Flight Booking Process: A Complete Guide for Airlines and OTAs

Complete guide to the flight booking process: PSS architecture, CRS, PNR, NDC vs GDS, 8 booking steps, IATA accreditation, and what airlines and OTAs need.

A customer completes a flight booking in around 15 minutes, from initial search to receiving a confirmation email with an e-ticket. Behind that interface sits decades of layered technology: passenger service systems handling reservation and inventory, central reservation systems holding the authoritative flight record, distribution layers routing inventory to thousands of points of sale, accreditation organisations regulating who can issue tickets, and a merchandising engine increasingly responsible for the revenue economics of the entire industry.

This guide is written for airline IT decision makers, online travel agency product leaders, and software development partners evaluating how the flight booking architecture works end to end. It covers the four core components of the airline distribution system, the eight steps in a typical booking transaction, the accreditation requirements that determine who can issue tickets, the business considerations facing operators building or extending booking platforms, and how Adamo Software approaches custom booking platform development.

Key Takeaways:

• Global airline ancillary revenue reached USD 148.4 billion in 2024, up 26% from 2023 and USD 39 billion above the 2019 pre-pandemic record (IdeaWorksCompany, 2025 Yearbook of Ancillary Revenue). For ultra-low-cost carriers, ancillaries now represent 52% to 62% of total revenue, making the merchandising layer of a booking platform as financially critical as the base fare engine.
• The flight booking transaction sits on a four-component airline distribution stack: the Passenger Service System (PSS), the Central Reservation System (CRS), the Passenger Name Record (PNR), and the distribution layer (GDS, NDC, or direct). Each layer carries different protocols (EDIFACT for legacy GDS, XML for NDC) and different cost models for airlines.
• Indirect channels (OTAs, GDS terminals, metasearch engines) and direct channels (airline e-commerce) route booking requests through different paths but converge on the same airline CRS. Channel choice drives commission economics, customer data ownership, and ancillary upsell opportunity.
• Ticket issuance is regulated. Sellers must be accredited by IATA’s Billing and Settlement Plan (BSP) for global ticket issuance, or by Airlines Reporting Corporation (ARC) for US-registered agents, before they can issue tickets on behalf of member airlines.
• The eight steps of a typical booking transaction (search, booking, ancillary, loyalty, payment, ticketing, check-in, baggage) each have their own system dependencies and integration requirements. Custom booking platform builds typically underestimate the integration scope across these eight steps.

I. Structure of airline distribution system in flight booking process

1. Passenger service system in the flight booking process

A passenger service system (PSS) is a collection of software modules that handles communication and interactions between an airline and its customers. It is an essential part of an airline’s IT infrastructure. It consists of three main modules: 

• Central or airline reservation system (CRS) 
• Airline inventory control system (ICS)
• Departure control system (DCS) 

In addition, the PSS incorporates or integrates with a revenue management tool, which leverages historical data to establish pricing strategies and rules. It also helps streamline and automate various passenger-related processes, ensuring smooth operations for airlines.  

PSS is crucial for airlines, particularly as they enable efficient management of end-to-end operations and enhance the passenger experience. It handles tasks ranging from ticket reservations to boarding, and any failures in the system can result in significant financial losses for airlines. 

Some notable players are:  

• Bravo PSS passenger service solutions
• Amadeus Altéa Reservation Desktop Web for airlines
• New Skies

2. Central reservation system 

The central reservation system (CRS) is the second key component of the airline distribution stack. It serves as a centralized storage system for crucial flight-related information, such as: 

• Schedule 
• Fare 
• Rules for each booking class 
• Passenger name records (PNRs) 
• E-ticket 

The CRS is responsible for: 

• Managing room rates and availability 
• Distribution of inventory 
• Integration with booking engine and channel manager 

While some airlines operate their own CRS as part of their overall passenger service system (PSS), many carriers opt to host and manage their reservations through one of the Global Distribution Systems (GDSs). 

A CRS is also a pivotal technology for any travel business that sells its inventory online, including hotels and airlines. It allows managers to have control over reservations across all distribution platforms, ensuring efficient management of available inventory. 

