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Re: Littles Law in Practice

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  • Dennis
    Jean, The Cycle Time, the cadence that the overall process releases product - in this case flights full of passengers, hasn t changed. The same number of
    Message 1 of 17 , Jan 1, 2010
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      Jean,

      The Cycle Time, the cadence that the overall process releases product - in this case flights full of passengers, hasn't changed. The same number of listed passengers are still making it to the gates and leaving on the same number of flights at the same intervals. The same ticket prices are in place. So from an airport and airline standpoint, the value exchanged is unchanged. But the increased Lead Times and the resulting increased Work in Process have increased costs and reduced the quality of service in the airport.

      Since we have a fixed cycle time (departure schedule) the airlines can't get passengers out of the airport any faster. The airlines need to decrease Lead Time (time passengers spend in the airport) to reduce WIP. To reduce Lead Time, they need to reduce the arrival rate of new passengers. To this end, they have been making public service announcements to show up at the airport no more than 2 hours before a domestic flight.

      Increasing internal costs to get them to the gate faster or increase services at the gate area may increase quality of service - but it does not improve the value exchange of the airport or the airlines.

      Dennis Stevens



      --- In kanbandev@yahoogroups.com, Jean Tabaka <jean.tabaka@...> wrote:
      >
      > Indeed Dennis,
      >
      > Thanks for sharing. Queue times and total cycle times are being strained ina
      > very real situation. Our dlilemma; who has put the cost of delay of the
      > queue sizes? Who is tracking the value stream? Hmm... The airlines are still
      > measured on on-time departures. This has not beeen correlated with "How many
      > listed passengers made it to the gate through the various queues?" In other
      > words, how much value did we get? Or, "We got our value because they already
      > paid for the ticket so we don't care." That sounds more like cost-tracking.
      >
      > Happy flying in 2010,
      > Jean
      >
      > On Wed, Dec 30, 2009 at 3:31 PM, Henrik Kniberg <henrik.kniberg@...>wrote:
      >
      > >
      > >
      > > Very interesting, thanks for sharing :o)
      > >
      > > /Henrik
      > >
      > >
      > > On Wed, Dec 30, 2009 at 10:46 PM, Dennis <dennis.stevens@...> wrote:
      > >
      > >>
      > >>
      > >> I was watching TV today and came across this news story.
      > >>
      > >>
      > >> http://www.freep.com/article/20091227/NEWS05/912270419/1319/Worries-turn-into-long-lines-at-Detroit-airport
      > >>
      > >> In Detroit's airport passengers that are concerned about delays in
      > >> security have started arriving earlier for their flights in normal -
      > >> effectively increasing passenger Lead Time in the terminal. Planes continue
      > >> to depart at the same historical rate - so cycle time has remained constant.
      > >> The result, WIP is increasing dramatically. The extra passengers are
      > >> actually increasing costs at the airport while reducing the quality of
      > >> service and security. This is very consistent with what we see in software
      > >> development organizations.
      > >>
      > >> Dennis Stevens
      > >>
      > >>
      > >
      > >
      > > --
      > > Henrik Kniberg
      > > http://www.crisp.se/henrik.kniberg
      > > +46 (0)70 492 5284
      > >
      > >
      >
    • Jean Tabaka
      Thanks Dennis. I am thinking about this in a similar way. And yet, looking at the fact, as you point out, that cycle time and the overall cadence for the
      Message 2 of 17 , Jan 1, 2010
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        Thanks Dennis.

        I am thinking about this in a similar way. And yet, looking at the fact, as you point out, that cycle time and the overall cadence for the airlines (a plane arrives at the gate at a certain time and departs at a certain) has not changed is too limited a view. The real problem likes in the extra time it takes to get through security now before we get into that unchanged airline cycle time. I believe also that, at the ticket counters, agents may be required to ask additional security questions. With both of these longer queues, I think there will be much larger WIP (more people stuck in the process) and a longer cycle time for anyone person (longer ticket counter and security queues) to get to the very regular cycle time of the aircraft arrivals and departures.

        So, I am thinking of situations where we have limited our view of the value stream. Say, the development process. We may not have to add resources there. But with all the additional steps to get to the development process, who will pick up the cost and add additional resources if we are not looking at a larger view of all the queues? The value has dropped even though the development process maintained its regular cadence.

