A Bell UH-1H helicopter returning from a firefighting mission fatally crashed in New Mexico in July 2022, destroying the aircraft and killing all four personnel on board. The U.S. National Transportation Safety Board (NTSB) concluded in its June 2024 final report on the accident that “poor maintenance” led to an engine failure, causing the helicopter owned by the Bernalillo County Sheriff’s Department to slam into the desert.
The crash highlights how critical helicopter maintenance is in the high-stakes world of aerial firefighting. According to experts, maintenance programs must be meticulous. Firefighting helicopters often have to operate at high levels of utilization in extremely challenging environments.
“In the context of firefighting, what is at stake is the safety of firefighters and, ultimately, of civil society,” Laurent Reynaud, head of business development for Airtelis, and Jean-Philippe Fiat, key sector manager for helicopters and maintenance, repair and overhaul for Segula Technologies, replied jointly to questions from Vertical Valor.
Airtelis is a French firm that operates helicopters under contract, including Airbus H215 and H225 helicopters used to fight wildfires in support of the French Civil Security. French company Segula maintains those helicopters.
“The main difference between classic helicopters and firefighting helicopters is the very high flight rates during fire season,” Fiat and Reynaud said. “The maintenance of firefighting helicopters is based on a conventional maintenance program, with particular attention paid to the number of load-carrying cycles.”
The helicopters are equipped with Bambi Buckets that have the capacity to carry 4,000 liters (1,057 US gallons) of water.
The load-carrying cycles “are scrupulously marked and tracked in the maintenance program, and give rise to a specific visual check,” they said. “The maintenance protocol is supplied by the manufacturer. The overall aim of all firefighting helicopter maintenance operations is to ensure that the aircraft has maximum potential for fire campaigns.”
Oregon-based Croman Corp. operates variants of the Sikorsky S-61 helicopter — including two used to help fight the Los Angeles wildfires. “There is relatively high utilization, particularly what you’re seeing in Southern California,” Croman director of operations Brian Beattie told Vertical Valor. “However, it’s not that the pace is so great that you can’t keep up with the maintenance.”
U.S. Forest Service contract requirements limit a mechanic to a 16-hour duty day, which means high-intensity operations like those in Los Angeles often require two maintenance crews, especially since maintenance has to be conducted at night when helicopters are needed to fly repeatedly throughout the day, he explained.
“It is incumbent on the operator to have the appropriate personnel to maintain the helicopter,” Beattie said. “So, if you’ve got four or five hours of inspections to do in the evening, you have to have a second crew. The operators know that they’ve got these maintenance requirements.”
The Forest Service is responsible for 193 million acres (78 million hectares) of land, and has approximately 600 aircraft under contract — including Croman helicopters — to conduct aerial firefighting missions.
“We fly about 70,000 flight hours annually on average,” said John Nelson, the Forest Service airworthiness branch chief based in Boise, Idaho. “The majority of those flight hours are in aerial firefighting helicopters.”
He added: “There are some things we encounter particularly in aerial firefighting, where there is more severity due to weather and environmental challenges the aircraft encounters. There are no FAA [Federal Aviation Administration] requirements for specifically flying in a fire environment.”
But helicopters contracted by the Forest Service have to adhere to certain maintenance requirements “because of the severity of the environment,” Nelson explained. This means doing things that may not be required on civil helicopters that are not conducting firefighting missions.
“We want mechanics to focus on airworthiness due to the challenges of the conditions,” he said.
Fiat and Reynaud noted mechanics perform a visual check of the firefighting helicopter both before and after each flight, as well as every five to 10 hours of flight time.
“More intensive maintenance operations occur every 20 to 25 flight hours,” they explained. “In particular, magnetic plugs are used to check for possible damage to the gears in the oil casings. In the event of damage, friction produces filings which are captured by the magnets. These operations are carried out by ground mechanics who are present at the base in the event of fire, but do not take part in operational flights.”
Each flight operated for the French Civil Security agency has a mechanic on board, they added.
Beattie noted that “almost everything on an aircraft has got an inspection interval that is part of its certification. When you certify a product, the FAA reviews it.” The agency has to approve the maintenance plan.
In terms of the H215 and H225 helicopters used to support French Civil Security’s wildfire missions, the 4,000-L (1,057-US gal) capacity Bambi Bucket — reinforced by polyester fabric and attached to the aircraft by slinging cables — presents a maintenance issue not present for other helicopters. Airbus stated last year that the H215 and H225 helicopters are “particularly well suited to slinging heavy loads … The helicopters are equipped with bubble doors to improve pilot visibility, cable cutters and versatile air inlets to protect the engines.”
