Originally Posted by
emma69
If one particular aircraft got grounded because of a technical fault (e.g. defective batteries) you could still operate some flights if you have spread your risk on more than one aircraft type.
An airline could still operate with an all-Airbus/Boeing fleet in that situation*, just with planes possibly too large or small for their routes. A fault affecting all types from a single company would be unlikely.
* Assuming they're not a LCC that's standardized on only one type (e.g. Southwest and the 737)