Cardiff City are "concerned" by the results of the latest report from the Air Accidents Investigation Branch (AAIB) into the death of footballer Emiliano Sala.
The striker, along with pilot David Ibbotson, went missing when their plane crashed over the English Channel in January, days after his move to the Premier League club from Nantes was announced.
Sala's body was later recovered from the wreckage, but Ibbotson has not been found.
A report from the AAIB released on Wednesday said Ibbotson was "likely" to have been exposed to carbon monoxide before the crash, while toxicology tests on Sala showed clear signs of exposure to the poisonous gas.
Cardiff say the latest findings show the plane carrying Sala was "not appropriate".
A club spokesperson said: "CCFC is concerned at the AAIB's latest report which once again highlights that the aircraft used for Emiliano Sala was not appropriate.
"We continue to believe that those who were instrumental in arranging its usage are held to account for this tragedy."
The AAIB, meanwhile, has responded to calls from Sala's family to recover the plane's wreckage.
"The reasons for our decision not to recover the aircraft wreckage have been explained in detail to both families concerned," the organisation said in a statement.
"In February our underwater search operation successfully located the wreckage, recovered the passenger's body and captured substantial video evidence from the scene using a remotely operated vehicle. It was not possible at the time to recover the wreckage.
"We have carefully considered the feasibility and merits of returning to attempt to recover the wreckage. In this case, we consider that it will not add significantly to the investigation and we will identify the correct safety issues through other means.
"In making our decision, we took into account the high cost of underwater recovery, the evidence we collected in February and the risk that, after a violent impact with the sea, the wreckage would not yield definitive evidence."