        Back to the real life example. Here in Denver, we have been told to start getting to the airport earlier than usual. For domestic flights, it is now 2 hours prior to departure instead of 1. For international, 3 hours instead of 2. I am interpreting that as accepting that there is more WIP and not enough resources will be applied to those (now longer) queues.

        I hope you can help me understand this more clearly because I think I am missing something. Thanks for answering. Oh, and I am flying internationally on Sunday so I may have some real time information to add :-)

        Jean

        On Fri, Jan 1, 2010 at 7:21 AM, Dennis <dennis.stevens@...> wrote:
         

        Jean,

        The Cycle Time, the cadence that the overall process releases product - in this case flights full of passengers, hasn't changed. The same number of listed passengers are still making it to the gates and leaving on the same number of flights at the same intervals. The same ticket prices are in place. So from an airport and airline standpoint, the value exchanged is unchanged. But the increased Lead Times and the resulting increased Work in Process have increased costs and reduced the quality of service in the airport.

        Since we have a fixed cycle time (departure schedule) the airlines can't get passengers out of the airport any faster. The airlines need to decrease Lead Time (time passengers spend in the airport) to reduce WIP. To reduce Lead Time, they need to reduce the arrival rate of new passengers. To this end, they have been making public service announcements to show up at the airport no more than 2 hours before a domestic flight.

        Increasing internal costs to get them to the gate faster or increase services at the gate area may increase quality of service - but it does not improve the value exchange of the airport or the airlines.

        Dennis Stevens



        --- In kanbandev@yahoogroups.com, Jean Tabaka <jean.tabaka@...> wrote:
        >
        > Indeed Dennis,
        >
        > Thanks for sharing. Queue times and total cycle times are being strained ina
        > very real situation. Our dlilemma; who has put the cost of delay of the
        > queue sizes? Who is tracking the value stream? Hmm... The airlines are still
        > measured on on-time departures. This has not beeen correlated with "How many
        > listed passengers made it to the gate through the various queues?" In other
        > words, how much value did we get? Or, "We got our value because they already
        > paid for the ticket so we don't care." That sounds more like cost-tracking.
        >
        > Happy flying in 2010,
        > Jean
        >
        > On Wed, Dec 30, 2009 at 3:31 PM, Henrik Kniberg <henrik.kniberg@...>wrote:

        >
        > >
        > >
        > > Very interesting, thanks for sharing :o)
        > >
        > > /Henrik
        > >
        > >
        > > On Wed, Dec 30, 2009 at 10:46 PM, Dennis <dennis.stevens@...> wrote:
        > >
        > >>
        > >>
        > >> I was watching TV today and came across this news story.
        > >>
        > >>
        > >> http://www.freep.com/article/20091227/NEWS05/912270419/1319/Worries-turn-into-long-lines-at-Detroit-airport
        > >>
        > >> In Detroit's airport passengers that are concerned about delays in
        > >> security have started arriving earlier for their flights in normal -
        > >> effectively increasing passenger Lead Time in the terminal. Planes continue
        > >> to depart at the same historical rate - so cycle time has remained constant.
        > >> The result, WIP is increasing dramatically. The extra passengers are
        > >> actually increasing costs at the airport while reducing the quality of
        > >> service and security. This is very consistent with what we see in software
        > >> development organizations.
        > >>
        > >> Dennis Stevens
        > >>
        > >>
        > >
        > >
        > > --
        > > Henrik Kniberg
        > > http://www.crisp.se/henrik.kniberg
        > > +46 (0)70 492 5284
        > >
        > >
        >


      • Dennis
        Got it. Thanks for clarifying. I see where you are coming from and you are right - the increased security will increase lead time. The airport would benefit
        Message 3 of 17 , Jan 1, 2010
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          Got it. Thanks for clarifying. I see where you are coming from and you are right - the increased security will increase lead time. The airport would benefit from reducing lead times.

          What I found interesting was that a big part of the problem Detroit is facing is behavioral. People are reacting to fear of delay by coming in - not 2 hours early (the requested and manageable service level) - but 5 and 6 hours before flights. Passenger's don't trust the airport to get them through in the 2 hour window. Fear is resulting in an unmanageable increase in WIP - a vicious cycle.

          We see this behavior in organizations. Something gets delivered late, so we get increased pressure to start sooner, this leads to greater WIP resulting in increased (not improved) lead times.

