To establish compliance times and grace periods for
Airworthiness Directives (AD) and Notices of Proposed Rulemaking
(NPRM), we rely on guidance set forth in FAA's Airworthiness
Directives Manual. This guidance and other information about the
FAA's AD process can be found on our website
http://www.faa.gov/certification/aircraft/ under Continued
Operational Safety. With this guidance readily available, we do not
consider it necessary to include it in NPRM's also. The AD manual
specifies that compliance thresholds must be established based on
engineering assessment of when action should be taken to detect or
prevent the unsafe condition. For those products that have already
exceeded the threshold, a grace period is established to preclude
products from being grounded unnecessarily. To determine the
appropriate grace period, the degree of urgency of the unsafe
condition must be balanced against the amount of time necessary to
accomplish the required actions, the availability of necessary
replacement parts, operators' regular maintenance schedules, and
other factors affecting the ability of operators to comply.
Decisions made on inspection thresholds and repeat inspection
intervals are based on the nature of the unsafe condition and rely
on engineering judgment. States of Registry may, at their
discretion, evaluate the requirements set forth in the AD/NPRM and
either adopt them or develop their own requirements to ensure the
continued airworthiness of aircraft on their register.
ATSB Note:
Based on the previous advice ATSB reclassifies the
recommendation as Closed-Partially Accepted (31 March 2008).
