Efforts to craft a compromise to end a partial shutdown of federal aviation programs faltered in the U.S. Senate on Monday night, raising the near certainty that the standoff will go through August.

The 10-day shutdown of airport runway and other improvement projects overseen by the Federal Aviation Administration has disrupted tens of thousands of construction jobs nationwide and prompted the furlough of 4,000 agency employees.

In addition, the shutdown lifted the requirement for airlines to collect certain ticket taxes, resulting in a loss of US$250 million in revenue so far that would have gone to a trust fund that helps pay for airport infrastructure projects.

A shutdown through August would raise that total to more than US$1 billion, congressional and other officials said.

Moreover, the shutdown has threatened progress on an approaching deadline for certifying airports to handle the new Boeing Co 747-8 freighter, the largest jumbo jet ever built by the company.

Congress is due to start its August recess as early as Tuesday after the Senate votes on legislation to increase the U.S. debt limit following passage in the House of Representatives on Monday.

The House left Washington on Monday night.

Still unresolved are disputes in temporary FAA funding legislation over subsidies for service to rural communities and an attempt to roll back a federal labour rule aimed at making it easier for unions to organize at airlines and railroads.

The temporary measure is a stop gap allowing Congress to continue negotiations on a long-term funding blueprint for the entire agency. Air traffic services are not affected by the partial shutdown.

The politically charged labour change that occurred last year could impact all airlines. It was pushed by Obama administration appointees ahead of high-stakes representation elections at mostly non-union Delta Air Lines that ultimately failed.

Labor Dispute

Unions intend to keep trying at that carrier, prompting its allies in Congress, in this case Republicans in the House, to try to reinstate the previous election rule.

Senator John Rockefeller, chairman of the Commerce Committee, which oversees aviation issues in the Senate, said Delta wants to ensure that lawmakers scrap the existing labour provision.

"We have inflicted far too much damage on our aviation system for the needs of one airline," Rockefeller said in remarks on the Senate floor.

Delta, in a statement, said it disagreed with Rockefeller's comments and expressed hope that Congress could work out its differences.

Senate Democratic Leader Harry Reid, who earlier in the day spoke with Transportation Secretary Ray LaHood about efforts to resolve the problem, said the labour issue "should not overhang" the temporary funding extension.

Republican Orrin Hatch of Utah, where Delta has a hub, said the labour issue needed to be addressed but could be worked out quickly.

Rockefeller said an attempt by he and Kay Bailey Hutchison, a Republican senator and leader on aviation issues, to forge a bipartisan compromise to extend temporary FAA funding fell short.