Basic logic of the decision:
1. Airliners are complex machines consisting of many smaller complex machines
2. Complex machines often suffer technical failures
Conclusion 1: an airliner risks being impacted by a technical failure
3. The failure of a component may impact the ability of the airliner to operate
4. Airlines comprise a plurality of airliners
Conclusion 2: an airline risks one or more airliners being unable to operate due to technical failures
5. Events are considered ordinary if they are expected to occur in routine course
6. Technical failures are expected to occur in an airline
Conclusion 3: an airline expects technical failures as part of routine course
ergo
Conclusion 4: Technical failure is an ordinary event
A volcano erupting is extraordinary. A meteorite smashing into the airport and wiping-out the fleet is extraordinary. A flap-track sticking is not.