called Airworthiness Certificate), is awarded by aviation regulating bodies (such as FAA in US and EASA in EU) to aerospace firms after it has been established that the particular design of aircraft, engines or propeller submitted has fulfilled the the regulating bodies' current prevailing airworthiness requirements for the safe conduct of flights under all normally conceivable conditions. Military types are exempted.
Initially, the applicant aerospace firm shall submit documents to the aviation regulating body (initially of the firms' home country) detailing how the proposed design would fulfill the airworthiness requirements. After investigations by the regulator, the final approval of such documents (after the required comments and amendments in order to fulfill the laws), becomes the basis of the certification. The firm follows it and draw a proposed timetable of actions required for certification tests.
An initial design sample known as a prototype is built. This refers to either the aircraft, engines or propeller, depending on the basis of the certification. For the purpose of illustration, the discussions shall be limited to aircraft. Normally a few prototypes are built, each subjected to different tests. The prototypes initially is submitted to ground and system tests. One of them (known as the 'static airframe') is subjected to destructive testing i.e. the prototype is subjected to stresses beyond normal and abnormal operations until destruction and readings taken and compared with initial submitted calculations to establish ultimate structural strenght.
Other prototypes will undergo other systems tests until the satisfaction of the regulators. With all ground tests completed, prototypes are readied 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 filght tests may cover the whole world. ETOPS testing may require tests over oceans or remote areas.
In tandem with aircraft testing, the applicant firm also draws up maintenance program to support continous 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 sucessful of completion of ground and flight tests along with an approved maintenance program, the prototype is approved, the firm is granted the type certificate 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 a template for aircraft production. Hence the aircraft rolling out of the factory should be identical to the prototype, and each given a serial number (a "series aircraft").
As the aircraft enters service, it is subjected to operational wear and tear which may cause performance degradations. The approved maintenance program serves to maintain the aircraft airworthiness. Users have to comply in order to maintain their aircraft's airworthiness certificate. The maintenance may be light or heavy (such as overhauls) as dictated by the schedules and tasks in the aircraft's maintenance program.
Sometimes during service the aircraft may encounter problems that may compromise the aircraft's safety which are not anticipated or detected in prototype testing stages. The aircraft design is thus compromised. The regulators will now issue an airworthiness directives to the type certificate holder and to all owners globally. The directives normally consists of additional maintenance or design actions that are necessary to restore the type's airworthiness. Compliance is mandatory. Airworthiness directives may also be raised with changes of the local or global aviation rules and requirements, e.g. requirement to fit armored cockpit doors for all airliners post 9-11.
With increasing in-service experience, the type certificate holder may find ways to improve the original design resulting in either lower maintenace costs or performance increases. These improvements (normally involving some alterations) are suggested through service bulletins to their customers as optional (and may be extra cost) items. The customers may excercise their discretion weather or not to incorporate the bulletins.
Changes to Type Certificate
Often the basic design is enhanced further by the type certificate holder. Major changes beyond the authority of the service bulletins, requires amendments of the type certificate. For example, increasing (or decreasing) its flight performance, range and load carrying capacity by altering its systems,fuselage, wings or engines; resulting in a new variant. Again the basic process of type certifications is repeated (including maintenance programs). However, unaltered items from the basic design need not be retested.Normally, one or two of the original prototype fleet is remanufactured to the new proposed design. As long as the new design does not deviate too much from the original, static airframes need not be built. The resultant new prototypes is again subjected to flight tests.
Upon successful completion of the certification program, the original type certificate is amended to include the new variant (normally denoted by a new model number additional to the original type designation). Typical examples are; the Boeing 737NG (737-600, 737-700, 737-800 and 737-900) which replaced the 737 Classic family (737-100, 737-200, 737-300, 737-400 and 747-500) and the Airbus A340-500 and the A340-600 which is based on the Airbus A340-200 and the A340-300.
Supplementary Type Certificate (STC)
Any additions, omissions or alterations to the aircraft's certified layout, built-in equipment, airframe and engines not initiated by the type certificate holder (i.e. third party), needs an approved supplementary type certificate. It could range from passenger cabin items up to major reengining and role change. STCs are applied due to either the type certificate holder's refusal (frequently due to economics) or its inability to meet some owners' requirements. STCs are frequently raised for out-of-production aircraft types conversions to fit new roles. Before STCs are issued, procedures similiar to type certificate changes for new variants are followed (may include flight tests if required). STCs belong to the STC holder and are generally more restrictive than type certificate changes.
Validity of Type Certificate
The type certificate holder keeps the type certificate valid by continiously following airworthiness directives, issuing service bulletins and as well as providing spares and technical support to keep the aircraft current with the prevailing rules. This is true even if the production of the type has stopped. This is what meant by supporting the type and in this manner many out-of-production aircraft continue useful lives. Typical examples are old Boeings, Airbuses, McDonell Douglases, Lockheeds, Fokkers, Dorniers and many others. STCs are also bound by the same rules. When the holder decides to stop supporting the aircraft type (due to many reasons mainly economics), the type certificate is returned to the regulators and the remaining aircraft fleet permanently grounded. In this manner the whole Concorde fleet was finally grounded when Airbus SAS surrendered its type certificate.
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