Some Ideas
Thanks glf..may I add a reminder here that once an a/c is airborne entering international aerospace, its airworthiness and compliance with international rules and regulations becomes an international concern and responsibility; meaning that regardless of its origin, registration or ownership, any violation can be reported to the relevant authority (e.g. EASA if it is overflying European aerospace, FAA if flying in a North American aerospace, etc). So provided one has a proof of an existing violation, it can easily be taken to the concerned authority that well and truly oversees and ensures regs compliance, unlike GCAA for instance. Moreover, PJ a/c land in airports across the world where airport authorities have the mandate to ensure compliance with the local as well as international rules and regulations. Those are places where one can submit the complaint with a proof. One of the rather simple issues that we had at European airports with PJ flights was with incomplete, missing or outdated certificates and licenses for a/c and crew members. Another more serious issues related to fake log books with false a/c maintenance history and defect rectification, not to mention counterfeit pilot licenses, etc.