How to aggregate origin and destination availability

Over the last few years more and more airlines have moved from leg to origin and destination (O&D) control. O&D control better reflects the value of a booking request in the availability calculation. O&D availability is usually calculated for each itinerary, booking class, point of sale and departure date separately. This paper tackles the question of how to aggregate O&D availability, eg for management reports. Management reports present data on a high aggregation level such as country to country and departure month. Since many different O&Ds compete for the same physical seat on a flight, a simple summation of O&D availability leads to double counting. This paper presents two different mathematical models which avoid and factor out this double counting.