Wichita ? Before buying Boeing Co.’s commercial airplane operations in Kansas and Oklahoma, Canadian investment conglomerate Onex Corp. discussed in e-mails plans to reduce the age of the work force to cut costs, according to recently released court documents in an age-discrimination lawsuit.

Former Boeing workers have sued Boeing and Spirit Aerosystems Inc., the subsidiary Onex formed to run the commercial aircraft operations in Wichita and Tulsa and McAlester, Okla. The workers claim they lost their jobs because of their age and filed suit in December 2005.

This week, lawyers for the workers filed documents to back up their request for class-action status for the suit. The documents included depositions and internal company memos that the plaintiffs say show that Spirit cut older workers using a “selective rehire” process in which all Boeing employees were laid off and forced to reapply for their jobs with the new company.

One memo Onex presented to its board of directors to support the purchase noted that the Boeing work force was “older and more expensive” than the work force the new company would have. Employees ages 45 to 54 were considered the most expensive, company memos show.

“We are moving from a demographically expensive population towards one that should be cheaper,” Spirit said in one internal document.

The court documents also indicate that when Boeing was trying to sell the division, it marketed potential cost savings prospective buyers could expect by reducing the number of workers. Onex finalized its purchase of the division in June 2005.

Spokesmen at the companies have declined to comment on this week’s filing, and calls to their defense attorneys have not been returned. But in earlier court documents, Boeing and Spirit denied any employment decisions were based on age.

Bob Brewer, Midwest director for the Society of Professional Engineering Employees in Aerospace, said Thursday that the companies were playing with people’s lives and careers for a few dollars.

“Most everything I’ve read today I was absolutely amazed and appalled at,” Brewer said.

When Boeing sold the Kansas and Oklahoma operations, it laid off all 9,300 workers at those plants. Onex then asked people to reapply for their jobs. At the time, Onex, which is not part of the lawsuit, said it had hired more than 8,000 former Boeing workers.

Spirit said in its own court filing that it expected “non-discriminatory hiring practices” would result in a work force with an average age closer to that of other aerospace employers.

Court documents also show that trustees with the Machinists union’s National Pension Fund would have required an extra $30 million if Spirit’s demographics hadn’t changed in three years. To avoid making the payment, advisers told Spirit there would have to be a five-year decrease in average service and a seven-year decrease in average age of its work force.

The former workers are seeking their jobs back, along with unspecified compensatory damages and at least $1.5 billion in punitive damages.