1998 q1-the role of computer simulation in reducing airplane turn time

8/13/2019 1998 Q1-The Role of Computer Simulation in Reducing Airplane Turn Time

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The Role of Computer Simulation in Reducing Airplane Turn Time

Airplane turn time -- the time required to unload an airplane after itsarrival at the gate and to prepare it for departure again -- has increased

since the mid-1970s. Boeing has created a computer simulation thatcan help airlines reduce one of the key elements of turn time: passengerboarding (enplaning and deplaning). Decreasing passenger boardingtime may significantly lower the amount of time between revenue flights,and so increase profitability to airlines.

As airlines face increasing pressure to improve profitability, they are striving tocarry the greatest number of passengers feasible while keeping their fleets inrevenue service as much as possible -- all without compromising passengerconvenience.

One way airlines can move toward this goal is to reduce airplane turn time. Turntime is the time required to unload an airplane following arrival at a gate and toensure that the airplane is ready and loaded for its next departure. The mostsignificant elements of turn time include passenger enplaning and deplaning,cargo loading and unloading, airplane fueling, cabin cleaning, and galleyservicing.(figure 1)For many airlines the largest factor in turn time is the passenger boardingprocess. Boeing has conducted studies to help understand the airplane'scontribution to turn time. The company is continually working with customer

airlines to develop the data and tools necessary to help reduce turn time withoutsignificantly affecting passenger convenience.During its studies, Boeing considered the following:1 Historical trends.2 Existing turn time documentation.3 Computer simulation tools.4 Discrete event simulation.5 Simulation validation and testing.6 Applications of computer simulation.1 HISTORICAL TRENDSThe majority of the standard body fleet has been experiencing a gradual increasein airplane turn time since 1975. A useful indicator is the airlines' reportedincrease in through-stop times, the ground time required for flights continuing onto other destinations.(figure 2)Increased turn time is further substantiated byBoeing boarding rate studies. Since 1970, the actual speed at which passengersboarded an airplane (enplane rate) has slowed by more than 50 percent, down toas low as 9 passengers per minute.(figure 3)Similar through-stop time increases
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and boarding rates have been observed for wide-body airplanes. The trends aregenerally attributed to increased passenger carry-on luggage, more emphasis onpassenger convenience, passenger demographics, airline service strategies, andairplane flight distance (stage length). Boeing believes that these trends willcontinue unless the root causes are understood and new tools and processes

are developed to reverse the trend.

2 EXISTING TURN TIME DOCUMENTATIONBoeing has documented airplane turn time, including the passenger loadingprocess, for many years. This documentation describes the "generic" flow timeexpected for each airplane.(figure 1)The information helps an airline scheduleground times and establish airplane ground handling procedures. However, thegeneral nature of this information does not help airlines evaluate alternativeprocedures that could shorten flow time or help the airlines predict the impact ofthese procedures on passenger convenience.

3 COMPUTER SIMULATIONBoeing developed a computer simulation model to help airlines reduce turn time.This model analyzes the impact of interior configuration changes and variationsin passenger boarding procedures on the passenger boarding process. Thesimulation can quantify potential changes that an airline would normally identifyonly through costly and potentially disruptive in-service experiments. Thoughusing the model does not completely eliminate the need to conduct passengerloading trials, it can effectively quantify the expected outcome. This allows theairline to limit in-service trials.

Called the Boeing Passenger Enplane/Deplane Simulation (PEDS), this

simulation helps the user evaluate different passenger boarding scenarios andairplane interior configurations. The simulation:

Calculates passenger loading and unloading time, allowing the airline toconduct turn time trade studies analytically.

Allows individual factors such as interior configuration, passenger mix, andboarding scenarios to be varied and then estimates the expected timesavings.

Evaluates potential changes to interior configurations. Evaluates the effect of passenger behaviors associated with different

traveling populations. Helps quantify the effect of passenger behavior variations that an airline

may encounter over time.

4 DISCRETE EVENT SIMULATIONPEDS analyzes the passenger boarding process as a set of interrelatedelements through a technique called discrete event simulation. This modelingtechnique uses computer software to combine the effects of mathematicalqueuing theory with an analysis of random behavior.
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Random behavior associated with passenger loading can occur either in activitytiming (when events happen) or in action decisions (how people act). The morecomplex the overall activities are, the more difficult it is to accurately predict theimpacts of the random behavior.

