Imagine watching a beautifully-painted red-and-white Boeing 737 using McCall Airport as its base while helping fight wildfires on the Payette National Forest. It could happen!

Coulson Aviation B737 water drop.

Coulson Group Ltd. is a family-owned business located in Port Alberni, British Columbia. They operate a diverse fleet of both fixed-wing and rotary-wing aircraft for helicopter logging, forest fire suppression, power-line construction, airliner passenger transport and many other industrial heavy lift operations. Started as a logging business in 1960, they expanded into aviation in 1985. In 1990, they created the wholly-owned subsidiary Coulson Aviation (USA) Inc., initially for heli-logging operations in Alaska. Under the leadership of owner Wayne Coulson’s oldest son Britton, age 31, Coulson Aviation added C-130 airtankers to operate as firefighting aircraft in the U.S. and Australia. And now, they’re utilizing modified Boeing 737 jets as airtankers – called Fireliners – a unique application for the iconic airliner. In October 2018 Coulson entered into a five-year contract with Australia to use the 737 airtanker fighting wildland fires during their fire season.

Coulson’s modified 737 can carry 4,000 gallons of retardant or water in its two tanks. Compare that to a Superscooper 415 – which we’ve seen at McCall Airport support firefighting on the Payette National Forest in the past – with a capacity of 1,600 gallons; single-engine tankers carrying 800 gallons; and P-3s with a 3000-gallon tank. The Lockheed C-130 Hercules (Coulson has two, with more on the way) carries 4,000 gallons, the same as the 737. C-130s are better suited to operate from higher-elevation and hotter runways, so while one might wish to see a Coulson 737 working out of McCall, it’s more likely a C-130 would operate from here.

Coulson is in the process of modifying a second 737. The 737s have been purchased from Southwest Airlines and are about mid-way through their anticipated lifespan. In all, Coulson plans on modifying at least five 737s into Fireliners. Each 737 airtanker operates with two pilots.

Federal Aviation Administration & U. S. Forest Service (USFS) regulations limit airtanker flights to eight hours per day; that can equate to eight to twenty missions depending on distance between fire and base. Because of the 737’s speed as well as its ability to access more bases – putting them closer to fires – the average sortie time is 34-40 minutes if the fire is within 100 nautical miles of base. They do a parabolic flight path to get to the fire, then spend five to ten minutes over it making one or more drops. If the fire is only 20 miles away, they could do 15-20 sorties during an eight-hour span. While the hours of flight are limited to eight, crews can be on duty up to 14 hours per day.

At most U.S. base airfields, the 737 spends 8-12 minutes on the ground refilling tanks with retardant or water and refueling. Currently Coulson’s first 737 Fireliner is fighting fires in Australia where they have been spending roughly 17 minutes between landing and takeoff from the Royal Australian Air Force base in Richmond, New South Wales.

Model showing tanks and passenger seats.

Turning the 737 Into Wildland Firefighting Airtanker   Modifying the first 737 to carry tanks and drop retardant or water provided unique challenges and involved over 100,000 hours of engineering, production and testing. The airplane’s low wings and gear position made it necessary to have two tanks – one in front of the wings, the other behind – in order to maintain the airplane’s center-of-gravity. Additionally, when dropping the water/retardant, to maintain that balance and center-of-gravity both tanks must deploy simultaneously and in equal amounts. Coulson’s engineers designed a system where each tank has left-side and right-side doors that open to drop contents. Those doors are isolated laterally, so for example, if the right door of the front tank opens, the right door of the rear tank also opens, independent of the left-side doors. All four doors can be opened at the same time. But if there’s a failure in one door, say the right front tank, then the right door on the rear tank will not open. This prevents an inadvertent shift in the center of gravity because water/retardant can only be dropped from both tanks simultaneously, or not at all.

When both tanks are filled, the 737 carries 4,000 gallons of fire retardant, roughly half the capacity of a small-sized backyard pool. The retardant weighs 36,000 pounds, or the equivalent of twelve family-size cars.

Coulson pilot Jonas Doherty, right, with the 737 airtanker in Australia in December 2018. The New South Wales Rural Fire Service named the airplane Gaia.

