informs ® Vol. 35, No. 3, May–June 2005, pp. 191–201 doi 10.1287/inte.1050.0135 issn 0092-2102 eissn 1526-551X 05 3503 0191 © 2005 INFORMS America West Airlines Develops Efficient Boarding Strategies Menkes H. L. van den Briel, J. René Villalobos, Gary L. Hogg Department of Industrial Engineering, Arizona State University, PO Box 875906, Tempe, Arizona 85287-5906 {[email protected], [email protected], [email protected]} Tim Lindemann, Anthony V. Mulé Airport Services, America West Airlines, 111 West Rio Salado Parkway, Tempe, Arizona 85281 {[email protected], [email protected]} In September 2003, America West Airlines implemented a new aircraft boarding strategy that reduces the air- line’s average passenger boarding time by over two minutes, or approximately 20 percent, for full and nearly full flights. The strategy, developed by a team of Arizona State University and America West Airline’s personnel, is a hybrid between traditional back-to-front boarding and outside-inside boarding used by other airlines. Field observations, numerical results of analytical models, and simulation studies provided information that resulted in an improved aircraft-boarding strategy termed reverse pyramid. With the new boarding strategy, passengers still have personal seat assignments, but rather than boarding by rows from the back to the front of the airplane, they board in groups minimizing expected passenger interference in the airplane. The analytical, simulation, and implementation results obtained show that the method represents a significant improvement in terms of boarding time over traditional pure back-to-front, outside-inside boarding strategies. Key words: transportation: travel; programming: integer, applications. History: This paper was refereed. traditional metric used by commercial airlines to turnaround time, a factor that is particularly difficult Ameasure the efficiency of their operations is air- to shorten is passenger-boarding time. Airlines have plane turnaround time. Usually turnaround time (or little control over passenger-boarding time because turn time) is measured by the time between an air- they have limited control over passengers. Further- plane’s arrival and its departure. Recently, commer- more, passengers expect levels of service correspond- cial airlines have paid a great deal of attention to ing to the airline and the class of service they pay turnaround time because they believe it affects the for, from no preassigned seats on a discount airline overall success of an airline. One of the main fac- to boarding preference in first class on a full-service tors cited for the success of discount (or no-frills) air- airline. Therefore, while airlines want to speed up lines is the quick turnaround of their airplanes, which the passengers boarding airplanes, they have been helps them achieve high airplane utilization (Allen cautious in making changes to increase operational 2000, Michaels 2003). Thus, they make efficient use efficiency. of their primary capital investment, the aircraft. Long America West Airlines has made efforts to improve turnaround times decrease revenue-producing flying its turnaround performance. We worked on a joint time, while short turnaround times please customers project between America West and Arizona State Uni- and can increase airlines’ revenues. versity to cut passenger-boarding times for America Some factors that determine turnaround time West’s narrow-body passenger airplanes, such as the include passenger deplaning, baggage unloading, Airbus A320 and the Boeing 737, which have a cen- fueling, cargo unloading, airplane maintenance, cargo tral aisle and rows of three seats on both sides of loading, baggage loading, and passenger boarding. the aisle. The project included gathering data, devel- While improving any of these factors can decrease oping and solving mathematical programming and 191 van den Briel et al.: America West Airlines Develops Efficient Boarding Strategies 192 Interfaces 35(3), pp. 191–201, © 2005 INFORMS simulation models, and validating and implementing time, thus improving turnaround times and utiliza- the results. tion of the aircraft fleet. Like most commercial airlines, America West tra- America West Airlines ditionally boarded passengers in groups of those sit- ting in contiguous rows, ordering these groups from America West Airlines is a major US carrier based in the back to the front of the airplane (back-to-front Phoenix, Arizona, from which it serves more destina- approach), after boarding special groups (usually tions nonstop than any other carrier. America West first-class and special-needs passengers). The logic has hubs at Phoenix Sky Harbor International Airport behind this boarding procedure was that freeing the in Phoenix and McCarran International Airport in Las passengers making the journey to the back of the air- Vegas, Nevada. The airline’s modern, fuel-efficient plane from aisle obstacles would minimize conges- fleet consists of Airbus A320s, Airbus A319s, Boeing tion in the aircraft aisle. However, the back-to-front 757s, and Boeing 737s. By the end of 2006, America