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N7926 accident description

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Tail numberN7926
Accident dateMay 05, 1997
Aircraft typeGrumman G-164A
LocationRosalia, WA
Additional details: None

NTSB description


On May 5, 1997, approximately 1800 Pacific daylight time, a Grumman G-164A, N7926, registered to Larry E. Denton, doing business as Denton Aircraft Company, operated by Joseph F. Dion, and being flown by a commercial pilot, was destroyed during an inflight collision with terrain during cruise near Rosalia, Washington. The pilot survived the ground impact but was unable to escape from the aircraft, and was fatally injured in the post crash fire. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was carrying a load of herbicide for aerial application, was to have been operated under 14CFR137, and originated from the Rosalia airport (elevation 2,170 feet above sea level), Rosalia, Washington, shortly before the accident.

The operator of the aircraft reported that the intent of the flight was to disburse herbicide over a 44 acre field about four miles east of the airport. The accident site was located approximately one mile east of the airport (refer to CHART I). An employee of the operator, who was at the Rosalia airport, reported that the engine sounded normal during the aircraft's takeoff.

A witness, who was driving eastbound on Malden Road, reported seeing/hearing "a double wing spray plane pass low and above and behind us" in his rear view mirror. He and his wife reported that they did not see the actual accident and that they were approximately 100 yards beyond Boozer Road on Malden Road when they saw the aircraft.

A second witness, who was driving westbound on Malden Road, reported that as he "came around (the) corner (he) saw a yellow bi wing airplane cartwheel on to (the) highway and roll into (the) ditch upside down about a quarter mile ahead of me." He also reported that the aircraft began to burn immediately and that he tried to extricate the pilot from the wreckage but was unsuccessful.


At the time of the accident, the pilot held a commercial pilot certificate. Records maintained by the Operator indicated that the pilot had accumulated a total flight time of 10,202 hours, with 75 hours in the Grumman G-164A. The pilot held a second class medical certificate that was dated February 17, 1997. The certificate was issued based on a statement of demonstrated ability which listed a visual field defect in the left eye.

Federal Aviation Administration (FAA) Medical records indicated that the pilot had been involved in another aircraft accident on January 20, 1987. The pilot sustained serious injuries which involved a head injury that resulted in unconsciousness for four days, surgical intervention including the removal of a kidney, and repair to his spleen, followed by extensive rehabilitation. The pilot recovered from his injuries, and after extensive neurological examinations, the FAA established that he was eligible for a second class medical certificate in 1989, under a special issuance. The pilot was given electroencephalograms (EEG's) at each renewal of his Special Issuance. In 1991, and 1992, the pilot's EEG's were interpreted as abnormal, showing potential epileptogenic foci. In 1991, the pilot's MRI (magnetic resonance imaging) was abnormal with evidence of old trauma and an area interpreted as a "lacunar infarct." The pilot's neurologist and the FAA consultant indicated that these abnormalities did not represent an increased seizure risk, as the pilot denied any episodes of seizure activity. The pilot continued to hold second class privileges at the time of the accident.

The operator reported to the investigator in charge that the pilot displayed a memory loss related to the previous aircraft accident. As a result, the operator did not assign the pilot more than one field at a time during spray missions.


The FAA inspector who responded to the site reported that approximately 220 gallons of Uran, Harmony and Bromate, a low risk herbicide, was carried within the aircraft at the time of departure. This was confirmed by the operator who reported that the ratio of pure herbicide mix to acre of dispersal was 2 gallons of mix to 1 acre of terrain. The ratio of herbicide mix to water additive was 2:3 such that there would have been 88 gallons of herbicide (44 acres) and 132 gallons of water aboard. Approximately 95% of the herbicide mix was composed of Uran and the remaining 5% composed of a small combination of Harmony and Bromate. The weight of a pure Uran solution varies dependent on percentage from 10.66 pounds per gallon at 28% to 11.04 pounds per gallon at 32%. Assuming the low range (28%), and discounting the variance in weight of the 5% of Harmony and Bromate, the weight of the total herbicide mix load would have been as follows:

88 gal X 10.66 pounds/gal (herbicide mix) = 938.1 lb +132 gal X 8.35 pounds/gal (water) = 1102.2 lb

220 gallons = 2040.3 lb

The operator reported that he was uncertain of the aircraft's fuel load upon departure, that the aircraft's fuel capacity was 80 gallons of 100 low lead aviation (avgas) fuel and that this fuel load would ensure approximately 2 hours of flight time. The total fuel load weight, based upon 5.87 pounds per gallons of avgas, assuming a 50% load (40 gallons) was calculated to be 234.8 pounds.

