This article discusses the fundamental design difficulties of the fully automated baggage system originally planned for the New Denver Airport, and their implications for airport and airline management. Theory, industrial experience, and the reality at Denver emphasize the difficulty of achieving acceptable standards of performance when novel, complex systems are operating near capacity. United Airlines will thus make the Denver system “work” by drastically reducing its complexity and performance. Automated baggage systems are risky.
Airlines and airports considering their use should assess their design cautiously and far in advance, and install complementary, backup systems from the start. Ref: “The Baggage System at Denver: Prospects and Lessons,” Journal of Air Transport Management, Vol. 1, No. 4, Dec. , pp. 229-236, 1994. The City and County of Denver have built a massive new airport, the New Denver International Airport. It extends over 13,568 hectares (about 53 square miles); has 3 parallel North-South runways, 2 parallel East-West runways, and room for a total of 12 major runways.
In many ways the New Denver Airport represents a model of the airport of the future (de Neufville, 1995). At opening, the Airport will have cost about US $ 5 billion including the US $ 685 million contribution of the Federal Government and the over US $ 400 million investment of airlines in fitting out their passenger buildings, catering facilities and cargo centers (US Government Accounting Office, 1994). At the end of 1994, the bonded debt of the municipally owned Denver Airport System was more than US $ 3. 8 billion (City and County of Denver, 1994b).
A mechanized baggage system is at the heart of the New Denver Airport, as for all major new airports. In the case of Denver, this was to be something unique: the “Integrated Automated Baggage Handling System”, originally designed to distribute all baggage -including transfers — automatically between check-in, the aircraft and pick-up on arrival. Unfortunately, massive problems plagued this automated baggage system. (See Henderson, 1994, for example. ) Consequently, the New Denver Airport did not open in October 1993 as scheduled.
After missing later opening dates in April and May 1994, the Airport seems — as of January — likely to be open in March 1995. The delay would then be around 16 months. This delay costs the owners a lot. The interest on their bonded debt exceeded US $ 271 million for the single year of 1994 (Deloitte and Touche, 1994). The costs of maintaining the new airport are extra. A commonly accepted estimate of their costs of delay, endorsed verbally by officials in Denver, has been US $ 33 million a month. By March 1995, the delays may thus have cost them around US $ 500 million.
A year after the original opening date for the airport, the City and County of Denver borrowed a previously unscheduled US $ 257 million (City and County of Denver, 1994b). This delay is also expensive for the airlines. United Airlines invested about US $ 261 million, and Continental 73 million, in peripheral facilities in anticipation of the 1993 opening (United Airlines, 1993; US Government Accounting Office, 1994). FedEx likewise created a sorting center for around US $ 100 million. By the time the airport opens, the opportunity cost of the idle investments may have cost the airlines around US $ 50 million.
Both the airport owners and the airlines will also suffer losses to the extent that the automated baggage system does not deliver the productivity and efficiency that they had bargained for. Airline and airport management can learn much from this unfortunate experience. As indicated by the discussion that follows, the most fundamental problems with the automated baggage system designed for Denver had been predicted by theoretical studies and consulting reports, were avoidable, and should not be repeated.
The basic lesson is that automated baggage systems are risky, and therefore that airlines and airports considering automated baggage operations should assess their design and performance cautiously, and should implement them with the insurance of backup systems from the start. Design of the Automated Baggage System The fully automated baggage system originally planned for the New Denver Airport was unique in its complexity, its novel technology, and its anticipated capacity. It was designed to deliver each bag, including transfers, individually from check-in or the unloading of the aircraft to the outward bound aircraft or baggage reclaim.
The delivery mechanism consists of about 9 km. (5. 5 miles) of conveyors and over 27 km. (17 miles) of track on which circulate 4000 individual, radio-controlled carts, the so-called “destination coded vehicles” or “DCVs” (US Government Accounting Office, 1994). The capacity of each track was supposed to be 60 DCVs per minute, one a second. The essential layout of the automated baggage system at Denver is that conveyor belts feed the central network of DCVs. The bags do not flow continuously from the conveyor belts, however, as they do in traditional systems.
Each bag must independently be placed on its exclusive cart, and thus the delivery of the bags from the conveyor belts must be carefully controlled. Furthermore, the conveyor belt can only advance when there is an empty cart onto which the leading bag on the conveyor belt can be placed. The speed at which the conveyor belts can advance — and thus the performance of the entire system — depends on the rate of delivery of empty carts to each conveyor belt. This is a crucial point, at the root of the deeper difficulties with the original design.
The destination of each bag and its individual cart is defined by bar-coded labels, and transmitted by radio to tags (the “radio frequency identification” or “rf ids”) on the constantly moving vehicles. The operation of these vehicles is to be entirely controlled by a network of about 150 computers (Myerson, 1994; US Government Accounting Office, 1994). Speed in handling baggage is critical to achieving acceptable boarding and transfer times at Denver, since the distances are much greater those at other airports.
