BAKERSFIELD, CA, USA
N231BY
Mooney M20K
While descending for an instrument approach in instrument meteorological conditions, the airplane's airspeed exceeded its never exceed velocity (Vne) of 196 knots. The elevators fluttered and separated from the airplane. Thereafter, the stabilizers departed, the nose pitched downward, and both wings failed in a negative direction. A ground witness heard a 'pop' sound, and observed airplane parts falling from the low clouds; the surface winds were reported by the witness as gusty. Earlier during the flight, the pilot had been cruising about 19,000 feet, and tracking in a southerly direction at 191 knots (ground speed). The winds aloft were westerly. While communicating with flight watch and radar controllers, he indicated that his airplane was not equipped with deicing equipment. The pilot was advised that icing conditions existed between 13,000 and 15,000 feet, and the freezing level was 7,000 feet. Due to traffic, at 0923 the controller cleared the pilot to descend to 15,000 feet. The pilot accepted the clearance, and requested a clearance to divert to a nearby airport. The controller approved the request. During the last 24 seconds of radar-recorded flight, the airplane's rate of descent increased to 3,500 feet per minute, and over its southerly course its ground speed increased to 240 knots. Shortly after this at 0930:21, the sound of an emergency locator beacon was recorded in the radar control facility. Pilot reports covering the area of the accident around the time of the event reported light to moderate turbulence and light to moderate rime/clear icing conditions. Engineering analysis and testing by the airframe manufacturer predicted the onset of flutter to occur at 241 knots. The airplane was modified by the installation of a larger engine with 95 additional horsepower available.
HISTORY OF FLIGHT On May 5, 1998, at 0930 hours Pacific daylight time, a Mooney M20K, N231BY, owned and operated by the pilot, experienced an in-flight breakup while descending. The airplane crashed into an open field about 11 nautical miles southwest of Bakersfield, California. Instrument meteorological conditions prevailed in the vicinity of the accident site, and an instrument flight plan was filed. The airplane was destroyed and the private pilot was fatally injured. The flight originated from Sacramento, California, at 0802. The Federal Aviation Administration (FAA) reported that the pilot spoke with Oakland Flight Watch personnel while he was cruising at flight level 190 (19,000 feet) and proceeding in a southerly direction en route toward his flight planned destination of Santa Monica, California. At 0855, Flight Watch personnel asked the pilot if he was aware of the forecast for icing and asked him if his airplane had deicing equipment. The pilot replied that he did not have deicing equipment, and he planned to fly above the icing condition. Flight Watch personnel advised the pilot that the forecast top of the layered clouds was 20,000 feet, and that the freezing level was forecast as low as 7,000 feet. At 0903, the southbound pilot was north of Bakersfield. A Los Angeles Air Route Traffic Control Center (ARTCC) controller advised him that around Shafter (near Bakersfield) the tops of the clouds started to rise to about flight level 220, and there were reports of a trace of mixed rime icing in the clouds. Also, south of Bakersfield, clear icing had been reported between 13,000 and 15,000 feet. At 0908, the pilot requested a 20-degree course deviation because of a buildup. The controller approved the request. A few minutes later, the pilot indicated that he was going to try skirting along the west side (of the weather) if possible. At 0923, the controller cleared the pilot to descend and maintain 15,000 feet due to traffic. The controller also stated that another band of thunderstorms was moving in from the west (of his route). The pilot advised the controller that he would like to turn around and go into the Bakersfield Municipal Airport, and that it didn't look too good up ahead. One minute later the controller cleared the pilot to descend to 14,000 feet, and indicated that he could expect a turn back to Bakersfield. The ARTCC controller then handed off further control of the airplane to a Bakersfield radar controller. At 0926:33, the airplane was descending through 15,400 feet, and was about 6 miles south of the Bakersfield Municipal Airport. The Bakersfield radar controller directed that the pilot fly on a 270-degree heading, and at 0927:10, the controller instructed the pilot to maintain 7,000 feet. The pilot acknowledged the clearance. The last communications with the pilot occurred between 0928:21 and 0929:40. During this period the controller advised the pilot to contact approach control, and to "turn the long way around to a heading of zero niner zero." The pilot repeated the clearance. At 0929:30, the pilot indicated that he was descending through 10,200 feet. At 0929:35, the pilot was cleared to descend and maintain 2,300 feet. The pilot responded at 0929:40 by stating "down to two thousand three hundred one bravo yankee." No further communications were recorded from the pilot. At 0930:21, the sound of an emergency locator transmitter (ELT) was heard in the Bakersfield Radar facility. About 6 minutes