Tory MPs Nicholas Soames and Howard Flight have joined the opposition to the possible expansion of Shoreham Airport.
East Worthing and Shoreham MP Tim Loughton has already stated his opposition to the idea of making the runway longer and having more daily flights.
Mr Soames and Mr Flight said they shared concerns over the potential flightpaths, which could start north of the Downs in the Mid Sussex district.
Arundel and South Downs MP Mr Flight said: "It is right initial plans should be formulated by the airport and its consultants, together with Worthing and Brighton and Hove councils.
"We then need to have a wider consultation to take account of the views of those affected further afield.
"With the proposed new longer runway, this would impinge on people living in Burgess Hill, Hassocks and Hurstpierpoint and the downland villages from Devil's Dyke to Fulking - not to mention the proposed South Downs National Park."
Mid Sussex MP Mr Soames said: "The current proposals are wholly impractical, badly thought out and poorly researched.
"If a formal planning application is submitted, a full environmental impact assessment should be conducted, along with a detailed analysis of flight operating times."
A detailed plan has not yet been submitted to Adur District Council.
If it was it would need the approval of local councils and would probably result in a public inquiry.
At the end of last year almost 200 people attended a public meeting to oppose expansion.
Brighton and Hove City Council and Worthing Borough Council say bringing in commercial flights is the only way to secure the airport's future.
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