This week's aviation headlines have been filled with news of a codeshare agreement between two of the world’s biggest airlines. <a href="https://www.thenationalnews.com/business/travel-and-tourism/2022/09/15/emirates-airline-and-united-airlines-announce-codeshare-agreement/" target="_blank">Emirates and </a><a href="https://www.thenationalnews.com/business/travel-and-tourism/2022/09/15/emirates-airline-and-united-airlines-announce-codeshare-agreement/" target="_blank">United Airlines</a> announced their new partnership in Washington on Wednesday. Emirates airline's president Tim Clark said the move was “a significant partnership that will unlock tremendous consumer benefit" and bring the UAE and the US closer. Scott Kirby, chief executive at United Airlines, added: “This agreement unites two iconic, flag carrier airlines who share a common commitment to creating the best customer experience in the skies." But how exactly does a partnership between two airlines impact travellers and why should holidaymakers care about codeshare announcements? Have you ever purchased a flight ticket with one airline, only to arrive at the airport to discover you’re actually flying with another airline? If so, chances are you’ve just experienced a codeshare partnership. <a href="https://www.thenationalnews.com/lifestyle/travel/you-can-now-earn-etihad-air-miles-on-gulf-air-flights-1.964629" target="_blank">Codesharing</a> is an agreement between two or more airlines to sell seats for the same flight. And, while multiple airlines can then issue their own tickets for a codeshare flight, only one airline will actually operate the plane and provide the crew. This is why travellers might find themselves flying with an airline other than the originally booked one. Most major airlines have codesharing partnerships with other airlines, and there are myriad reasons why. As a business arrangement between airlines, a codeshare can help expand into markets where they might not be as well known, extend their network coverage for a greater global reach and ultimately offer more opportunity to increase profits by selling tickets on more flights. While codeshare agreements sound like industry jargon, there are a few reasons why travellers might want to know about them. Perhaps the most obvious advantage is being able to earn frequent flyer miles, even when flying on a flight operated by another carrier. For instance, a member of the Etihad Guest frequent flyer programme flying on Swiss Airways would not normally earn miles. However, as these two airlines have a codeshare, passengers earn credit for those miles. To be eligible, the flight booked needs to have been sold and marketed by Etihad — an easy way to know if this is the case is to look for the airline's code at the start of the flight number. In this example, if the flight number starts with EY — then it's eligible for Etihad miles. Another big advantage is being able to book an entire trip on one ticket. This is especially useful for multiple connections. When no codeshare exists, travellers often have to book separate tickets with individual airlines for each leg of a lengthy journey. This means collecting baggage at each connection point, paying attention to the different weight allowances for each airline and checking-in at each airport. If there's a codeshare, all flights are booked on one ticket, with check-in once. Then the collection of luggage happens at the end of the journey. Codesharing also allows travellers to book flights on a platform they are familiar with to destinations not typically operated to by specific airlines. This is the case with Emirates's new agreement as travellers can book flights from Dubai to Hawaii on Emirates, or from New York to Karachi with United Airlines. Finally, premium passengers flying on a codeshare ticket can access more lounges, which can be useful flying from or through a destination by using the lounge belonging to the partner airline. Whether flying on a codeshare or not, there are a couple of drawbacks for travellers booking such tickets. The main disadvantage is that codeshare flights can be difficult to rebook or alter should travel plans change. This is because the airline passengers originally booked with doesn't have the final authority to make that change, instead it must coordinate with the operating airline to update any itinerary. Getting a free upgrade when flying on a codeshare ticket is also difficult. This is because as much as airlines are working in a partnership, they are still competitors and each airline would much rather prioritise a customer that has given money directly to them, than paid airfare to their competition. Airlines don’t hide the fact that a flight they are offering to sell is a codeshare. During the booking process, double check the operator for the flight. This information will be listed in the booking confirmation, as well as on the ticket. If booking a codeshare flight, make sure to go to the correct terminal to check-in. This might mean going to the terminal for the operating airline, not the airline that's been booked with.