The first lesson of this course listed the documents an aircraft must carry; this lesson opens two of them. The certificate of airworthiness is the state's signature on the machine itself: who issues it, what it takes to get one, and what keeps it alive. The certificate of registration has a visible twin painted on the skin: the nationality and registration marks, with rules about who assigns them and exactly where they go.
The certificate of airworthiness
The Chicago Convention makes the certificate of airworthiness (CofA) compulsory: every aircraft engaged in international navigation must carry a valid CofA, issued or rendered valid by the state in which the aircraft is registered: the State of Registry. That state's competent authority does the issuing; for an aircraft on a European Union register, that is the national aviation authority of the member state of registry, working to the common EU rules. Without a valid CofA the aircraft may not fly internationally at all, and under national law it will not fly domestically either.
What does it take to get one? In the EU the answer is written in Commission Regulation (EU) No 748/2012, the airworthiness and environmental certification regulation. A CofA is issued when the applicant shows two things: that the aircraft conforms to a type design approved under a type certificate (the design approval EASA issues for the aircraft type, as the previous lesson's certification role described), and that it is in condition for safe operation. A factory-new aircraft demonstrates this with the manufacturer's statement of conformity; a used aircraft brings evidence of its maintenance history and passes an airworthiness review. The certificate ties the individual machine to its approved design: the moment the aircraft no longer conforms (an unapproved modification, damage, an overdue mandatory inspection), the basis of the certificate is gone.
Keeping it airworthy
A certificate issued once would mean little for a machine that ages every flying hour, so the system watches it continuously. Responsibility sits where registration sits (the rule of ICAO Annex 8, the airworthiness Annex): the continuing airworthiness of an aircraft is determined by its State of Registry, which prescribes the maintenance, inspections and mandatory modifications the aircraft must receive and satisfies itself that they happen.
How the certificate then stays valid differs by system, and the exam wants both models:
The classic model — the CofA is issued for a limited period and renewed when the state's requirements, typically an inspection, are met again.
The EU model — the CofA is issued for an unlimited duration and remains valid as long as three conditions hold: the aircraft stays on the register, it is maintained in accordance with the applicable requirements, and it holds a valid airworthiness review certificate (ARC), the certificate produced by a periodic airworthiness review, normally every year.
Fail the review, lapse the maintenance, or deregister the aircraft, and the non-expiring CofA stops working; the authority can also suspend or revoke it directly.
Annex 7: what is an aircraft, and whose is it
Registration marks are the subject of ICAO Annex 7, and it opens with three definitions the exam quotes nearly verbatim:
Aircraft — any machine that can derive support in the atmosphere from the reactions of the air, other than the reactions of the air against the earth's surface. The second half of the sentence is the point: it excludes hovercraft, which ride on air pressed against the surface.
Heavier-than-air aircraft — any aircraft deriving its lift in flight chiefly from aerodynamic forces: aeroplanes, helicopters, gliders. The contrast is the lighter-than-air family (balloons and airships), which float on buoyancy.
State of Registry — the state on whose register the aircraft is entered. Every duty this lesson has named (issuing the CofA, determining continuing airworthiness) hangs on this definition.
Nationality, common and registration marks
An aircraft's identity is painted on: a nationality mark followed by a registration mark. A Dutch airliner wears PH-ABC: PH declares the state, ABC identifies the individual aircraft. Who assigns what:
Nationality marks — selected by the state from the radio call-sign series allocated to it by the International Telecommunication Union (ITU), and notified to ICAO. That is why the prefixes look like radio callsigns: they are drawn from the same international allocation.
Common marks — for aircraft of international operating agencies that are not registered in any single state, ICAO itself assigns a common mark to the common mark registering authority the agency's states designate. Rare in practice, but a favourite exam question precisely because the assigner is ICAO, not a state.
Registration marks — assigned by the State of Registry (or the common mark registering authority): the letters or numbers that follow the nationality mark and name the individual aircraft.