3. Passenger name record 

A passenger name record (PNR) or booking file is a digital document that stores comprehensive information about an individual traveler or a group of travelers, including: 

• Passenger information 
• Passenger travel itinerary 

PNRs are used to:  

• Facilitate check-in 
• Allocate seats 
• Handle special requests 
• Provide a seamless travel experience 

Each PNR is assigned a distinct code known as a booking reference or record locator, which enables easy retrieval of the file from the central reservation system (CRS) database.  

When a traveler purchases a flight, they receive this unique code via email, allowing them to access their flight details and conveniently check-in online. The PNR serves as a crucial reference point for managing and organizing travel information for a smooth and hassle-free experience.

4. New distribution capability 

The majority of flights are typically distributed through the global distribution system (GDS), which necessitates the exchange of data between various systems using the outdated EDIFACT protocol. But, this limits airlines’ ability to gather detailed passenger information and offer a wide range of ancillary services (such as in-flight meals or excess baggage options) to their customers. Moreover, airlines are required to pay additional fees for GDS services.  

To address these limitations, the International Air Transport Association (IATA) introduced the New Distribution Capability (NDC) standard. NDC allows travel systems to seamlessly share data with one another using standard travel APIs and the more content-friendly XML protocol. 

With NDC, airlines gain the ability to access customer information, personalize the user experience, and directly sell ancillaries and seats from a single source, bypassing many third-party intermediaries.  

While many airlines and IT companies have adopted NDC capabilities, GDS remains the primary distribution channel in the industry. NDC’s introduction has opened the path for more innovative, customer-centric flight distribution and ancillary services.

II. Key flight booking process steps

1. Flight search 

Passengers can search for flight information through indirect channels and direct channels.  

Indirect channel: online travel agency (OTA), GDS, Metasearch engine 

In the indirect channel, users typically search for flights using a flight booking engine on a third-party website or through a GDS terminal. Once the user selects a flight, the third-party intermediary sends the booking request to GDS, which accesses the airline’s CRS to complete the transaction.

Direct channel: Airline eCommerce website 

In the direct channel, travelers have the option to book flights directly from the airline’s own eCommerce website. The flight booking process will bypass the intermediary GDS and goes straight to the airline’s CRS. This allows travelers to interact directly with the airline and simplifies the flight booking process by eliminating the need for third-party involvement.

2. Flight booking 

As beforementioned, CRS performs essential functions such as inventory and reservation management, PNR generation, payment integration, customer information management, booking and cancellation management, refund management, and email notifications. 

That’s why during the flight booking process, customers have the option to select their seats. However, airlines often charge an additional fee for this service. Alternatively, seat selection can be done during online check-in or assigned randomly by the airline. 

Once the customer completes the ticket purchase, the CRS generates a unique PNR. This code contains the traveler’s information and itinerary details. The PNR serves as a reference point for the airline to track the passenger’s record and exchange information with other airlines if necessary.

Also read: Flight booking engine: explore solution to manage flight bookings

3. Ancillary booking in the flight booking process

Global airline ancillary revenue reached USD 148.4 billion in 2024, up 26% from USD 117.9 billion in 2023 and well above the 2019 pre-pandemic record of USD 109.5 billion (IdeaWorksCompany, 2025 Yearbook of Ancillary Revenue). For ultra-low-cost carriers, ancillary revenue now represents 52% to 62% of total revenue, making the merchandising layer of the booking platform structurally critical to airline profitability.  

Ancillary services in the airline industry refer to additional services that can be requested or purchased by travelers to enhance the flight experience. These services include various options such as seat selection, extra baggage allowance, in-flight meals, and access to airport lounges  

When a traveler adds ancillary services during their flight booking process, a merchandising system generates a special service request number (SSR). This SSR serves as a message to the airline, indicating the traveler’s request for a specific ancillary service that is typically not included in the standard ticket.  

Merchandising system is also responsible for dynamic pricing and discount offers. It handles services like changing the date or name on the ticket for a fee.  

Ancillary services can vary between airlines, and their availability and pricing may be subject to factors such as frequent flyer status and fare class. Some airlines may charge for services like seat selection, extra legroom, or additional baggage, while others may include them in the standard fare.

