I don't think the 9-sigma is calculated per operation cycle, I think it's per maintenance cycle which are from a few times a year to every 5 years, depending on

I don't think the 9-sigma is calculated per operation cycle, I think it's per maintenance cycle which are from a few times a year to every 5 years, depending on the type. http://en.wikipedia.org/wiki/Aircraft_maintenance_checks http://en.wikipedia.org/wiki/Aircraft_maintenance_checks