Limits to Growth
Most of what we now know today as the sustainability movement owes a lot to The Limits to Growth report prepared in 1972 for the Club of Rome (and to Rachel Carson for environmental activism). Every person (consciously or not) approaches problems with a mental model. The team who prepared this report created a model to help them think through long-term problems facing humankind. They came to one essential conclusion:
If the present growth trends in world population, industrialization, pollution, food production, and resource depletion continue unchanged, the limits to growth on this planet will be reached sometime within the next one hundred years. The most probable result will be a rather sudden and uncontrollable decline in both population and industrial capacity.
I am following through on my promise from the last newsletter to apply the lessons from some systems thinkers that I admire, to present day issues confronting the National Airspace. What are the limits of growth on the NAS? It helps to explore what systems thinkers like Dana Meadows taught us in the broader context of sustainability writ large.
If you care about a sustainable world, Donella (Dana) Meadows is required reading. The model3 in the The Limits to Growth predicted, with a surprising degree of accuracy, the outcomes we see in the world today. Though they suggested remedial actions, the world has moved mostly on the path of what they called, “business as usual” (BAU)scenario. They also examined how technological progress would influence the outcomes. There are limits to growth. Growth in and of itself, is not a worthy goal. Whether we agree on the findings and recommendations or not1 we cannot ignore the value of a well defined model in guiding our actions.
To connect this to aviation, first we have to visit another body of work exemplified in the paper - Risk Management in a Dynamic Society: A Modelling Problem - by Jens Rasmussen. That oft cited (and rightfully, very famous) paper is probably not light reading2 and is behind paywalls so I will quote a bit extensively here:
In any well designed work system, numerous precautions are taken to protect the actors against occupational risk and the system against major accidents, using a ‘defence-in-depth’ design strategy. One basic problem is that in such a system having functionally redundant protective defenses, a local violation of one of the defenses has no immediate, visible effect and then may not be observed in action. In this situation, the boundary of safe behaviour of one particular actor depends on the possible violation of defenses by other actors, see Fig. 3 (added below). Therefore, in systems designed according to the defence-in-depth strategy, the defenses are likely to degenerate systematically through time, when pressure toward cost-effectiveness is dominating. Correspondingly, it is often concluded by accident investigations that the particular accident was actually waiting for its release.
The important issue is that the stage for an accidental course of events very likely is prepared through time by the normal efforts of many actors in their respective daily work context, responding to the standing request to be cost-effective. Ultimately, a quite normal variation in somebody’ s behaviour can then release an accident. Had this particular ‘ root cause’ been avoided by some additional safety measure, the accident would very likely be released by another cause at another point in time. In other words, an explanation of the accident in terms of events, acts, and errors is not very useful for design of improved systems.
I read Rasmussen’s figure above as
a) The boundary to economic failure moving in as management and the ecosystem pushfor efficiency
b) The boundary to unacceptable work load as workers or unions modulating effort with the gradient to least effort pushing away from unacceptable workload boundary.
Both pushing the potential state of the system towards the limits of the boundary of acceptable performance. You will see the counter gradient of safety campaigns trying to push the system away from the riskier area. The “error margin” is a loose depiction of the uncertainty around safe operations. Where safety critical systems are involved, this is a useful model to have in your tool kit. And even for more mundane applications (say customer experience or company brand reputation) you could make an equivalent mental model. The system is somewhere within that safe zone. If workload increases and more resources are added (the economic boundary moves up) the system continues to have enough room to maneuver to accommodate daily perturbations. If economic boundary moves but workers shoulder more workload (the boundary of unacceptable workload moves down), again the system has room move around and be safe.
The NAS has natural limits on growth, peaking at roughly 53,000 to 56,000 flights on a clear day. Beyond this volume, airspace and ATC capacity become the hard constraints. However, capacity is only half the story; it must exist where people actually want to go. You can have infinite capacity to a remote location, but without demand, it is merely a "bridge to nowhere." The FAA’s SMART system is a high-leverage move—as Dana Meadows would say—designed to address these underlying constraints by shifting the fundamental goals and paradigms of how we manage flow.
As Rasmussen points out “defenses are likely to degenerate systematically through time” - decay in safety margins are inevitable - and FAA’S SMART has the potential to reposition the system away from the heavy workload area. Management and the aviation community must resist the temptation to overload the system back to the brink in search of unrealistic efficiencies. We must remember that, as Meadows points out, there are absolute Limits to Growth. In this framing, the physical geometry of our airspace acts as a non-renewable resource, while noise and carbon emissions serve as hard ecological constraints. If we use the 'breathing room' created by FAA’s SMART only to pack in more volume, we won’t be innovating - we will simply be accelerating our drift back toward the boundary of failure.
On the surface one would assume FAA’S SMART is going to reduce the workload (that is a stated goal) of the controller. I am deeply optimistic about it, and wish I was there to put my shoulder to the wheel, but some humility is warranted in acknowledging the uncertainty of location of the current NAS in the safety space as explained above.
1 50 years after the original report The Club of Rome did an analysis of the effectiveness of the original report. That and other analysis show the effectiveness and usefulness of the original study.
2 My good friends have already complained about the somewhat heavy nature of last week’s observations. But I have gone back time and again to these ideas and my hope is that this will be a gentle introduction to those unfamiliar with the work of Meadows and Rasmussen.
3 The model (page 106 in the original report) factored in just five key variables (population, food, capital, non-renewable resources, pollution). This model has been updated and results compared with observations. A relatively recent study is Herrington, Gaya. “Update to Limits to Growth: Comparing the World3 Model with Empirical Data.” Journal of Industrial Ecology [Cham], vol. 25, no. 3, June 2021, pp. 614–26, https://doi.org/10.1111/jiec.13084.