On an airplane carrying 100 passengers, how many customers does it take, on average, to cover the cost of the flight?
If you are in possession of the key metrics, break-even load factor BELF) is easy to compute. It is simply Unit Cost (expenses divided by capacity, measured in Available Tonne-km) divided by Yield (Revenues divided by traffic, measured in Revenue Tonne-km). Both yields and costs have been very volatile in recent years but in a ‘normal’ year, for full-service airlines breakeven would typically be around 68-70%.
That describes the utilisation of all capacity, passenger and cargo. In theory, separate breakevens could be calculated for passenger and cargo but that would involve allocating costs between the two, by no means an exact science. If I recall correctly, a standard methodology used by IATA was abandoned because it regularly gave nonsense results for cargo. Individual airlines may have in-house allocation models which give better results.
Caution: this algorithm may not work (in fact it almost certainly doesn’t) for the LoCo business model.