          Dennis


          --- In kanbandev@yahoogroups.com, Jean Tabaka <jean.tabaka@...> wrote:
          >
          > Thanks Dennis.
          >
          > I am thinking about this in a similar way. And yet, looking at the fact, as
          > you point out, that cycle time and the overall cadence for the airlines (a
          > plane arrives at the gate at a certain time and departs at a certain) has
          > not changed is too limited a view. The real problem likes in the extra time
          > it takes to get through security now before we get into that unchanged
          > airline cycle time. I believe also that, at the ticket counters, agents may
          > be required to ask additional security questions. With both of these longer
          > queues, I think there will be much larger WIP (more people stuck in the
          > process) and a longer cycle time for anyone person (longer ticket counter
          > and security queues) to get to the very regular cycle time of the aircraft
          > arrivals and departures.
          >
          > So, I am thinking of situations where we have limited our view of the value
          > stream. Say, the development process. We may not have to add resources
          > there. But with all the additional steps to get to the development process,
          > who will pick up the cost and add additional resources if we are not looking
          > at a larger view of all the queues? The value has dropped even though the
          > development process maintained its regular cadence.
          >
          > Back to the real life example. Here in Denver, we have been told to start
          > getting to the airport earlier than usual. For domestic flights, it is now 2
          > hours prior to departure instead of 1. For international, 3 hours instead of
          > 2. I am interpreting that as accepting that there is more WIP and not enough
          > resources will be applied to those (now longer) queues.
          >
          > I hope you can help me understand this more clearly because I think I am
          > missing something. Thanks for answering. Oh, and I am flying internationally
          > on Sunday so I may have some real time information to add :-)
          >
          > Jean
          >
          > On Fri, Jan 1, 2010 at 7:21 AM, Dennis <dennis.stevens@...> wrote:
          >
          > >
          > >
          > > Jean,
          > >
          > > The Cycle Time, the cadence that the overall process releases product - in
          > > this case flights full of passengers, hasn't changed. The same number of
          > > listed passengers are still making it to the gates and leaving on the same
          > > number of flights at the same intervals. The same ticket prices are in
          > > place. So from an airport and airline standpoint, the value exchanged is
          > > unchanged. But the increased Lead Times and the resulting increased Work in
          > > Process have increased costs and reduced the quality of service in the
          > > airport.
          > >
          > > Since we have a fixed cycle time (departure schedule) the airlines can't
          > > get passengers out of the airport any faster. The airlines need to decrease
          > > Lead Time (time passengers spend in the airport) to reduce WIP. To reduce
          > > Lead Time, they need to reduce the arrival rate of new passengers. To this
          > > end, they have been making public service announcements to show up at the
          > > airport no more than 2 hours before a domestic flight.
          > >
          > > Increasing internal costs to get them to the gate faster or increase
          > > services at the gate area may increase quality of service - but it does not
          > > improve the value exchange of the airport or the airlines.
          > >
          > > Dennis Stevens
          > >
          > >
          > > --- In kanbandev@yahoogroups.com <kanbandev%40yahoogroups.com>, Jean
          > > Tabaka <jean.tabaka@> wrote:
          > > >
          > > > Indeed Dennis,
          > > >
          > > > Thanks for sharing. Queue times and total cycle times are being strained
          > > ina
          > > > very real situation. Our dlilemma; who has put the cost of delay of the
          > > > queue sizes? Who is tracking the value stream? Hmm... The airlines are
          > > still
          > > > measured on on-time departures. This has not beeen correlated with "How
          > > many
          > > > listed passengers made it to the gate through the various queues?" In
          > > other
          > > > words, how much value did we get? Or, "We got our value because they
          > > already
          > > > paid for the ticket so we don't care." That sounds more like
          > > cost-tracking.
          > > >
          > > > Happy flying in 2010,
          > > > Jean
          > > >
          > > > On Wed, Dec 30, 2009 at 3:31 PM, Henrik Kniberg <henrik.kniberg@
          > > ...>wrote:
          > >
          > > >
          > > > >
          > > > >
          > > > > Very interesting, thanks for sharing :o)
          > > > >
          > > > > /Henrik
          > > > >
          > > > >
          > > > > On Wed, Dec 30, 2009 at 10:46 PM, Dennis <dennis.stevens@> wrote:
          > > > >
          > > > >>
          > > > >>
          > > > >> I was watching TV today and came across this news story.
          > > > >>
          > > > >>
          > > > >>
          > > http://www.freep.com/article/20091227/NEWS05/912270419/1319/Worries-turn-into-long-lines-at-Detroit-airport
          > > > >>
          > > > >> In Detroit's airport passengers that are concerned about delays in
          > > > >> security have started arriving earlier for their flights in normal -
          > > > >> effectively increasing passenger Lead Time in the terminal. Planes
          > > continue
          > > > >> to depart at the same historical rate - so cycle time has remained
          > > constant.
          > > > >> The result, WIP is increasing dramatically. The extra passengers are
          > > > >> actually increasing costs at the airport while reducing the quality of
          > > > >> service and security. This is very consistent with what we see in
          > > software
          > > > >> development organizations.
          > > > >>
          > > > >> Dennis Stevens
          > > > >>
          > > > >>
          > > > >
          > > > >
          > > > > --
          > > > > Henrik Kniberg
          > > > > http://www.crisp.se/henrik.kniberg
          > > > > +46 (0)70 492 5284
          > > > >
          > > > >
          > > >
          > >
          > >
          > >
          >
        • Dale Emery
          Hi Dennis, Since we have a fixed cycle time (departure schedule) the airlines can t get ... I see several additional factors here: Standard deviation,
          Message 4 of 17 , Jan 1, 2010
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            Hi Dennis,

