Correlating wildfire occurrence with aircraft use

Can crunching the numbers in the annual fire reports provide any insight about how many aircraft are needed?

Above: Tanker 912, a DC-10, drops on the Lolo Peak Fire near Florence, Montana south of Missoula. Photo by John Ames.

(Originally published at 9:39 a.m. MT March 4, 2018)

Every year the National Interagency Fire Center compiles a Wildland Fire Summary and Statistics Report. It usually runs about 70 pages and has piles of data about fire occurrence, weather, and the resources deployed. Since the number of large air tankers on exclusive use contracts has varied from 44 to 9 since 2002, (and 13 this year) an obvious question is, how many do we need? The number of Type 1 helicopters was cut in 2017 from 34 to 28, and that reduction will remain in effect this year.

These numbers do not count aircraft on call when needed (CWN) contracts — aircraft that may or may not be available when the call goes out. Since CWN vendors earn no money unless they are activated, the companies have to charge more to stay afloat. In 2017 the average daily rate for large federal call when needed air tankers was 54 percent higher than aircraft on exclusive use contracts. The hourly rate was 18 percent higher.

Two studies, completed 10 and 21 years ago, said there is a need for 35 or 41 air tankers.

I have been discussing the data in the annual reports with one of our frequent contributors, Bean Barrett, who has taken the data analysis to a different level. Some of the key information includes aircraft requests, unable to fill (UTF) rates, and fire occurrence. We both agree that UTF information is imperfect. It is very possible that if an Incident Commander or Dispatcher knows that no air tankers or helicopters are available, they may not waste time sending in a request. Tracking these historical non-requests at this time is impossible.

And, aircraft don’t put out fires. In ideal conditions they can slow it down enough to allow firefighters on the ground to move in and actually put it out — or at least stop the spread on a section of the fire.

With those caveats, check out the work below that Bean has done, crunching the numbers in the annual fire reports. On his graph legends, “T1-2” refers to Types 1 and 2 fixed wing air tankers. If there is an “H”, it is about helicopters. Type 1’s are larger than Type 2’s.

By Bean Barrett

Maybe there is a story in the data after all as far as air tankers go. All derived from NIFC data. Not exactly ops research but perhaps useful for some insight. Like all data, this was probably measured with a micrometer, marked with a felt tip pen, and cut with an axe. So don’t take this one to the bank.

Aircraft requests and fires larger than 40,000 acres

wildfire air tanker request data

I didn’t draw in the trend line on the fires above but the number of fires >40K acres is clearly increasing [red line].  The number of fires are on the right axis in red and the number of tanker requests by type are on the left axis.

Judging from the number of requests, the response to the increasing trend in large fires has been an increasing number of requests for T1/T2 air tankers [purple line]. Seems obvious.

What isn’t obvious is why the nearly straight line increase in fixed wing requests.  Is there some kind of learning curve going on that has resulted in a steady increase in the perceived or actual value of T1-2 fixed wing air tankers? This nearly constant rate of increase in demand needs explaining and nothing in the NIFC data helps.

The requests for helos remained flat. What is curious is that there is little difference between Type 1 Helos and Type 2 helos. You would think that there would be a larger increase in requests for Type 1 helos when there is an increase in the number of big fires.

Aircraft requests and the number of significant fires

wildfire air tanker request data

This slide looks at the number of requests and the number of NIFC significant fires. Significant fires are defined as >100 acres in timber or >300 acres in grass. The number of significant fires is on the right axis in red and the number of tanker requests by type are on the left axis.

I looked at significant fires because you would think that by the time a fire got to 100 acres / 300 acres someone would be thinking about air tanker IA support. Not much of a trend in the number of significant fires.

If anything, there has been a slight decrease in helo requests over the last three years while there has been a big increase in the number of significant fires. Why doesn’t the demand for helo support follow the number of significant fires? Aren’t helos used for IA? Are the majority of helo requests not related to suppression? Why isn’t the demand for helo support reflected in the number of fires?

Not much correlation between fixed wing requests and the number of significant fires pre 2014. Better in the last 3 years. Maybe fixed wing has been more involved in IA?  However, the next slide changed my mind.

