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
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
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
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
This 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.