Aircraft Certification Policy Letter (ACPL)

ACPL No.: 5
Issue No.:  1
Issue Date:  1994-03-04
AARD File:  5009-0-5

Aircraft Certification Policy Letter (ACPL)

Subject: Canadian Airworthiness Directives - Inspection Interval Tolerances

1.0 Background

Requests have been made to allow inspection interval time tolerances for repetitive inspections specified in existing Canadian Airworthiness Directives (ADs). For new ADs, current policy requires that inspection interval tolerances be considered during AD development. Requests for tolerances pertaining to foreign ADs are normally routed by TCA HQ to the appropriate Foreign Airworthiness Authority.

2.0 Purpose

The purpose of this policy letter (APL) is to provide airworthiness personnel with pertinent guidelines for determining when inspection interval time tolerances for repetitive inspections specified in existing Canadian ADs may be considered.

3.0 Policy

There are two methods for granting inspection interval time tolerances for Canadian ADs:

  1. Alleviation - An alleviation would normally be considered to allow a one-time inspection time tolerance or for an AD requirement which affects only a few operators. The request must be supported by the responsible Regional Office and reviewed by Headquarters prior to its approval.
  2. AD Revision - Where a request for inspection interval time tolerance is made for all subsequent repetitive inspections, and where a significant number of operators are affected, a revision to the AD may be considered.
3.1 Tolerances

In either of the cases stated in paragraph 3.0 above, a 5 % tolerance up to a maximum of 50 hours may be granted provided the following conditions or any other additional conditions specified by TCA are met:

  1. The AD does not specify a terminating action.
  2. The tolerance, if granted, will provide the necessary flexibility for the AD inspection to be completed within a prescribed regular maintenance schedule.
  3. The request for tolerance is supported by the appropriate TC Regional Office.
  4. The original equipment manufacturer (OEM) concurs with the change.


Tolerance for calendar time inspection intervals will be considered on an individual basis.

3.2 Revisions

Revisions to ADs will take the form of the following example:

"The 200-hour interval specified above may be adjusted up to a maximum of 10 hours (5 %) to permit accomplishment at scheduled maintenance inspections."

4.0 Termination Date

This APL will remain valid until these guidelines are incorporated in ASI No. 7 at its next revision.

Original signed by:

James A. Torck 
Director, Airworthiness Branch