Chicago ? United Airlines said Friday it had begun talks to win over mechanics who rejected wage cuts the company considers key in its bid to get badly needed loans. Wall Street analysts said bankruptcy for the world’s No. 2 airline appeared all but certain.

With hefty debt payments and other challenges looming, there’s almost no time left for United to find the financial backing it needs to avoid filing for bankruptcy protection.

Bankruptcy concerns prompted a heavy sell-off of United stock Friday. Shares in United parent UAL Corp. plunged $1.12, or 31 percent, to close at $2.51.

Other workers have agreed to a total of $5.2 billion in companywide labor cuts over 5 1/2 years, but mechanics’ rejection of their $600 million share Wednesday put United’s financial recovery plan in limbo as its cash reserves rapidly dwindle.

“The mechanics’ vote makes bankruptcy virtually inevitable for United and UAL,” said credit analyst Philip Baggaley of Standard & Poor’s, which downgraded the company’s long-term corporate debt rating deeper into junk status.

Other airline experts concurred, and United reiterated its intention to file for Chapter 11 protection if it can’t get mechanics to swiftly agree to the cuts.

“We need to reach that amount that we already agreed upon (with a coalition of union leaders) if we’re going to get a government loan guarantee,” United spokesman Jeff Green said.

The Machinists said late Friday that no formal negotiations had been held. A meeting is scheduled with United officials Sunday.

United’s application for a $1.8 billion federal loan guarantee was put in jeopardy by Wednesday’s vote.