# NTSB CHI93FA139: Cessna 172I, N8337L, Ettrick, WI, April 18, 1993 - Type: NTSB accident investigation - Classification: Accident · Fatal · Field investigation · Final report - Date: April 18, 1993, 09:30 local (14:30 UTC) - Place: Ettrick, WI - Coordinates: 44.159687, -91.259597 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=44.1597&lon=-91.2596&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Fatal - Injuries: 2 fatal - Status: Completed, report August 18, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 9157 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI93FA139 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/9157/pdf - Page: https://openairdocs.org/ntsb/CHI93FA139 ## Probable cause AN INFLIGHT EXPLOSION OF A TOLUENE-BASED FLUID INSIDE THE AIRPLANE'S COCKPIT. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Fire/explosion, cruise - normal - hazardous material - exploded (cause) - In flight collision with terrain/water, descent - uncontrolled ## Analysis WITNESSES REPORTED THAT THE AIRPLANE FIRST SOUNDED NORMAL, AND THEN ITS ENGINE RPM INCREASED, FOLLOWED BY AN EXPLOSION & SMOKE. THREE WITNESSES OBSERVED THE AIRPLANE DURING AN UNCONTROLLED VERTICAL DESCENT. ONE STATED THE AIRPLANE EXPLODED APPROX 100 FT ABOVE THE GROUND. ANOTHER STATED HE OBSERVED THE AIRPLANE DESCENDING VERTICALLY, LOSING SIGHT OF IT JUST PRIOR TO OBSERVING FIRE AND SMOKE. THE THIRD STATED HE OBSERVED THE AIRPLANE FLYING STRAIGHT AND LEVEL, THEN SUDDENLY PITCH DOWN. DURING THE DESCENT, HE OBSERVED GREY SMOKE COMING FROM THE AIRPLANE. A CAN OF TCP FUEL TREATMENT WAS FOUND IN THE BURNT WRECKAGE. THE FILLER NECK AND CAP HAD DISTORTIONS WHICH DID NOT MATCH. TCP IS COMPRISED MAINLY OF TOLUENE, A HIGHLY VOLATILE SUBSTANCE. FUMES FROM A TOLUENE-BASED FLUID SUCH AS TCP COULD EXPLODE DURING THE LIGHTING OF A CIGARETTE. THE CAN WAS KEPT IN THE BAGGAGE COMPARTMENT BY THE OWNER. EIGHT PIECES OF WINDSHIELD PLEXIGLASS WERE FOUND AROUND THE IMPACT CRATER; THE REMAINDER OF THE WINDSHIELD WAS NOT FOUND. ## Factual narrative HISTORY OF FLIGHT On April 18, 1993, at 0930 central daylight time (CDT), N8337L, a Cessna 172I, registered to Leo G. Stokes of Monticello, Minnesota, and piloted by a private pilot, was destroyed during a collision with the ground. Visual meteorological conditions prevailed at the time of the accident. The personal 14 CFR Part 91 flight was operating without a flight plan. The pilot and passenger were fatally injured. The flight originated from Monticello, Minnesota, at 0830 CDT. A witness, driving an automobile northbound along highway U.S. Highway 53, observed the airplane descending vertically toward hilly terrain. The witness's observation of the airplane's flight path was momentarily obscured by the terrain. Shortly after losing visual contact with the airplane the witness observed black smoke. A second witness stated he observed the airplane flying north followed by a turn to the south. He stated the airplane was flying straight and level after the turn's completion. Shortly after completing the turn, he said, the airplane suddenly pointed straight down with its engine making a louder noise. He said he observed grey smoke coming from the airplane after it started the vertical descent. The smoke, according to this witness, was continuous but not heavy. The witness was unable to state where the smoke was originating from. A third witness reported hearing the "... noise of an engine. It was running wild it wasn't in control at all." The witness stated the airplane "...was intact..." when he first observed it. He stated the airplane burst into flames with "... pieces (that) flew everywhere. Then the plane hit the ground. Once it hit the ground I didn't see anything." He said the wings separated from the fuselage during the explosion. A fourth witness, located approximately one mile north of the crash site, observed an airplane pass over him in level flight. He said the airplane's engine sounded normal. Shortly after observing the airplane he looked away, but said he heard an increase in RPM, followed by a loud bang. PERSONNEL INFORMATION The pilot obtained his private pilot's certificate on July 14, 1989. A third class medical certificate was issued to the pilot on January 1, 1993. His personal logbook showed a total time of 154.6 hours as of April 4, 1993. According to the logbook, his first flight in a Cessna 172 was on July 22, 1989. The logbook showed the pilot had flown the Cessna 172 type airplane exclusively since that date with one exception. The logbook showed the pilot had .6 of an hour of hooded instrument time. The last instrument time (.2 of an hour) flown by the pilot was on June 23, 1991. The logbook showed the pilot received a biennial flight review, on September 28, 1991. WRECKAGE AND IMPACT INFORMATION N8337l impacted a slopping, mowed, hay field. The soil was a mixture of sand and clay, recently moistened by rain. A ground scar approximately 21 feet long, varying in depth from three to five inches, aligned on a magnetic heading of 050 degrees, was observed with small fragments of green glass at its beginning. The ground scar lead to a tapered crater area which was approximately ten feet in diameter at the top and three feet deep. The dirt on the sides of the crater had various sized pieces of burnt carpeting, green colored plexiglass, and insulation on, and below, the surface. The materials located below the side surfaces of the crater were at a depth of approximately one to three inches. The deepest part of the crater contained irregular shaped fragments of green plexiglass approximately 1/2 inch to one inch in perimeter size. Fragments of green plexiglass and tan colored plastic were observed interspersed with pieces of aluminum around the edge of the crater. The airplane's engine and propeller were