PITTSBURGH — Where 600 flights used to take off and land every day here at Pittsburgh International Airport, there are now about 300. Partway down Terminal B, the moving sidewalk that used to lead to a dozen gates now stops abruptly at a plain gray wall.

Pittsburgh’s airport is struggling financially and mired in debt, with sharply lower traffic ever since US Airways began phasing it out as a bustling hub in 2004. Long gone are the days when British Airways flew 747s to London, and TWA flew to Frankfurt.

For salvation, airport officials are looking down — about 6,000 feet. The quiet runways, it turns out, are sitting on enough natural gas to run the whole state of Pennsylvania for a year and a half, and this month, Consol Energy will drill its first well here to tap the gas, which county officials say will bring them nearly half a billion dollars over the next 20 years.

The well is outside the airport fence but, with horizontal drilling, will extract the rich deposits that lie under the terminals and runways.