Idahoan Jonas Doherty is One of Coulson’s 737 Pilots   Jonas Doherty is an airtanker pilot based out of Boise. He grew up in McCall, and spent his most formative years here. “My family moved to Boise, but McCall was always my home so I came back every chance I got,” he says. “I still think of it has home.” While in college Doherty thought he’d like to be an airline pilot, so he got the required certificates and ratings but eventually realized that maybe he wasn’t suited to fly for an airline. Doherty kept building his flight hours, though. Knowing Boise is the wildland fire center for the U.S., he started applying for pilot jobs locally. From 2005-2010, working for AvCenter Inc., Doherty piloted the Air Tactical Group Supervisor platform, orbiting above all the other aircraft over a fire, an experienced ground firefighter who has been specifically trained to manage the aerial assets over a fire sitting in the right seat.

Doherty then moved to Oregon, working for the Forest Service from 2010-2013 as lead plane pilot, assessing the low-level environment by sampling the drop run prior to the arrival of the airtanker. “We are looking at turbulence and hazards the may not be readily visible from a high-level recon, monitoring the status of horizontal visibility from the drop height,” says Doherty. “I’d tell them what landmarks to look for, to fly out that canyon. I’d lead them in, flying in formation, telling them to drop their loads at the white rock or some other visible landmark.” Some of that flying was over the Payette National Forest. In 2013 Doherty moved back to Boise, flying lead plane for the Bureau of Land Management (BLM). In 2016-17 he worked as a DC-10 airtanker pilot for 10 Tanker Air Carrier before hiring on with Coulson Aviation in November 2017 as a pilot on their 737 airtanker project.

“Fire teaches lessons instantly,” says Doherty. “You could get the craziest fire on your first job. It’s better to teach a new airplane to a pilot with fire experience.” While at 10 Tanker Air Carrier, Doherty became their test subject for taking an experienced firefighting pilot with no DC-10 experience and training him in that airplane. “I was a captain-in-training in the DC-10. I went from a Beech King Air 200 to the DC-10. It worked well, it was a smooth transition.” Using that same approach with Coulson’s 737, Doherty and the other Coulson pilots are all skilled firefighting pilots who are now checked out in the 737.

“It was an opportunity to get in on the ground floor of a new program,” says Doherty, explaining his decision to fly with Coulson. “I couldn’t pass it up. The 737 is iconic, well-built, stout. It’s the right airplane for this job. They were just completing modifications to the first one. It was ready for flight testing when I was hired.”

Testing the Certifying the 737’s Abilities as an Airtanker   The Coulson 737’s Retardant Aerial Delivery System – RADS – offers the pilots variables for dropping retardant/water. “As pilots, we select coverage level, or quantity (percentage), and arm the system via a touch screen user interface that is located in the cockpit,” says Doherty. “Once the system is armed, we just push and hold a yoke-mounted button to make the drop. During the drop, the RADS controller is varying the drop doors to achieve the requested coverage level. The controller receives three inputs during the drop sequence: flow rate, which accounts for varying head pressure as the tank volume diminishes; groundspeed, which accounts for variations due to shifting winds; and height above terrain, which accounts for varying drop heights during operations in mountainous terrain.” Each tank in the 737 is V-shaped and the doors can be opened in a way that compensates for the rate of outflow as the tanks empty, helping it hit the ground more evenly. If flying over fire in grassy terrain the pilots might do a light level of coverage; if over steep timbered terrain, a heavier coverage. A quick drop of the entire capacity of the tanks takes just 1.3 seconds. They can split the drops as many times as necessary; it’s common for them to do repeats on an area.

Testing Coulson’s first modified 737, under the direction of former Boeing test pilot Paul Derochers of Test Pilot Inc., included many of the tests typically done when certifying a brand-new airplane: stalls, single-engine takeoffs, finding the edges of the operating envelope. Once that was accomplished and the FAA certified the airplane for use as an airtanker, Coulson did further tests to meet USFS regulations, something called a grid test to prove that the 737 could drop retardant in a good pattern for firefighters on the ground. “We did this down in San Bernardino,” says Doherty. “The Forest Service people create a big field full of stakes placed in the ground in precise intervals, each with a cup on top. People line both sides of the field, and as soon as we fly by and drop the retardant, those people run up and put lids on the cups to prevent evaporation. Then they collect all the cups, transport them to a nearby hanger, weight them one by one, putting the data into an Excel spreadsheet. They come up with grams of retardant per cup.” Coulson’s 737 successfully passed the grid test, obtaining an interim Interagency Airtanker Board (IAB) certification that approves the airplane for work with federal and state firefighting agencies in the U.S. After a season or two over fires – including their current flying in Australia – gathering evaluations from firefighters in the field, Coulson anticipates gaining full IAB approval. “Passing that test is a huge deal,” says Doherty. “It’s expensive, buying the retardant and doing the flying, but once obtained, it’s a world-wide standard so you’re good to contract anywhere.”