positioned approximately 31 feet from the crater on a magnetic heading of 075 degrees. The fuselage cabin area, tail cone, and empennage were located approximately 55 feet from the crater on a magnetic heading of 075 degrees. A section of N8337L's right wing was positioned approximately 34 feet from the crater on a magnetic heading of 095 degrees. The right wing strut was positioned 80 feet from the crater on a magnetic heading of 095 degrees. The left wing and the inboard section of the right wing were located 160 feet and 232 feet, respectively, from the crater on a magnetic heading of 095 degrees. The fuselage was crushed and burnt from the firewall attach point aft to the leading edge of the dorsal fin. The fuselage and empennage assembly from the vertical stabilizer's leading edge was bent upward approximately 60 degrees relative to the fuselage centerline. The left and right cabin entrance doors were found adjacent to the impact crater. Both doors had their forward edges crushed aft. The right door was crushed further aft than the left. The upper section of the vertical stabilizer was crushed aft. The vertical stabilizer and rudder were bent approximately 30 degrees to left of the airplane's vertical plane. The lower hinge point of the rudder had separated from its fuselage mount. The horizontal stabilizer's left and right leading edges were bent down from the tip to approximately two feet inboard. The right wing was fragmented, its components were confined to an area east of the impact crater and south of the fuselage/empennage remains. The wing root attach point had fire damage forward of the mid-chord point and around the wing fuel tank filler opening. The fuel cap was not found. The main wing spar, from the approximate wing tie down ring attach point to the tip, displayed aft bending of approximately 75 degrees. The wing skin sections had compression damage of varying magnitudes. The skin sections which were separated from their original positions displayed tension separations at the majority of their rivet holes. The wing strut was bent down approximately 80 degrees away from its central axis at the approximate 70 percent span position. The left wing was separated from the fuselage at the root junction. The bottom of the wing had fire damage on the outer surface. The sooting extended from the root to an area behind the landing light. The skin on the bottom of the wing, below the fuel tank position, had separated from the main structure. The wing's leading edge was collapsed aft from the root attach point to approximately five feet outboard. The wing flap was in the full down position, the aileron was not attached. The wing's top surface, outboard of the wing flap/aileron juncture was wrinkled. The leading edge was collapsed aft. The engine had separated from its fuselage at all four mount positions. The rockerbox covers were collapsed against the rocker arms. The exhaust and intake manifold systems had separated from the engine and were crushed. The voltage regulator did not have exterior, or interior, damage. The engine was rotated, the rocker arms for each cylinder moved with the propeller rotation. The cam shaft gear, at the aft end of the engine, moved during the rotation process. The top spark plugs to cylinder numbers one and three were removed and had a gray/tan color on the electrodes. Electrode contamination was not observed. The magnetos were separated from the engine and were destroyed. The vacuum pump's vanes were destroyed, the shaft was bent which prevented rotation. Chordwise scaring was observed on both propeller blade front surfaces. One propeller blade was bent aft approximately 12 inches outboard from the hub. This blade had a 90 degree twist along its span. The second propeller blade was bent aft approximately 45 degrees at the mid-span point. This blade had a 90 degree twist along its span. The propeller spacer had separated into two sections and was dirt filled. Trim tab and landing flap cable separations had broomed ends. Elevator control continuity w ## Aircraft - Registration: [N8337L](https://openairdocs.org/deregistered/N8337L-1994-11-17), registration cancelled 1994-11-17, S/N 17256537 (OpenAirDocs) - Reported make and model: CESSNA 172I - Registry model: [Cessna 172I](https://openairdocs.org/model/cessna-172i) (registry code 2072426) (OpenAirDocs) - Category: Airplane - Serial number: 17256537 - Engines: LYCOMING O-320-E2D 150 horsepower reciprocating - Damage: Destroyed - Fire: In-Flight - Flight: Personal, Part 91 - Operator: Leo G. Stokes - Registered owner: Leo G. Stokes - Airworthiness certificate: Standard, Utility; Standard, Normal - Last inspection: Annual, January 6, 1993 - Departed: 20Y, MONTICELLO, MN - Destination: UGN, WAUKEGAN, IL ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 43; private; airplane ratings: single-engine land; medical: class 3, valid medical--no waivers/lim.; seat: left; toxicology performed; flight hours: 155 total, 104 in this make and model, 118 as pilot in command, 11 in the last 90 days, 3 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 13 knots - Visibility: 8 statute miles - Lowest ceiling: 1,000 ft overcast - Temperature: 52 °F, dew point 45 °F - Altimeter: 29.00 inHg - Observed at: LSE, 21 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19930418009519A](https://openairdocs.org/incident/19930418009519A), Apr 18, 1993: Cessna 172I, Ettrick, WI, Destroyed, 2 fatal. Exploded inflight. Crashed and burned. Can of tcp fuel treatment on board. Vapors are explosive. ## Other investigations on N8337L (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB CHI70FDJ30](https://openairdocs.org/ntsb/CHI70FDJ30), Jun 11, 1970: Cessna 172 (N8337L), Baileys Harbr, WI, substantial damage From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.