The Conditional Maintenance Release
By Brian Whitehead
The Canadian Aviation Regulations prohibit anyone from operating an aircraft following maintenance, unless a maintenance release is signed in respect of the work done (CAR 605.85). In turn, CAR 571.10 outlines the details of the maintenance release. The responsible aircraft maintenance engineer (AME) must certify that the work was performed in accordance with the applicable standards of airworthiness. To enable this certification, the AME will usually have to confirm that the system in question is performing correctly. In some cases, this may not be possible without first flying the aircraft to check its operation in flight. This could occur, for example, following adjustment of a main rotor head assembly on a helicopter where auto-rotation performance must be confirmed before release to the flight line. Rectification of an engine problem that only shows itself at altitude is another example.
In such cases, the need to confirm the proper completion of the work before flight could lead to a "catch-22." To avoid this dilemma, CAR 571.10 provides for a conditional release. Using this provision, the AME can make the release subject to the completion of a satisfactory air test. The AME must specify the actual tests to be carried out. CAR 605.85 prohibits passengers from being carried on the air test, but permits observers if they are necessary for the purposes of the test. The most likely person qualifying under this provision would obviously be the AME who signed the original release. After the air test, the pilot must enter his findings in the aircraft journey log. If the findings are satisfactory, the release is complete, and the aircraft may commence normal operations. If the findings are unsatisfactory, the defect must be rectified before further flight.
To illustrate the process, the original release could say something along the lines of: "The described maintenance has been performed in accordance with the applicable airworthiness requirements, subject to an air test to confirm satisfactory directional control in the approach configuration, with propellers in the Beta range." The pilot's entry following a successful test could read: "Air test carried out — directional control satisfactory." This entry completes the process, and the aircraft is then eligible for routine flight operation.
With one exception, the decision whether to make a maintenance release subject to a satisfactory air test is solely up to the AME signing the release. The exception is where an approved maintenance organization (AMO) specifies in its approved maintenance policy manual (MPM) that certain actions shall always be subject to a conditional release. Note that the MPM must specifically state that a conditional release is to be used. Just listing tasks that are subject to an air test is not enough. An AMO may elect to make a whole range of tasks subject to an air test.
Air test requirements established in this way become part of the AMO's approved standards of airworthiness, but that does not, in itself, make the tasks eligible for a conditional maintenance release. CAR 571.10 specifically states that this procedure is only to be used for maintenance, "the satisfactory completion of which cannot be verified by inspection or testing of the aircraft on the ground."
For tasks not covered in the MPM, the AME has the last word. Even if the task is not specified in the MPM as being subject to an air test, the AME has the right to call for one if the qualifying circumstances are present.
The conditional release can be a useful tool, but it is not meant to be a crutch. The purpose of the system is to avoid putting an AME in the position of having to certify something of which he can have no knowledge, while at the same time ensuring that the procedure cannot be used to avoid legitimate responsibility. The rule is crafted to ensure that a conditional release cannot be used as a way of avoiding thorough maintenance and verification of the work performed.
Actually, cases where the work cannot be verified on the ground are rare. In place of a conditional release, it is often quite acceptable to provide a standard release, but to also make a logbook entry requesting a report following the next regular flight. Examples of this situation include adjustments to correct minor flying faults, engine settings, or cabin comfort items.
For example, following a prop governor adjustment when the results cannot be verified because ambient conditions do not permit the prop to come off the fine pitch stops with the aircraft stationary, the following entry could be made: "Please record the maximum RPM attained during takeoff." Another example of an air test that does not need a conditional release is where a rotary wing aircraft is undergoing rotor smoothing. This usually involves determining a level of comfort that the pilot can verify while still performing routine operations. In both cases, the effects of an incorrect adjustment would not be severe enough to warrant a dedicated test.
The key factor in deciding on this approach in place of a formal air test is whether the AME can be certain that the aircraft meets at least the minimum standard of airworthiness. This standard can be met even when the "state of tune" might be less than perfect. Another consideration, of course, is whether proper performance can be confirmed within the normal flight profile without unusual maneuvers. If you have been adjusting the stall strips, you would not want to check the effects of your work on a normal passenger flight!