            Since we have a fixed cycle time (departure schedule) the airlines can't get passengers out of the airport any faster. The airlines need to decrease Lead Time (time passengers spend in the airport) to reduce WIP. To reduce Lead Time, they need to reduce the arrival rate of new passengers. To this end, they have been making public service announcements to show up at the airport no more than 2 hours before a domestic flight.

            I see several additional factors here: Standard deviation, deadlines, and sentient WIP.

            In my extensive experience, a non-trivial percentage of airline passengers are sentient. And when a WIP item can adjust its own behavior, that complicates things.

            Further, unlike non-sentient WIP (e.g. someone waiting in line to purchase a country music CD), sentient WIP items have individual goals related to the system, and the goals have hard deadlines. Sure, they want to get through the system with the lowest Lead Time they can manage. But each has a more important goal: Be on the plane when the door closes.

            Given that, passengers need some way to accommodate not only the increased mean response time in the security queue, but also the (perceived or real) increase in standard deviation. If the mean wait at the security queue is okay, then airport, airline, and TSA staff may or may not care so much about standard deviation. But each individual passenger sure does. High mean response time is a bother; high standard deviation can be disastrous.

            So passengers do a reasonable thing: They trade off some mean for some standard deviation. They're willing (reasonably so) to wait far longer on average, as long as they don't miss their plane.

            Unfortunately, the the system involves an amplifying feedback loop: People report long waits at the airport, so passengers show up early, which increases the waits at the airport, which increases the reports of long waits at the airport...

            One challenge: How reliable is the information about Lead Time? And do passengers (sentient or not) believe what they're being told about various queue times in the system? If even a small percentage of passengers can't make their way through the whole system in two hours, then it's not a good idea to arrive only two hours before flight time.

            An airport queue story: At the Sacramento airport, there's an escalator up from the ticketing area to the security area. The zigzag stanchion starts at the very top of the escalator. Until a few months ago, there was always a TSA person at the bottom of the escalator who throttled the flow: If the stanchions were full, you had to wait at the bottom of the escalator until there was room. That small part of the airport was a limited-WIP pull system.

            Several months ago I noticed that the TSA was no longer throttling the flow. That was no big deal, though, because lately the airport hasn't been crowded. But one day I got to the top of the escalator and the stanchions were packed full. There was nowhere to go, and the packed escalator was still trying to dispense people. Complicating this, numerous non-sentient passengers had stepped off the escalator and stopped to adjust their undies rather than moving forward. I pushed forward (literally a push system now), but things were very awkward, especially given the woman, two toddlers, and baby carriage halfway up the escalator.

            When I got to the front of the stanchions, I told the TSA person there (the one who checks ID and boarding pass) about the problem. She said she'd take care of it. I didn't notice that she did anything, but by then I was focused on loading my crap onto the conveyor belt for the scanner.

            A few weeks later, I arrived at the airport, checked in, and headed for the escalator. But the escalator was taped off, and a sign directed passengers to take the old-fashioned manual-type stairs. Being a geek, I immediately thought of this in terms of queuing systems. The escalator is a server whose sole purpose is to deliver people from one queue to another. Removing that server consolidated the two queues into one. And then there's the whole "don't optimize the upstream servers if work is bunching up downstream" principle.

