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On March 13, 2008, at 0900 eastern daylight time, a Cessna 172S, N284SP, operated by Kemper Aviation Incorporated, was substantially damaged when it impacted flat terrain in Indiantown, Florida. The certificated airline transport pilot and three passengers were killed. The aerial observation flight departed Okeechobee County Airport (OBE), Okeechobee, Florida, at 0802 and was operated under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan had been filed.
The operator’s dispatch records revealed that the pilot was scheduled to embark one passenger at Palm Beach County Airpark, West Palm Beach, Florida, at 0630, and subsequently embark two additional passengers at OBE.
About 0900, a witness reported observing the airplane make multiple passes over cattle pastures near Indiantown. During one of the passes, at an estimated altitude of 200 to 250 feet above ground level (agl), the witness observed the nose of the airplane drop. The airplane then banked to the right with an accompanying increase in engine noise, and descended into the ground.
Handheld global positioning systems (GPS), Garmin GPSMAP 295, and Garmin GPSMAP 76, were recovered from the airplane. The GPS units were sent to the National Transportation Safety Board Office of Research and Engineering for data extraction. The data revealed that on the day of the accident, the airplane departed OBE at 0802 and flew southeast along the shore of Lake Okeechobee at a GPS altitude of 500 ft mean sea level (msl) (about 470 ft agl). Starting about 0815, the airplane began to fly an S-turn pattern progressing to the north. The airplane further continued to make multiple circling passes at two intermediate locations. During these circling passes, the airplane’s groundspeed varied between 42 and 100 mph, and the altitude varied between 297 and 615 ft msl. About 0856, the airplane began to circle a third time. After the third orbit, the airplane began to rapidly lose altitude from about 350 ft msl. The final descent rate, based on altitude lost between the final two GPS update points, was in excess of 3,000 feet per minute (fpm). The last GPS position location was recorded at 0900:03. The last calculated and recorded airplane velocity was 53 mph groundspeed, with a course of 053 degrees true.
The pilot, age 36, held an airline transport pilot certificate, with ratings for airplane single-engine land, airplane multiengine land, and instrument airplane. He also held a flight instructor certificate, with ratings for airplane single-engine, airplane multiengine land, and instrument airplane. Investigators were not able to locate the pilot’s logbook. Flight records recovered from the operator revealed that the pilot had flown a total of 331.6 hours with the operator’s aircraft since January 9, 2007, 6.3 hours of which were flown in the accident airplane. On his latest Federal Aviation Administration (FAA) first-class medical application, dated January 31, 2007, the pilot stated that he had amassed 2,900 hours of total flight time.
The pilot was the co-owner of Kemper Aviation Incorporated.
The four-seat, high-wing, fixed-gear airplane, serial number 172S8235, was manufactured in 1999. It had accrued a total time in service of 5240.3 hours at the time of the accident. Review of the airplane maintenance records documented that an airframe and engine annual inspection was completed on January 23, 2008, at 72.5 flight hours prior to the accident. The Lycoming IO-360-L2A 180-horsepower engine, serial number L-29492-51A, had accumulated a total time in service of 3,421.9 hours. The engine had accrued 72.5 flight hours since the most recent major overhaul, which was performed in December 2007.
The operator's dispatch log for the airplane documented an initial engine tachometer hour meter reading of 5,238.8 prior to the departure from West Palm Beach. The tachometer hour meter reading observed on the rpm gauge at the wreckage location was 5,240.3.
The Safety Board investigator-in-charge (IIC) reviewed the maintenance squawk records for the accident airplane. On February 20, 2007 and June 10, 2007, at 4472.4 and 4624.5 hours respectively, pilots operating the airplane reported an inoperative stall warning horn. The records state that on both occasions maintenance personnel inspected the system and found it to be operative.
The closest official automated weather observation system (AWOS) was located at OBE, about 17 miles northwest of the accident site. The elevation of the AWOS was 34 feet msl. An aviation routine weather report was issued at 0901. It stated: winds from 300 degrees at 4 knots; visibility 7 statute miles; clear skies; temperature 15 degrees Celsius; dew point 13 degrees Celsius; altimeter 30.07 inches of mercury.
WRECKAGE AND IMPACT INFORMATION
The airplane wreckage was observed inverted, and oriented on a bearing of 225 degrees magnetic. The initial impact point was characterized by a 2-foot-wide divot in soft dirt, followed by a 5-foot-long section of excavated grass. A debris path continued along a bearing of 025 degrees, for approximately 90 feet, to the main wreckage.
All flight control surfaces were accounted for at the accident site. The lower section of the fuselage, forward of the main landing gear, exhibited accordion crushing damage. The right wing tip was found separated from the wing, and a chordwise crease was observed 1 foot inboard of the right wing strut attach point. Outboard of the crease, the wing exhibited upward buckling through to the wing tip. The right main landing gear remained attached to the fuselage and was bent upwards at an angle parallel to the right wing strut. The tail section remained attached to the airframe and was canted about 15 degrees to the left. The flap actuator thread was measured, and according to a Cessna Aircraft Company technical representative, the measurement corresponded to a flap setting of 15 degrees. The elevator trim actuator thread was measured and corresponded to a 5-degree elevator tab up position. Control continuity was confirmed from the rudder to the forward lower section of the cabin, and from the ailerons and elevator to the yoke.
The engine was separated from its mount, and remained partially attached to the airframe by the throttle and mixture control cables. The fuel injector servo and fuel line from the servo output to the flow divider sustained impact damage. Postimpact fire damage was observed in the lower forward section of the engine aft of the alternator.
The crankshaft was rotated and valve train continuity was confirmed through to the accessory case. The top spark plugs were removed; the spark plug electrodes were gray, which corresponded to normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart. Both magnetos were rotated by hand and produced sparks at their respective terminals.
