Adequate insurance for an aerial filming trip is crucial. You will need to cover accident and injury for all of your team, loss or damage to equipment and possibly the cost of reshooting due to unforseen problems.
The first thing to decide is whether your flight is classed as Public Transport or Aerial Work. If it's Public Transport then check that the company you are using has an Air Operator's Certificate (AOC). This is a legal requirement.
Using a company without an AOC for a flight classed as public or commercial air transport can be illegal and may invalidate any insurance claims.