4. Use airline loyalty programs if have 

Loyalty program operations are managed by airline merchandising systems. 

When someone becomes a member of a frequent-flyer or airline loyalty program, they can use the points they have earned from their flights to purchase additional services from the airline. These points can be exchanged for discounts or benefits, such as upgrading to business class.  

Depending on the airline, customers can either log in to their accounts when purchasing tickets directly from the airline’s website or use a loyalty program participant’s number to make bookings through third-party platforms. These systems also reserve a specific number of seats for frequent flyers in the CRS.  

Now, let’s talk about fares and payment. To receive a ticket with a PNR, also known as a booking confirmation number, a traveler must pay the fare. The fare includes the cost of the seat, taxes, and any applicable third-party service fees. It may also include charges for ancillary services. 

The allocation of fees between airlines, GDS, OTA, and customers follows a specific process: 

• Airlines pay GDSs for their distribution services. 
• GDSs, in turn, pay OTAs to finalize the sale. 
• Travel agents who book through the GDS terminal pay a fee for using its services. 
• Customers who book via an OTA may sometimes need to pay a service fee.

5. Payment processing

If a customer makes a direct booking, they pay the airline’s payment gateway directly. Once the payment is processed, the CRS is notified and generates a booking confirmation number. On the other hand, if the booking is made through an OTA or a metasearch website, they use their own payment gateway for processing the payment. 

A payment process is a service provided by a third-party that manages financial transactions between customers and merchants. It not only processes payments, but also ensures the security of data. 

The main functions of a payment gateway include: 

• Verifying if the customer has enough funds to make the payment 
• Transferring the funds to the merchant’s account 
• Processing regular payments for purchases 
• Returning money to the customer 
• Refunding funds that have not been captured 

One advantage of using a payment gateway is that customers can book and pay for their purchases in one place.  

However, there are a couple of disadvantages.  

Firstly, processes like cancellation and refund are handled through the OTA side, rather than the CRS. Travelers booking through OTAs may have to pay an additional fee. 

Once the payment has been processed by the payment gateway, the airline’s CRS can generate a booking confirmation number and issue an electronic ticket. 

6. Ticket selection during the flight booking process

A flight ticket serves as an agreement between a traveler and an airline carrier. Therefore, ticketing is a crucial part of the flight booking process. If there are any errors in the ticket, such as an incorrect name, the traveler will not be able to board the flight. 

Ticketing refers to the process of securing a paid seat on a flight, ensuring that it is reserved for an individual. This is accomplished through a PNR.  

A PNR with 6-digit code found on an electronic ticket, allows airlines to validate the reserved seat. In cases where a trip consists of multiple flights operated by different airlines, an interline booking is made.  

To facilitate this, airlines establish interline commercial agreements for codeshare flights. Based on this agreement, the participating airlines issue a single ticket with a single PNR. The ticket is issued by one of the airlines as specified in the agreement. 

Sometimes, a single PNR for segmented flight occurs, called a super PNR. In such cases, the system creates multiple PNRs that are consolidated into a single code. Each number within this code represents specific details about the seat, such as the class and included ancillaries. 

Once the ticketing process is complete, the traveler receives a booking confirmation from either the OTA or the airline. This confirmation includes the traveler’s name, flight schedule, airport IATA codes, and the ticket price. Also, the traveler receives an e-ticket with a reference to the airline’s PNR. Then, the traveler will need to present it. 

7. Check-in and flight boarding

Now, in this step of flight booking process, we deal with the airline’s Departure control system (DCS).  

The DCS is a component of the PSS and is connected to the CRS as well as airport devices such as self-check-in kiosks, agent software, baggage drop, and even immigration control. 

It is responsible for processing all check-in and boarding-related procedures, starting with ticket validation. DCS also handles customs and border security reservations, aircraft weight optimization, and cargo handling. 

During the check-in process, a traveler is required to provide their PNR and name, allowing the system to match it with existing records in the CRS and assign a seat. The check-in process may vary slightly between online and offline scenarios. 

Online check-in 

Online check-in typically becomes available 48 hours prior to the flight, although this may vary depending on the airline. A traveler enters the details from their e-ticket on the airline’s website or app and gains access to an aircraft seat map, where they can choose a specific seat.  

