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Airworthiness Directives


Anyone who operates an aircraft should be familiar with the importance of government issued Airworthiness Directives, commonly referred to as AD’s (sometimes still referred to as AWD’s). These technical documents are issued by the originating country of the product type design and then forwarded to the current country of registration for that product. In Canada, we mostly see aircraft which have been type certified and manufactured in the United States and will therefore see AD’s originating from the FAA (Federal Aviation Administration). This includes, but are certainly not limited to, aircraft manufacturers like Cessna, Beechcraft, Piper and Cirrus. We are also familiar with the widely used Lycoming and Continental engines, McCauley and Hartzell propellers and several other components or miscellaneous items. The current country of registration, such as Canada, may also issue an AD against any aircraft which is registered here regardless of where it came from based upon their review of the latest safety data. Some Canadian manufacturers include Pratt and Whitney, Bombardier and Diamond Aircraft. Transport Canada would forward their AD’s to other foreign registered operators.

The purpose of an AD is to notify aircraft owners/operators of specific unsafe conditions affecting the continued airworthiness requirements for the aircraft. The context of the AD prescribes the mandatory action required for the continued safe operation of the aeronautical product (pertaining to either the airframe, engine, propeller or appliance). AD’s are often issued based upon an elevated concern for an existing condition which may have already been addressed by a manufacturer Service Bulletin. This escalated action prioritizes the condition from being a general concern to being more of a threat to continued airworthiness. In other cases, an AD may be issued as more of an immediate response to a new discovery yet subject to the same importance as a previously documented issue. Either way, the AD is essential to continuing Airworthiness by being presented as a Directive. Hence the name.

A common example of a Canadian issued AD applicable to aircraft operating in Canada is the CF90-03R2 Exhaust type cabin heat inspection which requires that all aircraft directing residual muffler heat as a source for cabin heat to be inspected at prescribed intervals. An undetected cracked muffler condition could permit carbon monoxide poisoning from the actual exhaust gases entering the cabin heat system. This AD identifies both an hourly and a calendar time requirement for the performance of this critical inspection (Each 150 hours or 12 months). These inspections must be done within the prescribed intervals otherwise the aircraft will no longer be in compliance with its airworthiness requirements whenever these intervals have been exceeded. The inspection itself must also be performed in accordance with the technical criteria listed in the AD in order to be considered in compliance with the AD. The aircraft exhaust system is already subject to a thorough inspection according to the approved check sheets but this does not effectively meet the requirements of the AD unless the AD criteria has also been specifically carried out as part of this routine inspection.

The nature of an AD may pertain to anything of serious concern ranging from design defects, bogus parts and unapproved field work to compromised processes or procedures. The issuance of an AD has been the most efficient means used to communicate with owners/operators that a potentially unsafe condition may already exist or is likely to develop on similar products to the one(s) already identified in their preliminary analysis. The referenced condition may be limited to a narrow serial range or remain inclusive to all models of a specific type of product. The actions determined to be necessary as described in the text of the AD may require immediate action before the next flight or simply require action within a pre-determined amount of operating hours and/or calendar time. Airworthiness Directives deemed to be of the utmost importance will be prioritized as an Emergency or Urgent AD. See Standard 593 Appendix A for more information on Canadian AD formatting.

Once the AD has been drafted and approved for distribution, it is sent to all registered owners of the affected product as well as to all Approved Maintenance Organizations (AMO’s). The information is also made available on applicable online databases and subscription services for reference throughout the industry. Operators and Maintainers can research a list of AD’s applicable to a specific aircraft including any AD’s that were previously issued throughout the life of the aircraft. In the real world of small privately owned aircraft, it is not unusual to uncover evidence that one or more older AD’s may not have been addressed upon the original date of release. This is where these AD listings become so integral to the process of purchasing a used aircraft as well. It is the owner’s responsibility to ensure that all applicable AD’s have been completed. The owner may need to work with an AME to help determine AD compliance but the final responsibility to ensure compliance ultimately rests with the aircraft owner.

In certain circumstances, compliance with an AD may be accomplished in a manner which deviates from the approved instructions provided that the proposal offers a degree of safety which is at least to the equivalent of that offered by the AD and then subsequently approved by Transport Canada. This is not intended as a work-around or a regulatory loophole and is only considered where it has been determined to be economically viable and/or necessary for certain operators. This procedure is referred to as an Alternative Means of Compliance (AMOC). See CAR Standard 625 Appendix H for more information on the steps required to be considered for an AMOC.

As mentioned above, the best approach to AD compliance may involve both the owner and the maintainer. Just as the owner is responsible for adopting a maintenance schedule for the aircraft, He or She is also responsible for maintaining the AD status. Standard 625 Appendix B (10)(i) states in part “In addition, any references in those checklists concerning compliance with Airworthiness Directives must be stricken out as not applicable, as it is the owner’s responsibility to advise the AME of any outstanding Airworthiness Directives or Airworthiness Limitations.”