Here’s video of a Coverage Level 6 partial drop test:

Tanker 137 CL6 Partial Drop

Below is a video from today of a partial Coverage Level 6 drop.

Posted by Coulson Aviation – Next Gen Firefighting on Tuesday, September 4, 2018

Coulson Aviation USA has made an enormous investment in modifying 737s as airtankers for wildland firefighting. “It takes vision, hard work and money to certify these airplanes,” says Doherty. “But we’re only there to support the ground firefighters; they’re doing the real work.”

The Role of an Airtanker in Fighting Fire   Doherty says that their job is to help the firefighters on the ground; they’re the ones actually putting the fire out. Normally this involves dropping retardant immediately in front of advancing flames to moderate fire behavior so ground firefighters can directly engage the fire. Sometimes – whether due to extreme fire behavior or lack of available resources – the direct attack strategy isn’t feasible and firefighters back off to more favorable terrain or conduct backburns with airtankers used to widen existing fire breaks. “Sometimes we just have to abandon the idea of controlling the fire in the short term and transition to point protection,” explains Doherty, “dropping retardant in a chevron shape in front of structures – a house, an antenna, a ski lodge – allowing the fire to bump into the retardant and ease around the structure.”

Video of the Coulson 737 dropping retardant in Australia:

The Large Air Tanker has been deployed to assist firefighters at the Possum Point fire (Snowy Valleys LGA). Gaia is assisting ground crews by building containment lines around a small breach of the containment line on the north-eastern corner of the fireground. There is currently no threats.

Posted by NSW Rural Fire Service on Tuesday, January 22, 2019

“Dropping retardant is more of an art than a science,” says Doherty. “There are a lot of factors at play: varying wind speed and direction, terrain, turbulence, and reduced visibility due to smoke to name a few. To be an accurate airtanker pilot means to consistently factor these variables into each drop, and to understand and anticipate what the firefighters on the ground need. The lessons that generate that level of understanding generally come only with direct on-the-job experience, and the lessons never stop. It is an incredibly humbling and rewarding experience to fly an airtanker; a dynamic job for sure.”

Two important variables are the airplane’s height above the ground and its ground speed. Typically, the 737 is 150-180 feet above the ground when dropping retardant, flying at 125-135 knots indicated air speed, which is similar to or just below its normal approach to landing except in this case, the gear remains up. “The drop itself is procedurally executed much like a rejected landing/go around,” Doherty explains. “The Fireliner has very nice handling characteristics throughout the drop sequence.”

The Fireliner cruises at typical 737 speeds and altitudes to and from the fire, Doherty explains. “In order to achieve that level of efficiency and speed, a critical design requirement was for the Fireliner to be capable of pressurizing while loaded. This involved a fair bit of engineering given the fact that the tanks share air with the cabin. The tank drop doors had to be engineered to withstand maximum differential pressure plus the weight of the fire suppressant at a two-G inflight maneuver.”

Another innovation of the Coulson 737 Fireliner is retention of passenger seats in part of the airplane. In addition to fighting fires, the Fireliner is certified to carry up to 72 passengers, although not at the same time that it’s dropping retardant. “The idea is that the aircraft will be primarily operated as an airtanker, but can also move firefighters as needed, and then seamlessly transition right back to supporting those firefighters in the field,” says Doherty. “Australia has shown a great deal of interest in the multi-role concept.”

