LARKSPUR, CO, USA
N9453L
Grumman American AA-1A
The 265-hour private pilot filed a VFR flight plan from Boulder, Colorado, to Pueblo, Colorado, and requested VFR flight following services. Thirty minutes later, the pilot reported he was encountering 'moderate turbulence,' then 'quite a bit of turbulence,' that he was turning around, and requested flight following services back to Boulder. Shortly thereafter, the pilot advised he was in a spin and unable to correct and that he was turning off his transponder. The airplane struck the ground in a near-vertical attitude. There was no evidence of a spin. His logbook indicated he had never been demonstrated a spin or had been given spin instruction. The Pilot's Operating Handbook prohibits spins and states: 'There is evidence that permitting a spin to go beyond one turn without initiating proper recovery procedures can allow a spin mode to develop from which recovery is not possible.'
HISTORY OF FLIGHT On July 5, 1998, at 1124 mountain daylight time, a Grumman-American AA-1A, N9453L, was destroyed when it collided with terrain during an uncontrolled descent approximately 3 miles northeast of Larkspur, Colorado. The private pilot, the sole occupant aboard, was fatally injured. Visual meteorological conditions prevailed, and a VFR flight plan had been filed for the personal flight being conducted under Title 14 CFR Part 91. The flight originated at Boulder, Colorado, at 1051. At 1015, the pilot telephoned the Denver Automated Flight Service Station (AFSS). After receiving a standard weather briefing, the pilot filed a VFR flight plan from Boulder, Colorado, to Pueblo, Colorado. The flight plan was activated at 1051. At 1053, the pilot contacted Denver Departure Control and requested VFR flight following services. He was assigned a discrete transponder code, identified on radar, and was given the current altimeter setting. The pilot requested an altitude of 8,500 feet, and he was instructed to maintain VFR. Control of the airplane was then transferred to the Denver Air Route Traffic Control Center (ARTCC). At 1100, the pilot advised he was level at 8,500 feet. At 1121, the pilot was advised he was leaving Denver TRACON (terminal radar control) airspace and that radar services were being terminated. The pilot reported he was encountering moderate turbulence. At 1123, the pilot reported he was encountering "quite a bit of turbulence," was returning to Boulder, and requested flight following services. He was assigned another discrete transponder code. At 1124, the pilot advised he was in a spin and unable to correct and that he was "turning off [his] transponder." This was the last known radio transmission from the pilot. An ALNOT was issued at 1219 and cancelled at 1707 when Civil Air Patrol aircraft located the wreckage. The accident occurred during the hours of daylight at a location of 30 degrees, 16 minutes, 7 seconds north latitude, and 104 degrees, 50 minutes, 29 seconds west longitude. CREW INFORMATION The pilot, Alfred Purdon, Jr., age 47, was born on June 3, 1951. He held Private Pilot Certificate No. 267023080, dated September 1, 1995, with an airplane single engine land rating. He was not instrument rated. He also held a third class airman medical certificate, dated June 24, 1997, with no restrictions or limitations. His most recent biennial flight review was dated March 15, 1997, and was accomplished in a Cessna 152. He was a physician. Dr. Purdon's pilot logbook was recovered from the wreckage. It contained entries from June 7, 1995, to July 4, 1998. None of the entries indicated a spin had been demonstrated to Dr. Purdon, nor did they indicate he had ever been given spin instruction. Dr. Purdon began flying the American AA-1A on November 15, 1997, and all his flight time thereafter was almost exclusively in N9453L. He has accumulated 265 hours of flight time, of which 128 hours were in the AA-1A. A summary of his flight time is attached as an exhibit to this report. AIRCRAFT INFORMATION The aircraft maintenance records were also recovered from the wreckage. The last annual and 100-hour inspection were performed on the airframe and engine, respectively, on September 24, 1997, at a tachometer time of 1,777:52. At the accident site, the tachometer registered 1,896:80, a difference of 124:28. Since the pilot reported he was in an "unrecoverable spin," three recurring airworthiness directives (ADs) pertaining to the American AA-1A are of particular