NTSB and Forest Service work to reduce in‑flight structural failures on air tankers

Metal fatigue cracking was identified as an issue in several crashes

T-910 on the Soberanes Fire south of Monterey, California in 2016. Photo by Wally Finck.

(Originally published at 9:50 a.m. MST March 5, 2018)

The National Transportation Safety Board published this article March 1, 2018 on their NTSB Safety Compass website. It provides details about how the U.S. Forest Service and the NTSB have worked together to attempt to mitigate some of the risks of flying old aircraft converted to air tankers low and slow close to the ground while experiencing high load factors.

By Jeff Marcus and Clint Crookshanks

One enduring image of the fight against forest fires, like those that devastated California last year, is of a large airplane flying low and dropping red fire retardant. These firefighting air tankers are invaluable, and they operate in extreme environments.

Over the years, we’ve investigated several accidents involving firefighting aircraft, identifying issues and making recommendations to ensure the safety of these important assets. For example, in 1994, we investigated an accident in which a retired Air Force Lockheed C-130A Hercules, which had been converted into a firefighting airplane and was under contract to the US Forest Service (USFS), crashed while battling a fire in the Tehachapi Mountains near Pearblossom, California, killing all three flight crewmembers. In June 2002, another retired Air Force Lockheed C-130A Hercules, also converted into a firefighting aircraft and under contract to the USFS, crashed while dropping fire retardant near Walker, California, killing the three flight crewmembers onboard. Just a month later, a retired Navy Consolidated Vultee P4Y-2 Privateer, again under contract to the USFS to fight forest fires, crashed while maneuvering to deliver fire retardant near Estes Park, Colorado, killing both flight crewmembers. We determined that the probable cause in each of these accidents was in‑flight structural failure due to fatigue cracking in the wings, and we concluded that maintenance procedures had been inadequate to detect the cracking.

Firefighting operations inherently involve frequent and high-magnitude low-level maneuvers with high acceleration loads and high levels of atmospheric turbulence. A 1974 NASA study found that, at that time, firefighting airplanes experienced maneuver load factors between 2.0 and 2.4—almost a thousand times more than those of aircraft flown as airliners. The NASA study concluded that, because the maneuver loading in firefighting airplanes was so severe relative to the design loads, the aircraft should be expected to have a shortened structural life. Repeated and high‑magnitude maneuvers and exposure to a turbulent environment are part of firefighting service, and these operational factors hasten fatigue cracking and increase the growth rate of cracking once it starts.

Aerial firefighting is an intrinsically high-risk operation; however, the risk of in‑flight structural failure is not an unavoidable hazard; rather, fatigue cracking and accelerated crack propagation should be addressed with thorough maintenance programs based on the missions flown. Aircraft maintenance programs, which are typically developed by airplane manufacturers, usually point out highly stressed parts that should be inspected for signs of fatigue cracking, and they give guidance on how often these parts should be inspected. When specifying a maintenance program, manufacturers typically consider the expected loads that an airplane will encounter; however, in the past, for many aircraft used in firefighting operations, very little, if any, ongoing technical and engineering support was available because the manufacturer no longer existed or did not support the airplane, or the military no longer operated that type of aircraft. The maintenance and inspection programs being used for the firefighting aircraft mentioned above did not account for the advanced age and the more severe stresses of the firefighting operating environment.

Range Fire air tanker
Air tanker 12 on the Range Fire in Southern California, August 27, 2016. Photo by Kern County Fire Department.

As a result of our investigations, we issued safety recommendations to the USFS to hire appropriate technical personnel to oversee their airtanker programs, improve maintenance programs for firefighting airplanes and to require its contractors to use these programs. The USFS responded promptly and effectively, substantially improving the safety of its firefighting operations. The USFS hired a team to build out its Airworthiness Branch, to lead their effort to comply with the NTSB recommendations, and with this staff of engineers and technicians made needed revisions to the contracting, oversight, and operations of the USFS program using airplanes to fight forest fires. The agency hired aircraft engineering companies that performed in‑depth stress analyses on the firefighting airplanes in operation. The results were used to improve maintenance programs by identifying parts of the aircraft structure in need of continuing inspections and proposed the time and use intervals needed between inspections to prevent fatigue cracks from developing into catastrophic structural failures. The USFS also outfitted firefighting aircraft (tankers as well as helicopters and lead aircraft) with equipment that measures and records the actual flight loads experienced while fighting forest fires, then used that data to further improve the inspection program for airplanes in use and to develop programs for new types of airplanes being introduced to fight forest fires.

Clint Crookshanks, an NTSB aviation structural engineer and aircraft accident investigator who worked on these airtanker accidents, helped the USFS review its contractors’ maintenance and inspection program documents and provided advice on how they could better address our recommendations. On November 5, 2010, the USFS issued its first iteration of a Special Mission Airworthiness Assurance Guide for Aerial Firefighting and Natural Resource Aircraft, which contained the method, schedule, and standards for ensuring the airworthiness of firefighting aircraft. The USFS has revised the guide twice since then, with the latest revision issued on November 6, 2015. The guide now includes standards for USFS aircraft contracts, which are required for all aircraft used in USFS firefighting missions, satisfying our recommendations. Since these improvements were implemented, no aircraft performing aerial firefighting missions for the USFS have experienced an in‑flight structural failure.

