REFILE-Southwest Airlines grounds 81 planes after emergency

(Refiles to add dropped letter in headline)

PHOENIX, April 2 (Reuters) - Southwest Airlines grounded 81 aircraft from its Boeing 737 fleet for inspection after a gaping hole in the fuselage forced one of its planes to make emergency landing in Arizona on Friday, the company said on Saturday.

Southwest (LUV.N) and Boeing (BA.N) engineers will inspect the aircraft to try to determine the cause, Southwest said in a statement. Passengers heard a loud noise and suddenly saw a hole about mid-cabin.

Southwest Airlines is working with the National Transportation Safety Board and the Federal Aviation Administration on the ground in Arizona to determine the cause of a sudden drop in cabin pressure on Southwest Flight 812 from Phoenix to Sacramento on Friday, airline officials said.

The flight, with 118 passengers and five crew members on board, landed safely at the Yuma Marine Corps Air Station, a military base, with a hole in the top of the aircraft, a Southwest spokeswoman said in a statement.

Preliminary reports showed the aircraft lost pressure and oxygen masks were deployed, Southwest said in a statement. Crew members confirmed a hole in the top of the aircraft near mid-cabin, the airline said.

One flight attendant and at least one passenger were treated at the scene for minor injuries, Southwest said in a statement.

Passengers described the scene to the CBS television affiliate in Sacramento, detailing the damage to the plane.

"They had just taken drink orders when I heard a huge sound and oxygen masks came down and we started making a rapid descent. They said we'd be making an emergency landing," a woman identified as Cindy told the station.

"There was a hole in the fuselage about three feet (one meter) long. You could see the insulation and the wiring. You could see a tear the length of one of the ceiling panels."

Another passenger tweeted that she was "happy to be alive."

"Still feel sick. 6 foot (1.8 meters) hole in the skin of the plane five rows behind me. Unbelievable," Shawna MalviniRedden wrote. She said she texted her husband while in the air, saying "I love you." (Reporting by David Schwartz; Additional reporting by Lauren Keiper in Boston; Editing by Greg McCune and Sandra Maler)