‘Why Don’t They Just Land?’: Why the Best Diversion Airport May Not Be the Closest

While over 150,000 flights per day land at their intended destination, some divert due to weather, mechanical, or medical reasons. When a flight diverts, we’re often asked why the aircraft didn’t land at the nearest airport. While there are instances when landing as soon as possible is the best course of action—such as the recent Southwest flight 1380 or Air France flight 66 in 2017—most of the time the best outcome involves a more complicated calculation about where to divert a flight.

Technical diversions

Once the need for an immediate landing is ruled out, crews assess the situation to determine the best diversion airport to quickly fix the problem and get the passengers on to their destination. One of the first considerations is the amount of fuel onboard the aircraft. That number will inform which airports are considered as diversion points and if the aircraft will need to burn or jettison fuel. Aircraft are subject to a maximum landing weight, which varies by aircraft type and configuration. If a flight needs to return to its origin airport or divert early in flight, it may still be above its Maximum landing weight requiring holding to burn or jettison fuel.

LX18 burning fuel in various holding patterns to reduce landing weight prior to return to Zurich due to technical issue

Once the crew and dispatchers know where a flight can go, they have to decide where it should go. Ideally, an airline will divert to an airport where it has maintenance staff and facilities and multiple flights on which passengers can continue their journey. In this scenario, a Delta Air Lines flight from New Orleans to New York might divert to Atlanta, Delta’s home base where maintenance personnel and spare parts and additional flights are readily available. If that’s not possible, the flight crew and dispatchers work to find the best alternate airport.

Aircraft can only safely divert to suitable airports, that is, airports that can accommodate the aircraft in its current condition. With a technical issue like single engine operation, stuck flaps, or a landing gear malfunction, airports that would normally be suitable may now be off limits. Similarly, weather conditions are nearby airports may be out of limits if the aircraft is suffering from a technical issues.

For long-haul flights, a technical diversion can often mean returning to the origin airport even if it means bypassing numerous airports that could handle the aircraft. Remember, the goal is to as quickly as possible repair the aircraft and get the passengers on their way. Returning to the origin airport allows airlines to more quickly find a replacement aircraft or put passengers on other flights. Returning to the origin airport, even at a great distance may also serve the added benefit of reducing enough fuel weight that the aircraft does not need to hold before landing.

A Lufthansa flight returns to Frankfurt due to technical issue. The flight held briefly over the North Sea to further reduce landing weight

For other flights, the best diversion may be an airport that is a base or focus city for an alliance partner. An Iberia flight from Madrid to Mexico City may stop in Miami, a hub for Oneworld alliance partner American Airlines. American offers multiple flights per day to Mexico City from Miami and there are additional airlines that also fly that route who could also be used.

Scott Ramsey, managing director of dispatch operations at the American Airlines Integrated Operations Center, says that from customer service perspective the questions are, “Is it a quick fix? Who else serves the city? And do we need a rescue mission?” In October 2016, Ramsey mounted just such a mission when an American Airlines 787 diverted to Cold Bay, Alaska after experiencing an engine issue. Ramsey also notes that thanks to technology now available, it’s often possible to diagnose the technical issue while still in the air, speeding the time it takes technicians to prepare to receive and fix the aircraft once it is on the ground.

Medical diversions

In a medical emergency, the first step is to determine the severity of the situation. The crew onboard is trained in first aid, but they are not diagnosticians. For that, many airlines employ a service that allows aircrews to communicate directly with doctors on the ground to help. Crews will relay the symptoms and condition to the doctor. The flight crew is ultimately responsible for diverting (or not) to provide the patient with the best outcome.

An Air Canada flight from Vancouver to London returning to Vancouver due to medical emergency

If the flight crew decides to divert, they work with the airline’s operation center to determine the best diversion airport. All of the previously mentioned issues regarding operational suitability are considered, but the patient’s condition and medical needs are also taken into account. If a flight is nearby a major medical center or outstanding medical care, priority can be given to that airport. If the situation is dire, the crew can divert to the nearest suitable airport with available medical facilities. If the patient’s condition is stabilized, the crew may also elect to divert to an airport that will speed the process of getting the flight back in the air.

When selecting a diversion airport, dispatchers will run operational performance engine numbers. No one wants to divert a flight to an airport from which they can’t take off. As Ramsey explains, “We’re most concerned with the second segment phase of climb.” It is this phase of climb just after takeoff that can limit an aircraft’s performance. In an engine-out takeoff scenario, it’s critical to still be able to clear all obstacles at the end of the runway.

After diverting, local emergency services will help the person experiencing the medical issue off the aircraft and the flight will be prepared for departure. When a long-haul flight results in a medical diversion, the crew  runs the risk of “timing out”. For safety reasons, crews are limited in the number of hours they can be on duty before needing to rest for a certain number of hours. If the flight has diverted to a remote airport—for example if an Emirates flight from Dubai to Houston diverts to Goose Bay due to a medical emergency—by the time the flight is ready to depart the crew may not have enough hours in their duty day to fly all the way to Houston. The airline could elect to fly to a closer airport like Toronto or New York and then put passengers on connecting flights. Or they could send a second flight to collect passengers and carry them onward. A third option is an overnight stay.

The best outcome for all

When a diversion is necessary, the goal isn’t always to land as quickly as possible. In nearly every diversion situation, the best outcome will come from a balance of technical and passenger service considerations. This can lead to seemingly odd or counter-intuitive flight paths, but pilots, dispatchers, and air traffic controllers are professionals who base their decisions on the needs of the aircraft, passengers, and crew to ensure the safest possible flight and the quickest return to the skies.