later, a Bakersfield radar controller stated to another aircraft that ". . . there is a weather area uh depicted uh right the uh where the aircraft dropped off the radar is right on the edge of a weather area . . . ." A ground-based eyewitness, located near Interstate Highway 5, reported hearing the sound of an engine at a high rpm, and a loud "pop" sound. He then observed the accident airplane falling beneath the overcast layer of clouds. About 3 to 4 seconds later, he saw debris falling down from the same general area. The main wreckage was found in an open field about 330 yards east of the highway. PERSONNEL INFORMATION Family members reported that the pilot had flown his airplane on cross-country flights during the previous week. Regarding the pilot's currency, he typically flew about two times per week. The pilot was issued a private pilot certificate in 1994. On a medical certificate application dated October 11, 1996, his total flight time was listed at 110 hours. He was issued an instrument rating on September 19, 1997. On the FAA rating application form he listed, in part, the following flight times: (A) Total Flight Time, 261 hours; (B) Total Dual Instruction Received, 74 hours; and (C) Total Instrument Time, 40 hours. All of the flight time was listed as having been received in single-engine airplanes. No current flight record logbooks were located. Historical data provided by family members indicated that between January 2 and March 19, 1998, the pilot logged 37 hours of flight time. During this period, he recorded having flown 4 instrument approaches in 7 hours of instrument flight time. On January 24, 1998, the pilot completed a "High Altitude Course" of flight and ground instruction. Acquaintances of the pilot reported to the National Transportation Safety Board investigator that the pilot used oxygen when flying above 8,000 feet. AIRCRAFT INFORMATION The airplane was manufactured in 1979, and it was not certified to fly in icing conditions. The FAA approved "Airplane Flight Manual" bears the following statement: "Do not operate in known icing conditions." The airplane underwent a "Rocket" conversion, which was completed in January 1998. The conversion was performed under FAA approved supplemental type certificate numbers SA00243SE and SA5691NM, and the airplane's flight manual was supplemented accordingly. In part, the conversion involved removal of the original Continental TSIO-360 engine and installation of a TSIO-520 engine, thus increasing the airplane's horsepower from 210 to 305. Other items changed included the propeller and engine controls, and the battery was relocated. As a result of Rocket Engineering's modifications, the airplane's maximum gross weight increased from 2,900 to 3,200 pounds. The airplane's velocity never exceed speed (Vne) remained at 196 knots. At the completion of the modification, the engine's recording tachometer registered 0.0 hours. METEOROLOGICAL INFORMATION The pilot checked the weather and filed an instrument flight rules flight plan prior to departure. At 0932, a "911" call was received by law enforcement officials. The reporting party stated that he observed debris falling from the sky. The party subsequently reported that at the time it was cloudy and a light intensity rain was falling in the area. About 10 minutes later, the rain intensity became heavy. No lightning was observed at any time. In response to the emergency call, a few minutes later a Kern County Sheriff deputy arrived at the crash site. Upon arrival, he observed the weather conditions "consisted of heavy rain and dense, low level clouds," with low visibility. He also remarked in his report that it was "windy." The closest aviation weather observation station to the accident site is located at the Meadows Field, in Bakersfield. At 0856, Bakersfield reported its weather as follows: Wind from 100 degrees at 6 knots; visibility 6 statute miles; mist; scattered clouds at 2,500 feet, broken 9,000 feet; temperature/dew point 16/14 degrees Celsius, respectively; and altimeter 29.85 inches of mercury. At 0956, Bakersfield's weather was reported as follows: Wind 260 degrees at 8 knots; visibility 10 statute miles; light rain; few clouds at 1,700, broken 5,500 feet, broken 7,000 feet; temperature/dew point 17/14 degrees Celsius, respectively; and altimeter 29.86 inches of mercury. AIDS TO NAVIGATION According to FAA records of facility operation, all electronic aids to navigation pertinent to the airplane's route of flight were functional. COMMUNICATION The FAA reported that none of the facilities, which were in contact with the airplane pilot, reported any communication problems. At no time during the accident flight was any transmission received from the pilot in which he indicated that he was experiencing difficulty flying the airplane. WRECKAGE AND IMPACT INFORMATION From an examination of the accident site and airplane wreckage, the main wreckage was found at an approximate elevation of 300 feet mean sea level. Its global positioning satellite coordinates are approximately: 35 degrees 13.405 minutes north latitude by 119 degrees 10.563 minutes west longitude. Along the 0.46-mile-long wreckage distribution path, the first components found were the outboard portions of the left and right elevators. The horizontal stabilizers