Boeing Co. said it bought AeroInfo Systems Inc., a Canadian maker of aircraft fleet-planning software, in the plane maker's third purchase of an aviation services business in just over a month. Terms weren't disclosed. AeroInfo Systems, a 14-employee company based in Richmond, Canada, develops software to help airlines schedule maintenance dates and store repair records online. The British Columbia firm had revenue in fiscal 2000 of $630,000. It would have taken Boeing two years to develop AeroInfo's software on its own, Boeing executives said. The Seattle-based aircraft builder plans to link AeroInfo's software with its own computerized manuals and engineering drawings, a spokesman said. Boeing has said it wants to build a stable services business to balance new-jet sales that tend to rise and fall with the economy. Boeing shares closed up 69 cents at $55.44 on the NYSE.