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  • Writer's pictureJohn Boguslawski

What is Virtual Interlining (VI)?

Updated: May 10, 2022

Virtual Interlining, also known as VI or Self-Transfer fares, is the act of combining flights between carriers without Interline agreements or Code-share agreements. These interlining agreements are common in the travel industry and provide several advantages for travellers that include:

  • Handle the passenger’s baggage between multiple airlines ensuring the baggage is checked through to the final destination.

  • Allow the passenger to check-in for all the flights through to the final destination.

  • Ensure the passenger does not have to transfer to another airport or other terminals that require unnecessary security checks.

So why is VI great for the traveller?

Interline and Code-Share agreements are key elements of the aviation industry, but are very limiting for travellers. Virtual Interlining (VI) is a new perspective on travel that provides more options, cheaper fares and at times the fastest connections.

How VI works

The first thing to realize is that traditional interline agreements limit the total number of combinations that could be made between 2 destinations. The easiest way to visualize this is with an example. Consider a route like Seattle (SEA) to Nice (NCE) that has very limited direct flights (high season) and most reasonably priced fares are 1 or 2 stop itineraries offered by the major alliances (Star, One World, Sky Team). Let us do a quick analysis of the results.

Quickest - 1-stop Delta flights (13hr 15min) -> $1,053 USD

Cheapest - 2-stop Virtual Interline (VI) Alaska + TAP Portugal (17hr 15 min) -> $475 USD

The example above demonstrates the power of Virtual Interlining; providing viable, significantly less expensive (over 50%cheaper) options with a slightly longer travel time but giving travellers more connections and better fares. The advantages of Virtual Interlining are easy to quantify and these VI itineraries are viable on 40%+ of all global routes as either the cheapest, fastest or best itinerary.

Are there disadvantages to the Traveller?

The technology has a few friction points for the traveller which ensure that the price must be attractive in order to provide a viable alternative to traditional fares. These include:

  • Passenger is responsible for the “self-transfer” of baggage between the two carriers at the self-transfer airport

  • Passenger is responsible to check into each flight since there are no agreements between the carriers and in some cases to pass through additional security checkpoints

  • Passenger is at risk of missing a flight (and having to rebook the flight at their own expense in case of a missed connection)

The baggage transfer and checking into each flight is a minor inconvenience compared with potentially missing a connecting flight and having to rebook at your own expense, but this is where VI technology from providers such as leverage the power of big data, analytics and great fares from Low-Cost-Carriers (LCCs) and Full-Service-Carriers (FSCs) to create the best possible itineraries and protect consumers from missed connections.

Virtual Interline Guarantee

Protecting the customer from missing connections due to delayed flights or schedule changes is not only the biggest source of friction for the passenger, but could also lead to losses by the Travel Agency offering the fares. TripStack’s Virtual Interline Guarantee protects the traveller for any “Self-Transfer” connection greater than 2 hours by only selecting the best connections as well as giving the passenger plenty of time to transfer between the flights. Usual “Self-Transfer” times range between 3 and 5 hours with connections between 1.5 and 2 hours also possible. In the unfortunate case of a missed connection the passenger is rebooked at TripStack’s expense ensuring a great experience for the traveller.

Computational Complexity

The complexity in building great VI fares is due to the huge number of computational permutations involved in building VI itineraries with 1 or 2 transfers. Let us break down the Seattle (SEA) to Nice (NCE) example in terms of the number of possible connections that can be built if traditional interline agreements are not considered.

1 Self-Transfer VI

  • Seattle connects to 848 airports via traditional connecting flights

  • Nice connects to 622 airports via traditional connecting flights

  • 420 of the airports are potential hubs for 1 Self-Transfer VI

  • Through the 420 airports there are on average 117 options on the first-leg and 67 options on the second leg

  • The simple math gives us an astounding 3.3M possible flight options for a single date.

With 2 Self-Transfers the combinations explode even further producing over 127M combinations that the VI algorithms compute and reduce to only the viable combinations that may be selected by the travellers based on the duration, # of stops and off course the price of the itinerary. The sheer number of fares and the number of calculations makes Virtual Interlining incredibly difficult and limited to a handful of global technology providers.

Virtual Interlining has grown from a niche product offered by a few online players to a viable travel option during the Covid-19 pandemic. As the world recovers, Virtual Interlining will continue to grow and continue to be embraced by travellers, OTAs and TMCs and provide travellers more options and better prices.

To find out more and learn how Virtual Interlining can transform your travel business please reach out to

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