interest: 72-06-02 (rudder, aileron, and elevator control cables), 72-07-10 (wear on elevator bungee housing), and 75-07-04 (rudder control bar assemblies). These ADs, due every 100 hours, were last complied with on September 17, 1996, at a tachometer time of 1,748 hours. The next scheduled compliance was at 1,848 hours. The last annual inspection of the airplane was on September 24, 1997, at a tachometer time of 1,777:52 hours. According to Dr. Purdon's logbook, he had flown the airplane 128 hours since the last annual inspection. The airplane had been flown a minimum of 48 hours over the required compliance time. The wreckage was reexamined on August 6, 1996. On rudder cable showed signs of wear in excess of that allowed by AD 72-06-02. The elevator bungee shear link was intact. There was no evidence of delamination of the bonded skin. FAA concluded that the airplane "did not meet regulatory airworthiness standards at the time of the accident," but that there was "no evidence that this lack of conformance to these ADs contributed to the accident." METEOROLOGICAL INFORMATION Visual meteorological conditions and low velocity surface winds were reported by stations nearest the accident site. Two pilot reports (PIREPs) reporting turbulence were filed. At 0944, about two hours before the accident, the pilot of a Cessna 172, flying at 9,000 feet and 15 miles southeast of Centennial Airport (APA), reported light to moderate turbulence. At 1211, the pilot of a Grumman AA-5, flying at 8,500 feet about 10 miles southwest of the accident site, reported moderate turbulence. WRECKAGE AND IMPACT INFORMATION The on-scene investigation was conducted on July 5 and 6, 1997. Physical evidence gathered at the accident site indicates the airplane struck the ground in a near-vertical attitude on a magnetic heading of 250 degrees. No evidence of a spin was noted. The wreckage was confined to a small area. All major airplane components were located and identified. The propeller blades bore numerous 90 degree chordwise scratches on the cambered surfaces. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was performed by Dr. Ben Galloway at and for the Douglas County Coroner's Office. According to his report, a package of Ultram (tramadol hydrochloride), an analgesic, was found in the pilot's clothing. In addition, a toxicological screen was performed by FAA's Civil Aeromedical Institute (CAMI) in Oklahoma City, Oklahoma, and ChemaTox Laboratory, Inc., in Boulder, Colorado. According to the latter's report, the blood alcohol level was 0.015g/100ml (15 mgm%). Dr, Galloway attributed this to "probable postmortem contaminant." No drugs were detected in the blood samples. According to CAMI's report (#9800190001), no ethyl alcohol, cyanide, or drugs were detected in the blood. Due to the lack of a suitable specimen, a carbon monoxide test could not be performed. TESTS AND RESEARCH CDR (continuous data recording) radar data was retrieved from Denver TRACON and plotted. The data showed the airplane flew a south-southeast heading. Altitude varied between 8,600 and 8,800 feet msl. Beginning at 1023:59, the pilot initiated a left turn. The last transponder reply was recorded at 1024:32, when the airplane was heading 102 degrees at an altitude of 8,900 feet msl. Airspeed was 104 knots. Two primary "hits" were then recorded, followed by "coast mode" (computer generated projections). ADDITIONAL INFORMATION The following excerpt is from the American AA-1A Pilot's Operating Handbook: "NOTE - The operating limitations of this airplane include SPINS PROHIBITED. A spin is not possible without a prolonged stall condition. All types of stalls (except whip, which are prohibited) can be performed in this airplane without spinning by simply recovering from the stall when it occurs (moving the control wheel forward sufficiently to reduce angle of attack for normal forward flight). "There is evidence that permitting a spin to go beyond one turn without initiating proper recovery procedures can allow a spin mode to develop from which recovery is not possible." The wreckage was released to Beegles Aircraft Service, Inc., on August 6, 1998. Other than the Federal Aviation Administration, there were no other parties of record to the investigation.
The pilot inadvertently stalling the airplane and entering an unrecoverable spin. A factor was clear air turbulence.
Source: NTSB Aviation Accident Database
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