            Dale

            --
            Dale Emery
            Consultant to software teams and leaders
            Web: http://dhemery.com
            Weblog: http://cwd.dhemery.com

          • Dean
            Nice discussion. Good point. This is not only a math problem. It is a social system. Knowledge of psychology is necessary. Little s Law helps us understand
            Message 5 of 17 , Jan 1, 2010
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              Nice discussion. Good point. This is not only a math problem. It is a social system. "Knowledge of psychology" is necessary. Little's Law helps us understand the system but it is not enough.

              And I agree, "knowledge of variation" helps us better understand the customer experience. Customer's don't care as much about the average performance. They care about their specific experience.

              This discussion reveals a real world application of Deming's theory.
            • Steve Freeman
              ... That said, in London the airports are essentially shopping malls with some planes attached. I wonder if the concessions are doing just fine out of this
              Message 6 of 17 , Jan 2, 2010
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                On 1 Jan 2010, at 15:21, Dennis wrote:
                > Increasing internal costs to get them to the gate faster or increase services at the gate area may increase quality of service - but it does not improve the value exchange of the airport or the airlines.

                That said, in London the airports are essentially shopping malls with some planes attached. I wonder if the concessions are doing just fine out of this mess.

                S.
              • Akbar Zamir
                Just what I was thinking, although I don t know how directly BAA (in the case of London) benefits from increased takings by the concessions. The original post
                Message 7 of 17 , Jan 2, 2010
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                  Just what I was thinking, although I don't know how directly BAA (in the case of London) benefits from increased takings by the concessions.

                  The original post referred to the increasing costs to the airport of this extra 'WIP'. Can anybody elaborate on the source of this cost increase - apart from any additional labour costs incurred by the modified security procedures? 

                  Akbar


                  2010/1/2 Steve Freeman <smgfreeman@...>
                   

                  On 1 Jan 2010, at 15:21, Dennis wrote:
                  > Increasing internal costs to get them to the gate faster or increase services at the gate area may increase quality of service - but it does not improve the value exchange of the airport or the airlines.

                  That said, in London the airports are essentially shopping malls with some planes attached. I wonder if the concessions are doing just fine out of this mess.

                  S.


                • Dennis
                  The original article talked about how passengers, who feared missing their flights, were showing up five to six hours early for flights. The airport has
                  Message 8 of 17 , Jan 2, 2010
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                    The original article talked about how passengers, who feared missing their flights, were showing up five to six hours early for flights. The airport has capacity to effectively handle two hours worth of passengers and get them to the gates in time. If passengers were showing up two hours early, they would make their flights. However, passengers are showing up five and six hours early (double and triple the manageable lead time) - causing an unmanageable increase in WIP and overburdening the security and maintenance resources.

                    There is a vicious cycle in place here. The greater the WIP, the greater the lead time, the more resource is needed to get the people to the gate in time. As people hear about the long lead time, they get to the airport earlier and earlier - further burdening the airports capacity. More people would get to the gate faster and with less expense if the passengers would arrive two hours before their flights.

                    Dennis

                    --- In kanbandev@yahoogroups.com, Akbar Zamir <akbar_zamir@...> wrote:
                    >
                    > Just what I was thinking, although I don't know how directly BAA (in the
                    > case of London) benefits from increased takings by the concessions.
                    >
                    > The original post referred to the increasing costs to the airport of this
                    > extra 'WIP'. Can anybody elaborate on the source of this cost increase -
                    > apart from any additional labour costs incurred by the modified security
                    > procedures?
                    >
                    > Akbar
                    >
                    >
                    > 2010/1/2 Steve Freeman <smgfreeman@...>
                    >
                    > >
                    > >
                    > > On 1 Jan 2010, at 15:21, Dennis wrote:
                    > > > Increasing internal costs to get them to the gate faster or increase
                    > > services at the gate area may increase quality of service - but it does not
                    > > improve the value exchange of the airport or the airlines.
                    > >
                    > > That said, in London the airports are essentially shopping malls with some
                    > > planes attached. I wonder if the concessions are doing just fine out of this
                    > > mess.
                    > >
                    > > S.
                    > >
                    > >
                    > >
                    >
                  • Akbar Zamir
                    Thanks Dennis. I understand the reinforcing loop dynamic, and the inconvenience to passengers. What wasn t obvious to me was the source of cost increase to the
                    Message 9 of 17 , Jan 2, 2010
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                      Thanks Dennis.

