Safety Alert issued for low retardant drops

On May 20, 2019 officials within the US Forest Service and the Department of the Interior released a Safety Alert regarding the safe height for retardant drops. This could be related to the fatality following a drop by the 747 Very Large Air Tanker  on the Ranch Fire in 2018 east of Ukiah, California, the drop by a DC-10 VLAT on the Liberty Fire in 2017 that damaged the roof and knocked out windows in a home and vehicle east of Murrieta, California, and perhaps also a drop by an MD87 in 2018 on the Boxcar Fire near Maupin, Oregon.


Retardant safety alert

Subject: Retardant Safe Drop Height
Area of Concern: Safety of Ground Personnel
Distribution: All Fire Aviation Operations

Discussion: The optimum release height or safe drop height for fire retardant can be defined as the distance below the airtanker at which the retardant begins to fall vertically (Figure 1). When the retardant is dropped, the velocity of the aircraft is imparted to the retardant. In other words, the retardant is traveling at the same speed as the aircraft. When the retardant has lost all of its forward momentum and is falling vertically as a heavy rain, the danger to firefighters is reduced and effectiveness is increased.

retardant drop heightIf a Very Large Airtanker (VLAT) is traveling at 150 knots and is well below the recommended safe drop altitude, the 8,000-19,000 gallons of retardant released will impact the earth at a similar velocity. If personnel are underneath the retardant pattern, they can be struck with the fast moving retardant, broken trees, other debris, or all of it. ¹Figure 2 shows a drop that was released below the safe drop height maintaining considerable velocity as it reached the ground. The force of the retardant dropped from too low of an altitude can topple trees up to 90 feet in height and a trunk a foot in diameter.

Page 2

Drop Safety Considerations

  •  Aerial drops are hazardous and caution should be used when working in areas with aircraft operations. Serious injury and/or property damage can occur from any excessively low tanker drop, including S2’s and SEATs.
  • The Red Book, Interagency Aerial Supervision Guide and the Interagency Incident Response Guide all have slightly different verbiage, but basically state that the Aerial Supervisor/ASM/Airtanker pilot and the identified ground contact/personnel must ensure all fireline personnel are notified of impending aerial drops (fixed wing and rotary wing).
  • Pilots must ensure that they have received confirmation that all people and moveable property have been cleared prior to commencing drops of any fire-fighting agent (water, foam, retardant or gel).
  • Pilots must ensure they do not drop below a safe drop height. This becomes more difficult in mountainous terrain or if the aircraft is not equipped with a radar altimeter so it’s imperative that pilots develop the site picture and practice proper technique for the appropriate drop height for their respective aircraft.
  • Pilots must remember that lower is not always better. Drops that are too low fail to provide retardant in an efficient manner with the desired coverage level. This is not only dangerous, but fails to provide the support ground crews require.
  • Fireline personnel must maintain situational awareness. Personnel who are using cell phones to video the aerial retardant drops can easily become distracted by recording the retardant drops which impairs their ability to recognize the hazards and take appropriate action should it be necessary (Figure 3).
  • Keep in mind that a pilot will, at any time, jettison the entire load quickly during an in-flight emergency.

Firefighting is not a spectator sport. Be alert, be ready, be safe.

(The document was signed by Keith Raley, Chief, Aviation Safety, Training, Program Evaluation, and Quality Management for the DOI Office of Aviation Services; and by Sean Aidukas, Acting Branch Chief, Aviation Safety Management Systems, US Forest Service.)

1. Firefighter Injuries and Fatality, CAL FIRE GREEN SHEET, August 13, 2018. 18-CA-MEU-008674, 18-CA-MEU-009504. References: Incident Response Pocket Guide, NWCG, April 2018. Greg Lovellette, Safe Drop Height for Fixed-Wing Airtankers, March 2000; PMS 505: Interagency Aerial Supervisors Guide, April 2017; Interagency Standards for Fire and Fire Aviation Operations (Red Book) January 2019.

One thought on “Safety Alert issued for low retardant drops”

  1. I have been hit by a very low drop in the 80s, I was on a nozzle behind our engine and noticed the engineer rapidly rolling his window up while looking in the mirror with eyes wide open, I turned my head to look behind me and all I saw was wall of red, it hit me so hard I literally went in a feet over head backwards flip landing on my neck/shoulder and a boot came off, yes it was tied tightly, covered in retardant and sore as hell, I looked up at the guy who was on the front nozzle and he was about 8 feet from where he had been also covered in retardant. The engineer? Sitting in the cab still and laughing so hard he had tears, I wasn’t laughing though. Got a call about a week later from Hoser apologizing for the wayward drop, we were a volunteer department so it took some time tracking us down I guess, he didn’t need to do it at all, was just the kind of man he was I guess.got a tour of the grass valley base out of it.

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