"We need a fresh look at the environmental viability and total cost of expanding Heathrow," he said.
"The airport has a history of spending recklessly to gold-plate projects and paying guaranteed dividends to shareholders while minimising the environmental significance of expansion."
The highly controversial expansion would see a third runway added to the airport and could potentially add capacity for some airlines.
However, some in the aviation industry have complained there is little to stop the costs spiralling out of control, which would then be passed onto customers.
Walsh himself has complained on multiple occasions there was no incentive for keeping costs down.
This is due to a quirk which sees Heathrow owners able to earn more money by increasing spending.
Investment can be levied through passenger charges, with the airport's owners recently trying to foist £3.3bn of spending onto passengers.
The CAA has put a clause into Heathrow's licence that penalises the airport if it goes over its budget in a bid to stop costs spiralling.
A CAA spokesperson said: "The licence condition covers the operation of the airport and is also one of the tools the CAA is developing so that Heathrow expansion is delivered in a way that is affordable, financeable and, critically, in the interest of consumers."
Heathrow said: "
(c) 2019 City A.M., source