Significant fires exceeding 40,000 acres and air tanker UTF rate

wildfire air tanker request data

Since there was no NIFC data on early suppression success rates when compared to tanker availability, I made an assumption for this and the next slide. I divided the number of fires > 40K acres by the number of significant fires and assumed that percentage roughly represented the significant fires that were not successfully suppressed before they could grow >40K acres. Percentage of significant fires that grew to >40K acres is on the right axis and the UTF % for T1/2 tankers is the left axis.

Up to 2014 it looks like fixed wing T1/2 UTF rates were correlated with the percentage of fires that grew >40K acres.  [High UTF rates meant more significant fires grew >40K acres].

However, UTF rates went down for the last 3 years and were unrelated to the number of significant fires that grew >40K acres. Fixed wing availability didn’t correlate well with suppression efforts that kept significant fires from growing >40K acres. Perhaps the majority of fixed wing requests are not for suppressing significant fires.

Significant fires exceeding 40,000 acres and helicopter UTF rate

wildfire helicopter request dataThis slide might be the most important one provided someone can sort out the difference between correlation and causation. The red line is the percentage of significant fires that grew>40K acres [right axis].  The UTF rate for helo types is on the left axis.

Interpretation 1. Helo availability is THE key to more effective early suppression and preventing significant fires from turning into large costly fires. When helo UTF rates were below 20%, significant fires that grew >40K acres were at or below 1.5%.  If this is indeed a causal relationship, contract for a much larger helo fleet for IA and the huge wildfire suppression bills will come down considerably.

Interpretation 2. Helos aren’t requested until a significant fire becomes unmanageable and then a large number of requests saturate the system resulting in a high UTF rate.   I tend to discount this interpretation because [see # Requests and Significant Fires above]  total request numbers don’t go up when the number of fires go up. They don’t. Only the UTF changes. This would indicate an overall helo inventory shortfall.

Either way, there simply aren’t enough helos when they are needed. If the number of helos under contract was closer to a reasonable objective, UTF rates would not have the peaks shown above.


Unable to fill requests for air tankers increased in 2016

In 2016 there was an increase in the percentage of requests for large air tankers that went unfilled, increasing from 10 percent in 2015 which was the lowest since 2009, to 13.4 percent in 2016.

Counting the U.S. Forest Service HC-130H air tanker there was a maximum of 21 large and very large air tankers on exclusive use contracts in 2016. However, the two Erickson MD-87 aircraft were not available for most of the year due to problems with the retardant system. The company claims they have fixed the issue and they should be ready to go this summer. A few other call when needed (CWN) large and very large air tankers were activated for weeks at a time in 2016. Unless new contracts for CWN air tankers are issued that will be effective this year, the number of available air tankers in 2017 should be about the same. A new exclusive use contract is expected to be in effect in 2018.

Tanker 12 Trailhead Fire
Tanker 12 on the Trailhead Fire. A Cobra helicopter is in the background. Photo July 1, 2016 by Matthew Rhodes.

The number of acres burned in the lower 49 states (which excludes Alaska) was virtually the same in 2015 and 2016, with both being pretty close to average. There were also few extended fire sieges involving multiple large fires occurring at the same time that required a high number of air tankers. Having the fires spread out over time minimizes the number of air tanker requests that go unfilled.

wildfire acres per year
The number of acres burned in wildfires in the lower 49 states (excludes Alaska).

Here are some of the Unable to Fill numbers we computed from the data reported by the National Interagency Fire Center for 2016:

  • Type 1 and 2 large air tankers: 13.4%
  • Single Engine Air Tankers: 21.1%
  • Type 1 helicopters: 12.3%
  • Type 2 helicopters: 8.6%
  • Type 3 helicopters: 8.3%

There were only seven requests for MAFFS air tankers, and all were filled.

Summary of air tanker use, 2014

There were more requests for large air tankers (LATs) in 2014 than in any of the last 18 years. That is one of the facts in the 2014 version of the Wildland Fire Summary and Statistics put together by the National Interagency Fire Center.

