Environmental Concerns Over the use of Fire Retardant and a Lawsuit

A federal lawsuit filed over the use of fire retardant dropped by aircraft was filed in Montana in October of 2022. I am sure that this is old news for many of you as it has been covered in social media and other media sources, see for example Bill Gabbert's October 12, 2022 article in Wildfire Today Bill said in part:

An environmental group filed a lawsuit in a Montana federal court Tuesday alleging that the US Forest Service has polluted waterways by inadvertently dropping fire retardant in or near waterways.  The retardant was dropped by aircraft under contract with the Forest Service while assisting wildland firefighters on the ground.

The suit says government data released earlier this year showed more than 760,000 gallons of fire retardant was dropped into waterways between 2012 and 2019. The lawsuit alleges the continued use of retardant from aircraft violates the Clean Water Act and requests a judge to declare the pollution illegal.

I was reminded of this lawsuit recently when I came across a video thanks to my friends at the New Jersey Forest Fire Service Section B10 who shared this video last week in their daily videos on their home page. This short video from ABC 10 in Northern California mentions the lawsuit, the environmental concerns posed by fire retardant and how fire retardant helps fire fighters on the ground. For some context, I know that fire retardant is widely used  in the western United States when aerial resources are deployed to help fight wildfires. I am less certain how fire retardant is use in the eastern portions of the United States, I believe that most of the aerial resources deployed to wildfires in New Jersey do not use fire retardant. To the best of my understanding, most helicopters with buckets do not use fire retardant. I am less certain I found the video educational and enlightening and thought that some of you might enjoy this video.

Direct link to video from ABC10 on YouTube

Wildfires in treated versus untreated fuels

In writing about aerial wildland firefighting, a lot of the focus is on tankers dropping retardant on or near wildfires in support of the wildland firefighters on the ground. In this 16 minute from the National Interagency Fire Center (NIFC) you will learn about the difference between how wildfires burn when treated with retardant compared with wildfires burning in untreated fuels.


direct link to video

more on emergency retardant drops

I recently wrote about emergency retardant drops here. I was going through some files on my computer earlier today and saw a draft of an article that I wrote in Dec. 2009, one of a series of articles on the DC-7 tanker. Most of the articles that I posted in December 2009, were on DC-7 air tankers, so here is a link if you are interested in the entire series. The article that interested me today is called Up close and personal with DC-7 tankers: retardant drops pt 2 of 2, written on Dec. 18, 2009. In this article, Larry Kraus, pilot of DC-7 tanker 62 speaks about emergency retardant drops. I am reposting the entire article here because of its relevance to my recent post. Enjoy!

Up close and personal with DC-7 tankers: retardant drops (pt 2 of 2)
Originally posted on Dec. 18, 2009 Random Ramblings: Aerial Wildland Firefighting Blog.

In my last post, I was writing about the Aero Union multi-door tank system (8 doors) used by Butler's DC-7's. I'll let Larry explain to you the sequence he goes through making a typical retardant drop:

To drop a full load at Coverage Level 6, I would have the co-pilot arm the tank system, and I would set the intervelometer to the 12 o'clock position (1), set the timer to 0.4 and set the doors to open selector to 8. Assuming that we'd gone through the Descent Check List while descending into the drop pattern I should be set. All that I have to do next is to determine the correct place to begin the drop and hold down the drop button (located on the yoke) until all of the doors open.

I know that there are times when tanker pilots must make an emergency drop of a retardant load. If an emergency happens near a tanker base, there is usually a designated place, e.g. coordinates, where emergency drops can be made. Otherwise, the pilot tries to look for a safe place -- no houses, no people on the ground, away from water sources, etc. -- to make the emergency drop. As I understand it, if a tanker pilot were to drop the entire load at once (aka a salvo) while making an emergency drop, the nose will do a sudden pitch up because of the sudden loss of 27,000 pounds of retardant. Often the pilots have a few hairy moments when this happens as they bring the tanker under control.