Boeing began using discrete event simulation to understand interactions in thefactory environment. In 1994, Boeing started applying the discrete event model inpassenger boarding studies. PEDS assigns each passenger certain attributes,such as walking speed, type of carry-on luggage, luggage put-away time, andrelationship with other passengers (traveling alone or with a group). Thesimulation accounts for random behavior by applying probability distributions topassenger attributes.

In discrete event simulations, each activity happens at specific intervals. Theactivity starts, continues for a finite period of time, then stops. Similar to a carpassing along a city street, each airplane passenger enters the cabin and

"travels" to his assigned seat. Various other activities, such as passengersstanding in the aisle, assisting family members, or waiting to store luggage in theoverhead bins, act as traffic lights that prevent passengers from speedingthrough the cabin to their seats. PEDS breaks down the passenger loadingprocess into a series of finite elements of starting, moving, stopping, waiting, andrestarting, beginning with the moment the first passenger enters the cabin andending when the last passenger is seated.

In the computer model, engineers use the software to create a mathematicalscene of the interior of the airplane, complete with seats, overhead bins, aisles,and doors. Each passenger is individually modeled and assigned attributes that

describe some segment of the traveling population. The simulation then governsthe decisions of each passenger based on these attributes and the timing of eachevent (waiting or moving) as he or she passes through the cabin. In addition to varying passenger "speed," the simulation allows variation in otherattributes. Each run of the simulation calculates the total elapsed time andprovides visibility into the various "choke" points identified by the scenario. Toeliminate statistical bias, multiple simulations are run on the identical interiorconfiguration using different random number starting points, and the results arethen averaged over the multiple runs.The process begins by establishing a general airplane simulation. This simulationis then "tailored" using the airline's specific interior configuration, boardingprocedures, and passenger demographics. A series of baseline runs isconducted to validate PEDS predictions with the airline's in-service experience.This turn time baseline allows the airline to evaluate potential changes to interiorlayout or boarding procedures against existing time lines.


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5 SIMULATION VALIDATIONAND TESTINGA simulation is valid only if it accurately predicts what happens during actualevents. In order to validate PEDS, Boeing conducted two types of activities:

In-service observation.

Actual passenger loading tests.

In-service observation.Boeing engineers observed revenue passenger loading activities with differentairlines at several different airports around the world. The loading process wastimed and correlated to simulation predictions. These exercises were conductedon a random basis so that timed data would be representative of actualexperience. However, this method of validation had two limitations:

It did not allow observations of all the interac tions between passengers orwith the air plane configu ration.

It only validated simulation predictions of existing airline loadingprocedures.

Actual passenger loading tests.In order to provide additional information, Boeing conducted a series ofpassenger loading tests.The tests were conducted on a fully configured 757-200 airplane located in aBoeing factory. A loading platform was modified to simulate an airport passengerloading bridge, and a staging area was used to simulate an airport gate waitingarea. Trained airline flight attendants used procedures inside the airplane and at

the loading bridge that reflected actual airport and airline operations.

A total of 600 non-Boeing people, representative of the typical travelingpopulation, participated in the enplane/deplane tests. Each passenger wasrequested to bring carry-on luggage typical for a three- to four-hour flight. Thepassenger population was varied for each test, with each passenger participatingin only two sets of enplane/deplane tests to prevent "learning"that could alter thetest results. The following four enplane/ deplane scenarios were then run:

Door 1 only. Door 2 only.

Both Door 1 and Door 2. Both Door 1 and 2 with an alternative passenger loading method called

"outside-in."

The outside-in scenario involves loading passengers at the window seats first,middle seats next, and aisle seats last. The outside-in test was designed tovalidate the simulation's ability to handle nontraditional procedures.


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Each test was timed and videotaped for comparison with the simulation'spredictions. Video cameras located on the loading bridge and throughout thepassenger cabin recorded each test for later analysis.The tests showed that PEDS performed well in predicting both enplane and

deplane times for each scenario. However, the videotapes documented someunexpected interaction among passengers during the loading process. Forexample, several passengers stowed their carry-on luggage in overhead binslocated away from their seats. This happened while they were waiting behindpeople who were blocking the aisle, rather than waiting for the aisle to clear andthen stowing their luggage when they reached their seats. This additionalinformation allowed Boeing to refine PEDS to account for this type of behavior.

6 APPLICATIONS OF THE COMPUTER SIMULATIONPEDS offers several applications both for airlines and for Boeing:

Analysis of the impact of airplane interior configuration on turn time. Evaluation of potential changes to passenger loading procedures.

