What happens when a manufacturer designs a new aircraft? How does an aircraft move from concept/design through to an accepted and authorized safe flying state? This article looks at the well-established aircraft certification process.
Certifying each new model for a ‘type certificate’
Any new aircraft designed by a manufacturer will need to be submitted to appropriate regulatory authorities for testing for a type certificate. In the US this is the FAA (Federal Aviation Administration), and in Europe EASA (European Aviation Safety Agency).
Test guidelines are published, and followed, by each regulator. For example, the FAA uses AC25-7D – “Flight Test Guide for Certification of Transport Category Airplanes.”
Interestingly, the concept of type certification began in the UK in 1919. The first regulations were published by the Secretary of State for Air, Winston Churchill, as the ‘Air Navigation Regulations.’
Expensive and lengthy testing
The process for this involves extensive testing – first in simulators based on aircraft design, then on the airframe structure, and finally in the air. This is a lengthy process and often very expensive. It forms a major part of the cost of development and often has a significant impact on the commercial success of the new model.
The certification process usually involves building several prototype models. These are often used just for testing and will never see active service with an airline.
To give an idea of this testing process, look at the figures quoted by Airbus for A380 and A350 testing. They quote that the 2006 certification of the A380 (by both the FAA and EASA) took 2,600 flight hours and a fleet of five test aircraft. The A350 underwent a 14-month testing program, again requiring five test aircraft.
Some of the main areas of testing include tests to the airframe and flights tested, summarised here.
Structural airframe tests
Before an aircraft even takes to the air, it is subjected to extensive structural tests. These stress the airframe and wings, in most cases significantly exceeding expected maximum loads that will be experienced in service.
Tests include wing loading and deflection, aileron and spoiler functionality during wing loading, fuselage pressure tests, fatigue tests, and flight cycle simulations.
These tests will push the airframe more than it will experience in service. For example, Airbus quote that during A380 testing 47,500 full flight cycles were made. This is 2.5 times the number of flights it would make in over 25 years of operation. These, of course, are not full flights, but instead, loads are repeatedly placed on the airframe to simulate flight.
Extensive flight tests
Flight tests are carried out to assess the aircraft’s general handling and performance, and also to test operations in extreme conditions.
This includes operations in extreme heat, cold and at altitude. For this, aircraft are often flown to other locations. Northern Canada, for example, is common for extreme cold weather tests, and the Middle East for hot weather tests. La Paz, Bolivia is often used for high altitude and Iceland for strong wind testing.
The various operational tests an aircraft must undergo include:
- Operation of aircraft systems, including autopilots.
- Water ingestion tests, to ensure water won’t enter aircraft systems.
- Flutter testing, where vibrations are measured to ensure they won’t cause structural damage.
- Low speed take off.
- Rejected takeoff (including testing at full aircraft load, with worn brakes).
- Assessment of the aircraft’s environmental footprint, including fuel burn.
Airworthiness certificate for produced aircraft
The type certificate confirms that the aircraft design is airworthy. Each produced aircraft then needs an airworthiness certificate, which will involve specific production and flight tests for each aircraft of that type. Only then is the aircraft ready to fly.
Ongoing operations and changes to type certificates
The issuing of a type certificate is just the beginning of the aircraft’s operation, and regulation. Regulators will monitor operations and issues, and issue additional airworthiness directives for any issues that may arise. These are issued to manufacturers and aircraft owners, and state actions that are required to restore the type’s airworthiness. The ongoing issues with the Boeing 737 MAX are just one example of this.
The type certificate can also be amended for changes to the aircraft model or variant. Examples include the 737-600, 737-700, 737-800, and 737-900 family. These changes require re-testing (often using a re-build of the prototype aircraft used for initial model testing). Unchanged areas do not usually need to be re-tested. Upon successful testing, the original type certificate is updated to include the new model variant.
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