In the case of the DC-7, Larry tells me that emergency dump switch (outlined in blue in the photo) is centrally located on the cockpit panel. When Larry or his co-pilot lift the guard and activate the system by flipping the switch to the up position, the doors open at an approximate coverage level 5 drop. If I am thinking about this correctly, an added benefit is that an emergency drop at an approximate coverage level of 5 means that any pitch up of the nose of the tanker will not be nearly as bad as a sudden salvo of all doors at coverage level 8 (or higher). Larry provides some more details on emergency drops:

As far as having to jettison retardant in an emergency, it all depends on the severity of the emergency, the location and other local circumstances. In most cases, such as an engine failure deep in a canyon, there will be time for some quick (maybe 15-30 seconds) of trouble-shooting followed by determining if there is time (and the terrain allows) to fly to a suitable drop area. If we really are deep in a canyon, a suitable drop area will be anyplace nearby that doesn't contain a water source, people, vehicles or structures.

Again, it all depends on the circumstances. Generally, it will be possible to fly a few miles to an open area, but it's better for a spot on the ground to be covered with retardant than the flaming wreckage of an airplane. It would be unlikely that we would climb out of a canyon with 3 engines to carry the load to a designated jettison area. However, if the failure occurred enroute to the fire at altitude, that could be an option. There are also other emergencies not involving engines. Hydraulic problems being high on the list. I also once had a failure causing the loss of the fabric on the rudder on Tanker 62 during a drop run.

As I've mentioned before, nothing is ever easy in the tanker business.

Dumping retardant in an emergency

Unless there are firefighters and other individuals on the ground that might be in danger from falling retardant, a tanker pilot can jettison their entire retardant load if in the event of an emergency such as an engine failure or an encounter with bad winds. Typically the pilots will jettison the retardant in a controlled matter to avoid sudden pitch-up of the nose of the tanker. The hope is that once the retardant is jettisoned, the crew of the tanker in trouble can make it safely back to the nearest tanker base.

From what I understand, most if not all tanker bases have a designated area near the base for jettisoning retardant. These jettison areas are important when something goes wrong with the tanker during or after take-off. Most tankers can not land with a full load of retardant, so the pilot will jettison the retardant in the designated jettison area before returning to base to have their tanker repaired.

I promised you some numbers for the weight of load of retardant for a couple of air tankers. If memory serves, one gallon of water weighs about 8.35 gallons. Retardant weighs a little more than 9 pounds per gallon (ppg).

I will talk about three tankers: a DC-7 tanker, a P-2V tanker, and CAL FIRE's S--2T tanker.

Some of you may recall that I wrote extensively about Butler's T-62, a DC-tanker that has been piloted by Larry Kraus for over 27 years. Larry was very generous with his time and his knowledge of the tanker business, so it was easy for me to find information from my blog about weight specifications of T-62 that may found here.

The DC-7 tankers, including T-62, carry 3,000 gallons of retardant. Multiply this by 9 ppg and we can see that the weight of a full load of retardant on T-62 is roughly 27,000 pounds. Larry told me the normal take-off weight of T-62 with a full load of retardant is 108,000 pounds.

The maximum gross weight of a P-2V, for example those operated by Neptune Aviation is 80,000 pounds. While the P-2 can carry about 2,700 gallons of retardant, the current contract load according to Neptune Aviation is 2,082 gallons. 2,082 gallons of retardant comes in at a total weight of 18,738 pounds.

According to CAL FIRE, the S-2T tanker has a maximum gross weight of 29,150 pounds, carrying 1,200 gallons of retardant which weighs a total of 10,800 pounds.

The example of these three tankers, demonstrate how much lighter the tanker is with empty retardant tanks.

I am glad to post this tonight, prior to our latest round of winter. I may have more to say about this subject, but that may have to wait for a bit. In the meantime, enjoy!

DC-7 air tanker (T-62): working with leadplane/air attack

Larry Kraus, pilot of T-62, and I spent some time chatting over e-mail about how he works with lead planes when flying fires. The situation that we are talking about is when he flies with an ASM (a PC-7) that often functions as a lead plane. When the ASM is functioning as a lead plane, the ASM flies at low altitudes (under 500 ft above ground level) with the goal of scoping out where the tanker can make a safe and effective drop. When the lead plane crew have determined where the drop should be made, that information is communicated to the tanker (in this case T-62). The tanker follows the lead plane in, following their route and makes the drop where indicated by the lead plane.