and rudder components were found to the south of the elevators. Further south were the left and right wings. The heavily impact damaged main wreckage, consisting of the propeller, engine, cockpit, and fuselage, was found together, southeast (135 degrees, magnetic) from the elevators. The airplane's recording tachometer was found in the wreckage. It was reading 82.53 hours. Also, an oxygen bottle was noted in the wreckage. The airplane came to rest upside down on a northwesterly heading. The propeller hub was about 2 feet below ground level. The three propeller blades were found with the hub. No evidence of oil streaking was noted on the airplane, and there was no evidence of fire. The inboard 5 1/2 feet of left wing was found attached to the fuselage. The entire right wing was found separated. MEDICAL AND PATHOLOGICAL INFORMATION On May 6, 1998, an autopsy was performed by the Kern County Sheriff/Coroner's Office, 1832 Flower Street, California 93305. The FAA's Civil Aeromedical Institute (CAMI) performed toxicology tests on specimens from the pilot. The test results were negative for all screened drugs and ethanol. TESTS AND RESEARCH Engine Examination. The engine manufacturer participant reported that normal operating signatures and nominal erosion was evident with the spark plugs. All of the piston domes were found intact and exhibited normal operating signatures. No scoring or discoloration was observed on the cylinder walls. The fuel pump drive coupling was intact, and the metering unit fuel inlet screen was clean. Residual fuel was found in the lines. The right magneto was functionally tested and it was found operable. Lubrication was present in the accessory section of the engine. In summary, the participant opined that no evidence of any preimpact malfunction or failure was noted with the engine. Speed Brake Position. The speed brake on the right wing was found in the raised (up) position. In the left wing it was observed stowed. Based upon their mechanical system of deployment and the preimpact separation of both wings, their in-flight position was not ascertained. Trim and Descent Flight Test Study. Rocket Engineering conducted flight tests to ascertain maximum achievable descent rates and pitch trim configuration data with two engine power settings and with two wing spoiler positions. In pertinent part, Rocket reported that when descending with 72 percent power, at 205 knots and no spoilers used, the maximum achievable rate of descent was 1,700 feet per minute. In this configuration the pitch trim was 90 percent nose down. During another test, when descending with 50 percent power, at 197 knots and the spoilers up, the maximum rate of descent increased to 2,900 feet per minute. In this configuration the pitch trim was 75 percent nose down. Breakup. The Mooney Aircraft Corporation, manager of structures, examined the airplane under the supervision of Safety Board investigators. Following a review of the observed evidence, the company reported that its preliminary conclusion is the aircraft may have had a failure to the horizontal stabilizers caused by flutter, initiated after buckling of the horizontal stabilizers due to excessive loading above the design allowable limits, or due to previous damage. An FAA airframe specialist from the Ft. Worth, Texas, Airplane Certification Office, examined the recovered wreckage. In part, the specialist noted the following: 1) There was no indication from the structural fractures of corrosion or fatigue failure being present; 2) Both horizontal tail surfaces and elevators left the airplane in the air. The right side did a negative/positive cycle to come up and hit the vertical tail and rudder. The left side only indicated a positive cycle up and back; 3) Both the left and right elevator balance weight horns were missing and appeared to have separated from the elevators prior to ground impact; and 4) The trim of the empennage was in the full nose down position. In follow up, the FAA's Airplane Certification Officer manager reported that the specialist's conclusion was that "the airplane lost the horizontal tail due to some type of induced flutter, and then tumbled tail up and over, until the wings broke down and off, prior to impact with the ground." During a discussion regarding flutter, the participants indicated that the onset of elevator flutter in this model airplane occurs at speeds in excess of about 241 knots calibrated airspeed. Ground Speed Computation. Based upon the FAA's recorded radar data, between 0920 and 0923 while cruising at 19,100 feet, the airplane's ground speed was 191 knots. During the airplane's last 24 seconds of recorded flight, while descending between 9,600 and 8,200 feet, the airplane's ground speed increased to 240 knots. Also during this time interval, the airplane's average rate of descent was approximately 3,500 feet per minute. ADDITIONAL INFORMATION The main airplane wreckage was released to the owner's representative on April 7, 1999.
The pilot's operation of the airplane at a speed well in excess of it's designed never exceed speed that resulted in elevator flutter and in-flight failure of the airplane. Turbulence and icing conditions were factors in the accident.
Source: NTSB Aviation Accident Database
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