We used data from the report to update statistics that we have been collecting over the years, including the chart below.

Graph, request for large air tankers

One of the more interesting trends is the number of requests for LATs that cannot be filled, referred to as Unable to Fill, or UTF. After reaching a high of 48 percent in 2012, it declined to 21 and then 12 percent in the next two years even as the number of requests for LATs was increasing.

One thing we don’t know is how many Incident Commanders needed air tankers but didn’t bother to request them because they knew that none were available.

Acres burned in wildfires

Two stats for 2014 indicate there would be a reduced urgent need for air tankers. The number of acres burned in the 48 contiguous states in 2014, 3.4 million, was significantly below the 10 year average of 5.7 million. And the number of structures burned, 1,953 was less than the 10 year average of 3,098.

At the beginning of 2014 there were 10 LATs on exclusive use contracts. By the end of the year there were 17 — eight were added and Minden’s P2V had a landing gear problem (see below) which took it out of service indefinitely. The additional air tankers on exclusive use contracts included:

  • 2 RJ-85s from Aero Flite;
  • 2 MD-87s from Erickson Aero Tanker;
  • 1 DC-10 from 10 Tanker Air Carrier; and
  • 3 BAe-146s from Neptune

In the list of eight additional air tankers listed above, the DC-10 and the three BAe-146s were brought into service as “additional equipment” on a 1-year temporary basis under an exclusive use contract awarded in 2013. Due to a change in Department of the Interior procurement policies, this will not be done again in 2015.

Minden was awarded a Next-Gen contract for a BAe-146 in 2013, but never delivered the aircraft. Recently the USFS terminated the contract for default.

MAFFS 3 hard landing
The MAFFS 3 air tanker experienced a hard landing at Hill Air Force Base on August 17. There were no injuries. Photo supplied by the Air Force, originally from Fox 13.

One air tanker was borrowed in 2014 from Canada for 10 days. Saskatchewan provided a Convair 580 and a TurboCommander 690 Bird Dog beginning on July 21. The air tanker group was in place until July 30, when it returned to Canada following a recall from Saskatchewan due to increased fire activity there.

Two Modular Airborne FireFighting System aircraft, C-130s from the military, were activated on July 20 and positioned at Boise. MAFFS 3 experienced a hard landing at Hill AFB when they had a problem with the nose landing gear. While no injuries occurred, the damage ended the service of MAFFS 3 for 2014, but MAFFS1 remained until August 24. MAFFS units provided retardant delivery to the Great Basin, Northwest and Northern Rocky Geographic Areas while employed from July 20 through August 24, delivering a total of 244,406 gallons while conducting 97 sorties. This is down from 2013 when 576 sorties were flown delivering 1,387,881 gallons of retardant.

Other notable aircraft mishaps or crashes in 2014:

  • Pilot Geoffrey “Craig” Hunt was killed when his S-2T air tanker impacted the ground while he was attempting to make his second retardant drop on the Dog Rock Fire October 7 near Yosemite National Park in California.
  • An air attack fixed wing aircraft, an Aero Commander 500, overshot the runway while landing at Wilcox, AZ on July 2.
  • Tanker 73, one of CAL FIRE’s 23 S-2Ts, had a problem while landing at Hemet-Ryan Airport Friday, October 3 in southern California. The preliminary information indicated that it was a landing gear issue.
  • A Bell 206-L3 made a crash landing into a river May 29 while recertifying for water bucket operations near Missoula, Montana.
  • On June 15, Minden’s P2V, Tanker 48, was substantially damaged when the nose wheel landing gear collapsed during landing roll at the Fresno Yosemite International Airport (FAT), Fresno, California.
  • On October 4 an air attack aircraft ran off the runway at Nevada County Airport near Grass Valley, California.
  • An air attack plane under contract to the Department of the Interior crashed May 17 at Fort Huachuca, Arizona. The Rockwell Aero Commander 500S impacted the ground shortly after takeoff. The aircraft was on an orientation flight for a new pilot on the air attack contract. Two company employees, but no agency personnel, were on board. There was an unconfirmed report that one person died several days later.