Williams co-founder Sir Patrick Head has returned to the team as they try to recover from a sobering start to the new season.
The 72-year-old is working on what Williams describe as "a short-term consultancy basis".
The team were 1.3 seconds behind the next slowest car at the first race of the season in Australia two weeks ago.
Head left the sport at the end of the 2011 season.
He is renowned as one of the greatest engineers in F1 history, having led Williams to seven world drivers' championships and nine constructors' titles between 1980 and 1997.
He co-founded Williams Grand Prix Engineering with Sir Frank Williams in 1977. With the pair at the helm the team had a series of hugely successful eras from 1980-82, 1985 to '87, and 1991 to '97. Alan Jones, Keke Rosberg, Nigel Mansell, Nelson Piquet, Alain Prost, Damon Hill and Jacques Villeneuve all became world champions for Williams.
Williams chief technical officer Paddy Lowe went on a leave of absence before the start of the season, after the team missed the first two and a half days of pre-season testing because the car was not ready.
Lowe, who joined from world champions Mercedes in 2017, is not expected to return to work at the team.
Lowe became a shareholder when he joined Williams, buying out Head's remaining stake to do so.
Answering big questions
Williams will be hoping Head can use his expertise to help them understand how they have ended up with a car that is so uncompetitive - and to offer guidance on the steps required to get the team back on the right track.
The car's lack of performance has come as a surprise to the team's top management, who had been hoping Lowe's leadership would help them start back on the road to competitiveness.
They finished last in 2018, with a car that was on average the slowest on the grid but that machine had specific aerodynamic problems that made it difficult and unpredictable to drive. Williams also had an unconvincing driver line-up of Russian Sergey Sirotkin and Canadian Lance Stroll.
For this season, Williams signed Formula 2 champion George Russell, a Mercedes young driver and regarded as a potential star of the future, and Robert Kubica, returning after an eight-year absence caused by the life-changing injuries the Pole sustained in a rally crash in 2011.
They hoped that by solving the aerodynamic inconsistencies of the 2018 car and adding what is considered to be a stronger driver line-up they would be able to make a move up the grid.
Instead, although the 2019 car is more predictable to drive, it is lacking in aerodynamic downforce, is overweight and lacking in a number of other areas.
Insiders say there is no realistic hope of a major upturn in form this season with Head's consultancy aimed at making sure the team make the right decisions and properly understand where the have gone wrong.