In a note last week to employees, Boeing Co. Chief Executive Jim McNerney wrote that the world's biggest aerospace company by sales is "well positioned" to weather the financial turbulence because it has a solid credit rating and a big backlog of commercial airplane orders. But addressing how the government's financial-industry bailout might affect Boeing's more than $30-billion-a-year defense business, Mr. McNerney said: "No one really yet knows when or to what extent defense spending could be affected, but it's unrealistic to think there won't be some measure of impact."