The FAA recently mandated that many circuit breaker switches were defective and must be replaced within a certain amount of time. Problem #1-there were no circuit breaker switches available: Problem #2-the manufacturer of the aircraft was not going to pay for the switches replacement: Problem #3-problem #1 could be alleviated by a General Aviation Maintenance technician with an Inspection Authorization by filling out a lot of paperwork and submitting it to two divisions of the FAA: Problem #4-the owner of the aircraft had to pay for the technician's time to apply for the AMOC (Alternate Means of Compliance) compliance paperwork to allow the aircraft to continue to fly until the switches became available.
The FAA method of mandating compliance is through Airworthiness Directives (AD's). FAR 39 is the regulation that describes AD's (see http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=674341c1d150e72204d368fdd89db006&tpl=/ecfrbrowse/Title14/14cfr39_main_02.tpl) for the actual rule. The FAR is relatively simple in scope but the data that is associated with it is very extensive.
AD's are issued because a problem has been discovered in an aviation product that affects safety or airworthiness of that product. The product may be an aircraft, an engine, a propeller, an appliance or any part of these items. The circuit breaker switches in paragraph 1 of this blog were found to cause smoke in the cockpit of a few aircraft and after an investigation, there were many circuit breakers made the same way that possibly could cause the same problem. In order to prevent this from happening again, the FAA issued an Airworthiness Directive mandating replacement. Another recent example that was prominent in the news was the grounding of many airline aircraft until wiring was inspected and deemed to be airworthy.
General Aviation Maintenance technicians find many items affecting safety or airworthiness during their normal duties. If a technician feels that the item is not an isolated discrepancy, but is of a recurring nature, the FAA requests that this item is reported to them through a system know as Service Difficulty Reports (SDR's). The FAA builds a data base of SDR's, analyzes them and if necessary will issue an AD to mandate corrective action. An AD also may be issued from findings from an accident or from a Service Bulletin issued by the manufacturer of a product.
When performing certain maintenance on an aircraft, the general aviation maintenance technician will check for applicability or compliance with airworthiness directives. Something as simple as an oil change on an engine may be complicated by the requirements of an AD. One AD requires inspection of an oil filter adapter for looseness or leakage every time the oil filter is removed. Another AD requires inspection of the oil suction screen and servicing the engine with a special anti-scuff additive. Not complying with such simple AD's causes the technician and the aircraft owner/operator to be in violation of Federal Law.
Some AD's are as simple as changing an engine induction air filter every 500 hours time in service and some are as complicated as installing major structure to reinforce wing main spars.
AD's for aircraft, engines and propellers are usually relatively easy to research. The applicablilty section of the AD will list the model numbers and serial numbers of the affected products and the compliance section will describe what has to be done.
Appliance airworthiness directives give the general aviation maintenance technicians many problems. First-the aircraft must be inspected to determine if the affected product is installed; second-the product part number, model number, serial number and more recently the software version must be recorded; third-the aircraft records must be checked to see if the AD has been complied with on this product and if there are recurring compliance items due. General Aviation Aircraft maintenance records are not always kept up to date and this whole process can take quite a bit of time. Appliance items include such things as: circuit breakers, strobe light flashtubes; fire extinguishers; magnetos; ignition switches; combustion heaters; autopilots; tires; hoses; turbochargers; etc.
Airworthiness Directives are an efficient method of keeping the fleet safe to fly.