GRAND CANYON, AZ, USA
N4634H
Mooney M20K
The pilot was deviating for weather and reported cumulous buildups and electrical discharges with tops at and above his flight level. Radar data showed the aircraft ground track turning north as it began an unannounced descent. The descent continued until radar contact was lost. Witnesses reported seeing the aircraft break out of the overcast, making a series of random turns, climbs, and dives before it collided with the canyon wall. The aircraft collided with the canyon wall near Pima Point. Thunderstorms had developed along the route several hours sooner than forecast. Examination of recorded weather radar data disclosed that a level 6 thunderstorm with tops to 49,000 feet was present at the location and time of the accident. There was no record of the pilot requesting or receiving updated weather information after his final DUATS briefing 4 hours prior to the accident. No evidence of mechanical discrepancies were found during the wreckage examination.
HISTORY OF FLIGHT On August 2, 1996, about 1008 hours mountain standard time, a Mooney M20K, N4634H, en route to Shalz Field in Colby, Kansas, descended from flight level (FL) 210 and collided with a canyon wall and burned in the Grand Canyon National Park, Arizona. The aircraft was destroyed and the pilot, the sole occupant, received fatal injuries. The aircraft was being operated as a personal flight by the pilot/owner when the accident occurred. The flight originated in Torrance, California, at 0742 on the morning of the accident. Instrument meteorological conditions prevailed at the en route cruising altitude and an IFR flight plan was filed. At 0906, the Los Angeles ARTCC Sector 6 controller advised the pilot that he had lost his transponder signal and requested that he recycle the code 7372. At 0908, the controller advised the pilot that he was receiving his transponder and that he was now 15 miles south of Needles, California. The pilot replied that he was 13.4 miles south and the controller agreed. At 0909, the controller advised the pilot that he had an intermittent transponder and asked if he had another one onboard. The pilot replied that he did not, but that he would recycle his code again. The controller mentioned to the pilot that the transponder was working fine until he began his climb. At 0911, the pilot reported level at 17,000 msl and was advised that he was in radar contact over Needles. At 0916, the controller handed off the pilot to Denver ARTCC. At 0939, the Denver controller advised the pilot that the current altimeter for Grand Canyon was now 30.35 inHg. At 0948, the pilot requested a climb to FL190 and deviations to the north of course which were approved. The pilot was asked to advise when he would be able to resume his direct route to Colby. At 0956, the pilot requested and received a clearance to FL210. The controller asked the pilot if he was deviating for weather and he replied affirmatively. The controller asked how much further he would have to deviate and for a description of the weather. The pilot replied that there were cumulous buildups with discharges showing on his Storm Scope. He said the tops appeared to be from FL210 to FL230. At 1001, the pilot reported level at FL210. At 1003, the pilot reported turning back on course and the controller responded by instructing the pilot to contact Denver ARTCC on 127.55. The pilot reported on frequency with Sector 36 reporting level at FL210. At 1004, the full data block for N4634H showed FL214 and then altitude data was lost. At 1005, the pilot reported deviating back to the left (north). At 1006, the full data block on N4634H showed "XXX" with no altitude reported. At 1007, the full data block showed the coast mode. At 1008, the Sector 36 controller asked the pilot to reset his transponder code to 7372 with no response. The controller tried to contact the pilot several more times without success. Attempts were also made by several other controllers without success. After all attempts were negative, Denver Center notified the FAA Western Region operations center that the aircraft was missing. (The Denver ARTCC flight summary is appended to this report.) A review of the FAA DART Log Sort radar data showed that about 1004:11 the aircraft was on a course of 045 degrees with the Mode-C altitude of 21,000 feet and the beginning of a climb to 21,400 feet. About 1005:14, the pilot reported that he was "deviating back to the left." About 1004:53, the aircraft began an unannounced descent. After that time, radar data showed the aircraft's course changing from 060 degrees northward until reaching 342 degrees. About 1006:41, radar contact was lost with the Mode-C altitude showing 8,700 feet. At the Grand Canyon National Park, Arizona, witnesses at various locations along the south rim observed a single engine aircraft break out of the overcast. Their statements generally described a single engine aircraft making a series of random turns, climbs, and dives before descending into the canyon. Although many people witnessed the aircraft in-flight, no one reported seeing the aircraft strike the canyon wall. One witness, a National Park Service helicopter pilot, was at the heliport (elevation 6,920 feet msl) when he reported hearing the sound of an aircraft engine. He reported that a very light rain was falling, but that there were no other atmospheric restrictions to horizontal visibility. At the time of the accident he estimated the lowest cloud base to have been about 2,000 agl. A witness with a video camera inadvertently captured the aircraft as it flew through a scene he was filming from his position at Pima Point. On review of the videotape, investigators found it showed the grainy image of the aircraft descending in a left-to-right direction across the field of view. (Witness statements are appended to this report.) About 10 to 20 minutes after the accident, another witness stated that heavy rain began in the Mohave Point area accompanied by gusty surface winds, lightning, and thunder. PERSONNEL INFORMATION According to logbook entries, the pilot began taking flight instruction on January 24, 