But the ASM can have a second function, that of air attack. As I understand it, the primary function (but not necessarily the only function), of air attack is to coordinate aircraft over the incident fire. This would include communications with the incident commander on the ground and communication with aircraft working the fire.

I'll let Larry explain the ASM function in a little more detail:

The ASM can function as an Air Attack if there is no other Air Attack available over the fire. When that's the case,the ASM will orbit the fire at 1000 ft or higher between tankers to allow the Air Attack to get a good view of the fire in order to plan and co-ordinate the attack on the fire by all resources. The Air Attack will normally be in radio contact with the Incident Commander (Fire Boss),with Dispatch and the air resources.

It's not unusual for the ASM to go to a fire as an initial attack resource and decide that tankers are not needed and then remain over the fire as Air Attack, even if there are no other air resources (helicopters,for instance) are assigned. In that case, the Air Attack will be talking to the firefighters on the ground and with dispatch.

When a tanker arrives,the ASM functions as a leadplane.It then reverts to Air Attack when the tanker leaves. If there is a full time Air Attack available over the fire, the ASM can still take over and act as Air Attack if the normal Air Attack needs to go in for fuel or relief.

Up close and personal with DC-7 tankers: retardant drops pt 2 of 2

In my last post, I was writing about the Aero Union multi-door tank system (8 doors) used by Butler's DC-7's. I'll let Larry explain to you the sequence he goes through making a typical retardant drop:

To drop a full load at Coverage Level 6, I would have the co-pilot arm the tank system, and I would set the intervelometer to the 12 o'clock position (1), set the timer to 0.4 and set the doors to open selector to 8. Assuming that we'd gone through the Descent Check List while descending into the drop pattern I should be set. All that I have to do next is to determine the correct place to begin the drop and hold down the drop button (located on the yoke) until all of the doors open.

I know that there are times when tanker pilots must make an emergency drop of a retardant load. If an emergency happens near a tanker base, there is usually a designated place, e.g. coordinates, where emergency drops can be made. Otherwise, the pilot tries to look for a safe place -- no houses, no people on the ground, away from water sources, etc. -- to make the emergency drop. As I understand it, if a tanker pilot were to drop the entire load at once (aka a salvo) while making an emergency drop, the nose will do a sudden pitch up because of the sudden loss of 27,000 pounds of retardant. Often the pilots have a few hairy moments when this happens as they bring the tanker under control.

In the case of the DC-7, Larry tells me that emergency dump switch (outlined in blue in the photo) is centrally located on the cockpit panel. When Larry or his co-pilot lift the guard and activate the system by flipping the switch to the up position, the doors open at an approximate coverage level 5 drop. If I am thinking about this correctly, an added benefit is that an emergency drop at an approximate coverage level of 5 means that any pitch up of the nose of the tanker will not be nearly as bad as a sudden salvo of all doors at coverage level 8 (or higher). Larry provides some more details on emergency drops:

As far as having to jettison retardant in an emergency, it all depends on the severity of the emergency, the location and other local circumstances. In most cases, such as an engine failure deep in a canyon, there will be time for some quick (maybe 15-30 seconds) of trouble-shooting followed by determining if there is time (and the terrain allows) to fly to a suitable drop area. If we really are deep in a canyon, a suitable drop area will be anyplace nearby that doesn't contain a water source, people, vehicles or structures.

Again, it all depends on the circumstances. Generally, it will be possible to fly a few miles to an open area, but it's better for a spot on the ground to be covered with retardant than the flaming wreckage of an airplane. It would be unlikely that we would climb out of a canyon with 3 engines to carry the load to a designated jettison area. However, if the failure occurred enroute to the fire at altitude, that could be an option. There are also other emergencies not involving engines. Hydraulic problems being high on the list. I also once had a failure causing the loss of the fabric on the rudder on Tanker 62 during a drop run.

As I've mentioned before, nothing is ever easy in the tanker business.

