The counter point to operating one type is on display here: if the regulator grounds the type, your whole airline is stuck.
The only thing that eliminates/highlights issues is time. The 320 and 220 are faced with major engine issues and groundings due to looks at notes not QAing the metal powder used in the sintering process for over 8 years.
The only thing that eliminates/highlights issues is time. The 320 and 220 are faced with major engine issues and groundings due to looks at notes not QAing the metal powder used in the sintering process for over 8 years.