                      I understand the reinforcing loop dynamic, and the inconvenience to passengers. What wasn't obvious to me was the source of cost increase to the airport. I think you've made that clear: airport maintenance labour costs increase as a result of more people milling about in the terminal.

                      As for the fear of missing one's flight, and that reinforcing loop: given that airport security appears to be the bottleneck, maybe they could control access to boarding passes - i.e. throttle the upstream process? I seem to recall that before the advent of online check-in facilities, check-in (i.e. upstream of security) times used to be more effectively constrained, so that it wasn't possible to enter the queue for airport security many hours in advance of the flight.

                      If it weren't possible to get a boarding pass until (say) 2 hours before the scheduled flight departure, wouldn't this prevent paranoid 'early bird' passengers from contributing to the queues at the security bottleneck?

                      When waiting in line at airport security, I certainly feel that the FCFS (First Come First Served) queuing discipline needs to be modified to take account of differing 'due times' for people.

                      Regards,

                      Akbar

                      2010/1/2 Dennis <dennis.stevens@...>
                       

                      The original article talked about how passengers, who feared missing their flights, were showing up five to six hours early for flights. The airport has capacity to effectively handle two hours worth of passengers and get them to the gates in time. If passengers were showing up two hours early, they would make their flights. However, passengers are showing up five and six hours early (double and triple the manageable lead time) - causing an unmanageable increase in WIP and overburdening the security and maintenance resources.

                      There is a vicious cycle in place here. The greater the WIP, the greater the lead time, the more resource is needed to get the people to the gate in time. As people hear about the long lead time, they get to the airport earlier and earlier - further burdening the airports capacity. More people would get to the gate faster and with less expense if the passengers would arrive two hours before their flights.

                      Dennis



                      --- In kanbandev@yahoogroups.com, Akbar Zamir <akbar_zamir@...> wrote:
                      >
                      > Just what I was thinking, although I don't know how directly BAA (in the
                      > case of London) benefits from increased takings by the concessions.
                      >
                      > The original post referred to the increasing costs to the airport of this
                      > extra 'WIP'. Can anybody elaborate on the source of this cost increase -
                      > apart from any additional labour costs incurred by the modified security
                      > procedures?
                      >
                      > Akbar
                      >
                      >
                      > 2010/1/2 Steve Freeman <smgfreeman@...>

                      >
                      > >
                      > >
                      > > On 1 Jan 2010, at 15:21, Dennis wrote:
                      > > > Increasing internal costs to get them to the gate faster or increase
                      > > services at the gate area may increase quality of service - but it does not
                      > > improve the value exchange of the airport or the airlines.
                      > >
                      > > That said, in London the airports are essentially shopping malls with some
                      > > planes attached. I wonder if the concessions are doing just fine out of this
                      > > mess.
                      > >
                      > > S.
                      > >
                      > >
                      > >
                      >


                    • Francisco Trindade (Frank)
                      When waiting in line at airport security, I certainly feel that the FCFS (First Come First Served) queuing discipline needs to be modified to take account of
                      Message 10 of 17 , Jan 3, 2010
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                        "When waiting in line at airport security, I certainly feel that the FCFS (First Come First Served) queuing discipline needs to be modified to take account of differing 'due times' for people."

                        That's what doesn't happen in check-in counters of big companies (EasyJet is my favorite example) , and causes a huge amount of stress (and probably cost increase, due to lost flights, delays in boarding passengers,etc..).

                        People try to avoid missing a flight by coming very early and then are in front of others who have less time to go through the queue. Unfortunately some companies havent understood this problem yet. If you try to take an EasyJet flight from London Gatwick, what you will see looks more like a fish market, with attendants shouting about the flights which are in the last call, so the passengers who are still stuck in the queue can move forward.

                        Cheers,
                        Francisco

                        On Sat, Jan 2, 2010 at 4:28 PM, Akbar Zamir <akbar_zamir@...> wrote:
                         

                        Thanks Dennis.


                        I understand the reinforcing loop dynamic, and the inconvenience to passengers. What wasn't obvious to me was the source of cost increase to the airport. I think you've made that clear: airport maintenance labour costs increase as a result of more people milling about in the terminal.

