PORTLAND, Maine (AP) _ Precision-Northeast Express Airlines, which operated as Northwest Airlink throughout the Northeast and into eastern Canada, ceased operations Monday.

Most of its routes immediately were taken over by Business Express.

Precision, with headquarters in Manchester, N.H., had filed for Chapter 11 bankruptcy protection on May 28 after Northwest Airlines said it would not renew its agreement to operate as Northwest Airlink. On Monday, the filing was converted to Chapter 7, which calls for a liquidation of assets.

The airline had operated with Boston as its hub since it became affiliated with Northwest Airlines. Precision-Northeast Express operated 33 airplanes and employed more than 550 people.

Business Express, based in Portsmouth, N.H., operates the Delta Connection out of Boston and New York, and also will operate as Northwest Airlink out of Boston. Business Express had announced on June 1 it had agreed to operate Northwest Airlink out of Boston beginning Nov. 26.

Passengers holding Precision tickets were able to use them on Delta Connection, as well as Air Canada, USAir and other airlines that serve Precision destinations not served by the Delta Connection.