Flights over Flames

FLIGHTS OVER FLAMES: EXPLORING THE SCIENCE OF AERIAL SUPPRESSION
BY COLIN MCFAYDEN, DAVID CALKIN, FRÉDÉRIQUE GIROUD, EMILY HOPE, RANA KAMH, DOMINIQUE LEGENDRE,
NICK MCCARTHY, MATT PLUCINSKI, OWEN PRICE, MELANIE WHEATLEY, RAZIM REFAI, AND HEATHER SIMPSON

Wildfire management is complex and uncertain, and it can be hazardous, particularly when fires escape the initial attack and grow large.

Fire managers regularly make decisions about what actions to take, when and where, all while considering available suppression resources working in time sensitive and critical environments.

Aviation resources have become an iconic symbol of wildfire suppression. When wildfire response is depicted in the media, we often see images of aircraft battling the fire. Aircraft help ground resources, and they can be instrumental in many situations, such as facilitating a rapid initial attack, and helping ground crews gain the upper hand in tough conditions, but they are also one of the most expensive resources. What do we know about the effectiveness of aircraft?

What is aerial suppression? We are lumping airtankers (fixed-wing aircraft) together with helicopters to include all aircraft capable of dropping water, chemical suppressant or retardant on to wildfires from a tank or bucket system.

Those who regularly fly and work with the airtankers see how they function in real time and a considerable pool of expertise has been developed over the years. The research challenge is to better understand how aerial suppression helps fire managers meet objectives and how aerial suppression contributes to or aligns with broader societal objectives of fire management.

WILDFIRES

Fire is essential in many ecosystems and important to people and cultures worldwide but can also have devastating consequences for people, communities, the economy and the environment. In the last five years alone there have been multiple protracted and damaging wildfire events such as Australia’s Black Summer in 2019-2020, the record-breaking 2023 Canadian fire season, large or widespread fires in eastern Russia, and consistently challenging fire seasons for South America with 2024 standing out as particularly severe for Chile and the Amazon. There also have been severely impactful wildfires in the United States (Texas, New Mexico, Colorado, Hawaii, and California), and Europe and Asia have not been immune.

Many of the most devastating and publicized and high-fatality events have occurred under extreme fire weather conditions (blow-up fires such as Black Saturday, Australia 2009, Portugal 2017, Greece 2018, Hawaii 2023, and California). On these extreme fire weather days, when there are high winds, turbulence, smoke, and low visibility, it can be too dangerous for aircraft to fly, let alone be effective in low-to-ground suppression action.

The safe operation of aircraft is typically limited to maximum wind speeds of 20-25 knots (37-46 km/hr or 23-29 mph) for crosswinds with gust limits of 30-40 knots (56-74 km/hr or 35-46 mph) depending on the type of aircraft. Rotary-wing or larger aircraft can tolerate higher wind speeds, but their maneuverability decreases under such conditions, making precision tasks like suppression drops more challenging. In extreme fire weather conditions, the fire may be too hot or intense to be slowed or be halted by aerial suppression. Soley increasing the number of aircraft is not the silver bullet to these challenging days.

Research has warned us that across the globe, wildfires are increasing in frequency and severity, driven by the effects of climate change and the legacy of a century of wildfire suppression. Simultaneously, the encroachment of buildings and infrastructure into wildland areas are putting more assets and people at risk. In response, the people and organizations that manage wildfire seek to address these mounting challenges through some degree and combination of fire management levers including prevention, mitigation, community engagement and suppression strategies.

The way countries manage wildfires is as diverse as their landscapes, people and cultures. While the specific methods used around the globe differ to the local needs and contexts, there are some shared approaches and tools in the toolbox, such as using aircraft to support suppression efforts. One question across all these countries is how hard we should and can pull on the suppression ‘lever’ of aircraft, noting it is not without risk.

By finding and recognizing the limit of the aerial suppression lever, we can look at using aircraft to keep fire risk “as low as reasonably practical” without incurring disproportionate costs. Importantly, this cost is more than financial; it includes real safety risk to our people and trade-offs with other management levers.

This concept is shown in figure 1 (page 11), where there is a point at which the level of risk cannot be further reduced without disproportionate costs or risk to aircrew and firefighters relative to the benefit gained. Beyond this point, doing more and spending more puts people in potentially dangerous situations with little extra benefit.

 

 

THE ROLE OF TACTICAL AIRCRAFT IN WILDFIRE SUPPRESSION
While aircraft aren’t needed or used to suppress all wildfires, they are often deployed to fires that have the potential to threaten lives and property, as well as to fires that are inaccessible to ground crews or to aid ground crews by cooling or slowing a fire to allow the ground crews to be more effective. Remember, it’s the ground crews who extinguish the fire. Aerial suppression can support both initial attack and sustained action efforts, providing rapid initial response to new fires and prolonged suppression support on larger fires.

