Austin, NV, USA
N807MA
AIR TRACTOR AT-802A
The pilot was dropping fire retardant onto a saddle area located between the intersection of two perpendicular ridge lines. One of several witnesses reported that the airplane circled the area and then began a steep descent towards the intended drop point. The pilot did not release the load of retardant over the drop area. The witness observed the nose of the airplane pitch up and “mush through the flare.” The underside of the airplane then made contact with rising terrain within the saddle and continued uphill on its main landing gear toward a crest where the terrain dropped away. It then descended and collided with terrain in the valley below. Postaccident examination did not reveal any anomalies with the airplane, engine, or retardant dispersal system that would have prevented operation. The dispersal system’s operating procedures recommend that it be turned off during flight to prevent inadvertent dumping of the load. According to other pilots it is not uncommon to forget to re-engage the system prior to the drop. The dispersal system included an emergency manual release mechanism that could be used in the event of a primary system failure or an inadvertent oversight by the pilot to turn the system on; however, impact damage prevented an accurate determination of the system's armed status prior to impact. Global Positioning System (GPS) information revealed an excessive rate of descent just prior to the expected drop, which corroborated witness accounts. Analysis of the accident location, with respect to the GPS data, density altitude, airplane load, and witness statements, would indicate that the airplane probably encountered a stall/mush at the drop area. The high density altitude and the airplane's flap settings would have diminished the climb performance considerably in its retardant loaded state. The airplane's continued trajectory after initial impact, as well as propeller witness marks and internal engine damage, indicated that the engine was producing power at the time of the accident.
HISTORY OF FLIGHT On August 20, 2009, at 1543 Pacific daylight time, an Air Tractor AT-802A, single-engine Air Tanker (SEAT) N807MA, Bureau of Land Management (BLM) designation T-857, collided with rising terrain during an attempted fire retardant drop at the Hoyt Fire, in the Clan Alpine Mountains, near Austin, Nevada. Minuteman Aerial Application, Inc., owned the airplane. The BLM, U.S. Department of the Interior (DOI), was operating the restricted category airplane as a public-use fire suppression flight. The pilot, the sole occupant, was killed. The airplane was substantially damaged by impact forces. The flight departed Battle Mountain Airport, Battle Mountain, Nevada, at 1513. Visual meteorological conditions prevailed, and a BLM flight plan had been filed. The BLM was utilizing an Airborne Aerial Supervision Module (ASM), which was an aircraft operated by a supervisor controlling the air assets working on the fire. The supervisor instructed the tankers on where to drop fire retardant. The pilot was assigned the task of dropping fire retardant onto a saddle area located between the intersection of two perpendicular ridgelines, thereby joining the retardant coverage of two previous drops. Multiple witnesses located both on the ground, and in the air, observed the accident airplane approach the designated drop area from the south. Their accounts describe the airplane approaching the drop area, but not releasing its load of retardant. Shortly thereafter, the airplane made contact with rising terrain within the saddle. The airplane continued uphill, while still in contact with the ground, towards a crest where the terrain dropped away. The airplane then departed the end of the crest, descended, and collided with terrain in the valley area below. A witness located on a ridge overlooking the saddle area from the east, observed another airplane make a drop along the ridgeline. He estimated the airplane to be flying about 200 feet above ground level (agl) when it made its drop. A few seconds later he observed the accident airplane fly along a similar heading, but at a lower altitude. He stated that he was immediately concerned because the airplane was approaching rising terrain. The airplane then disappeared behind the ridgeline, and out of his view. A few seconds later he observed the airplane, "launch" from the end of the ridgeline, "tumble" and collide with terrain below. The ASM Supervisor had just supervised the drop of retardant at the perpendicular ridgelines prior to the accident. He stated that the accident airplane was circling the drop area, and he relayed the position of the required drop to the pilot. The pilot reported that he could see the drop area, and did not require the ASM to guide him into position. The accident pilot stated that he could perform a salvo retardant drop if necessary, but the supervisor replied that this type of drop was not necessary. The supervisor then observed the airplane turn towards the final leg of the drop, and pitch nose-down into the valley at a rate he considered excessive for the terrain. The airplane then continued to descend, but did not release its retardant over the drop area. He then observed the nose of the airplane pitch up and the airplane, “mush through the flair.” The underside of the airplane then made contact with terrain as it continued up the hill. The left wing then struck a tree and the airplane spun around its nose, launched off the ridge, and collided with terrain below. An impact damaged Garmin 295 global positioning systems receiver (GPS) was recovered from the accident site. The unit was sent to the National Transportation Safety Board Office of Research and Engineering for data extraction. The data revealed the entire flight sequence, beginning at Battle Mountain, and continuing to the accident site. The GPS data revealed that the airplane departed Battle Mountain at 1510, on an outbound course of about 217 degrees magnetic, towards the direction of the fire. Over the next 22 minutes the airplane gradually climbed to an altitude of about 8,800 feet (GPS). As the airplane