                        As for the fear of missing one's flight, and that reinforcing loop: given that airport security appears to be the bottleneck, maybe they could control access to boarding passes - i.e. throttle the upstream process? I seem to recall that before the advent of online check-in facilities, check-in (i.e. upstream of security) times used to be more effectively constrained, so that it wasn't possible to enter the queue for airport security many hours in advance of the flight.

                        If it weren't possible to get a boarding pass until (say) 2 hours before the scheduled flight departure, wouldn't this prevent paranoid 'early bird' passengers from contributing to the queues at the security bottleneck?

                        When waiting in line at airport security, I certainly feel that the FCFS (First Come First Served) queuing discipline needs to be modified to take account of differing 'due times' for people.

                        Regards,

                        Akbar

                        2010/1/2 Dennis <dennis.stevens@...>

                         

                        The original article talked about how passengers, who feared missing their flights, were showing up five to six hours early for flights. The airport has capacity to effectively handle two hours worth of passengers and get them to the gates in time. If passengers were showing up two hours early, they would make their flights. However, passengers are showing up five and six hours early (double and triple the manageable lead time) - causing an unmanageable increase in WIP and overburdening the security and maintenance resources.

                        There is a vicious cycle in place here. The greater the WIP, the greater the lead time, the more resource is needed to get the people to the gate in time. As people hear about the long lead time, they get to the airport earlier and earlier - further burdening the airports capacity. More people would get to the gate faster and with less expense if the passengers would arrive two hours before their flights.

                        Dennis



                        --- In kanbandev@yahoogroups.com, Akbar Zamir <akbar_zamir@...> wrote:
                        >
                        > Just what I was thinking, although I don't know how directly BAA (in the
                        > case of London) benefits from increased takings by the concessions.
                        >
                        > The original post referred to the increasing costs to the airport of this
                        > extra 'WIP'. Can anybody elaborate on the source of this cost increase -
                        > apart from any additional labour costs incurred by the modified security
                        > procedures?
                        >
                        > Akbar
                        >
                        >
                        > 2010/1/2 Steve Freeman <smgfreeman@...>

                        >
                        > >
                        > >
                        > > On 1 Jan 2010, at 15:21, Dennis wrote:
                        > > > Increasing internal costs to get them to the gate faster or increase
                        > > services at the gate area may increase quality of service - but it does not
                        > > improve the value exchange of the airport or the airlines.
                        > >
                        > > That said, in London the airports are essentially shopping malls with some
                        > > planes attached. I wonder if the concessions are doing just fine out of this
                        > > mess.
                        > >
                        > > S.
                        > >
                        > >
                        > >
                        >





                        --
                        --
                        Francisco Trindade

                      • Dale Emery
                        Hi Francisco, When waiting in line at airport security, I certainly feel that the FCFS ... I noticed a failed attempt to improve the queuing system at
                        Message 11 of 17 , Jan 3, 2010
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                          Hi Francisco,

                          "When waiting in line at airport security, I certainly feel that the FCFS (First Come First Served) queuing discipline needs to be modified to take account of differing 'due times' for people."

                          I noticed a failed attempt to improve the queuing system at check-in counters--related not to flight times but to another criterion for prioritizing: premier customers (i.e. first class and frequent fliers).

                          In the last six months I made enough cross-US flights that I nearly always earned an upgrade into first class. United has a special check-in line for first class passengers. On a typical day, the high priority queue would have eight passengers and one server. The economy queue would have twenty passengers and three or four servers. And every now and then the four-server economy queue was actually shorter than the one-server high-priority queue. So most of the time I got in the economy queue.

                          I don't think I ever spent more time in the economy queue than I would have in the "high priority" queue. From time to time I spent more time in the high-priority queue than I would have in the economy queue. Yes, I admit that I tracked that.

                          Dale

                          --
                          Dale Emery
                          Consultant to software teams and leaders
                          Web: http://dhemery.com
                          Weblog: http://cwd.dhemery.com

                        • Chris
                          I had the joy of standing in a queue a few weeks ago. The best solution I could come up with was two queues into all the servers. The first class queue gets
                          Message 12 of 17 , Jan 3, 2010
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                            I had the joy of standing in a queue a few weeks ago. The best solution I could come up with was two queues into all the servers. The first class queue gets serviced before standard class. This would prevent the first class server being idle as well. 

                            Regards

                            Chris
                            (Sent from my iphone.) 