The Fireliner has not yet been used by the USFS; it was just approved as an airtanker in November of 2018. In fact, Coulson Aviation learned approval had been secured while on their way to Australia to fight fires in New South Wales. Australia is where the 737 debuted and where the pilots and crews are gaining valuable experience. A Coulson crew will bring the 737 back to Canada in March. Doherty says it will likely go to work fighting fires in the U.S. during our fire season, either for the USFS or CalFire. Coulson Aviation is currently modifying a second 737 and as soon as that one’s done will begin modifying a third. Coulson anticipates having them ready for our 2020 fires season. “We’ll have to double our current number of 737 pilots,” says Doherty.

Coulson’s team of firefighting aircraft, including the 737 (N137CG), covering ground in Australia, January 28, 2019.

Fighting Fire Down Under During Our Winter Season   Flying in Australia during their fire season – our winter, their summer – is rewarding, says Doherty, but also a strain on one’s family life. Right now, Coulson has three airplane captains and they rotate duties; Doherty expects they’ll upgrade a couple more pilots soon. Doherty got married two years ago, in the Frank Church River of No Return Wilderness, and he and his wife Holly are expecting their first child in March. He has been in Australia since the middle of November, with just three weeks off over the holidays, and admits it’s tough being away from home so much especially with a baby on the way. “I asked my wife what day she wanted me home,” Doherty says. “She said March 1st. I have my ticket.”

“I love this job,” continues Doherty. “The fact that it’s tactical, mission-driven and dynamic, supporting the ground crews and their accomplishments. No two flights are ever the same. Low level, smoke, flames, winds…it’s the most rewarding flying experience I can think of. Flying the 737 is the most fun I’ve had in my flying career. I’m really looking forward to fighting fire with it in the United States.”

Doherty also admits to missing skiing, since he’s not in Boise for winter. “I haven’t been once this year,” he says. “I guess that’s just one of the downsides of chasing fire season across the world. I’ve managed to get by with substituting my love for skiing with my love for riding bikes. I bought a road bike and the morning rides have been a really great way to experience the Australian countryside.” Mostly, though, the pilots and crews are too busy fighting fires to enjoy any real sightseeing while in Australia. “We do, however, have the opportunity to see the country from a pretty unique perspective,” says Doherty. “So far this season, the fires have taken us as far north as Queensland and all the way south to Tasmania.”

One benefit of spending so much time working while in Australia is forging friendships with their Australian counterparts. “So often, it’s easy to focus on the shiny airplane and forget the huge network of support that goes into allowing us to do what we do,” says Doherty. “From the crews who transport the retardant to the base, the mixing and loading crews, air base managers, and the folks making decisions at the New South Wales state air desk, we are all a team, and there are lots of people to befriend. The Australians have been incredibly hospitable and they’re always up for a chat, which is always entertaining given their cool accent.” An Australian firefighter friend recently gave Doherty a platypus stuffed animal to bring home for his new baby’s room.

(Author’s Notes: This interview with Jonas Doherty occurred in mid-February while he was in Australia. Also, the author confesses to having an affinity for 737s; her father, Boeing test pilot Lew Wallick, was copilot on the first flight of the 737 on April 9, 1967, with pilot Brien Wygle. The author was ten when she watched them take off from Boeing Field in Washington state.)

Photos and videos courtesy Coulson Aviation. Follow their firefighting efforts on Facebook.

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About the author

Rebecca Wallick

Rebecca is a freelance writer and publisher living near McCall, Idaho. A Seattle native and recovering attorney, she much prefers the quiet, slow pace, and distinct seasons of the West Central Mountains, enjoying the skiing, hiking and running opportunities provided by the nearby Payette National Forest. Rebecca is a Contributing Editor with Bark magazine, and the author of Growing Up Boeing: The Early Jet Age Through the Eyes of a Test Pilot’s Daughter (Feb 2014).

1 Comment

  • 30 years ago when I was a young engineer with the Forest Service, in March there were a bunch of fires in North Carolina, and they ran short of regular fire fighters because it was too early for the seasonal crews to be on duty. So they recruited qualified regular employees such as myself to go back to North Carolina to do mop-up and other chores. They had to get several bus loads of us to transport from Colorado to North Carolina, and I remember we all climbed in a big military carrier (I think it was a C-130 Hercules). That flight must have taken some logistics to arrange, and we did not have windows! This 737 described in the article sounds more fun to be a passenger in.

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