Travel Technology for Dummies: What Is a Booking Reference or PNR?

Complicated topics explained in a simple way: Today let us look at booking references or PNRs.

What is a booking reference or PNR? A booking reference, also referred to as a PNR or Record Locator, is the airline’s internal identifier for your flight booking within their computer system. It is generated by the airline’s computer system, not by the travel agent or GDS. If your flights involve different airlines, there are often separate PNRs for each carrier for use within their respective systems, but you may be given only the ticketing airline’s PNR.

Instead of the term “booking reference”, most times in the travel industry your hear Passenger Name Record – hence PNR. Per definition, in the airline and travel industry, a PNR is a (passenger name) record in the database of a Computer Reservation System (CRS*) that contains the itinerary of a passenger. So what is an itinerary? A travel itinerary is a schedule of events relating to planned travel, generally including destinations to be visited at specified times and means of transportation.

Everything at a Glance: the Super PNR

Now the question is: What is the difference between an itinerary and a PNR? PNR is the technical term for some or all parts (sometimes referred to as segments*) of an itinerary. In other words, an itinerary can have several PNRs. PNRs can consist of one or more segments. A PNR can be booked in one or more reservation systems (CRS) via various distribution channels (e.g. Global Distribution Systems – GDS). In order to be able to access these various PNRs in different systems, from time to time a Super PNR (sometimes also referred to as master itinerary) becomes necessary. A Super PNR is similar to a PNR, however, it can contain multiple PNRs which belong to the same trip.

Example: You fly from Europe/Asia to New York and further on to Orlando. While there are airlines which fly both legs (a leg is one flight from one departure airport to one arrival airport), most likely the most cost-efficient way would be to use a low-cost carrier (LCC) to fly domestic within the United States. In such a case, the flight from Europe/Asia to New York would be booked on a traditional carrier through a GDS, and the domestic flight directly with such LCC. Car rental could be added through another provider as well as accommodation through e.g. Airbnb. A PNR is booked in each of the respective systems with all of these PNRs belonging to the same itinerary. In this example, a Super PNR (e.g. SPNR01) would be created, which consists of e.g. EMEA01, DOME01, CAR001 and HOTEL1.

Sometimes even for the same segment of a booking, different PNRs will be created: e.g. when items are booked through one system (which could be a GDS) and stored in another system – a CRS. This is sometimes referred to as a carrier PNR. Even a simple return flight booking can have two or more PNRs: the GDS PNR and the carrier PNR (the one of the CRS). Now, if interline is added to the mix, which means a code share and thus a different operating carrier (e.g. booked on Lufthansa but actually flown on United), there might even be several PNRs in different CRSs for the same leg (the operating carrier PNR).

As you can see, there are a number of PNRs and it can be tough to keep the overview. Hence the above-mentioned Super PNR: basically a record consisting of all the different PNRs in order to find the respective booking in the respective system that belongs to the itinerary.

How Often Do PNRs Get Recycled?

The number of classical PNRs (not modern Super PNRs) with six digits is obviously not endless and thus PNRs need to be recycled. If you are lucky, you may win the lottery or get the same PNR number again after a few years (I would actually opt for the 1st option). The question is: How long until a PNR is refurbished? A booking reference is 6 character alphanumeric (36), so there are 36^6 = 2.18 billion possible combinations. The odds of winning the so far biggest lottery jackpot of $1.5 billion on January 13, 2016 were much higher than receiving the same PNR number twice: 175 million to one. Still, in 2016, according to IATA, 3.6 billion passengers (PAX) traveled. Flights can be booked 12 months in advance with a ticket being valid for up to 12 months after the first flight – so to be safe, PNRs may not be recycled within 24 months. These numbers would suggest that there are already not enough PNRs for the number of PAX. The answer to this problem lies in the fact that PNRs are system-specific. Two airlines can have PNRs of 123ABC with no risk of confusion. In order to get a unique trip identifier, the combination of system/airline code and PNR is needed. Even the largest airlines carry less than 150 million passengers per year (in 2015: American: 146 M, Southwest: 144 M, Delta: 136 M) and not all airlines are hosted by the same PSS, which provides enough room for unique identifiers before PNRs need to be recycled.

Latest News


One reference, one process, one industry: An IATA initiative known as ONE Order, now in early testing, could bring big changes to the airline industry's order-management systems. It is the concept of a single Customer Order Record, holding all data elements obtained and required for order fulfillment across the air travel cycle. Thus it eliminates today’s Passenger Name Record (PNR), Electronic Ticket (ETKT) and Electronic Miscellaneous Document (EMD) and combines the content of those into a single retail and customer focused order. The goal of this new data communications standard is to support the vision of simplified and improved airline sales.