approached the drop area it descended to about 7,800 feet and began a circling left orbit; the last leg of which flew directly over the intended drop point. The airplane then began a left crosswind turn. During the transition from the downwind to base leg, it began to descend at an average rate of about 700 feet per minute (fpm). The airplane continued the descent through to the final leg, which was in line with the drop area, on a heading of 350 degrees and an elevation of 6,889 feet. The final two GPS locations prior to reaching the impact area corresponded to a descent rate of 1,632 and 2,136 fpm, with ground speeds of 139 and 145 mph, respectively. After the accident, the ASM supervisor directed another SEAT to drop retardant in the area originally designated for the accident flight. The retardant was applied successfully. PERSONNEL INFORMATION A review of FAA airman records revealed that the 44-year-old pilot held an airline transport pilot certificate with ratings for airplane multiengine land, and commercial privileges for airplane single-engine land. The pilot was issued a second-class medical certificate on April 27, 2009, with no limitations or waivers. The pilot additionally held an Airframe and Powerplant mechanics certificate. DOI aviation management training records, completed by the pilot on March 11, 2009, indicated a total pilot-in-command (PIC) time of 6,955 flight hours. At that time he reported a total PIC flight time of 512 hours in Airtanker/Dispensing Operations, and 2,064 hours of Low Level Operations (<500’AGL). Training documents provided by Minuteman Aerial Application, Inc., revealed that the pilot completed a SEAT refresher course on May 18, 2009. This course included flight instruction in target acquisition, target entry, and target exit. On September 27, 2007, the pilot was involved in an incident with the accident airplane near Ogden, Utah. According to the DOI, who investigated this event, the left wing of the airplane struck a tree during a retardant drop. The wing sustained visible external damage to its skin during the sequence. Analysis by the DOI resulted in a conclusion that the pilot’s misunderstanding of the contractual drop height, along with “target fixation” resulted in the tree strike. Additionally, the investigation determined that the pilot showed poor judgment by not landing immediately after the collision, but instead returning to his base, and in the process flying for an additional 28 minutes over two suitable airports, and a heavily populated metropolitan area. On the day of the accident, the pilot reported for duty at 0900. He had dropped two prior loads of retardant on the fire earlier in the day using the accident airplane. AIRCRAFT INFORMATION The low-wing, tailwheel equipped, fixed-gear airplane, was manufactured in 2003. It was powered by a Pratt and Whitney PT6A-67AG turboprop engine, driving a Hartzell 5 blade constant-speed propeller. Additional equipment included an 800 gallon hopper, and an emergency fuel control override system. Maintenance records indicated that an annual inspection was completed on June 8, 2009, at a total airframe and engine time of 2,789.9 flight hours. The recorded time on the Hobbs hour meter at the accident site was 2,797.7. At the time of the annual inspection the propeller had accumulated a total time since overhaul of 455.8 flight hours. Dispersal Gate System In May 2007, at a total airframe time of 2,539.5 hours, the airplane had been modified in accordance with Supplemental Type Certificate (STC), SA00961CH, by the addition of a Turbine Conversions Ltd., Dispersal Gate System (Fire Gate). Commonly referred to as the ‘Hatfield Gate’, this system had been approved for use by the Interagency Airtanker Board. The Hatfield Gate is retrofitted to the belly of the airplane, below the original hopper. The system comprises of a set of longitudinally hinged aluminum doors, the operation of which is controlled by the pilot utilizing a cockpit mounted master panel, and a control stick trigger switch. The system utilizes two hydraulically controlled actuators located at each end of the doors. The actuators drive a gear rack, which turns gear driven shaft assemblies connected to the doors by over center linkages. The system is governed by a series of solenoids, check valves, and proximity switches. Hydraulic pressure is maintained independently of the airplane’s hydraulic system by use of an electrically driven hydraulic pump. In the event of a loss of hydraulic pressure in the primary system, an emergency backup consisting of an accumulator and set of check and ball valves provide enough hydraulic pressure to actuate the linkages, and jettison the load. The emergency system is independent of the master panel, does not require electrical power, and is actuated by the pilot through the use of an emergency dump handle located in the main cabin. A representative from Minuteman Aerial Applications stated that the fire gate master panel had been modified from its original configuration by the addition of a hydraulic power indicator lamp, hopper level indicator, hopper vent push/pull control, arm switch guard cover, and pump rinse switch. An associate of the pilot, who was flying a similarly equipped airplane during the fire fighting missions, reported that the pilot modified the firegate master system arm switch and guard, such that its operation was inverted. In the modified configuration the switch guard cover and enclosed master switch needed to be pulled downwards to arm the system. He also stated that it is not uncommon for pilots to inadvertently leave the master switch in the off position. With the master arm switch in the off position, the load can only be jettisoned by use of the emergency dump handle. METEOROLOGICAL INFORMATION The closest aviation weather observation station was Derby Field Airport (KLOL), Lovelock, Nevada, located 54 miles northwest of the accident site. The elevation of the weather observation station was 3,904 feet mean sea level (msl). An aviation routine weather report (METAR) was issued at 1553 PDT. It stated: winds calm; visibility 10 miles; skies clear; temperature 