Up close and personal with DC-7 tankers: retardant drops pt 1

The tank system used in the DC-7 is an Aero Union multi-door tank system with eight doors where each of the eight tanks holds 375 gallons.Up until now when I have written about retardant tank systems in use by firefighting aircraft (e.g. the Erickson AirCrane and the AT-802), I have written about constant flow tank systems with either one variable single door or multiple doors. As I understand it, both of these systems are controlled by computers. Where the PIC has only to set the desired coverage level and possible the quantity of retardant to be dropped. These systems are easier to use, but come at a price. According to Larry Kraus, an Aero Union constant flow variable single door system for the DC-7 would cost at least$250,000 (perhaps more), representing a significant hunk of change out of Butler's budget.

The panel shown in this photo is located on the co-pilots side of the cockpit. The red light over the drop arming switch marked "off" is constantly on until the tank is armed, in which case it goes off. By the way, this switch is configured the same way across all of Butler's DC-7 tankers. Moving on, the switch on the left side of the drop panel marked "Flow/High/Low has been disabled as they no longer use the flow feature.

 

The dial in the photo above is called an intervelometer. Larry uses this dial to set how many tanker doors open at once. In this photo, it is set to safe, meaning that the doors will not open, moving clockwise:

LFT is the four doors on the left opening at once,
RT is the four doors on the right, and
ALL is the salvo of all eight doors opening at once

Continuing clockwise, to open double doors at a time, the dial is set to 1-2, and to open a single door at a time, Larry sets the dial to 1.

Larry provided an interesting piece of history about the intervelometer: "As far as the intervelometer, it was a surplus military item, as were a number of parts in the Aero Union 8 door tank. It originally was used for selecting the firing sequence for air to ground rockets on fighter bombers."

 We are not done yet, there are two more dials Larry uses, one sets the interval between door openings in tenths of second when pilot-in-command (Larry) presses the drop button that is located on the top left side of the yoke. The second dial sets the total number of doors to open. Larry explains the settings in this picture:

"In this picture,they are set to 0.4 seconds and 8 doors. At 130 kts. and 150 ft. above the terrain, with the intervelometer set for single doors, I would get approximately a coverage Level 6, or 6 gallons of retardant every 100 square feet (a 10 ft by 10 ft area) on the ground."

On Friday, I'll be writing more about retardant drops, so stay tuned!

Good Drop, Effective Drop

When I started working on this article on the factors that make for an effective retardant drop, I was thinking about things like drop height (altitude), drop speed (aircraft speed) and winds. Then as sometimes happens, I set the draft aside for a few days. During this period I took some time to go through some files that I have accumulated over the last several months, along with some correspondence with a couple of my tanker pilot friends. The result, thanks to my reading (listed at the end of this article) and my correspondence with a couple of my tanker pilot friends is what you see here.

As I read through my files and reviewed some of my correspondence, what was driven home to me is that a good drop is when the crew completes the drop in a safe manner and returns home.

What makes for an effective drop then? Well, I have already talked about two factors: the tank system (some examples of tank systems currently in use may be found here, here, and here) and retardants . Other factors include the right altitude (height at which the retardant is dropped), correct airspeed, and calculating the drift of the retardant due to winds.

To set the stage, it is important to say what an ideal drop is, that is what is the tanker pilot aiming to do in making the drop? I understand from my reading as well as e-mails with a couple of tanker pilot friends that the goal in making an ideal drop is that retardant has no forward speed and rains down on the vegetation.

One of my tanker pilot friends tells me that one of the reasons that you want to eliminate forward speed of the retardant  is to (hopefully) eliminate shadowing. As I understand it, shadowing means that all the retardant is plastered against the side of the tree, bush, even grass facing the drop while the backside is left untouched by retardant. Eliminate forward speed of the retardant and shadowing of the retardant is eliminated.

In addition, retardant drops at forward speeds can be very dangerous to ground crews who have not moved away from the drop zone. Fortunately, Incident Command will usually be able to clear ground crews from the drop zone to avoid these situations.