                            On 3 Jan 2010, at 22:05, Dale Emery <dale@...> wrote:

                             

                            Hi Francisco,

                            "When waiting in line at airport security, I certainly feel that the FCFS (First Come First Served) queuing discipline needs to be modified to take account of differing 'due times' for people."

                            I noticed a failed attempt to improve the queuing system at check-in counters--related not to flight times but to another criterion for prioritizing: premier customers (i.e. first class and frequent fliers).

                            In the last six months I made enough cross-US flights that I nearly always earned an upgrade into first class. United has a special check-in line for first class passengers. On a typical day, the high priority queue would have eight passengers and one server. The economy queue would have twenty passengers and three or four servers. And every now and then the four-server economy queue was actually shorter than the one-server high-priority queue. So most of the time I got in the economy queue.

                            I don't think I ever spent more time in the economy queue than I would have in the "high priority" queue. From time to time I spent more time in the high-priority queue than I would have in the economy queue. Yes, I admit that I tracked that.

                            Dale

                            --
                            Dale Emery
                            Consultant to software teams and leaders
                            Web: http://dhemery. com
                            Weblog: http://cwd.dhemery. com

                          • Michele
                            What if every passenger got an airport entry ticket . This ticket should have a time window which said when he could enter the airport (or a certain area of
                            Message 13 of 17 , Jan 4, 2010
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                              What if every passenger got an "airport entry ticket". This ticket should have a time window which said when he could enter the airport (or a certain area of it). That way the WIP could be controlled.

                              To take this to the next level, the time window could be calculated automatically and sent as sms to the passengers. This would also make it possible to move passengers back and forth in the queue (but maybe this violates the rule of Little's law that the system should be non-preemptive).

                              The time window would need to be large enough not to stress the passengers arriving through traffic, but small enough to make the lines short.


                              Michele


                              --- In kanbandev@yahoogroups.com, "Dennis" <dennis.stevens@...> wrote:
                              >
                              > I was watching TV today and came across this news story.
                              >
                              > http://www.freep.com/article/20091227/NEWS05/912270419/1319/Worries-turn-into-long-lines-at-Detroit-airport
                              >
                              > In Detroit's airport passengers that are concerned about delays in security have started arriving earlier for their flights in normal - effectively increasing passenger Lead Time in the terminal. Planes continue to depart at the same historical rate - so cycle time has remained constant. The result, WIP is increasing dramatically. The extra passengers are actually increasing costs at the airport while reducing the quality of service and security. This is very consistent with what we see in software development organizations.
                              >
                              > Dennis Stevens
                              >
                            • Rob Park
                              The premier line has a sometimes bigger effect in security. Such as in Denver last Monday. Premier line in security took about 15 min, where I d guess
                              Message 14 of 17 , Jan 6, 2010
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                                The premier line has a sometimes bigger effect in security.  Such as in Denver last Monday.  Premier line in security took about 15 min, where I'd guess economy security was 30-45 min.  This definitely has to mess with their standard deviation at that station.  

                                As much as we don't want to focus too much on any local optimization, what are we actually wanting to optimize?  I believe to reduce overall CT (from arrival at the airport to takeoff from the runway) and not reduce throughput, the place to focus is on the bottleneck, security.

                                Now at Columbus on Christmas Eve, lead time was 0 for both lines... plenty of capacity in the system.


                                On Sun, Jan 3, 2010 at 5:05 PM, Dale Emery <dale@...> wrote:
                                 

                                Hi Francisco,

                                "When waiting in line at airport security, I certainly feel that the FCFS (First Come First Served) queuing discipline needs to be modified to take account of differing 'due times' for people."

                                I noticed a failed attempt to improve the queuing system at check-in counters--related not to flight times but to another criterion for prioritizing: premier customers (i.e. first class and frequent fliers).

                                In the last six months I made enough cross-US flights that I nearly always earned an upgrade into first class. United has a special check-in line for first class passengers. On a typical day, the high priority queue would have eight passengers and one server. The economy queue would have twenty passengers and three or four servers. And every now and then the four-server economy queue was actually shorter than the one-server high-priority queue. So most of the time I got in the economy queue.

                                I don't think I ever spent more time in the economy queue than I would have in the "high priority" queue. From time to time I spent more time in the high-priority queue than I would have in the economy queue. Yes, I admit that I tracked that.

                                Dale

                                --
                                Dale Emery
                                Consultant to software teams and leaders
                                Web: http://dhemery.com
                                Weblog: http://cwd.dhemery.com





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