104 degrees Fahrenheit (F); dew point 21 degrees F; altimeter 29.95 inches of mercury. The Desatoya Mountain (GRVN2) Remote Automated Weather Station was located at an elevation of 6,200 feet, about 34 miles south of the accident site. At 1538, it reported winds south-southeast at 22 miles per hour (mph); temperature 95 degrees F; with a dew point of 5 degrees F. Based on a pressure setting of 29.95 inches of mercury, the calculated density altitude at this location was about 9,700 feet. Photographs taken just after the accident revealed smoke trails indicating a wind direction out of the north. WRECKAGE AND IMPACT INFORMATION The main accident site was located at the northern edge of the Clan Alpine Mountain Range, about 34 miles northwest of Austin. The site was characterized by dirt and rocky terrain dispersed with brush and trees ranging in height from 3 to 5 feet. The first identified point of contact (FIPC) consisted of two, 225-feet-long ground scars located at an elevation of about 6,450 feet msl. The scars continued to travel up rising terrain, on a heading of 330 degrees. The spacing between the scars corresponded to the dimension of the airplane’s two main landing gear. Trees located within the immediate vicinity of the scars were severed at the 4-foot level. Seven, 2-feet-long diagonal slash marks were observed between the main scars, 100 feet from the FIPC. The spacing of the slashes ranged between 14 and 48 inches, and correlated with the positions of rotating propeller blades, when compared to the main landing gear scars. A twisted fragment of propeller blade tip was located 20 feet west of the markings. The two main ground scars continued until the terrain crested at an elevation of about 6,570 feet, and dropped away. The main wreckage was located about 760 feet beyond the crest at an elevation of about 6,460 feet. The debris path from the crest to the main wreckage consisted of the left main landing gear and wing fragments. The main wreckage site was characterized by a 30-foot-long ground disruption on a heading of 350 degrees magnetic, followed by a 100-foot debris path to the fuselage, wings, and engine. The aft elevator push-pull tube and fragments of the fire gate doors and their associated actuators were located within the initial disruption. Fire retardant enveloped the entire wreckage site in a fan-shaped pattern forward of the initial ground disruption. The engine remained attached to its mount. The propeller hub had become separated from the reduction gearbox, and was located 20 feet beyond the main cabin. Two propeller blades were separated at the hub. The blades exhibited chordwise scratches, leading edge nicks, and varying degrees of axial twist. The propeller governor housing appeared fractured, exposing the flyweights. Removal of the engine fuel control filter bowl revealed that the filter was free of debris, and the bowl was full of clear fluid consistent in odor with Jet-A aviation fuel. The odor of jet fuel was present throughout the site, and all major sections of airplane were accounted for. MEDICAL AND PATHOLOGICAL INFORMATION Toxicological tests on specimens from the pilot were performed by the FAA Civil Aeromedical Institute. Analysis revealed no findings for carbon monoxide, cyanide, or ethanol. The results for screened drug substances indicated Pseudoephedrine was detected in the urine. Refer to the toxicology report included in the public docket for specific test parameters and results. An autopsy was conducted by the Washoe County Medical Examiner’s office. The cause of death was reported as the result of multiple injuries due to blunt force trauma. TESTS AND RESEARCH Airframe Examination of the airframe at the accident site revealed a flap actuator jack screw dimension which, according to the Airtractor representative, correlated to a flap deployment of 24 +/- 3 degrees. No pre-impact mechanical anomalies were identified with the airframe or flight control system. A summary of the examination is contained within the public docket for this accident. Engine The engine and its associated accessories were recovered from the accident site and examined at a Pratt and Whitney facility in the presence of the NTSB investigator-in-charge (IIC) and technical representatives from Pratt and Whitney. The gas generator and accessory sections were largely intact. The exhaust ducts exhibited malleable crush deformation, and were free of pock marks. The compressor bleed valve was noted in the closed position; the sides of its piston were free of contamination, with the piston coated in red material similar in color and texture to fire retardant. The engine inlet area was coated with ingested soil material; the first stage stator blades and shrouds exhibited small nicks consistent with soil ingestion. Rotation of the compressor rotor by hand resulted in a corresponding rotation of the compressor turbine and accessory gearbox. Separation of the combustion liner sections revealed equidistant and unremarkable flame patterns. Vanes, shrouds, and blades throughout the compressor and first/second stage power turbine sections displayed indications of circumferential rubbing and sooting. The reduction gears of the forward gearbox appeared free of nicks, chips or distortion. The web of the second stage carrier shaft coupling exhibited torsional deformation. All recovered chip detectors and filters were clear and free of debris. Fuel Control Unit (FCU) The FCU including the pump, sustained external damage and had become separated from the engine. The fuel pump was visually examined and tested in accordance with applicable acceptance test standards; the pump passed all tests. The condition lever assembly of the FCU had sustained damage, and as such a complete test schedule was not possible. A set of partial FCU tests were performed, and the unit passed these tests. The FCU was
The pilot’s failure to maintain a stabilized approach prior to the retardant drop and his subsequent failure to release the retardant load, resulting in a stall/mush and collision with terrain.
Source: NTSB Aviation Accident Database
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