A dogfight in the skies over New Jersey forced a packed airliner to make an emergency landing yesterday.

A 12-pound Manchester terrier — apparently channeling Snoopy’s Red Baron — got loose on a US Airways flight and declared war on the passengers and crew, rampaging down the aisle, biting anybody in her way.

Mandy and her owner, an 89-year-old woman who said she was too embarrassed to be publicly identified, had boarded Flight 522 in Newark for a ride to Phoenix.

The pooch had been in a carrier under her owner’s seat. But when Mandy’s dog tranquilizers wore off, the elderly woman put the carrier on her lap and took her best friend out of it.

When Mandy refused to calm down, a man seated nearby tried petting her.

Then Mandy made her great escape.

First, she bit the man. Then she darted off, barking madly.

A heroic stewardess tried to put herself between Mandy and the passengers.

But she was no match for the hot-dogger and became a casualty herself.

The pilot made the emergency landing so Mandy’s two victims could get medical attention — treating all 122 passengers to a surprise visit to scenic Pittsburgh.

They cooled their heels for an hour before everyone — except Mandy and her owner — got back aboard.

The pair were put on a later flight.

US Airways pinned the blame on the woman.

“This passenger let their dog out of the carrier even though they’re not supposed to do that,” groused Valerie Wunder, an airline spokeswoman. “She was told not to.”

Mandy’s owner was questioned by Pittsburgh cops — who decided not to file charges.

Wunder said the airline had not decided what, if any, action would be taken against the woman, but doubted she’d be banned from future flights.

She had no comment on whether Mandy — whose ticket cost $100 — would be welcomed back.