If the user does not select, the system will randomly assign a free seat and issue an electronic boarding pass. The same principle applies to check-in kiosks in flight booking process.  

Airport check-in 

When checking in at the airport, a person presents their e-ticket to an airport agent at the check-in counter. The agent then enters the necessary details, reserves a seat or multiple seats for segmented flights on a seat map, and checks the baggage. As a result, the agent issues and prints a boarding pass.

8. Handling baggage 

At the end of the booking and check-in flow, baggage handling integration ensures that checked items are tracked accurately from drop-off to final delivery. When a passenger checks in their baggage, it is sent directly to the baggage handling system, where it is scanned and assigned a unique code. 

Once the baggage handling system scans the code, it is registered in the International Air Transport Association’s (IATA) worldwide baggage tracking system. This allows for real-time tracking of the baggage throughout its journey. 

Airports also assign a distinct 10-digit code to each item. This code is generated by specialized baggage management systems such as SITA Bag Manager or ARINC SmartBag, based on the flight’s itinerary. Each time a passenger checks in their luggage through an airport agent or a self-service drop, a baggage tag with a unique code is issued and attached to the baggage. This ensures that the baggage can be easily identified and tracked throughout its transportation process. 

III. Pre-requisites to issue airline tickets in the flight booking process 

Ticketing in the airline industry is a crucial step in flight booking process, and airlines have strict requirements for who can issue tickets on their behalf. This is primarily driven by financial considerations. 

Airlines aim to have a global network of agents and booking sites to sell their tickets. But, they also want to ensure that this process is controlled and regulated. That’s why accrediting organizations have been established to act as payment intermediaries between airlines and agents. These organizations provide a payment guarantee to airlines for tickets sold by agents, so that agents can sell tickets on behalf of the airlines. This means that sellers must be accredited to sell tickets on behalf of an airline. 

There are two major organizations that provide ticketing accreditation on a global scale: 

International Air Transport Association (IATA) 

The IATA is the largest international airline association in the world, representing nearly 300 member airlines from over 170 countries. One of IATA’s key responsibilities is managing the Billing and Settlement Plan (BSP).  

BSP is a payment processing system that collects and distributes payments and commissions among member airlines and agents. For agents registered outside of the United States to issue tickets for any IATA airline, they must be IATA accredited. 

Airlines Reporting Corporation (ARC)

The ARC is another significant organization that provides ticketing accreditation in flight booking process, specifically for agents registered in the United States or US territories. CAR has over 200 member airlines and acts as a payment intermediary between agents and airlines through their payment processor.  

The ARC (Airlines Reporting Corporation) is the second major accreditation organisation, providing ticketing accreditation specifically for agents registered in the United States or US territories. ARC has over 200 member airlines and acts as the payment intermediary between US agents and airlines. Agents registered in the United States must be ARC-accredited to issue tickets for ARC member airlines. To sell tickets directly on behalf of airlines, sellers must hold either IATA or ARC accreditation.

These accreditation requirements ensure that the ticketing process is secure and reliable for both airlines and passengers, while also maintaining financial accountability between airlines and agents.

IV. How flight booking system benefits process of ticket booking

If we see from the customer’s end, an online booking engine offers a passenger with various benefits.  

1. Direct versus indirect channel economics

The fundamental decision for any airline is the mix between direct distribution (airline website, mobile app) and indirect distribution (GDS, OTAs, metasearch, traditional travel agents). Direct distribution preserves customer relationship, eliminates GDS distribution fees that typically range from USD 6 to USD 18 per booking, and enables direct ancillary upsell. Indirect distribution captures audiences the airline cannot reach efficiently on its own, particularly business travel managed through corporate booking tools.

The trend over the past decade has been steady investment in direct channels supported by NDC, but indirect channels still dominate in many markets and customer segments. The booking platform architecture must support both, with consistent inventory, fare, and ancillary visibility across channels.