1978. He obtained his private pilot license on December 12, 1978, and obtained his instrument rating on December 2, 1990. He was checked out in a Mooney M20 on December 23, 1990, and an M20C on June 10, 1991. He checked out in a M20K, the accident aircraft, on November 2, 1992. His last flight prior to the accident was on July 21, 1996. He did not log time in any other aircraft after checking out in a Mooney M20K. The pilot had a statement of demonstrated ability waiver No. 10D99425 for a second-class medical certificate. He had defective distant vision, 20/200, that was corrected to 20/20 bilaterally. He was required to wear corrective lenses while exercising his pilot privileges. The pilot had undergone physiological training for hypoxia at Mather AFB on March 25, 1991. AIRCRAFT INFORMATION An Insight Avionics Strike Finder was installed on July 20, 1994, by Flite-Comm Electronics, Inc. The certificate holder of the repair station reported that the unit he installed was not heading stabilized. (The Strike Finder User's Guide is appended to this report.) On December 10, 1994, Service Aviation reinstalled the KI-256 flight director after it was overhauled by Pan Pacific Instrument Service. The aircraft was equipped with a KFC 200 autopilot. Entries in the aircraft logbook and an invoice from Autopilots West showed that the KS-272 trim servo was adjusted for roll and pitch gain on June 12, 1996. (A copy of the Autopilots West invoice is appended to this report.) The aircraft engine was equipped with a Rayjay turbocharger with a Merlyn Products, Inc., fixed wastegate utilizing a turbocharger differential control system. An oxygen bottle was found at the accident site. The regulator was broken off and the system was not subsequently tested or examined. METEOROLOGICAL INFORMATION The pilot obtained a DUATS "Inter Alt Weather Brief" at 0606 on August 2, 1996. The forecast predicted thunderstorms would be developing along the route of flight. According to the 0954 station observation for the Grand Canyon, convective activity had developed several hours earlier than forecast. (The DUATS weather briefing and the Los Angeles ARTC Center weather report are appended to this report.) A weather study conducted by a meteorologist at the Safety Board revealed that at 1011, a strong to very strong VIP Level 3 to VIP Level 4 weather echo was located about 6 miles from the accident site. At the same time, a very strong to intense VIP Level 4 to VIP Level 5 weather echo was detected about 2.5 miles west of the accident site. At 1016, an extremely strong VIP Level 6 weather echo was detected about 2 miles west of the accident site. The maximum echo tops in the area were about 49,000 feet msl. (The Meteorological Factual Report is appended to this report.) WRECKAGE AND IMPACT INFORMATION The aircraft collided with the canyon wall on the south rim at approximately 4,250 feet msl. The site was fixed by investigators using a hand-held GPS at 36 degrees 04.521 minutes north latitude by 112 degrees 11.643 minutes west longitude. After the initial impact, portions of the aircraft wreckage slid about 40 feet down the face of the wall, coming to rest on a series of rock ledges. The direction toward the canyon wall through the average center of the wreckage was 134 degrees. Components identified with the propeller, left and right wing tips, and rudder were located in the immediate vicinity of the impact point. Additional components identified with the flight control surfaces were found, however, control continuity was not established due to the extent of impact damage. The autopilot system was destroyed by impact forces. The elevator trim jack screw was not located. Both propeller blades were found separated from the hub. Each blade exhibited fractures along with leading edge damage, compression, and chord-wise striations. The engine was examined after the aircraft was recovered. The crankcase was shattered with many pieces not recovered. The crankshaft was broken in half; however, all the journals were smooth with no evidence of scoring. The cylinders were separated from the crankcase with two of the cylinder heads further separated from their respective cylinders. The remaining cylinders exhibited scarring and deformation. All cylinder bores were smooth and showed no evidence of scoring. The connecting rods were intact and bent to varying degrees. Several of the connecting rod bolts had snapped in half. The camshaft was bent with all the lobes and journals smooth and free of scoring. The outer edges of the turbocharger turbine blades were distorted in the opposite direction of rotation. FAA airworthiness inspectors reviewed the aircraft, engine, and propeller logbooks, and they concluded that the aircraft had been maintained in an airworthy condition. Since the Hobbs meter and recording tachometer were destroyed in the accident, the aircraft total time and time since the last inspection were not determined. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was conducted on August 2, 1996, by the Office of the Coconino County Medical Examiner with specimens retained for toxicological examination. The toxicological test results were negative for alcohol and all screened drug substances. (A copy of CAMI's findings are appended to this report.) FIRE A fire occurred on impact and engulfed major portions of the aircraft wreckage. Because the site was inaccessible to fire fighters, the fire burned itself out. ADDITIONAL INFORMATION The aircraft was recovered by personnel from Air Transport and taken to their facility in Phoenix, Arizona. The wreckage was released to a representative of the registered owner's estate on August 12, 1996. (A copy of the wreckage release is appended to this report.)
due to an in-flight loss of control resulting from a probable incapacitation for unknown reasons. The loss of control occurred while the aircraft was being flown in close proximity to a level 6 thunderstorm. The failure of the pilot to obtain current weather information was a factor in this accident.
Source: NTSB Aviation Accident Database
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