We continue to work with the staff at the USFS to improve the safety of firefighting flights. At the beginning of January 2018, Clint attended a meeting in Missoula, Montana, to discuss the current and future large airtankers on contract to the USFS. Our recommendations are still relevant to the USFS and its contract operators and were the basis for most of the discussion at the Missoula meeting. The current USFS contract requirements have ensured that all contractors have effective maintenance and inspection programs that account for the extreme operating environments seen in aerial firefighting. Aircraft providing aerial firefighting services contain equipment that records the loads on the aircraft and even provides an alarm in real-time when a flight’s loads may have overstressed the airplane. In addition, the data recorded is downloaded and supplied to Wichita State University for mission profile development. British Aerospace, which originally manufactured the jet powered BAe 146 and RJ-85 airplanes currently used for USFS firefighting operations, provides technical support for these airplanes’ operators. The US Air Force also provides firefighting service using C-130 airplanes equipped with a Mobile Airborne Firefighting System (MAFFS) to assist the USFS on an as needed basis. The manufacturer of the C-130, Lockheed-Martin, is working with the Air Force to continually monitor and analyze the loads on airplanes used in the firefighting mission.

The importance of keeping these unique aircraft and their crews safe and functional becomes even more evident during every forest fire season. The lessons we’ve learned from our accident investigations have been used to identify needed changes that have made it possible to more reliably and safely fight forest fires from the air and protect life and land.


Jeff Marcus is an Aviation Transportation Safety Specialist in the NTSB Office of Safety Recommendations and Communications. Clint Crookshanks is an aviation structural engineer and aircraft accident investigator in the NTSB Office of Aviation Safety.

Thanks and a tip of the hat go out to Isaac.
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Elk brings down helicopter in Utah

The two-person crew sustained minor injuries.

Above: helicopter brought down by an elk during a net gunning operation. Photo by Wasatch County Search and Rescue

(Originally published at 10:18 a.m. MT February 14, 2018)

An elk took down a helicopter Monday afternoon during a net gunning operation in Utah. It happened about 40 air miles east of Provo near Currant Creek Reservoir (map).

Officials from the Division of Wildlife Resources hired the crew and the helicopter, a Hughes 369D, to capture elk using a net fired from a gun. As the helicopter flew 10 feet above the ground the gunner in the back seat fired the net over the cow elk, but its legs were not entangled as hoped. It jumped and struck the tail of the helicopter which became uncontrollable and crashed.

elk helicopter crash
Photo by Wasatch County Search and Rescue

The 2 people aboard the chopper are okay except a few small cuts and bruises. They were both checked out by Fruitland EMS. As for the chopper not so good. Not something you see every day when an elk brings down a chopper.” – Wasatch County Search and Rescue Facebook page

Photos show the tail rotor was no longer attached to the helicopter.

Net gunning is a commonly used practice for relocating animals, collecting biological samples, and placing radio tracking collars on wildlife. Some contractors use a modified shotgun to fire the net that falls over the animal, entangling its legs and trapping it. The helicopter then lands and the crew subdues the animal which can be treated at the site or transported in a cargo net to another location for processing.

elk helicopter crash
Photo by Wasatch County Search and Rescue


UPDATE at 11:11 a.m. MT Feb. 14, 2018. Unfortunately, the elk did not survive.

Empty water bucket contributed to New Zealand helicopter crash

New Zealand’s Transport Accident Investigation Commission (TAIC) has determined that an empty water bucket contributed to the cause of a fatal helicopter crash on February 14, 2017.

David Steven Askin was piloting a helicopter for Way To go Heliservices working on a wildfire near Christchurch when it went down in the Port Hills.

Steve Askin
Steve Askin. Way To Go Heliservices photo.

The TAIC determined that a cable from the water bucket struck the tail of the Eurocopter AS350-BA.

The TAIC explained:

In the early afternoon, one of the helicopters, a Eurocopter AS350 ‘Squirrel’, registered ZK-HKW, crashed while the pilot was returning to the dipping pond to refill the firefighting ‘monsoon’ bucket. The helicopter was destroyed and the pilot was killed. Evidence shows that the likely cause of the crash was the empty monsoon bucket swung back into the tail rotor, damaging the tail rotor and causing the loss of the vertical stabiliser from the tail boom. After the loss of the vertical stabiliser, the helicopter gradually rolled to the right and descended until it struck the ground.

The TAIC’s investigation was aided by video from a camera mounted on the aircraft which showed the bucket swinging up toward the tail as the helicopter was enroute to a dip site.

Below is an excerpt from the Stuff website:

An abbreviated mayday call was heard by several pilots about 2.05pm, but it was not clear which radio frequency the call was made on.