approach created congestion in a reduced area of the West expects to take delivery of new 110-seat Air- aisle among passengers of the same group, imped- bus A318s. The average age of the planes in America ing their access to overhead bins for stowing carry- West’s fleet is about 10 years. on luggage and making it difficult for them to reach America West is the only major airline not only their assigned seats. We conjectured that a different to survive, but also to thrive since the US airline boarding approach, with the groups composed of pas- industry was deregulated in 1978. The carrier began sengers dispersed throughout the airplane, might per- service on August 1, 1983, with three airplanes and form better. This conjecture was the basis for our 280 employees. It grew rapidly and, by 1990, had recommendation that America West should replace become a major airline, with annual revenues of over the existing back-to-front groups with groups made $1 billion. up of a widespread cross-section of the plane. Other Today, America West is a low-fare, full-service air- airlines have experimented with such alternatives as line. Its coast-to-coast route system includes 90+ des- the outside-in approach; but we found no formal and tinations across the United States, Mexico, Canada, comprehensive analysis of this approach or of the and Central America, with more than 800 daily back-to-front approach in the open literature. departures. It uses its Phoenix and Las Vegas hubs as gateways for travel throughout its route net- Previous Works and Project Strategy work. America West Express provides regional ser- vice through code-sharing agreements with Mesa Marelli et al. (1998) described a simulation-based Airlines, and Air Midwest, which are wholly owned analysis performed for Boeing. They designed the subsidiaries of Mesa Air Group, one of the largest passenger enplane/deplane simulation (PEDS) to regional airlines in the world. These regional carri- test different boarding strategies and different inte- ers channel traffic to America West’s hubs. Through rior configurations on a Boeing 757 airplane. PEDS the agreement with Mesa Air Group, America West showed that by boarding from the outside in, that is, window-seats first, middle seats second, and plans to extend its route system and enhance its aisle seats last, airlines could reduce boarding times flight schedule as America West Express increases its significantly. regional jet fleet to 77 airplanes by 2005. Shuttle by United was one of the first airlines to actually employ the outside-in strategy. While Kimes Project Objectives and Young (1997) reported that the airline imple- America West Airlines asked members of the indus- mented the method with a good degree of suc- trial engineering department of Arizona State Univer- cess, United Airlines later discontinued the method sity to take a critical look at the existing boarding and replaced it with its current approach: boarding procedures and to propose new strategies. all premium-class customers first, economy-plus cus- Our task consisted of recommending a boarding tomers second, customers seated in the last 10 rows of strategy that would minimize the average boarding economy third, and all remaining customers fourth. van den Briel et al.: America West Airlines Develops Efficient Boarding Strategies Interfaces 35(3), pp. 191–201, © 2005 INFORMS 193 Van Landeghem and Beuselinck (2002) conducted Problem Analysis another simulation-based study on airplane boarding Boarding interference is defined as an instance of a that showed that the fastest way to get people on an passenger blocking another passenger’s access to his airplane would be to board them individually by their or her seat. We assume that there is a correspon- row and seat number by calling each one of the pas- dence between minimizing the expected number of sengers individually to board the aircraft. Although passenger interferences and minimizing the board- this approach seems impractical, the authors claimed ing time. A passenger blocked by another passen- that it could halve total boarding time. In their study, ger takes longer to reach his or her seat than one they analyzed many alternative boarding patterns. who has free access. Therefore, as the number of pas- One pattern that seemed practical and efficient was sengers facing interference during the boarding pro- boarding passengers by half-row, that is, by splitting cess increases, the total boarding time increases. Thus, each row into a starboard-side group and a port-side by minimizing passenger interferences, we shorten group and then boarding the half-rows one by one. individual passengers’ seating times, which will ulti- While traditional computer-based simulation stud- mately shorten overall boarding times. ies are good tools for testing the performance of al- We defined two types of interferences: seat inter- ready identified alternatives, they do not provide effi- ferences and aisle interferences. Seat interferences occur cient mechanisms for constructing the most promising when passengers seated close to the aisle block other alternatives.