Massive capital requirements. Which you can mitigate by leasing, but this increases your cost. Massive unit operating costs, where the cost difference between

Massive capital requirements. Which you can mitigate by leasing, but this increases your cost. Massive unit operating costs, where the cost difference between it flying and sitting on the ground is not that different (for a commercial aircraft that's still in flyable condition, it needs to keep being maintained constantly) Large numbers of staff - pilots, cabin crew, gate staff, baggage/cargo loaders, tug operators, ground crew, refuelling, operations (scheduling, route planning), customer service, maintenance crew, etc. Some of those can be outsourced, depending on the airport. Some of those (like flight crew) have mandated maximum operating hours. You need to have hotel rooms, meal allowances, and transport to/from the airport for flight crew when they're off-duty at an airport that isn't home-base. Dealing with someone who calls in sick means you need stand-by crew ready to go in all the locations that you fly out of (or be prepared to fly replacement crew into those locations - and thus potentially sacrifice a seat that could've gone to a paying customer) All these operating costs and we've not even sold a single seat. Depending on the airline, they might not be breaking even until the flight is nearly 70% full.