How these aircraft are deployed and used to fight wildfires varies based on their type and capabilities: some drop suppressant directly on flames to slow fire spread, while others release retardant chemicals ahead of the fire to alter its course and protect critical areas. There is also extensive use of aircraft for intelligence, coordination and monitoring of crew movement and logistics functions, but we are focusing on the tactical aircraft that conduct the drops. These tactical aircraft come in a range of sizes and configurations, often differentiated by drop capacity, filling methods and delivery mechanisms. Wildfire management organizations operate with fleets often composed of multiple different types of aircraft to address the challenges of operating in a variety of environments, different levels of fire behaviour, and varying suppression objectives. From helicopters with buckets delivering 300 to 400 liters (80 to 105 gallons) to supertankers releasing a staggering 45,000 liters (11,887 gallons).

While these aircraft can often play a critical role in combating fires, like all frontline fire fighting, aerial suppression also carries significant risks, and the use and misuse can lead to dangerous situations for aircrew and firefighters alike. In some parts of the world, studies have shown a large proportion of firefighter fatalities were linked to aviation accidents, underscoring the inherent dangers of aerial firefighting and the need for safety-first approaches.

Wildfire management organizations that operate aerial suppression fleets devote large portions of their operating budgets towards them. Airtankers are expensive to purchase, contract, maintain and operate, and the costs associated with their use are increasing.

Wildfire management organizations often do not have the financial resources, or personnel to operate enough aircraft to address every fire that could benefit from aircraft action. One clear but thankfully rare example of this is in a mass lightning ignition event, where dozens to hundreds of fires can ignite in a single day. In these situations, it’s not feasible for any organization to maintain enough resources for the extreme peak but infrequent demand. Recent examples include November 2019 during the Black Summer season in southeast Australia and August 2020 in California. In both instances, the lightning fires burned more than 1 million hectares.

It’s also not the case that having more aircraft means every fire will be extinguished. There are instances where it’s just too dry and too windy to stop a fire in its tracks, and even when aircraft are effective, they often provide the initial hit to then allow ground-based firefighters to make access and do the hard work of truly extinguishing the fire.

However, when there are shortages of aircraft, some organizations augment their fleets by borrowing from other jurisdictions (nationally and internationally) and using resource sharing agreements and contracts. Airtankers are highly mobile and can easily move between low- and high-risk areas and be shared across jurisdictional borders. This too is not without expense and trade-offs, as with all scarce resources.

Of course, the cost of operating aerial suppression pales to the potential impact posed by some of the most destructive fires. We’ve listed numerous examples of high-cost and damage wildfires, some with damage estimates in the billions of dollars, many with even higher costs in less direct impacts such as public health. Could changes in aircraft usage have prevented some of these damaging fires? Or were the damages inevitable given the extreme fire weather conditions? Decision makers must decide how to use their limited number of aircraft resources to prevent fires from escaping containment efforts and reduce the potential negative impacts of the fires that do escape.

Allocating airtankers to appropriate fires where they can be most ‘effective’ and safe is the best outcome, but these decisions rely on tactical experience that is difficult to quantify and share, and assumptions about the effectiveness of aerial suppression.

To the experienced wildfire tactician, aircraft can be a welcome tool for crew safety, fire intelligence, and to stop a fire from escaping initial attack and becoming one of those stories of devastation. Allocation decisions are not straightforward, and there are influences (e.g., the incentives for decision-makers and cultural factors) that affect the deployment and use of aircraft. This often leaves us with questions like “Is the appropriate level of aircraft use consistent with the objectives of the fire relative to what’s achievable and what is safe to do?”. A 2021 study suggested the risk management protocols of aviation and fire management may not be appropriately scaled in terms of how the tactical use of aircraft aligns with the incident strategy and broader societal goals of fire management. For large fire incident management, this can translate to a culture of “get them if you can and use them if you’ve got them.”

There have been several recent efforts to better understand aerial suppression use in wildfire management from a scientific and economic perspective, such as the Aerial Firefighting Use and Effectiveness study in the United States, the LABEX (Largage Bombardier d’Eau EXpérimentation) experiments in France and the aptly named Australian Why fly? project.

The continued use of aerial suppression across the decades by those on the frontlines speaks to their role as one of the more versatile and rapidly deployable suppression tools in the toolbox. However, compared to the extensive research on how fires ignite and spread far less attention has been given to studying the effectiveness of aircraft fighting fire despite their iconic presence, widespread use, and growing demand.

AERIAL SUPPRESSION EFFECTIVENESS AS A RESEARCH AND OPERATIONAL CHALLENGE
Quantifying aerial suppression effectiveness can lead to improved firefighting strategies, optimal use of suppression resources, and more informed strategic investments by fire management agencies. If we know more, we can do more safely and invest appropriately. This is especially pressing given the high costs, limited availability of airtankers, and the mounting challenges of a changing climate to manage more fire, more often, in more areas.