*Some Definitions


One flight is a segment. Thus a non-stop round trip consists of two segments, a round trip with connection of at least 4 segments. Add a hotel and you get another segment. Add a rental car: another one. The industry average is about 2.5 flight segments per ticket. There is also the term “passive segment”. A passive segment (or passive booking) is a segment entered in a GDS that does not result in a ticket being issued. Typically passive segments are used by agents to generate itineraries or make notes. Passive segments are also used to enter bookings made outside the respective GDS in order to capture those bookings for further processing (e.g. back office processes such as expense management, etc.).

CRS (Central Reservation System)

A CRS is a Central Reservation System which is the airline reservation system – sometimes used along with a GDS (Global Distribution System) which is the distribution system (see difference here). The term CRS is not used so much any longer as it became part of a bigger system: the Passenger Service System (PSS) – which we will look at in a different post.


Open-jaw bookings can be one of the following: Destination open-jaw, where a passenger flies from one city to another but returns to the original city from a different place (MIA-FRA, MUC-MIA), origin open-jaw, where the passenger leaves from one city to another but returns to a different place (MIA-JFK, JFK-FLL), or double open-jaw with two totally separate legs (MIA-JFK, BOS-FLL). Using different airports in the same city is not considered an open-jaw, so MIA-JFK, EWR-MIA would still be a return trip as both airports are considered to be in New York. The open gaps between the cities show on the itinerary as ARNK, the same code that shows on an airline or agency’s GDS, which means “arrival unknown”. The reason for this is that airline reservation systems (and major GDSs) require the segments following on sequentially, so arriving at one city and then departing from another will cause the system to return an error message. The ARNK field tells the system that this is intentional and also allows for the ticketing system to blank the unused coupons of a ticket.

Ancillary services or merchandising:

Ancillary revenues are revenues introduced in the US in 2008 by almost all major airlines following the example of profitable low-cost carriers. Passengers pay extra for services which were previously included in the fares. An example of this is the baggage fee. In 2008, airlines had already earned more than USD 10.25 billion with ancillary revenues. One of the only airlines not introducing baggage fees was Southwest Airlines: their PSS was unable to process ancillary fees such as bag fees. Southwest converted this into the marketing campaign “Bags fly for free.” In 2014, airlines collected a staggering $38 billion in so-called “ancillary” revenues, which represents around 5 % of their total revenue. For some tickets, a merchandising revenue of up to 70 % of the total trip prize is not so far-fetched any longer.

Picture credit: Shutterstock / pCasper1774 Studio

This Post Has 17 Comments

  1. Avatarwp-user-avatar wp-user-avatar-150 alignnone photo
    Michael Strauss

    Dear Lena, the Booking Code is unique for the time being until it is recycled .. which is probably every 2 years. This is more or less what you can do with a 6 digit code limited to around 26 characters of the alphabet. Thanks, Michael

  2. Avatarwp-user-avatar wp-user-avatar-150 alignnone photo

    Hi Michael. The question is if the Booking Code unique is. In which cases it isn’t?

  3. Avatarwp-user-avatar wp-user-avatar-150 alignnone photo
    Michael Strauss

    Thank you, Christopher. This is very interesting. My readers as well as I are very blesse to have such knowledgeable people in our community who share their knowledge.

  4. Avatarwp-user-avatar wp-user-avatar-150 alignnone photo
    Christopher Bird

    On allocation of Record Locators (RLOCs) and their reuse.

    The actual possible number of RLOCs is rather less than the possible permutations. For Amadeus, the first character of the RLOC is only chosen from only about 10 characters. Also, I was working for an airline where we wanted to make sure that the returned RLOC did not contain words that would not be safe for work. Since I was the person tasked with this, my emails contained a lot of words that would not be normal in a corporate environment. Needless to say, in house security came to pay a visit.
    “Algorithms” for allocation of RLOCs really are not published. It is internal to the reservation systems. And they don’t necessarily get allocated in any sequence. Again, taking the Amadeus PSS, the reuse of RLOCs can happen pretty quickly. RLOCs are released just after the last “segment” has been flown. It is a bit more convoluted than that, but it is quite possible for an RLOC to be reallocated within a day or so of a PNR expiring. In an airline that uses tickets, the original RLOC is stored with the ticket, but since that RLOC may have been reused, the actual domain key for PNR is a concatenation of the airline code, RLOC, and PNR creation date.

  5. Avatarwp-user-avatar wp-user-avatar-150 alignnone photo
    Michael Strauss

    Dear Martin,

    An airline ticket used to be either a paper ticket, which contained either coupons or vouchers or an electronic ticket (commonly referred to as an e-ticket). Since 2008 IATA airlines no longer issue paper tickets, hence today we basically refer to an e-ticket.

    I hope this helps. BTW, the Wikipedia entry in this case is pretty accurate and shows some good pictures of previous coupons/papertickets in case you are interested:


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