Airplane interior configuration.Both Boeing and the customer airline can usePEDS initially to help configure the airplane interior. PEDS improves theirunderstanding of how a proposed configuration affects passenger loading.Passenger boarding times become part of interior configuration decisions, similarto decisions made about aesthetic appearance and passenger comfort.Evaluation of potential changes to passenger loading procedures. Thesimulation also helps airlines evaluate potential changes to passenger loading

procedures. Boarding alternatives such as outside-in, multiple preboarding, oreven unassigned seating can be evaluated using an airline's target passengerpopulation. Airlines can quantify potential savings without incurring the expenseof boarding trials or risking passenger inconvenience. Airlines can use PEDS toevaluate even small procedural changes, such as increased involvement by flightattendants or emphasis on reduced passenger carry-on luggage.

Alternatives that show significant promise can then be tested in the field. PEDShelps airlines develop detailed implementation plans for new procedures andlogistics needed to decrease turn time, including flight attendant training andairport logistics.Boeing is currently working with a number of airlines to evaluate PEDS for theirspecific applications.SUMMARYDecreased airplane turn time can positively affect airline profitability. A newcomputer simulation developed by Boeing offers airlines an analytical method forevaluating changes to airplane configuration or passenger loading techniques


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and their impact on airplane turn times. The simulation is a cost-effective tool tohelp airlines rapidly predict results with a high degree of success.-------------------------------------------------- GETTING HELP WITH TURN TIME REDUCTIONThe Boeing Passenger Enplane/ Deplane Simulation (PEDS) offers airlines anadditional tool to help reduce turn time. Depending on an individual airline'soperation, other elements of turn time, such as cargo handling, cabin cleaning, orgalley servicing, may also be improved.Boeing has a team of turn time experts that can work with airlines to analyzespecific areas of concern. Airlines interested in evaluating solutions to their turntime problems should contact their local Field Service or Customer Requirementsrepresentative for assistance.--------------------------------------------------

EVALUATING TURN TIME ON THE NEW 757-300The initial application of the Boeing Passenger Enplane/Deplane Simulation(PEDS) was on the new 757-300 airplane. PEDS helps evaluate variouspassenger boarding scenarios to determine how to reduce airplane turn time.The 757-300 is a stretched derivative of the 757-200. It is 23 feet, 4 inches longerthan its predecessor and holds approximately 40 more seats.

Several potential customers for the 757-300 had told Boeing that, based on their

experience with other standard-body airplanes, they were concerned about thenew airplane's potentially greater turn time.

Boeing used the 757-200 as a baseline for evaluating passenger boarding on the757-300. PEDS predicted that passenger loading for the 757-200 would takeapproximately 22 minutes and that deplaning would take about 10 minutes. Thepredicted overall turn time for the 757-200 was 52.5 minutes, including cargohandling, fueling, galley servicing, and cabin cleaning. The estimated time wasbased on actual airline in-service turn times for the 757.

Applying PEDS to a 757-300 dual-class configuration with 240 passengers

showed that passenger loading would require 26 minutes, and that unloadingwould take about 12.5 minutes. The predicted overall turn time was 59 minutes,an increase of only 6.5 minutes over the 757-200.(figure 5a)Boeing then used PEDS to evaluate a number of alternative boarding scenarios.Simulation predictions were compared to the 757-200 passenger boarding test tovalidate results. Based on these validated predictions, it was possible to identifysignificant potential reductions to overall turn times for the 757-300. For example:
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Using Door 2 instead of Door 1, boarding time (enplaning and deplaning)was reduced by one minute.

Using Door 1 and Door 2 together saved five minutes. If alternative loading procedures were used -- such as the "outside-in"

method of loading (window seats first, middle seats next, and aisle seats

last) -- the savings could be as great as 17 minutes.(figure 5b)

PEDS showed that the new 757-300 could be operated within the normal 757turn time window of 60 minutes without making notable changes to existingprocedures. It also showed that turn time could be reduced significantly if airlinesused alternative passenger boarding methods.figure 1

figure 2
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figure 3

figure 5a


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figure 5b


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Scott Marelli, P.E.Senior Math/Modeling AnalystApplied Research and TechnologyBoeing Shared Services GroupGregory MattocksLead Engineer757 Configuration and Engineering AnalysisBoeing Commercial Airplane GroupRemick MerrySenior Specialist EngineerNew Airplane Customer ServiceBoeing Commercial Airplane Group

1998 q1-the role of computer simulation in reducing airplane turn time

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