An aircraft is a man made and like other human creation, it is not perfect . There could be a flaw on the aircraft system due to design, manufacturing or environmental factor. But if we want to compare with the the other mode of transportation, aviation is highly and heavily regulated industry and every problem will be taken seriously in order to maintain the safety of the aircraft on the acceptable level.
To maintain the safety level of an aircraft, one of the requirement for the operator or airline is to comply with Airworhiness Directive (AD). For definition, the AD is a notification to owners and operators that a known safety deficiency with a particular aircraft, engine, avionics or other system exists and it must be corrected.
If a certified aircraft has outstanding airworthiness directives that have not been complied with, the aircraft is not considered airworthy. Thus, it is mandatory for an aircraft operator to comply with an AD. The purpose of an AD is to notify aircraft owner:
– that the aircraft may have an unsafe condition, or
– that the aircraft may not be in conformity with its basis of certification or of other conditions that affect the aircraft’s airworthiness, or
– that there are mandatory actions that must be carried out to ensure continued safe operation, or
– that, in some urgent cases, the aircraft must not be flown until a corrective action plan is designed and carried out.
AD usually result from service difficulty reporting by operators or from the results of aircraft accident investigations. They are issued either by the national civil aviation authority of the country of aircraft manufacture or of aircraft registration. For example, most common ADs are issued by Federal Aviation Administration (FAA) for Boeing aircraft and European Aviation Safety Agency (EASA) for Airbust aircraft.
The corrective actions may include any of the following:
• Additional Inspection
• Modification / Design Change
• Replacement of Parts / Removal from service
• Change of operating limitations or procedures
For example, one of the recent AD that related to famous 787 aircraft problem is about lithium ion battery failures that resulted in release of heat damage, and smoke on airplanes. The FAA issued this AD to install main battery and auxiliary power unit (APU) battery enclosures and environmental control system (ECS) ducts; and replace the main battery, APU battery, and their
respective battery charger. This need to be done before further flight, that means the affected aircraft would not be able to fly if this action has not been done. See here for example of AD.
For those who are not familiar with AD, they may find that it is not easy to understand the AD because they are written in a form of legal document. But interpreting & understanding AD requirement is very important to ensure the aircraft safety is maintained.
Ir. Edie Fendie
24 Jan 2014