The air attack supervisor asked for a role call of all aircraft involved. Askin did not respond.

After a brief search, another pilot found the wreckage of Askin’s helicopter on a steep slope near the head of a gully east of Sugarloaf.

According to TAIC’s report, the helicopter had struck a steep, tussock-covered slope. Main rotor strikes on the slope indicated the helicopter had tumbled further down the slope.

TAIC recommended several solutions, including using heavy ballast slings, and having someone monitor the operation from the ground.

Thanks and a tip of the hat go out to Chad.
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One dead after helicopter makes emergency landing in South Korea

A firefighting helicopter crew member died Monday during operations in the Gangwon Province of South Korea.

According to The Korean Times, the man “passed out as the aircraft made an emergency landing in Samcheok.” He was pronounced deceased after he was transferred to an area hospital, and early indications suggest the helicopter was forced to land after striking a high-tension power line.

At least 60 helicopters and 10,000 people have been mobilized for firefighting efforts in three areas, and residents across the region were urged to evacuate, the Korea JoonGang Daily reported. 

Fire monitoring helicopter crashes in Russia, reportedly killing three

A helicopter used for monitoring wildfires crashed May 4 in the Russian republic of Bashkortostan, according to TASS which received information from regional emergency services. Three people were on board when it went down 30 kilometers south of the community of Inzer in the Beloretsk district. The reports are that there were no survivors.

Below is an excerpt from TASS:

The helicopter belonged to the Lightair company. The news it went missing came at 14:20 Moscow time. The helicopter had left Bashkortostan’s capital Ufa for Beloretsk. The distress signal from its emergency beacon was picked up by a satellite rescue system. The local office of the Investigative Committee has launched a probe.

Our sincere condolences go out to the family, friends, and coworkers.

Firefighting helicopter goes down in Florida lake

Above: photo by Marion County Sheriff’s Office.

A Marion County Sheriff’s Office helicopter went down in a lake during water bucket operations on a wildfire in Florida Tuesday at about 6:30 p.m. In his last radio transmission pilot Sgt. John Rawls said he was going down, then after the helicopter rolled over at least once he exited the ship and swam about 50 yards to shore.

Only the tip of one rotor blade sticking out of the water is visible at the lake now, according to officials. The Sheriff’s Office said the helicopter experienced a malfunction as it was refilling the water bucket.

The Florida Forest Service and Marion County Fire Rescue assisted Sheriff deputies in making a path to the lake with heavy equipment in order to reach the pilot. Sgt. Rawls was transported to the hospital and is currently in stable condition.

The NE 212th Street Road fire is in Marion County, Florida about 20 miles northeast of Ocala. It has been burning for about a month.

map fire helicopter crash florida
Map showing the approximate location of the fire that the helicopter was working on when it crashed.

Sgt. Rawls has been with the Marion County Sheriff’s Office since 1998. He is also an Army helicopter pilot veteran who served during Operation Iraqi Freedom.

“Our pilot is OK and, though he does have some injuries, he should be fine,” said Sheriff Billy Woods. “The Marion County Fire Rescue and the Florida Forest Service did an outstanding job in helping us get to our pilot out there in order to get him to the hospital, and I want to thank each of them for the services that they provided to us. We are extremely grateful to everyone who worked tirelessly to make sure Sgt. Rawls got the emergency care he needed.”

Firefighting pilot killed in New Zealand helicopter crash

A helicopter pilot was killed February 14 while working on a fire in New Zealand. David Steven Askin was flying the aircraft at a wildfire when it went down in Christchurch’s Port Hills.

Mr. Askin was a pilot and instructor for Way To Go Heliservices, a company based in Rangiora, New Zealand.

Steve Askin
Steve Askin. Way To Go Heliservices photo.

Previously he had been a member of New Zealand’s Special Air Service, a special forces unit of the Army.  He served in Afghanistan and was wounded in a firefight with the Taliban after his unit came to the aid of Afghan police when they were attacked at the InterContinental Hotel in Kabul in a five-hour battle.

Police, the Civil Aviation Authority, and the Transport Accident Investigation Commission are investigating the crash.

There are reports that 15 helicopters were fighting the recent wildfires near Christchurch that have burned 600 hectares (1,483 acres).

Our sincere condolences go out to Mr. Askin’s family, friends, and coworkers.

Thanks and a tip of the hat go out to Chris.

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Aircraft reseeding burned area crashes in Utah

The pilot walked away with minor injuries

An Air Tractor 802 crashed January 17 in Utah about eight miles west of Vernon while reseeding an area that had previously burned. The pilot, who had minor injuries, told police the aircraft lost power and was unable clear terrain in the Sheeprock Mountains.

It occurred at about 5 p.m. after which the pilot walked for about two and a half hours until he was found by crews flying Utah National Guard Apache helicopters equipped with infrared sensors who happened to be training in the area.

Air Tractors are often used as air tankers, but this one was dropping seeds instead of retardant.

Thanks and a tip of the hat go out to Dave.

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