French investigators are recommending tighter governance of non-revenue flights following the fatal Mediterranean Sea Airbus A320 accident last November.
The crash occurred ahead of a pre-delivery flight back to Air New Zealand, as the twin-jet attempted a low-speed test, at low altitude, during approach to Perpignan.
France's Bureau d'Enquetes et d'Analyses says the type of flight - while "not exceptional" - is not included in the list of non-revenue flights details in the EU-OPS regulations governing European air transport.
The investigation agency says it has been "unable to identify any text" applying to EU states that sets a framework for non-revenue or acceptance flights.
"In addition, no documents detail the constraints to be imposed on these flights or the skills required of the pilots," the BEA adds.
"As a result, operators are obliged to define for themselves the programme and operational conditions for these flights in their operations manual, without necessarily having evaluated the specific risks that these flights may present."
Air New Zealand and the A320's operator at the time, XL Airways, had agreed a series of in-flight checks to be performed on the jet as it came off lease from XL, but this was based on an Airbus programme used for delivery of a new aircraft to a customer.
"These flights are performed by Airbus acceptance pilots and engineers," says the BEA.
It says its investigation shows there is "great diversity" in operators' description, preparation and execution of non-revenue flights as well as in the selection and training of pilots.
When combined with the "almost total absence" of any standards on non-revenue flights, this diversity can also lead to "improvising" of tests, with crews performing them in "inappropriate parts of airspace" or during periods of high workload.
BEA is recommending that the European Aviation Safety Agency details the various non-revenue flights that European operators are authorised to conduct, and require that such flights be described precisely in operations manuals - including details of relevant preparation and training.