30 July 2012

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USA–  An aging fleet of contracted fixed-wing airtankers and two fatal crashes in 2002 led the U.S. Forest Service to investigate how to recapitalize its fleet of airtankers. The Forest Service asked RAND for assistance in determining the composition of a fleet of airtankers, scoopers, and helicopters that would minimize the total social costs of wildfires, including the cost of large fires and aircraft costs. The research team developed two separate but complementary models to estimate the optimal social cost-minimizing portfolio of initial attack aircraft that is, aircraft that support on-the-ground firefighters in containing a potentially costly fire while it is still small. The National Model allocates aircraft at the national level, incorporating data on ten years of historical wildfires, and the Local Resources Model provides a more nuanced view of the effect of locally available firefighting resources, relying on resource allocation data from the Forest Service’s Fire Program Analysis system. Both models favor a fleet mix dominated by water-carrying scoopers, with a niche role for retardant-carrying airtankers. Although scoopers require proximity to an accessible body of water, they have two advantages: shorter cycle times to drop water and lower cost. Two uncertainties could affect the overall optimal fleet size, however: future improvements in the dispatch of aircraft to fires and the value attributed to fighting already-large fires with aircraft.

Key Findings

Research Questions

What is the optimal mix of aircraft in the U.S. Forest Service’s fleet to minimize the social costs of large wildfires?

What are the costs and capabilities of each candidate aircraft type (airtankers, helicopters, and scoopers)?

What are the costs and benefits of large wildfires, and what are the costs and benefits of their suppression?

Across All Analyses, Scoopers Were the Dominant Component of the U.S. Forest Service’s Optimal Fleet Mix

Scoopers are considerably less expensive to own and operate than larger helicopters and fixed-wing airtankers ($2.8 million versus $7.1 million per year).

When fires are near water, scoopers can drop more water than airtankers can drop retardant.

At least two-thirds of historical fires have been within ten miles of a scooper-accessible body of water, and about 80 percent have been within five miles of a helicopter-accessible body of water.

Airtankers have a niche role in fighting wildfires that are not proximate to scooper- or helicopter-accessible water sources.

The Forest Service May Require a Somewhat Larger or Smaller Overall Fleet

If the Forest Service has sufficient insight into where fires will next occur, has the freedom to move its resources to any airport to optimize an attack, and sends aircraft only to fires that require them, the total size of the necessary fleet would be substantially smaller than if the Forest Service had poorer intelligence on future fires, less flexibility in pre-positioning aircraft, or less insight into which fires were most appropriate for aircraft to fight.

Although there is a dearth of evidence of the effectiveness of aircraft against already-large fires, airtankers and other aircraft are currently used in this capacity, potentially adding to the size of the Forest Service’s required fleet.


The U.S. Forest Service should acquire an initial attack fleet that is predominantly composed of water-bearing scoopers.

The Forest Service, and wildland firefighting efforts more broadly, would benefit from a detailed examination of the effectiveness of water versus retardant in different fire-suppression applications. This would enable a more precise valuation of the contributions of airtankers to firefighting operations.

Given the frequency with which airtankers are employed to fight already-large fires, there should be more research on the outcomes and the impact of air support in these scenarios.

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