My tanker pilot friend made a couple of more pertinent points on retardant drops. First, he told me that dropping retardant at too high an airspeed (aka drop speed) can shear the retardant load apart so that it disperses too much leaving gaps in the coverage. Two, dropping to high, especially in high winds means that pilots won't be able to predict where the retardant will land.

Finally, he went on to say that if it is safe to do so in these high wind conditions, pilots might be able to make a retardant drop from a lower altitude so that some retardant line can be built. There might be gaps in the line, and the pilots may not be able to predict the coverage level, but at least there will be some retardant line that will slow the fire until the ground crews can get there.

As I was doing my background reading for this article I was impressed by the problems of making retardant drops in high winds. That is, when making drops in high winds, not only does the pilot/crew risk not knowing where the drop will end up, they are flying in very extremely dangerous conditions.

References:

I am including links to some of the USFS documents that I read while doing background research for this article. Before you read the documents below, I should caution you that some of the numbers cited are under ideal conditions in the laboratory, so to speak. Aircraft performance in actual drop conditions on the fire line will be different.

Lavalette, Greg. Safe Drop Height for Fixed-Wing Airtankers. 0057-2317-MTDC. Aviation Tech Tips (March 2000). US Forest Service, Technology and Development Program, Missoula Technology and Development Center, Missoula, MT.

Suter, Ann. Aerial Delivery Systems User Information: Wind Speed and Drop Height. ug-7. Wildland Fire Chemical Systems - MTDC. February 2005. US Forest Service.

Suter, Ann. Aerial Delivery Systems User Information: Drop Speed. ug-13. Wildland Fire Chemical Systems - MTDC. February 2005. US Forest Service

Additional Aerial Delivery Systems User Information documents, Safe Drop Height for Fixed-Wing Airtankers, and other documents relating to testing aerial delivery systems may be found on this USFS webpage.

Engine failures with happy endings

You will recall from my first post in the density altitude series that low air density -- which equals high density altitude -- affects engine performance. Engine failure in any plane can lead to disaster. In ideal conditions, engine failure in a multi-engine plane does not have to end in a crash. But in a tanker carrying a load of retardant, engine failure often means dumping retardant in order to avoid a crash. Most air bases used by tankers have a designated area where retardant can be safely dumped without harm to people, property, or the environment. But in an emergency situation, the pilot is not always able to reach the designated dump area.

Air density can affect how much time the pilot has to dump the retardant in the event of engine failure. My friend G (air tanker pilot) has this story:

I lost an engine in a P-2 on take-off out of Missoula on a fairly cool day, about 78 degrees.  It was almost a non-event.  I feathered the bad engine and continued to climb out to a spot where I could jettison the load without endangering anybody on the ground.  On a hot day, it would have been an entirely different story.

Engine failures can require quick action and a measure of luck irregardless of air density. Here are some more stories from G:

1. I saw a DC-4DC-6 lose an engine right at rotation, about six inches above the runway. The DC-4 DC-6 is not overpowered and that guy had to pitch the load in a heartbeat.  His retardant tank couldn't have been more than three inches off the runway and he just painted the Kalispel, MT airport runway all the way down.  That shut down the airport for two hours, but the crew lived to tell about it.  That crew was Canadian and I made sure he got the safety award that month for averting an airplane crash with quick thinking.

2. I lost an engine at Chico, CA in a P-2 right when I got the nose wheel off the ground and I knew we couldn't fly out of there.  I had to decide and act in about a second and a half, so I shut it down and did a panic stop, using every inch of available runway and a little more.  But, we were alive.

3. I lost an engine in the PB4Y2 out of Jeffco, CO and I had to find a spot to pitch the load pretty quickly.  Fortunately, there was a big field behind some houses right off the end of the runway and it went there.

Newscrew's close encounter with Phoscheck

on retardant and aerial firefighting

I saw a good article on inciweb last week about retardant and aerial fire fighting. It is called Retarding the Flames, and it is one of the news releases in conjunction with the Station Fire:

One of the most dramatic sights on a wildfire is the vision of an air tanker releasing its red payload of retardant near the fire. Behind this picturesque vision is a long history of science in the development of a valuable tool for firefighters - the use of fire retardant. Today retardant is used when appropriate to help suppress wildland fires.

