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Last updated: 25 June 2021
Status:
Date:Saturday 21 July 1979
Time:18:10
Type:Silhouette image of generic B17 model; specific model in this crash may look slightly different
Boeing B-17G
Operator:Black Hills Aviation
Registration: N66573
MSN: 8217
First flight:
Crew:Fatalities: 2 / Occupants: 2
Passengers:Fatalities: 0 / Occupants: 0
Total:Fatalities: 2 / Occupants: 2
Aircraft damage: Destroyed
Aircraft fate: Written off (damaged beyond repair)
Location:16 km (10 mls) SW of Superior, MT (   United States of America)
Phase: Maneuvering (MNV)
Nature:Fire fighting
Departure airport:?
Destination airport:?
Narrative:
The air tanker was engaged in fighting forest fires in Montana, USA. The aircraft was re-loaded with 1,800 gallons of retardant and departed from the airport at 17:48 on the second run in the Lolo National Forest.
Upon returning to the fire, the aircraft made a high pass over the fire and then an approach for a second pass. The fire was located near the top of a mountainous ridge on an even slope that provided an easy target for a retardant drop. Once the pass had been made, no retardant had been dropped. Immediately after the airtanker passed over the drop target, it made a steep left turn and impacted a densely timbered hillside. Ground impact occurred in an estimated 5 to 10 degree nose low attitude and approximately a 40-degree left bank.

Probable Cause:

The investigation team determined that during the sequence of events, the airtanker’s flight path during the left turn was taking it too close to the mountainside. This required more bank angle and gravity forces to increase the rate of turn and hold altitude in order to clear the mountainside. Unfortunately, as bank angles and load factors increased, induced drag, which predominates at low speeds, also increased dramatically. These factors would have required significant increases in power to maintain flight and preclude stalling.
The airtanker’s situation, already critical because of its low airspeed, low altitude, and the turning space restriction, was compounded by the additional bank angle and increased load factor. The fringe of a stall was entered and aggravated by the addition of aileron and elevator input to increase the rate of turn. Power was insufficient to maintain flight and a few seconds later the airtanker completely stalled when performance demands could not be maintained. Close proximity to the ground precluded the use of normal stall recovery techniques, and the airtanker descended into the trees.

Classification:
Controlled Flight Into Terrain (CFIT) - Mountain

Sources:
» United States Department of Agriculture Forest Service Fatal Aviation Accident History / Compiled By: Candy S. Rock FitzPatrick


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This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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