FRANKFURT  Thu Apr 3, 2014 11:20am EDT

(Reuters) - Lufthansa (LHAG.DE) pilots said they hoped to resume talks with management as early as this weekend over a retirement scheme dispute that grounded Germany's largest airline for a second day on Thursday.

The three-day stoppage planned by over 5,000 pilots has led Lufthansa to cancel 3,800 flights, or around nine out of ten flights. Lufthansa has refused to negotiate while the strike is ongoing.

The two sides said on Thursday that they would be open to negotiations after the industrial action comes to an end.

"I hope that we've put on so much pressure with the strike that we can hold talks at the weekend or early next week," Markus Wahl, board member at the Vereinigung Cockpit pilots' union told Reuters.

As the pilots have agreed not to strike again until the end of the Easter school holidays, that gives two weeks for talks.

Lufthansa said it hoped to reach an agreement by the start of May, when the holidays come to an end.

The walkout is expected to cost the airline tens of millions of euros and has disrupted the travel plans of around 425,000 passengers.

About 700 flights were cancelled on Thursday in Frankfurt, Europe's third-biggest hub by passenger numbers, and a couple of hundred flights were affected in Munich, airport representatives said.

The pilots are demanding Lufthansa reinstates a scheme that allowed them to take early retirement and still receive a proportion of their pay.

Lufthansa says that now the maximum age at which pilots can still fly has been increased to reflect longer life expectancies, there is no need for the scheme.

Lufthansa is aiming to return its flight schedule to normal for Saturday.

The strike is a boon for Germany's state railway company Deutsche Bahn, which is expecting an extra 20,000 customers a day. It normally transports around 360,000 people a day.

(Reporting by Victoria Bryan and Kirsti Knolle; Editing by Mark Potter and Elaine Hardcastle)