Aerial drops of retardant have come a long way since the first recorded water drop in 1930, when a Ford Tri-Motor airplane used a wooden beer keg filled with water. Now air tankers can drop 500 to 2000 gallons of retardant at a time to help suppress fires. Helitankers, which are helicopters with built-in tanks, can drop up to 2000 gallons; retrofitted DC-10s have an 11,000 gallon capacity, and Boeing 747s 20,000 gallons.

Fire retardant is just one of many tools in the arsenal of firefighters. Like any other tool, it must be used under the right conditions and for the right job in order to be effective. Firefighters consider many factors in deciding which tools to use at a particular location and time to suppress a fire. Characteristics of the terrain, weather variables such as temperature, humidity, wind direction and force; the types of vegetation in the fire area; proximity to homes and other buildings; and the first priority of safety of the public and firefighters are all factors in choosing the right tools for the particular circumstances.

Retardant drops are most often used in extreme fire conditions. The retardant is usually dropped just ahead of the advancing edge of the fire and the flanks of the fire. This cools and so slows the fire, helping firefighters on the ground. It reduces the rate of spread and the intensity of fires, and slows larger, more damaging, and therefore can reduce the cost of fires. Often, using retardant to fight fires is the most effective and efficient method of assisting firefighters in protecting people, resources, private property and facilities. The remoteness of many wildland fires can delay the arrival of firefighting ground forces. Retardant drops can rapidly reduce the intensity and spread of the fire until firefighters can safely take action. Topography in the fire area and windy conditions are some of the factors limiting the effectiveness, and therefore the use, of retardant.  . . .

Go here to read the complete article

Tankers don't always carry full loads

I want to briefly mention something that I will spend more time writing about later after I have had a chance to do some research as well as talking to my aviator friends. That is, more often than not, tankers and helos will not carry a full load of retardant or water in their tanks due to aeronautical concerns. So, when the reports are saying that the Martin Mars can carry 7,200 gallons of water/gel mixture or that the Evergreen 747 supertanker can carry 20,500 gallons of retardant, they will carry these loads under "ideal" circumstances. The word "ideal" may be a misnomer, but it will have to suffice for now.

So, the Martin Mars was, as Bill Gabbert pointed out the other day, was carrying a smaller load of water (about 4,600 to 5,500 gallons). Chances are the Evergreen 747 supertanker was carrying a smaller load of retardant. Those of you who are aviators, or firefighters more familiar with aeronautics than I will know that one of the main reasons that tankers (and I assume helos) carry a lower load is because of something called density altitude. I will be writing some articles later about density altitude. I had begun discussions with some of my fire aviator friends several weeks ago about points such as density altitude and retardant coverage levels. I am beginning to revisit these issues.

One final point, while I am on the subject. When the Fox newscasters were covering the other day about the Evergreen 747 supertanker's retardant drops, one of them said that the supertanker could lay down a retardant line 3 miles long. This was also under "ideal" conditions and when the load is dropped in one run. I will add here that they were reading from specifications and other data on the supertanker, as they should. Having read specs myself, what I have to remember is to read words like "maximum" or the data sheet might say something like "the supertanker can drop a retardant line up to three miles long." Point being that I have to remember to think about these words as I listen to newscasts or read articles online.

Returning back to retardant line laid by the Evergreen 747 supertanker, the supertanker split the load into two runs, as all tankers are able to do. Likewise, at full capacity and under ideal conditions, the Martin Mars can cover 4 acres with its water/gel mix. If I understand things correctly, each water/gel load dropped by the Martin Mars covered less than 4 acres. Again, in later articles, I will try to write more about this issue.

I will also be writing about other aerodynamic issues relating to retardant and water drops. In some sense this planned series of articles will be a continuation of the short series of articles I wrote several weeks ago on wing stalls as relates to retardant drops. I won't link to this here, but if you look at the labels on the lower left side of this page, you will see a label that says "aerodynamics." If you click on that label you will get all my posts on aerodynamics to date, including posts on wing stalls.

Look for this series down the road a bit.

