United Airlines parent UAL Corp. ( UAL), facing nearly $1 billion of loan payments this week, filed for Chapter 11 bankruptcy protection Monday. United, which becomes the biggest U.S. carrier ever to make such a filing, intends to continue operating as it restructures. The airline employs about 83,000 people. The bankruptcy filing was voted unanimously by UAL's board after a meeting Sunday. UAL's efforts to avoid reorganization were thwarted last week when the federal government refused to grant it nearly $2 billion in loan guarantees, citing a risk to taxpayers. UAL was pushed to the brink of insolvency when a weak economy and declining passenger traffic followed the Sept. 11 terrorist attacks, in which two of its planes were hijacked. The airline heads into Chapter 11 with a two-part financing package in hand: a $300 million term loan arranged by Bank One and a $1.2 billion facility arranged by J.P. Morgan and Citigroup, according to The Wall Street Journal.