The propeller was separated from the engine at the crankshaft flange. One propeller blade exhibited chordwise abrasions and torsional S-bending. The other blade exhibited chordwise abrasions and slight aft bending.
Fuel and vent lines from both wing tanks were separated at the wing roots. During the airplane recovery, approximately 5.5 gallons of clear blue fluid, consistent in appearance and odor with aviation gasoline, were removed from the left tank, and 4 gallons were removed from the right tank. After the airplane was recovered, a strong smell of aviation gasoline was detected in the soil areas that were underneath the wing roots.
The stall warning horn was visually inspected at the accident site and observed undamaged. The horn was tested with suction in accordance with the Cessna Normal Procedures Checklist, and did not produce a clearly audible tone.
MEDICAL AND PATHOLOGICAL INFORMATION
Autopsies were conducted on the pilot and passengers by the Florida District 19 Medical Examiner, and the cause of death for all occupants was reported as blunt force trauma injuries. Toxicological tests on specimens from the pilot were performed by the FAA Civil Aeromedical Institute, and the Florida Medical Examiner, the results were negative for all screened drug substances and ingested alcohol.
TEST AND RESEARCH
The stall warning horn was recovered from the airplane and sent to Safety Board Office of Research and Engineering for examination.
The stall warning horn was disassembled and the internal components were examined. It was found that on the output section, an aluminum reed section was detached. The fracture surface on the reed was examined, and the entire surface of the fracture was observed to be covered with a heavy oxide layer, which obscured the fracture features. No yielding or deformation was apparent adjacent to the fracture, but several areas of surface corrosion were apparent.
The detailed examination report is contained in the public docket for this accident.
The POH for the Cessna 172S provided the following procedures for preflight inspection:
"Stall Warning Opening – CHECK for blockage. To check the system, place a clean handkerchief over the vent opening and apply suction; a sound from the warning horn will confirm system operation."
The Safety Board IIC interviewed a certified flight instructor (CFI) from Kemper Aviation Incorporated. He stated that the purpose of the accident flight was to survey bird activity in the vicinity of Lake Okeechobee. The flights were conducted as a research project for Florida Atlantic University and generally took place with the pilot and two or three researchers. The CFI stated that these flights were conducted at least two times per week, and that he was usually the pilot. On the day of the accident, the CFI was sick and the accident pilot flew in his place. He further stated that he believed this was the first time the accident pilot had flown the surveying flights.
The CFI explained that a typical flight would consist of him departing West Palm Beach at dawn with a Florida Atlantic University researcher onboard. They would then continue onward to embark another one or two researchers at Okeechobee. Depending on the load, the pilot would then add fuel at OBE such that the airplane was close to its maximum gross weight. Generally the research leader would sit in the front right seat with the remaining researchers sitting in the rear of the airplane.
The flight would then depart to Lake Okeechobee and fly 4-kilometer wide transects from east to west on the first day, followed by north to south transects on the second day. Depending on the results of these flights, they would often fly a third day. Markings were placed on the wing struts to aid in identifying the viewing area, which was always below the airplane. The flights generally were flown at an altitude of 500 to 1,000 feet agl, typically at 85 knots and with flaps extended between 0 and 10 degrees. If anything of interest was noted during the transects, they would reverse course and perform turns around a point, circling the item of interest. Often in the turns the pilot stated he would fly the airplane in a ”slip” condition to allow a better view of the area below. The turns generally would be conducted at an airspeed of 60 knots, with flaps extended between 10 and 20 degrees. All observations were of birds on the ground, not in flight. Typically they would fly 6 to 8 hours in a day, making fuel stops at OBE.
The CFI stated that the research leader, who was fatally injured in the accident, was the same person who had flown and organized all the previous surveying flights. He further stated that on multiple occasions the research leader requested that he descend the airplane to altitudes in the range of 200 to 250 ft agl. He stated that during the turns the research leader would often ask him to fly slow and “on the stall horn.”
A previous employee of Kemper Aviation Incorporated was interviewed by the Safety Board IIC. He stated that he had flown the bird surveying flights on multiple occasions. He described a technique, commonly used for photography, which was to fly the airplane “low,” then climb at full engine power and maneuver the airplane “into a slip.” Researchers would then take photographs out of the rear windows of the airplane. This technique would allow for a centered shot of birds on the ground without the appearance of movement. He explained that he would often hear the stall warning horn sound during these maneuvers.
Weight and Balance
The operator’s fueling records were reviewed by the Safety Board IIC. The records disclosed that the airplane was last serviced with the addition of 17.9 gallons of aviation fuel prior to departure from West Palm Beach. According to the pilot’s operating handbook (POH), the airplane had a total fuel capacity of 56 gallons. The weight and balance sheet located onboard the airplane revealed a basic empty weight of 1,696.2 pounds and a useful load of 861.8 pounds. According to medical examiner records, the measured total weight of the front seat occupants was 402 pounds and 366 pounds for the rear seat occupants. The baggage that was recovered from the airplane at the accident site was weighed at 40 pounds; this baggage was distributed throughout the cabin.
The POH and FAA-approved airplane flight manual for the Cessna 172S states that at the most rearward center of gravity, with a gross weight of 2,550 pounds, at an angle of bank of 0 degrees, and with the flaps extended to 10 degrees, the airplane will stall at 50 knots calibrated airspeed (CAS) under power off conditions. At a 30-degree angle of bank, the airplane will stall at 54 knots CAS. With a 45-degree angle of bank, the airplane will stall at 59 knots CAS, and with a 60-degree angle of bank, the airplane will stall at 71 knots CAS.