The space between the midfield concourses provides for two taxiways (one is standard) between the tails of the aircraft parked at the concourses, and the terminal building in which passengers check-in and pick up their bags is separated from the first concourse by an office block, a garage, and the Customs and Immigration (FIS) facilities. Speed has been considered crucial to the commercial success of the New Denver Airport, which the owners have marketed to the airlines as a highly efficient platform for hubbing operations because of its multiple parallel runways and prospective ability to 1
turn around aircraft flights very rapidly. United Airlines, the dominant airline at Denver, insisted on a rapid baggage handling system before signing its lease with Denver (Flynn, 1994b). The Denver system was thus originally designed to deliver bags much faster than current norms at major airports — at up to 38 kmh (24 mph) (US Government Accounting Office, 1994). The maximum delivery time was apparently set at 20 minutes for narrowbody and 30 minutes for widebody aircraft (Leigh Fisher, 1994).
The installers are quoted has having planned a “design that will allow baggage to be transported anywhere within the terminal within 10 minutes” (Airport Support, 1993). Despite the central importance of the automated baggage system, its design was largely an afterthought. This is a common practice, unfortunately. The Denver system was detailed well after the construction of the airport was under way and only about two years before the airport was to open. Being late, the design was thus subject to two important constraints. First, the geometry was tight.
The automated system had to fit within the confines of the airport passenger buildings and the underground tunnel connecting the concourses and the terminal; in many instances it was shoe-horned in at considerable inconvenience. Second, the schedule was tight. The system was to be implemented within 21 months, since Denver executed the contract only in January 1992. This schedule precluded extensive simulation or physical testing of the full design. Remarkably, the design of the fully automated baggage system at Denver did not include a meaningful backup system.
The planners provided neither a fleet of tugs and carts that could cope with the level of baggage expected, nor even access roads between the check-in facilities and the aircraft. Obvious Problems Highly visible mechanical problems have plagued the automated baggage system at Denver. As shown by television and widely reported in the trade and popular press, the baggage carts have jammed in the tracks, misaligned with the conveyor belts feeding the bags, and mutilated and lost bags (Flynn, 1994; Henderson, 1994; Myerson, 1994).
In 1994, United Airlines accounted for well over 60% of the passengers at Denver. Continental Airlines, which was the launch tenant for the New Airport and which used to operate a considerable hub at Denver, has largely canceled this operation: as of November 1994 it closed its crew base in Denver and cut its daily departures to 23 — about a tenth of the number offered by United. The airport consultant to the City and County of Denver predicted that by 1995 the United System will account for 90% of the passenger traffic at Denver (Leigh Fisher, 1994).
To deal with these difficulties, the contractors are installing additional equipment. For example, more laser readers will reduce the probability of misreading the destination of each bag. More controllers will slow down the carts, reduce misalignments with the conveyors feeding bags, and minimize the momentum that tossed bags off the carts. Overall, solutions to the mechanical problems come at the price of increased costs, reduced performance, and lower cost-effectiveness of the system. Deeper Problem of Reliable Delivery
The blatant difficulties with the automated baggage system designed for the New Denver Airport are almost certainly only the tip of the iceberg. There is a deeper, fundamental problem associated with all complex systems of handling baggage, cargo or materials. The more extensive and long-term difficulty is that of “reliable delivery times”. The fully automated system may never be able to deliver bags consistently within the times and at the capacity originally promised. This difficulty is a consequence of the extreme complexity of its design combined with the variability of the loads.
The entire system consists of well over a hundred waiting lines that feed into each other. For example, bags can only be unloaded from the aircraft and put into the system when the unloading conveyor belt is moving, this belt will only advance when there are empty carts on which to place bags, empty carts will only arrive after they have deposited their previous loads and have proceeded through the system, and so on. In short it is a complicated “cascade of queues”. The patterns of loads on the system are highly variable.
These depend on the season, the time of day, the type of aircraft at each gate, the number of passengers on these aircraft, the percentage traveling with skis, etc. , etc. There may be over a thousand reasonable scenarios! Managing a complex network of interacting, fully loaded queues efficiently for any single scenario is complicated. Managing these flows under all the realistic scenarios is exponentially more difficult. Learning how to do this appears to be a major, long-term research project.
Both airports, such as Frankfurt am Main, and companies attempting to automate their materials handling, have routinely spent years trying to make their systems work correctly under all circumstances (Auguston, 1994; Zitterstein, 1994). It is not clear that anyone, anywhere, is currently capable of managing a fully automated baggage system – one without any backup system or use of tugs and carts for transfers — to ensure full capacity, on-time performance, or is likely to be able to do so anytime in the near future (Knill, 1994).
Causes of Reliable Delivery Problem Any automated baggage system is subject to risk. The difficulties at Denver are not due to any obvious bad luck or incompetence. On the contrary, the contractor responsible for the installation (BAE Automated Systems) had enjoyed the reputation of being among the best and, on the strength of its good work, has been responsible for most of the major baggage systems recently installed in the United States.