Reviewing AD’s for applicability demands attention to the details contained in the AD instructions. The AD may specify applicability only to particular models, series or serial ranges. Compliance may also require a one-time inspection/action or recurring inspections at prescribed intervals. Once you have committed to tracking a recurring AD for ongoing compliance, it also becomes necessary to ensure that continued reference is made to the most current revision as additional details may be issued from time to time (suffixed by R#). The recording of AD activity referencing an outdated revision does not imply continued compliance. The revision may (or may not) have included updates pertaining to the recurring activity being performed. In certain cases, although not as common, an AD has also been re-issued under a completely new number. There have also been instances of FAA issued AD’s where Transport Canada has also issued a corresponding AD on the same subject in order to re-inforce particular details of compliance. As a Canadian Operator in this case, you would be required to enter the Canadian AD number into the technical record. A common example of this would be the Cessna seat locking and rail inspection from 1987 that was eventually revised and re-issued under a new number. Standard 625 Appendix H (2) states “CAR 605.84 recognizes the mandatory status of foreign ADs and equivalent notices issued by the aviation authority having jurisdiction over the type design of the aeronautical product. In the case of a conflict between an AD issued by TC and one issued by a foreign aviation authority that has jurisdiction over the type design, the AD issued by TC prevails.”

Another possible scenario for AD compliance may require multiple actions where they have been sub-divided into separate and very specific actions at different intervals. In this case, the technical entry must clearly indicate which parts have been complied with at the time of entry and which parts will be due at another time. An AD requiring multiple actions at different times cannot just be certified in the technical record without indicating the open details unless all of these requirements have actually been completed at that time. An example might include completion of Part 1 of the AD only with Part 2 due at a later date. A similar situation applies to AD’s which require a recurring inspection of the existing part until a terminating action for the AD is performed through the addition of an improved part. These preceding examples signify the importance of good AD record keeping and attention to detail.

Recording of AD activity is entered into the technical log for the product (and journey log for an aircraft) and certified with a maintenance release. The standard green technical log (pt. II) has long been considered the accepted means of recording AD and Service Bulletin history for the aircraft due to its simplicity and familiarity. This green log does not represent the certification of the AD since that is entered in the appropriate airframe, engine, propeller or component record usually as a maintenance event. The green log is nothing more than a record of AD and special inspection history to aid in the research and quick review of such events. Sometimes AD entries are made with reference to an item that is not applicable to the aircraft and entered as such simply to show that it has been addressed. A complete AD entry should include the most current revision of the AD reference, the subject matter, and indication that it has been either complied with (c/w) or determined to be not applicable (n/a). An AD considered to be no longer applicable to the aircraft due to a specific terminating action must also be clearly entered as such. Neglecting these details may be cause for more unnecessary work later on.

In Canada, A search for Airworthiness Directives applicable to a specific aircraft can be performed through the Continuing Airworthiness Web Information System (CAWIS) on the Transport Canada website (tc.gc.ca). You will often see these listings printed off and marked up to show applicability or non-applicability to the aircraft. A copy is usually found stapled into the green log or at least included somewhere amidst the paperwork related to the technical record for the aircraft. This record of AD history may have also been performed using a similar subscription program or database. Standard 625 Appendix H (2) (iv) goes on to state “Transport Canada (TC) endeavors to transmit to Canadian registered owners the ADs in respect of foreign aeronautical products received from foreign overseeing authorities, and that are accepted by TC. Transport Canada simply advises the registered owners of equivalent notices because the owners are expected to avail themselves of all type certificate holders’ instructions for continuing airworthiness.” And (v) “As it is impossible for Transport Canada to know on which aircraft a particular appliance is installed, distribution of ADs on appliances is limited to local Transport Canada Centers (TCC). Therefore, the miscellaneous section of the printed or electronic indices must be browsed to identify those ADs applicable to equipment installed on a particular aircraft.”

The primary lesson here remains with the owner being responsible for the continued airworthiness of his/her aircraft. Part VI of the CARs speaks to General Operating and Flight Rules which are basically the rules for owners/operators to consider when operating an aircraft. CAR 605.84 (1) states in part, “…no person shall conduct a take-off or permit a take-off to be conducted in an aircraft that is in the legal custody and control of the person, other than an aircraft operated under a special certificate of airworthiness in the owner-maintenance or amateur-built classification, unless the aircraft…(b) meets the requirements of any airworthiness directive issued under section 521.427…”

As you can see, tracking AD’s is critical to maintaining the continued airworthiness of an aircraft. We will continue to examine other areas of continuing airworthiness throughout the year.,


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