The fourth classification is a Special C of A - Limited, that includes aircraft that were previously issued a flight permit prior to, 1 January 1989. As well, it includes ex-military aircraft that were designed to military specification standards that have been accepted by the Minister for limited use within civil aviation. This could include aircraft that participate in air shows or banner towing, for example.
The fifth and final certificate, is a Special C of A - Owner Maintenance, a new classification associated with recreational aircraft. The regulatory requirement supporting this document is now in its final stages of promulgation, with a list of eligible aircraft still being finalized. Transport Canada recently developed this category in response to industry requests. It recognizes an aircraft that may no longer meet the design standards of airworthiness that prevailed at the time of certification, but nonetheless are still in a safe condition for flight. Look for this certificate to join the other four in the very near future.
Flight Permits are also divided into two main categories: Experimental and Specific Purpose. The Flight Permit - Experimental is quite straightforward as it includes those aircraft that have been modified to show compliance with airworthiness standards, or that may otherwise be engaged in aeronautical research and development. On the other hand, the Flight Permit - Specific Purpose, has many uses and applications as it includes those aircraft that do not conform to the applicable airworthiness standards — yet are still capable of safe flight. These may include: aircraft that must be ferried to a base for maintenance or repair; importation or exportation flights; exhibition; demonstration; market survey; or crew training flights; air tests following repair, modification, or maintenance; and finally, a catch-all to accommodate the rarely needed — other temporary purposes.
As you can see, there is quite an array of flight authorities that can be issued to the many types of aircraft that are operated within today's civil aviation environment. Most of the classifications were born out of an era where flight authority distinction was heavily influenced by aircraft design characteristics alone, and didn't necessarily reflect present day reality. As such, it is conceivable that at some point in the future, many of these documents will disappear in their present form so that rationalization more appropriately mirrors current operational requirements. In that regard, and from a regulatory perspective, there are many ways of controlling safety besides issuing differing types of flight authorities — operational and maintenance control systems are but one alternative. However, until changes do occur, international commitments and other economic factors will cause us to stay the course.
While this is only a cursory review of the different flight authorities and some of their characteristics, it does provide some food for thought. Remember that an aircraft may qualify for one or more of these authorities, and hold several of these documents simultaneously, to support different configurations. In that regard, aircraft that operate in multiple roles can often move from one configuration to another with little effort. As such, it is important for the AME to confirm which of the configurations is being addressed when issuing a maintenance release, as a conformity inspection will require measurement against a particular configuration. This is especially important for those aircraft engaged in international flight, where Flight Permit status isn't readily recognized by member states of the International Civil Aviation Organization (ICAO), regardless of aircraft size or operational status.
The important point to be remembered is to take all of the applicable regulatory requirements into account — before signing on the dotted line.