A passenger service system (PSS) is an airline's own core software. It sells the airline's seats, stores every booking and, at the airport, checks passengers in and boards them. Every airline in India runs one. Most airlines rent their PSS from a few large companies, such as Amadeus and Sabre, instead of building their own.
A PSS has three main parts. The reservation system stores each booking as a passenger name record, or PNR. A PNR holds the passenger's name, the flights, a phone number and the ticket number. The inventory system knows how many seats are left on each flight, in each fare class. A fare class is a group of seats sold at one price with one set of rules. The departure control system (DCS) is the airport part, for check-in, bags and boarding.
Here is how the inventory works. Take, for example, an evening flight from Hyderabad to Kolkata with 186 seats. The airline does not sell all 186 at one price. It opens 30 seats in the cheapest class at ₹4,100. When those are sold, the PSS closes that class, and the next class opens at ₹5,300. A week before the flight, only the ₹8,900 class is still open. The PSS may also sell a few more seats than the aircraft holds, perhaps 190, because a few passengers usually do not turn up. This is called overbooking. If more passengers turn up than there are seats, DGCA rules require the airline to compensate the passengers it cannot board. The PSS updates the seat count each time a seat is sold, whether on the airline's app, through a global distribution system (GDS) or over NDC.
The PSS is the airline's system of record for passengers. If a booking is not in the PSS, the passenger has no seat, even with a printed ticket. So the PSS must never stop. A failure of a few hours can stop check-in at every airport the airline flies to.
After each sale, the PSS sends the ticket to airline revenue accounting, which records the money. After each flight, it sends the miles each passenger earned to the airline's loyalty programme. Some programmes let members move those miles to other programmes through a loyalty points exchange. For international flights, the airline must send each passenger's passport details to the border authorities of the destination country before departure. These details also come from the PSS.
Replacing a PSS is one of the hardest IT projects an airline can take on. Every booking already sold for the coming year must move to the new system without losing a single seat. When two airlines merge, they must combine their two passenger service systems into one.