What insurance do you need for a commercial airline business?

In a Word, lots.

The commercial airline business is not intrinsically risky, after all, the most dangerous sector of an airline flight is the drive to the airport, but when an accidet happens, it gets VERY expensive, and only a limited number of specialist insurers will handle it.

Insurance is required to cover loss or damage to aircraft and cargo, injury or death of passengers and crew, loss or damage to third party people and property, and last but not least, acts of war or vandalism.