An aircraft design is a time consuming and complicated process. The design is depending on many factors such as customer and manufacturer demand, safety protocols, physical and economic constraints etc. For some types of aircraft, the design process is regulated by national airworthiness authorities. Aircraft design is a compromise between many competing factors and constraints and accounts for existing designs and market requirements to produce the best aircraft. Generally, there are 4 goals in aircraft design process:
Safety is a key element which is everybody’s responsibility: the airlines, the aircraft manufacturers and the airworthiness authorities. The safety is governed by the airworthiness authorities via regulations (FAR/JAR/EASA, etc..), and directives giving instructions to the manufacturer for design, tests, inspection programs establishment and to the Airline for aircraft operation.
Long Service Life
The current generation of civil transport aircraft were designed for at least 20 to 25 years and up to 40 000 flight cycle. This is called Design Service Goal (DSG). DSG being the period during which the structure will be reasonably free of significant cracking. This does not mean that no damage will occur. In reality, damage can and will be incurred due to, for example, nvironmental or accidental reasons. In any case, a design for long service life means a compromise in between high performance and moderate maintenance
To be competitive the structure must be light enough. The gross weight limits are in fact contractual. Any increase of weight leads to a reduction of fuel (range) and/or payload. In order to meet the targets, optimizations are made by using the best available materials (giving the best compromises in between strength/density keeping in mind, of course, the other requirements such as corrosion resistance, fracture toughness, production costs, repairability, etc…
As far as possible, design choices made according to the 3 other parameters for maintainability:
– The access should be easy (inspections, repair…),
– Easy to inspect,
– Easy to repair (in terms of processes, materials, feasibility).
Even the most modern aircraft design gone through very detail and stringent process, it does not mean that the aircraft will be free from issue once it enters the service. Over the time, this aircraft need to be inspected and modified accordingly to maintain it’s performance and safety to the desired level. One of the requirement is to comply with Airworthiness Directives to maintain the aircraft through it’s service life. Click here: Airworthiness Directives if you want to read my post about it.
Ir. Edie Noreffendi
17 Feb 2013