The layoffs will occur at Gates Learjet's facilities in Tucson and Wichita, Kan., over the next several weeks. The company said the layoffs are attributable to a sluggish market for commercial jets. Gates had 1,119 workers in Tucson and 1,507 workers in Wichita at the beginning of August, company officials said. The Wichita plant manufactures parts for commercial jets, which are assembled in Tucson. Wichita also works on military contracts.