An investigation into the plane crash which killed footballer Emiliano Sala will focus on the validity of the pilot's licence.
The Air Accidents Investigation Branch (AAIB) named "regulatory requirements" as one of four areas in which further work will be carried out.
Its interim report noted that the type of licence held by the pilot meant he could only fly passengers in the European Union on a cost sharing basis, rather than for commercial flights.
Pilots with his licence "must have a bona fide purpose for making the flight", according to the AAIB.
Argentinian footballer Sala had just signed for Cardiff City from French club Nantes for £15 million when the plane crashed into the Channel in January.
He was the only passenger on board the Piper Malibu aircraft flying from Nantes to the Welsh capital.
His body was recovered on February 6 but pilot David Ibbotson, 59, of Crowle, Lincolnshire, has not been located.
Mr Ibbotson's family hope a fresh search for his body will begin this week after setting up an online fundraising campaign which has reached £250,000.
The aircraft remains underwater off the coast of Guernsey after an attempt to recover it was hampered by bad weather.