$inQuery = join(",",array_fill(0,count($search_terms),"?"));

$stmt = $wacdbpdo->prepare("
                        SELECT
                        *
                        FROM airportdetails
                        WHERE airport_icao_code IN ($inQuery)
                        OR airport_iata_code IN ($inQuery)
                        OR airport_faa_code IN ($inQuery)
                        " );
$stmt->execute($search_terms);

Warning: PDOStatement::execute(): SQLSTATE[HY093]: Invalid parameter number:
number of bound variables does not match number of tokens in ...