So, what does effectiveness mean with aircraft? It comes down to the objective you are trying to achieve. To the firefighter, it might mean how reliably they can prevent a fire from crossing a control line, and the multiplier effect having an aircraft can have. A dispatcher may assess effectiveness in terms of efficiency, for example, by how quickly an aircraft responds to a fire. An organization administrator may judge effectiveness by the costs and benefits. To the aircrew, it could mean achieving any number of things relative to what’s happening on the ground in a rapidly changing and dynamic situation. Because the notion of effectiveness means different things depending on the objectives, it’s far from straightforward to describe and more complicated to research. One of the key research challenges is just trying to identify the objectives.

MEASURING EFFECTIVENESS
Understanding the different aspects of ‘effectiveness’ starts with asking questions like: What happens to the drop once it leaves the aircraft? How much of it gets its target (flames or fuel)? What happens to the fire when a suppression action is taken with an aircraft? Does it reduce intensity, slow or alter spread rates, or provide critical time for other firefighting resources to intervene, and if so, by how much, how long, at what cost and risk?

Some studies have shown aerial suppression increases the chances of successfully halting a fire when used during the initial attack of new fires. However, we do not have a strong quantitative understanding of how much liquid makes it through the canopy to targeted fuels, how long the impacts of water or retardants last, or at what point the efforts made by aircraft are no longer making a meaningful difference. This fundamental understanding of aircraft effectiveness would provide the basic building blocks needed to start answering many aspects of effectiveness that support the questions stated above.

Collecting the data needed to research these questions is difficult given the characteristics of dropping mechanisms and the dynamic nature of wildfire, yet valuable for ongoing learning, improvements, and guide investments. Beyond the challenges in studying fire behaviour, incorporating the suppression component creates added complexities. Environmental factors like wind, topography, fuel type and structure significantly influence how the fire will behave and how the fire responds to aerial suppression. Aircraft characteristics (e.g., speed, maneuverability, drop patterns, etc) and pilot skills will also influence outcomes. Dropping water or retardant is not as simple as letting gravity do the work. For example, how water leaves an aircraft is not the same for each type of airtanker. There are losses due to evaporation, wind drift and heat from the fire, and depending on the aircraft, its speed, altitude and coverage level, its load can come down as a light mist that gets caught up in a forest canopy or a thunderous force, breaking off tree tops off on the way to the ground. All of this is compounded by the interactions with the effectiveness of ground-based suppression activities where aerial suppression drops can knock down flames so that firefighters can finish extinguishing them. Without the drop firefighters may not have safe access; without the firefighters, flames will soon rebuild and spread as if the drop never happened.

These complexities make it challenging to gather the data needed to quantify, assess and model aerial suppression performance with scientific rigour. Moreover, data on fire and aviation that is recorded and archived by fire management organizations can be hard to access and infer conclusions due to complexities in aircraft use and underlying decision-making. A common example is images of retardant where fire has stopped implying effectiveness, but the absence of data may prevent observers from knowing if the fire stopped before retardant was applied. In most cases the actual decisions are not documented in a way or with sufficient context or accessibility for evaluation. This lack of documentation, available data and empirical understanding leaves many questions unanswered.

ADDRESSING THE GLOBAL CHALLENGE
Wildfires are a shared challenge that are expected to become more complex and difficult to manage in the future. We seek ways to keep potentially destructive wildfires small and communities safe when possible. Building our scientific knowledge on aerial suppression effectiveness and how to best use these aircraft is a way researchers can support the development of suppression strategies and long-term policy decisions around the configuration of firefighting aircraft fleets. Collaboration among researchers, fire managers, and policymakers is essential to obtaining this robust evidence-based knowledge. This includes building and communicating the evidence around the effectiveness and limits of aircraft, especially considering the mounting expectation of the public who expect to see aircraft when a fire starts. By addressing gaps in research and exploring innovative ways to evaluate airtanker effectiveness, the research community can help fire managers deal with wildfires more effectively.

Colin McFayden was born and raised in Northwestern Ontario and has spent 30 years working in fire management. Starting in the mid 1990s on a FireRanger crew, McFayden spent most of his career working for the Province of Ontario in roles from coordinating aerial fire detection to leading the wildland fire science program. In 2022, McFayden joined the federal Canadian Forest Service as part of the WildFireSat mission leadership team. McFayden co-authored the Reference Guide to the Drop Effectiveness of Skimmer and Rotary Wing Airtankers, published in 2023 by Natural Resources Canada.

