Speaking at the Capa Global Aviation Summit in Heathrow, the IAG chief executive said of the £17.6 billion bill predicted for the project, just £200 million is required to build the runway itself.
With much of the bill potentially being passed on to the airport’s airline customers in the form of increased landing charges and tariffs, he questioned the thinking behind the entire project.
Walsh said: “1% of the bill is for the runway, 99% goes in to, in my opinion, some ridiculous glory project.
“If they can demonstrate that they can expand Heathrow without increasing capacity charges I’m supportive and I imagine every airline operating at Heathrow would support the proposition.”
He added British Airways has been supportive of expansion at the airport since 2005 when it originally approached the facility’s operators with a plan for a third runway.
He also supported a plan proposed by Surinder Arora, founder and chairman of hotel business Arora Group, that would see Heathrow’s expansion completed but at a cost of between £6 billion and £7 billion less than the current proposals.
Walsh said: “The incentive he has as a private business man is different from Heathrow’s.”
He added the last time BA had been able to seriously grow capacity at Heathrow was in 2012 when the airline bought bmi, and got 52 additional slots as a result.
He argued if BA were to end up paying money towards the expansion, any rewards would have to be in proportion.
“If we pay for 60% of the expansion and end up getting 15% of the new routes, that doesn’t make sense,” he added.
Walsh also used his time on stage to urge Dublin Airport to deal with overcrowding issues that are seeing runways and taxiways dealing with serious traffic that could impact airline punctuality.
He said: “Dublin is becoming impossible, we won’t operate Dublin as a hub unless they deal with it.”