2. Merchandising and ancillary revenue is no longer optional

For ultra-low-cost carriers, ancillaries now generate 52% to 62% of total revenue (IdeaWorksCompany, 2025). For traditional carriers, ancillaries account for 12% to 18%. In either case, the merchandising engine of a booking platform is no longer a downstream upsell feature. It is a core revenue system that must support dynamic pricing, personalised offers, branded fare bundles, and integration with loyalty programmes at every step of the booking flow.

Booking platforms built without merchandising depth from the architecture stage typically require expensive refactoring within two or three years of launch.

3. NDC adoption: A strategic decision, not just technical

The New Distribution Capability standard developed by IATA is now mature and adopted by most major airlines, but adoption depth varies widely. NDC enables airlines to share rich content (ancillaries, branded fares, bundled offers) that the EDIFACT-based legacy GDS protocol cannot easily handle. It also reduces dependence on GDS intermediaries and gives airlines more control over their distribution.

For OTAs and travel management companies, NDC integration is now a competitive requirement. Booking platforms built today should treat NDC as a primary distribution channel alongside GDS, not as a future enhancement.

4. Payment and refund architecture is more complex than it looks

A multi-currency, multi-payment-method booking flow with appropriate refund handling, PCI DSS Level 1 compliance, fraud screening, and chargeback management is one of the most operationally critical components of the platform. Failure modes here directly hit revenue. Payment gateway selection, currency conversion strategy, settlement timing, and refund workflow design should be architectural decisions, not late-stage configurations.

5. Regulatory and accreditation scope drives integration complexity

For an OTA or travel agency, the path from “I can show flights” to “I can issue tickets” runs through IATA BSP or ARC accreditation, which requires demonstrated financial standing, operational controls, and bonded payment arrangements. The platform must support BSP/ARC reporting requirements from the start. For airlines operating across multiple jurisdictions, regulatory variation across passenger rights legislation (EU 261, US DOT rules, ANAC in Brazil, CAA in the UK) drives material variation in booking flow design, particularly around disruption handling and refund rules.

6. Mobile and offline experience matter at the edges

The booking flow does not end at confirmation. Mobile check-in, boarding pass delivery, real-time flight status, baggage tracking, and disruption notification are increasingly the touchpoints that determine customer retention. Booking platforms that treat mobile as a downstream channel rather than a co-primary surface miss the loyalty-driving moments of the journey.

V. How Adamo Software approaches flight booking platform development

Adamo Software builds custom travel software across the booking, distribution, and operations stack. Our work in flight booking and related travel platforms draws on production deployments for clients across Europe, Asia, and Australia, including TravelGate (a travel API gateway and connectivity platform serving European OTAs), Flexlog, Productpine, Adventure Tours, Air Canada and OTA clients whose platforms operate at meaningful daily transaction volume.

The technical patterns required for a flight booking platform, including real-time inventory query across GDS and NDC sources, multi-currency pricing with dynamic conversion, payment orchestration across multiple gateways and settlement systems, PNR generation and management, merchandising and ancillary upsell engines, and integration with downstream systems for check-in and disruption handling, are the same patterns we have built and operated for our travel clients. Our travel and hospitality software practice has shipped GDS integrations (Amadeus, Sabre, Travelport), NDC-enabled distribution platforms, and end-to-end booking flows in production environments.

We work with airlines, OTAs, and travel management companies on three engagement models for booking platform projects. Full custom builds for operators whose business model or technical requirements are not adequately served by mainstream booking products. Extension and customisation of existing booking platforms, including custom merchandising modules, NDC migration, payment infrastructure upgrades, and integration with specific GDS, NDC, or direct airline connections. And integration projects connecting booking platforms to upstream inventory sources, downstream operations systems, payment gateways, and customer-facing apps.

VI. Build a Flight Booking Platform That Captures the Right Revenue

A booking platform succeeds or fails on three things: distribution depth across GDS, NDC, and direct channels; merchandising architecture that treats ancillaries as core revenue rather than upsell; and payment, refund, and regulatory infrastructure built right from day one. Adamo Software combines travel engineering expertise, GDS and NDC integration capability, and the operational depth to ship booking platforms that handle real-world scale. If you are evaluating a custom build, NDC migration, or significant booking platform extension, our team can walk you through architecture decisions and realistic scope estimates.