Quality Assurance

Some of the issues that have come up in regards to aging aircraft is how they are maintained. Quality assurance personnel are responsible for making sure that maintenance cards are carried out in a timely and accurate manner to make sure the aircraft keeps it's airworthiness capabilities. Maintenance planning documents are prepared by the manufacturer, can be customized by the operator, and reviewed by the regulatory authority. The manufacturer is also responsible for determining an ultimate life to assigned to their aircraft or engine model in order to ensure that the aircraft or engine does not exceed limits and becomes a hazard.

Airframe life is important to determine because there is constant stress being applied to the airframe as it pressurizes and depressurizes during a single cycle. Think of the airframe as a rubber band, under continued stretching and release eventually the elasticity weakens and the rubber band breaks. This is the same as what can happen to an airframe as the elasticity of the metal is weakened and eventually becomes brittle and breaks. Under the same rules it's important that when the aircraft is part of a fleet that it is used on a regular basis because exposure to the elements and constant sitting also reduces the properties of the metal.

Most other parts of a particular aircraft have life limits much like that of the airframe. Once a life limit is reached the part must no longer be used. This is true for landing gear and engines. In general for landing gear there is a list of limited parts with an expected life span in cycles and months. For engines the expected life span is expressed in flight cycles or flight hours depending on the part. The manufacturer is responsible for determining these life limits. Keep in mind that when a new engine model is created the life limit may be far lower than the expected ultimate life. Engines are generally utilized differently per airframe model that it is attached to and how the operator uses the aircraft. Aloha air utilized their 737's as "puddle jumper" airplanes and increased the stress put on the engines by using shorter flight hours and more cycles per flight hour. This is different then Alaska air who may be running an engine with one flight cycle per every 4 flight hours.

It is quality assurances responsibility to ensure that the life limits for all parts on the airplane are not exceeded. You wouldn't want an engine coming apart because of a life limited part that has exceeded its recommended life just as you wouldn't want to open a life jacket and realize that the material is degraded because it has exceeded it's expected life as well. Operators have a way to track and monitor this information and do so on a regular basis to ensure that the aircraft is safe for flight. It is quality assurances responsibility to ensure that the maintenance on all components of an aircraft is completed. Aged aircraft just tend to have more frequent maintenance tasks that have to be performed.