Members of the Air Line Pilots Association hold an informational picketing session on Wall Street yesterday about their upcoming contract talks with Continental Airlines The pilots were addressing a number of issues, including Continental’s possible merger with United Airlines and concessions they gave up in their last contract. Meanwhile, the mechanics union at US Airways reached an agreement on a contract yesterday. The pact still must be ratified by the airline’s 3,300 International Association of Machinists members. The airline’s mechanics currently earn between $16.10 and $23.69 an hour and would see 10-percent raises immediately once they ratify the agreement. Those raises would be followed by 3-percent raises every year until 2011, plus new overtime rates.

AP / Henny Ray Abrams

DALLAS — Southwest Airlines Co. yesterday grounded 43 planes to examine if they were structurally sound enough to carry passengers after it recently acknowledged it had missed required inspections of some planes for cracks.

The move affects about 8 percent of its fleet and comes as Southwest faces a $10.2-million civil penalty for continuing to fly almost 50 planes after the airline told regulators that it had missed required inspections of the planes.

Southwest is the largest carrier at T.F. Green Airport in Warwick, with more than half the total number of passengers. The airline did not say which airports the grounded planes served.

The Federal Aviation Administration, which announced the penalty last week, has also come under fire for failing to ground the Southwest jets last year, when agency inspectors learned they had not been inspected for cracks in the fuselage.

Southwest initially said it grounded 41 planes, but spokeswoman Linda Rutherford later said 38 planes were taken off the schedule for additional inspection, along with five others that were already in hangars undergoing routine maintenance.

Rutherford said the airline pulled the planes out of service after getting clarification from manufacturer Boeing Co. on Tuesday night about the type of inspection — visual or magnetic, or a combination of both — needed for areas around the windows on some older Boeing 737-300 and 737-500 jets.

By midday yesterday, six planes had undergone the 90-minute inspection and were returned to service, Rutherford said. She said the remaining planes were expected to be back flying by last night. A 44th plane covered by the Boeing instructions had already been retired, she said.

Southwest had cancelled 118 flights by midday yesterday, or about 9 percent of its scheduled flights, according to Flightstats.com, which tracks airline operations. Rutherford said some of the cancellations were due to bad weather in Houston.

The company said it had 520 Boeing 737 jets at the end of last year. Nearly 200 of them are older models, the Boeing 737-300, that were supposed to undergo extra inspections for cracks in the fuselage.

Southwest chief executive officer Gary Kelly had said Tuesday he was concerned by findings from an internal investigation into the missed inspections. He announced that the Dallas-based company had placed three employees on paid leave while it investigated the situation.

The FAA said acting administrator Robert A. Sturgell met yesterday with Kelly, who gave a briefing on the steps the airline is taking to comply with inspection orders. The FAA is conducting its own review.

Earlier, Sturgell called the events “a twofold breakdown in the aviation system” — first, Southwest’s failure to properly inspect its planes; and the FAA’s failure to ground the jets as “at least one FAA inspector looked the other way.”

The $10.2-million penalty is the largest the FAA has ever imposed on a carrier. Southwest has said it will appeal.

Southwest shares fell 91 cents to end at $11.49 in trading yesterday after they earlier fell to a 52-week low of $8.87.