An investigation into whether the missing flight that was carrying Premier League footballer Emiliano Sala was properly licensed is taking place.
The Piper PA-46 Malibu disappeared on Monday with Cardiff City’s new £15m signing and pilot Dave Ibbotson on board.
A search near Guernsey was called off on Thursday afternoon despite pleas from Sala’s sister.
The Air Accident Investigation Branch said it had launched a probe.
“We are looking at all operational aspects of the flight including licensing,” a spokesman said.
Mr Ibbotson, 59, of Crowle, Lincolnshire, held a private pilot’s licence and passed a medical exam as recently as November, according to Federal Aviation Administration records.
The Civil Aviation Authority said the aircraft was registered in the US, so fell under its regulations.
US law states private pilots cannot make a profit by carrying passengers.
Argentine striker Sala, 28, signed for Cardiff from Nantes last weekend and was travelling between the cities on Monday night.
At 19:15 GMT, Mr Ibbotson made a request to descend, before losing contact with Jersey air traffic control.
An extensive search took place, but Guernsey’s harbour master explained a “difficult” decision was made to call it off, saying the chances of survival were “extremely remote”.
However, Romina Sala said she feels her brother is still alive and pleaded with rescuers not to give up hope.
Mr Barker acknowledged the family were “not content” with the decision to stop actively searching but said he was “absolutely confident” no more could have been done.
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He insisted UK coastguard protocols were followed and said he hoped the families of the missing pair found some comfort in the incident remaining open, despite searches ceasing.
Cardiff City’s owner Vincent Tan said: “Monday evening’s news shook everyone at Cardiff City FC to the core.
“The response from the football community has been truly touching and we place on record our sincere thanks to those who have sent messages of support.
“We also thank everyone involved with the search and rescue operation, and continue to pray for Emiliano, David Ibbotson and their families.”
His former club Nantes, along with many of its players, backed Ms Sala’s calls for the search to resume, saying: “FC Nantes learned searches for the missing plane have been called off. These cannot stop.”
Three planes and five helicopters racked up 80 hours combined flying time looking for the plane, working alongside two lifeboats and other passing ships.