The Conservatives say their proposal is a 'green decision'
Tory plans to scrap a third runway at Heathrow and build a high-speed rail line instead, "beggars belief", says British Airways' chief executive.
Willie Walsh told an audience in the City the plans would damage the economy and create "decades of delays".
He said the Conservatives were "all over the place" on aviation proposals.
The Tories have argued that a high speed rail network would improve transport links without the environmental impact of a new runway.
The Tories were not immediately available to comment on Mr Walsh's latest comments.
They are proposing to create a new 180mph line linking London St Pancras, Birmingham, Manchester and Leeds - saying it would cut Heathrow flights by 66,000 a year, or 30% of the planned capacity of the third runway.
Theresa Villiers, the shadow transport secretary, announced to the party's conference in Birmingham on Monday that a Conservative government would say no to a third runway at Heathrow.
Mr Walsh says the latest idea that a rail link from Leeds and Manchester to Heathrow would be an adequate substitute for a third runway "beggars belief".
"Flights to Manchester and Leeds are less than three per cent of Heathrow’s current operation. The runway capacity this would free up would be swallowed almost immediately by natural growth.
"And even this tiny and temporary benefit would not be forthcoming until 2027.
"So the Conservatives apparently want to undermine the UK’s efforts to succeed in a global economy - and condemn Heathrow to permanent status as the most delay-prone airport in Europe".
He added:"The Conservatives may have an election to win but they must not forget that if they are successful, they will have a country to govern."