Two aerial firefighting jets, including one based in Missoula, have been grounded because of corrosion apparently caused by a new fire retardant the U.S. Forest Service approved for use beginning last year.
Two large air tankers — mid-size passenger jets converted to carry 3,000 gallons of retardant each — used a magnesium chloride fire retardant product while fighting wildfires last year. Both are grounded pending a joint investigation by the National Transportation Safety Board, National Institute of Standards and Technology and the Forest Service.
The magnesium chloride retardant was in limited use last fire season, loaded into the two large air tankers and some smaller, single-engine aircraft also in Montana. After the discovery this winter of corrosion in areas of the large air tankers where the retardant accumulated, the Forest Service decided not to use it this year. Instead, the agency will continue its widespread use of ammonium phosphate fire retardant that has been the go-to retardant nationwide for years. Aerial fire retardant is a mainstay of modern wildland firefighting and is often the most visible sign of crews trying to slow or contain a fire. The usually bright-red chemical slurries function by coating foliage ahead of a fire front and making it less susceptible to ignition.
People are also reading…
The magnesium chloride retardant was developed by Fortress North America. Founded in 2016 and partially based in Stevensville, south of Missoula, Fortress touted its formula as more environmentally friendly than ammonium phosphate. The company highlighted that distinction after an environmental group sued the Forest Service in 2022 over drops of ammonium phosphate retardant into waterways, which a judge found had illegally degraded aquatic habitat. (The judge declined to halt the use of that retardant, citing the importance of aerial fire retardant in combating wildfires.)
Perimeter Solutions, the longtime sole provider of the Forest Service's ammonium phosphate retardant, is based in a suburb of St. Louis, and will continue to provide retardant this year. Compass Minerals, a Kansas-based salt and magnesium chloride company, purchased Fortress in May 2023. Compass Minerals previously owned a minority share of Fortress.
When the Forest Service approved Fortress' retardant for its Qualified Product List in December 2022, the company claimed it was the first long-term aerial fire retardant product added to the list in more than 20 years.
A spokesperson for the Forest Service refused to answer questions from the Missoulian about corrosion and the magnesium chloride retardant.
Compass Minerals, which produces its magnesium chloride from an evaporation facility in Utah's Great Salt Lake, announced March 25 that the Forest Service "informed the company that it will not be entering into a contract for the use of magnesium chloride-based aerial fire retardants for the 2024 fire season."
Winter evaluations of aerial firefighting aircraft mandated by the Forest Service found "significant signs of corrosion" where the retardant accumulated in aircraft that used the product, the company stated.
"While we are disappointed with the findings of the initial inspection, we share the USFS' prioritization of safety above all other factors," Edward C. Dowling Jr., president and CEO of Compass Minerals, said in the statement. "As we work collaboratively with the USFS, NTSB and NIST on the more detailed assessment to be conducted, we have to assume based on this new information that Fortress' proprietary, magnesium chloride-based aerial fire-retardant formulation will not be utilized for the foreseeable future in the fight against wildfires."
Nic Lynn, vice president of operations at Missoula-based Neptune Aviation, confirmed that the company's Tanker 02 used the magnesium chloride retardant from Compass Minerals last year. The plane is one of Neptune's nine active BAe-146 quad-jet tankers. It has not flown since it returned to Missoula from San Bernardino, California, on Dec. 19 last year. The company's other aircraft were not affected.
Although Tanker 02 is currently grounded during the investigation, Lynn said it "will be operational for the fire season."
Kevin McLaughlin, director of production and certification at Oregon-based Erickson Aero Tanker, confirmed that the company's Tanker 106 used Compass Minerals' retardant last year and would be grounded for the 2024 fire season. It last flew Dec. 14 last year when it returned to Madras, Oregon, from Porterville, California. The six other aircraft in Erickson's fleet — all MD-87 jets like Tanker 106 — were unaffected.
Lynn and McLaughlin each declined to comment on the specifics of the damage to the aircraft, citing the ongoing investigation. Both companies' aircraft operate across the U.S.
The Ronan Single-Engine Air Tanker (SEAT) Base north of Missoula was the lone test site for Fortress' current magnesium chloride formula in 2022, and SEATs there used the product again last year after Compass Minerals fully purchased Fortress. The base, located within the Flathead Reservation, is operated by the Confederated Salish & Kootenai Tribes Division of Fire and the U.S. Bureau of Indian Affairs.
Robert McRae, the Ronan SEAT manager, did not respond to a voicemail seeking comment. Todd Coture, the base's operational manager, was unavailable for comment.
The revelation of corrosion serious enough to ground aircraft — and that it was seemingly caused by a Forest Service-approved retardant — led to the United Aerial Firefighters Association to call on the Forest Service to halt the testing and certification of new retardants until the agency develops new testing procedures to prevent a potentially corrosive retardant from getting on the Qualified Products List. The group also asked the agency to wait for the NTSB/NIST investigation report to be released.
"As it must, the USFS prioritized the safety of aircraft, aerial firefighters, and the public," UAFA Executive Director Paul Petersen wrote in a letter to lawmakers and Forest Service officials, "however, this development underscores the urgent need to reassess and update the current process for adding new products to the USFS Qualified Products List."
UAFA is an industry group whose membership includes Neptune Aviation, Erickson Aero Tanker, Fortress North America and Perimeter Solutions. Petersen's letter said that repair of the two affected aircraft could cost millions of dollars.