According to paperwork maintained by the owner, the aircraft's maximum gross takeoff weight was 4,500 pounds. The empty weight (load weight) was documented as 3,319.3 pounds. An entry stapled within the airframe log and dated May 8, 1996, stated "Aircraft N7926 Ser. #812 Flight checked on May 8, 1996 by Larry E. Denton C-1245782 in accordance with C.A.M. 18.10-3(e) and found to be safely controllable and operate satisfactorily with the following special purpose load of 2,640 pounds" (refer to ATTACHMENT L). The weight of the aircraft was calculated as follows:

WEIGHT (Pounds)

Spray load weight 2,040 fuel weight 235 oil weight (8.7 gal) 65 pilot weight 170 seat cushion weight 5

Accident flight load weight 2,515

Aircraft special load weight 2,640 Accident flight load weight -2,515

The aircraft was equipped with a two blade propeller, and a Pratt & Whitney 600 horsepower R-1340-AN1 radial engine with an engine to propeller gear ratio of 1:1. The aircraft's airframe log showed the last inspection (annual) to have been conducted on March 18, 1997, at a total time of 9,063.37 hours. The time accrued between that date and the accident were not reported.


Aviation surface weather observations taken at Spokane International (GEG) airport (25 nautical miles north northwest of the site) and the Moscow-Pullman Regional (PUW) airport (31 nautical miles south southeast of the site) reported winds and temperatures as follows:

GEG 1756 hrs 150 deg @ 3 knots 63 deg F. PUW 1745 hrs winds calm 68 deg F.


An FAA Inspector from the Spokane, Washington, Flight Standards District Office, responded to, and documented the accident site. The rolling terrain was covered with low crop vegetation approximately five inches in height. The elevation of the accident site was approximately 2,200 feet. Initial impact ground scars leading to the aircraft's final resting place were oriented along an approximate 030 degree magnetic bearing line roughly parallel and slightly northwest of a power line (refer to photographs 1 and 2). Slash marks in the soil approximately perpendicular to this bearing line were observed (refer to photograph 3). The distances between these slash marks were documented and are discussed further under the "TESTS AND RESEARCH" section of this report. The ground impact scars continued along a 030 degree bearing (refer to photograph 4) and then down an approximate 10 foot high embankment to the south edge of Malden Road, a paved, two lane road (refer to photograph 5). The aircraft crossed the road and came to rest in an inverted attitude on a slight downhill berm along the north side of the road (refer to photograph 6). Debris was scattered across the road. A post-crash fire consumed the fuselage, engine, and the inboard area of the wings. The terrain at the site was characterized as uneven, gently rolling hills (refer to photograph 7). The entire ground track from initial ground impact to the aircraft's final resting place was approximately 190 feet (refer to page 3 of Supplement I).

There was no evidence found prior to, or at the initial ground impact site, of herbicide having been discharged from the aircraft.


The following equation, from the Handbook for Aircraft Accident Investigation (NAVAIR 00-80T-67), solves for engine RPM:

(V x R x 101.3) X 1/(N x d) = Engine RPM

where: V = airspeed (knots) R = gear ratio N = number of propeller blades d = distance between successive prop slashes (ft)

For the Pratt & Whitney R-1340-AN1 engine installed on N7926 the equation resolves as follows:

(V x 1.0 x 101.3) X 1/(2 x d) = Engine RPM


(V x 50.65)/d = Engine RPM

Assuming a ground speed of 85 knots:

PROP SLASHES DISTANCE ENGINE RPM (@85 KT) Last mark ____ ^ ____>-----3.417' 1260RPM | ____>-----2.667' 1614RPM | ____>-----2.000' 2153RPM | ____>-----2.250' 1913RPM | --\-------4.417' 1949RPM* | __/ | ____>-----2.833' 1520RPM | ____>-----1.667' 2583RPM | ____>-----1.333' 3230RPM first mark ____>-----1.500' 2870RPM

*Intermediate prop slash mark in between the 4.417 foot slash marks.


Post mortem examination of the pilot was conducted by Morgan S. Wilson, M.D., at the facilities of Pathologists' Regional Laboratory in Lewiston, Idaho, on May 7, 1997.

Toxicological evaluation of samples taken from the pilot was conducted by the FAA's Toxicology and Accident Research Laboratory and resulted in the following findings: 0.002 ug/ml of Tetrahydrocannabinol (Marihuana) detected in blood, 0.08 ug/ml of of Tetrahydrocannabinol Carboxylic Acid (Marihuana) detected in blood, and 0.035 ug/ml of Tetrahydrocannabinol Carboxylic Acid (Marihuana) detected in urine (refer to attached Toxicology report).

(c) 2009-2011 Lee C. Baker. For informational purposes only.