S-2T: making the retardant drop

When an air tanker such as an S-2T is deployed to a wildland fire, the air tanker pilot will be in touch with either the incident commander on the ground or some one known as the air tactical group supervisor (ATGS). The ATGS oversees aerial support for the fire, including retardant drops from a tactical aircraft, sometimes known as an air attack plane flying over the fire. The ATGS will be in touch with the incident commander (IC) on the ground. CAL FIRE’s tactical aircraft are known as OV-10’s and there is one OV-10 at each air attack base. The ATGS, after consulting with the IC, will give the S-2T tanker the information that s/he needs to make the drop, including but not limited to the location. In initial attack the S-2T pilot may make his own determination about the necessary settings and where to make the drop.

The settings that S-2T air tanker pilot (and other air tanker pilot’s) use for the retardant drops are on a panel on the cockpit. This is the same one pictured in the preceding post, so I will be using that picture as a reference. Perhaps you will want to open up a new window in your browser so you can look at TL Stein’s photograph and follow along.

The pilot adjusts the dial on the left to set the amount of retardant to be dropped while the dial on the right is set to determine the coverage level (also known as gpc). The coverage level is gallons of retardant per 100 square feet. Coverage levels are somewhat technical, depending on the type of vegetation on fire (fuels) and the fire behavior. The coverage settings dial is scaled from .5 to a maximum of 8 (gallons per 100 square feet). A switch known as the arm-disarm switch is set in the disarm position until it is near time to make the actual retardant drop. This prevents accidental drops. The button that the pilot pushes to make the drop, drop control switch (not pictured), is on the pilot’s control panel for ease of access. The door control (switch in the middle), is set to automatic.

Once the settings on the two dials are made, and the pilot is at or near the location and correct altitude for the drop -- 150 feet above ground level for the S2-T -- the pilot flips the arm-disarm switch to arm the system. The pilot has only to push the drop control switch at the appropriate time, the tank doors open and the drop is made. It is not merely the cockpit controls that make the retardant drop possible, there are various avionics (aviation electronics) and hydraulics that make the retardant drop possible.

If there is an emergency situation, the pilot can make an emergency retardant drop by pulling an emergency handle (not pictured).

C-130 MAFFS: retardant drop

The loadmaster, who sits at the loadmaster station on the MAFFS module in the cargo area in the back of the tanker works with the co-pilot in making the drop. You may recall from my earlier post, that the retardant flows through two discharge tubes that stick out the rear cargo doors of the aircraft. This means that cargo doors are left open and the load master wears a safety harness tethered to the rear of the plane. When it comes time to make the drop, the loadmaster monitors and then arms the system using the master control panel at the loadmaster station. It is the co-pilot, sitting in the cockpit, who pushes “the button” to drop the load.

The C-130 MAFFS works with what is known as a lead plane in making the drop. The lead plane flies as close as 1,000 feet in front of the tanker showing the path and height that the tanker will fly in making the drop. There is a nice article an the CAL FIRE MAFFS webpage about the role of lead planes in MAFFS missions. The article is called “exactly who is leading this mission”, it may be found here. Both civilian air tanker and military MAFFS pilots train with a lead plane every year.

To see a short you tube video on a C-130 MAFFS working with a lead plane go here.

drop patterns

The IAT website that I referred to in yesterday's post has a good SEAT training module (part 3) on fire operations. In other words the module talks about the parts of a fire along with different retardant drop patterns.

The module may be found here. Enjoy! I keep going back and reviewing this module, along with the one on fire behavior that I referred to yesterday.

The retardant drop

After the retardant is loaded, there is one thing that may be done before take off. That is, the ground crew who loaded the retardant onto the plane will wash down the side of the plane. This is necessary because the retardant will oxidize the paint and metal if it is not washed away. The ground crew moves away, the pilot is cleared to start the engine and then cleared for take off.

Moving to the fire itself, and before getting to the drop, I need to discuss two important people, One is the incident commander (IC). According to the glossary of fire terminology from the National Wildfire Coordinating Group, the incident commander is the “individual responsible for the management of all operations at the incident site.” The air coordinator is in an airplane flying overhead and is thus able to get a bigger view of the fire than the IC on the ground. The air coordinator looks at conditions that will affect the drop such as wind direction, hazards such as powerlines and trees, and if and how the drop will aid the fire fighting crews on the ground.

