There are several reasons why Aer Lingus might not allow you to check in online, and understanding these can help you avoid last-minute stress and ensure a smooth travel experience. Online check-in is generally available for most flights, but certain situations or booking types can restrict this option. One common reason is that your booking may include special requirements or services that need to be handled directly by the airline. For example, if you are traveling with infants, require special assistance, or have specific medical needs, Aer Lingus usually requires you to check in at the airport so that the staff can provide the necessary support and verify all documentation. Another frequent cause is related to international travel regulations. If your itinerary involves flights that require additional visa checks or travel authorizations, especially when flying to or from countries with strict border controls, online check-in might be disabled until these documents are verified at the airport. Codeshare flights are another factor; if your ticket is booked through Aer Lingus but the flight is operated by a partner airline, you may be required to check in with the operating carrier directly, which can prevent Aer Lingus from offering online check-in for that segment. Technical issues can also sometimes prevent online check-in. This can include website errors, problems with your booking reference, or incomplete passenger information such as missing passport details. Ensuring your booking is fully up to date and that all required personal information is provided can often resolve these issues. Additionally, certain fare types may have restrictions. Some discounted or group fares might limit the availability of online check-in, requiring passengers to visit the airport counter instead. Lastly, timing can affect your ability to check in online. Aer Lingus typically opens online check-in 36 hours before departure for most flights, so attempting to check in too early or too late—outside of this window—will prevent access to the service. If you try to check in too close to the flight time, the system may automatically disable online check-in for security and operational reasons. In all these cases, checking in at the airport is the alternative, where Aer Lingus staff can assist you personally. It’s advisable to arrive early at the airport to allow enough time for check-in, security screening, and any additional document verification. To avoid problems, always verify your booking details, passport information, and travel documents well in advance. Contacting Aer Lingus customer service can also clarify specific restrictions related to your booking. Understanding why Aer Lingus might not allow online check-in helps passengers prepare accordingly and avoid delays on the day of travel.