 

 

Dave Calkin is a supervisory research forester with the US Forest Service, Rocky Mountain Research Station in Missoula, Montanna. Calkin’s work is designed to improve risk-informed decision making through innovative science development, application, and delivery incorporating economics with risk and decision sciences. Calkin’s research interests include risk assessment, collaborative wildfire mitigation and response planning, suppression effectiveness, and risk informed decision making. Calkin developed and leads the Wildfire Risk Management Science (WRMS) team within the US Forest Service Rocky Mountain Research Station.

 

 

Frédérique Giroud is the director of CEREN, the testing and experimentation Center of ENTENTE Valabre. She holds a PhD in fluid mechanics and heat transfer. She collaborates with scientists, firefighters and crisis managers to conduct various projects at the national and European level. Her main areas of research related to forest fires are fluid mechanics, fire spread modelling, chemical additives, wildland-urban interface management and fire instrumentation. Giroud is in charge of establishing contacts between French scientists and European stakeholders in the firefighting domain. Since 2018, Giroud has managed the reference laboratory for the French standardization of firefighter equipment. Since 2021, CEREN has been the approved inspection laboratory of French Civil Protection in the chemical additives area.

 

 

Emily Hope is a PhD candidate at the University of Toronto, studying the economics of wildland fire aviation. Hope’s research will focus on key cost components associated with aerial suppression and explore how those costs might change into the future; her analyses will examine several issues, including optimal contracts, various aircraft ownership structures, labour and mechanic shortages, and maintenance scheduling.

 

Rana Kamh is a senior communications advisor at Natural Resources Canada. She supports communications for the department’s emergency preparedness files, which include wildfires. Kamh has an MA in global development studies from Queen’s University.

 

 

 

Dominique Legendre is a professor at Toulouse INP and the Institut de Mécanique des fluides de Toulouse (IMFT). He received his PhD in Fluid Mechanics at IMFT–Toulouse INP in 1996. He is president of the governing board of the International Conference on Multiphase Flows (ICMF). His work focuses on dispersed multiphase flows, and he has developed research investigation on the drop efficiency of airtankers by conducting both experiments in wind tunnel and numerical simulation.

 

 

Nick McCarthy is a senior research and development officer with Country Fire Authority’s Research and Development team in Victoria, Australia, focusing on suppression effectiveness, future firefighting trends, and field data collection on fire behaviour. McCarthy previously worked as a postdoc with the U.S. Forest Service in Missoula, Montana, and completed a PhD at the University of Queensland in fire-atmosphere interactions.

Matt Plucinski is a senior research scientist at CSIRO in Canberra and has more than 20 years bushfire research and firefighting experience. Plucinski has conducted many field and laboratory experiments on topics associated with bushfire behaviour and suppression effectiveness, including evaluations of the effectiveness of large airtankers and assessments of wildfire suppressants and retardants. Plucinski’s research has been used to inform risk management planning, response strategies during bushfires and for fire danger assessment.

Owen Price is director of the Centre for Environmental Risk Management of Bushfire at the University of Wollongong and for 18 years has been researching the evidence of impacts
of bushfires on biodiversity and buildings and the effectiveness of strategies to reduce bushfire risk; this includes research on prescribed burning, construction standards and suppression with techniques involving spatial, statistical modelling and simulation. Price was born in the United Kingdom and graduated as a biologist before moving to the Northern Territory in 1992, where he worked for 13 years in wildlife research for the National Parks and Wildlife Service. He has authored 140 papers and 50 reports and in 2020 he was joint winner of the Eureka Prize for applied environmental science for analysis supporting the NSW inquiry into the 2019-2020 Black Summer inquiry.

Razim Refai is a senior researcher with the wildfire operations research group at FPInnovations. His research focuses on aviation suppression efficacy and wildfire chemical effectiveness. Rafai also works with wildfire management agencies in Canada on program reviews to forecast provincial and territorial aviation resource needs.

 

 

Melanie Wheatley, PhD, is a wildland fire research scientist with the Ontario Ministry of Natural Resources, Aviation Forest Fire and Emergency Services. Her research focuses on applied fire management problems to support operational fire management decision making, including the development of situational awareness and decision support tools. Wheatley also specializes in aerial suppression effectiveness research, using a combination of data-driven methods and field observations to examine the effectiveness of waterbomber aircraft in the boreal forest. Wheatley has more than a decade of experience with the fire management program in Ontario, in working in various fire response and research related capacities.

 

 

 

Heather Simpson, a project manager at the Canadian Interagency Forest Fire Centre (CIFFC), brings a unique blend of frontline firefighting experience and academic expertise in wildfire management. With a decade of experience as a seasonal firefighter with the BC Wildfire Service, Simpson has firsthand knowledge of the complexities of wildfire suppression. She further honed her expertise by pursuing a PhD in fire management in Australia, where her research focused on improving fire line operations and developing advanced strategies for effective wildfire management. At CIFFC, Simpson leverages her extensive background in operations, liaison, and administration roles to inform policy, guide decision making, and drive innovation in wildfire management.