For example, the IC may ask for an anchor point on one of the flanks of the fire and allow the air coordinator or air operations (AirOps) to determine the optimal plan for the retardant drops. After AirOps has decided on the drop, they will tell the air tanker pilot exactly where to make the drop along with how much retardant to drop. Sometimes the pilot will make a dry run before making the actual drop, especially in cases where the pilot has not flown in the area on prior occasions. When the pilot is not familiar with the area, a dry run allows the pilot to scope out potential hazards that AirOps might have missed, look for escape routes, and get a feel for how the terrain might affect the wind. After the dry run, if any, is done, the actual retardant drop is made.

I would again like to thank TL Stein for our e-mail correspondence discussing discussing what happens from the loading of the retardant to the time the drop is made.

Terminology from the National Wildfire Coordinating Group

Anchor Point: An advantageous location, usually a barrier to fire spread, from which to start building a fire line. An anchor point is used to reduce the chance of firefighters being flanked by fire.

Flanks of a Fire: The parts of a fire's perimeter that are roughly parallel to the main direction of spread.
Incident: A human-caused or natural occurrence, such as wildland fire, that requires emergency service action to prevent or reduce the loss of life or damage to property or natural resources.

Incident Command System (ICS: The combination of facilities, equipment, personnel, procedure and communications operating within a common organizational structure, with responsibility for the management of assigned resources to effectively accomplish stated objectives pertaining to an incident.



Incident Commander (IC): Individual responsible for the management of all incident operations at the incident site.

avoid stalls during retardant drops

Remember the two stall speeds that I referred to for the AT-802F that I referred to here? There is a V-speed or velocity-speed known as Vs where Vs is the stall speed or minimum steady flight speed for which the aircraft is still controllable. As you can see from this wikipedia article on V speeds, there are many different V-speeds. Now, if I am thinking about this correctly, then Vs should be slightly higher then this AT-802F performance specification:

Stall Speed, Flaps Down: 91 mph (146 kph) at 16,000 lbs (7 257 kg)

The speed that an airtanker flies at when making retardant drops on a fire is related to Vs. This is expressed as a formula (1.3*Vs). According to the specs found on the Queen Bee web site, the drop speed is in the 120 to 130 mph range. For a more detailed discussion of the calculation of the drop speed (from which I based this discussion) using the AT-802 as an example, go to this BLM aviation page, an automatic download of a MS word document.

TL Stein offers this explanation of stalls, retardant drops, terrain, and fire-produced weather:

Stalls are to be avoided in ALL cases, excepting the landing phase of an aircraft.  In the air tanker world, landing is the only place you want a STALL.  Fire produces it's own weather conditions.  A tanker making a drop in a canyon can experience a tailwind on approach to the drop, which drops the forward airspeed.  Over the fire, a severe lift condition can and does occur, due to the heat raising from the fire.  During the drop phase, the aircraft releases it's load and becomes much lighter.  Consider the thermal wind activity over the drop zone, combined with a sudden tail wind.  The aircraft can loose enough forward airspeed over the wing to cause it to stall and crash.  This is why airspeed / drop speed are critical to the aircraft and the mission.  In the real world, stalls are practiced at a good altitude to enable a successful recovery.  This is mandatory for a "type rating" in the aircraft you will be certified to fly.  Stalls close to the ground, in a fire fighting scenario leave no room for recovery.  There are a lot of memorials to pilots who stalled and crashed.  Why?  Constantly changing conditions over the fire is a good start.  You can make two passes over a fire and the flight conditions will never be the same on each pass.  The best tanker pilots on earth know this.  Each drop you make you run the risk of something going wrong, it's a given and we know it.

SEAT dropping retardant

Check out this really cool (but short) video of a single engine air tanker (SEAT) dropping retardant (the red liquid) on a fire in Idaho. Remember that retardant slows down the fire.

I'll be writing more about retardant in a later post. I need to spend a little more time reading about retardants before I do so.