The Marignane, France-based aircraft manufacturer pointed out that an H225 was bought by Airtelis secondhand in November 2023. Airbus noted how much more utilization the aircraft is getting than prior to the purchase.
“The helicopter, which entered into service in 2014, had an initial, relatively inactive career in the offshore industry, with just 900 flying hours to its credit,” Airbus said.
“On board, the pilot can open the Bambi Bucket to release the water, but must also be able to release it completely to save the aircraft in the event of imbalance,” Fiat and Reynaud explained. “Maintenance is carried out by visually checking and lubricating the rope and pulley systems.”
Another challenge specific to firefighting helicopters is that the aircraft routinely operate in rural areas where a makeshift takeoff and landing site must be established. Much of the time, conventional heliports are simply unavailable.
A maintenance operation, including on-hand spare parts, must serve helicopters using the designated spot, which could be located on farms, large fields and even in people’s yards. These landing spots also need to be located near water sources, such as rivers, streams, ponds or lakes — and on occasion swimming pools — where the helicopter can quickly conduct hovering refills of buckets and tanks. This further limits where these ad hoc heliports can be located.
“Even before they are deployed, the aircraft undergo extensive preparation, and the mechanics keep complete support kits on hand at all times to deal with any breakdowns that may occur,” Fiat and Reynaud said. “These kits, prepared in advance, are kept in the aircraft’s hold. They contain parts adapted to the planned removal schedule — for programmed replacements based on estimated wear, as well as stock parts useful in the event of unexpected failure of a sub-assembly.”
Beattie said Croman has a service van that travels to the temporary takeoff spots, where it supports maintenance operations. “In that service van, you have all of your manuals that are FAA required, mostly they’re electronic,” he explained. “You have what we refer to as consumables — the oils, O-Rings and gaskets and all the things that you use on a daily basis to keep the aircraft viable. And then you have high-use items.”
If a helicopter requires routine replacement of parts in a fast-moving environment, those are usually in the service van. “Anything that can shut you down for the day and you can reasonably keep in the service van, you keep in the service van,” Beattie said. “So, you’re not keeping spare engines or spare transmissions in there, but you’re keeping spare fuel gauges, spare engine oil — the list is very long. It’s just based on each operator’s experience with their aircraft and what routinely needs maintenance.”
Nelson said firefighting helicopter operators need to “create an environment in the field with support equipment, tooling, [and] personnel able to maintain the aircraft as it needs to be maintained, but still be able to perform those critical firefighting functions.”
Serious consequences
Any maintenance lapse can prove deadly. The UH-1H that crashed in New Mexico in 2022 was observed by two witnesses, who said the helicopter “rapidly descended without making any turns.” The witnesses saw “a large plume of dust” after the aircraft impacted the desert ground.
The NTSB chronicled a maintenance failure that it concluded caused the accident. “About 17 flight hours before the accident, an engine chip event occurred, and a small piece of ferrous metal was found on the magnetic chip plug,” the report stated. “Following the chip event, the oil system was drained and flushed and the filter elements were removed, cleaned and reinstalled. No further engine chip lights were reported after the engine chip event.”
The NTSB said the chip and an oil sample were sent to a lab to be analyzed. “The results of the lab analysis were not used by the operator to troubleshoot the reason for the chip event,” the NTSB detailed. “Had the operator conducted an analysis, they could have potentially identified the deteriorating component and impending failure … The total loss of engine power [was] due to the fatigue failure of the starter-generator input [zerol] gear, which failed due to poor maintenance.”
According to the maintenance manual for the accident engine, mechanics should conduct regular oil sampling and testing for wear metals. The NTSB said these metals include “silicon, aluminum, chromium, copper, iron, magnesium, nickel, silver and titanium.”
The engine was installed in 2018 on the UH-1H helicopter built in 1970. The oil sample following the flight before the accident flight marked the tenth and final such sample taken since the engine’s installation.
The crash aircraft had conducted several firefighting missions supporting the New Mexico Forestry Division. It refueled at Las Vegas Municipal Airport and then flew to the staging area, picking up the full crew of four — the pilot, two tactical flight observers, and a rescue specialist. The flight back to its base in Albuquerque proved fatal, with the helicopter crashing near Chapelle, New Mexico.
“Metallurgical examination of the zerol gear revealed multiple fatigue fractures, as well as gouging on both the leading and lagging flanks and lands of the gear teeth,” the NTSB said. “The zerol gear was determined to have failed in fatigue from a crack that formed 90 degrees to the original, progressing across the gear. No material anomalies were observed that would result in the crack initiation.”