Part of a seat cushion washed up on a beach in north west France on Monday morning.
Later that day another section of cushion washed up on the same beach at Surainville on the Cotentin Peninsula in Normandy, around 60km from Guernsey.
Investigators from the Air Accidents Investigation Branch (AAIB) said: “From a preliminary examination we have concluded that it is likely that the cushions are from the missing aircraft.”
“Through the Ministry of Defence’s Salvage and Marine Operations (SALMO) Project Team, we have commissioned a specialist survey vessel to carry out an underwater survey of the seabed to try to locate and identify possible aircraft wreckage.”
AAIB investigators said their underwater search will last three days.
“Since we opened our safety investigation on Tuesday 23 January, we have been gathering evidence such as flight, aircraft and personnel records, and have been analysing radar data and air traffic tapes. We have been working closely with other international authorities and have kept the families of those involved updated on our progress,” said a spokesman.
The £15m striker, 28, was flying back to the UK after signing for Cardiff City in a record deal on the 21st January when the plane disappeared into the English channel.
The Piper PA-46 Malibu plane was being flown by pilot David Ibbotson from Nantes in France for Cardiff when it requested permission to descend before losing contact with Jersey air traffic control.
Football agent Willie McKay arranged for the flight to take Sala from Nantes to Cardiff but had no involvement in selecting the plane or pilot.
McKay’s son, Mark, was the acting agent for Nantes in a move which made Sala a club-record transfer for Cardiff.
Members of Sala’s family launched a separate search for the wreckage of the plane using funds donated by well-wishers, which is still ongoing. The target was £259,000.
AAIB investigators said they were “liaising closely with those involved” with the family’s search efforts to “maximise the chance of locating any wreckage and ensure a safe search operation.”
After the private search got under way on Sunday, the family said they were “struggling for answers”.
Spokesman David Mearns, who is understood to be assisting the family, had said they still have hope.
Speaking to reporters in Guernsey, he said: “The family still have some hope, they’re looking at this as a missing person, a missing plane, and until they are satisfied, that’s the mode that we’re in.”
He added: “This is a family that have come from Argentina with this huge shock out of nowhere and (is) struggling with what had happened, with very, very few answers about an unexplained loss.”
Cardiff captain Sol Bamba has said some players at the Welsh club are afraid to fly after the disappearance of Sala.
“It is very difficult to even describe how the players are feeling,” said Bamba. “It is a very unusual situation, a big tragedy. We have all been affected by it, the lads, the city, the whole club.
“We have had some help. We travel by plane and some of the lads have been thinking, ‘I do not want to go on it anymore.’ It was that deep.
“We are going to have to fly because we play games up north and flying is the easy way to get there and make sure we can rest. Of course when this happens you say you are not going to fly anymore, but unfortunately you have to.
“It is about making sure everyone is in the right frame of mind to fly again.”
Cardiff lost 2-1 to Arsenal at Emirates Stadium last night in their first match since Sala disappeared. It should have been the forward’s debut.
Bamba said: “It was very difficult last night in these circumstances. But he would have been proud of us because we did well.”