The Woodlands, TX, USA
N16CG
Mitsubishi MU-2B-40
Visual meteorological conditions prevailed for the planned cross-country flight for which the pilot obtained a weather briefing, filed an IFR flight plan, and received an ATC clearance. Approximately 8 minutes after takeoff, radar indicated the airplane was at 11,200 feet msl, heading 241 degrees, with a ground speed of 180 knots. No distress calls or additional communications with the pilot were recorded, and radar contact was lost. The airplane impacted the ground in an uncontrolled descent. The right wing tip tank separated from the airplane and was found 0.18 nautical miles from the main wreckage. The teardown and examination of both engines disclosed that the type and degree of damage was indicative of engine power section rotation and operation at the time of impact. There were no complete systems intact at the accident site due to the impact sequence and post-impact fire which consumed the aircraft. The landing gear and flaps were found in the retracted position. The portion of the right propeller shaft coupling found at the site was fractured through 360 degrees. Metallurgical examination revealed that the propeller shaft coupling failed in fatigue. The presence of the fatigue cracks indicated the coupler fractured in fatigue in service, and the fatigue cracks were not the result of ground impact. The circumferential fracture intersected the ends of several internal spline teeth. The origin of the fatigue crack could not be determined because of severe corrosion damage on the fracture surface. Fatigue propagation was in the aft direction and from the inside to the outside of the coupling. The engine core rotating components would have bee free to rotate when uncoupled from the propeller shaft. The maintenance records indicated that the failed coupling had accumulated approximately 4,000 hours since new, and 1,250 hours since engine overhaul in 1989. Since 1990, as a result of fatigue fractures, the manufacturer introduced several design changes for the propeller shaft coupling via optional Service Bulletins to be accomplished at the next access or hot section inspection (HSI). Impact and thermal damage of the right propeller precluded a determination of the in-flight blade angles. The calculations by the airplane manufacturer indicated that "the [intact] airplane was capable of continued flight" with the right propeller feathered, and that the "airplane can keep attitude, but cannot climb and cannot maintain altitude" with the right propeller in the flat pitch or wind milling positions, respectively. Metallurgical examination of the component brackets and associated bolts from the right tip tank revealed the separation of the tip tank resulted from a single-event overstress fracture of both the forward and aft tank attachment fittings. Calculations showed that a 3.763 radians per second (35.9 RPM) spin rate would cause the failure of the forward wing fuel tank attachment fitting. There had not been a previous in-flight separation of a wing tip fuel tank on this model airplane.
HISTORY OF FLIGHT On May 1, 2001, approximately 1242 central daylight time, a Mitsubishi MU-2B-40, twin-engine turbo propeller driven airplane, N16CG, struck trees and terrain during an uncontrolled descent near The Woodlands, Texas. The airplane, co-owned by the pilot and passenger, was operated by the pilot under 14 Code of Federal Regulations Part 91. The commercial pilot and his passenger sustained fatal injuries, and the airplane was destroyed by impact forces and a post-impact fire. Visual meteorological conditions prevailed in the vicinity of the departure airport. An instrument flight rules (IFR) flight plan was filed for the personal cross-country flight which departed Conroe, Texas, at 1233, with a planned destination of Alamorgordo, New Mexico. Witness interviews were conducted by the NTSB investigator-in-charge (IIC), FAA inspectors, and local authorities. One witness stated that "it did not seem as though the propellers were under power, but free and rotating. The rudder appeared to be in the opposite direction of the spin." Several other witnesses stated that one of the propellers was not turning. One witness reported hearing an engine "roaring." One witness reported that "engine surges continued for three or four cycles then changed to an oscillating sound" Subsequently, this witness went into his house, and upon returning to the outside, recalled that the "oscillating sounds were louder and sounded like he still had power on." One witness reported that at least one engine was running at high power and surging out of control. Another witness stated that "the engine would idle roughly, then accelerate extremely rapidly, then choke back down and idle roughly, then accelerate at full power again." One witness heard "the airplane engine revving up and idling down, not cutting out, and observed the airplane flying erratic, then enter a flat spin, and the right fuel tank was missing." Several witnesses at a local construction job site reported that "the end piece of a wing" was missing. Witnesses at a local practice football field heard "a loud buzzing noise that would cut in and out." The witness at a local football field, who had initially observed the airplane, reported that "the airplane was in a flat spin", and subsequently, other witnesses observed the airplane in a "vertical spin." Another witness reported the airplane was in a "flat spin" and the right fuel tank was missing. This witness described the airplane as "trying to come out of the spin." Subsequently, the airplane "went into a flat spin again." One witness, who was located in his back yard, heard an "unusual engine noise. The noise was repetitive with about a two second count between the loudest parts of the sound." This witness did not hear any stopping, starting, or stalling of the engines. This witness who observed the twin engine airplane at an estimated altitude of 4,000 feet, "spinning as though one wing was anchored and spinning about that point," stated that one of the wing tip fuel tanks and a portion of the wing outboard from the engine was missing. Further, this witness reported that when the airplane came out of the spin, the engine noise sounded normal. Another witness heard "the sound of a turboprop feathering it's blades on and off." This witness observed the airplane at about "1,500 feet in a flat spin, nose 5 degrees down" until the airplane went below the tree line. One witness, near the local golf course, reported that the airplane "appeared to be having engine trouble. The noise was very loud. The engine would idle roughly then accelerate extremely rapidly then choke back down and idle roughly then accelerate at full throttle again. This occurred at least a dozen times." One witness at the local golf course described the sound like "engines out of sink." This witness observed the airplane in a right hand flat spin with the nose in a slight down position (10-20 degrees). According to this witness, the airplane made about 6 turns before it went behind the tree line. Another witness observed the airplane approximately 600-800 feet above ground "spinning and tumbling end over end and falling at about 45 degrees" toward a creek. One witness observed the airplane "in a circular motion, counterclockwise" as it disappeared behind the tree line. PERSONNEL INFORMATION A review of the FAA records by the NTSB IIC revealed that the pilot was issued his most recent FAA third-class medical certificate on January 24, 2000, with the limitation that he wear corrective lenses while acting as a pilot. The pilot held a commercial pilot certificate with the ratings and limitations of airplane multiengine land and instrument, and private privileges for airplane single-engine land. According to the pilot's flight data supplied by the family, the pilot began flight training in September 1967, and in May 1969, he received his private pilot certificate with the airplane single-engine land rating. The instrument rating was added in December 1987, and the multiengine land rating was added in June 1991. The pilot obtained his commercial pilot certificate, in April 1992, with the airplane multiengine land and instrument ratings. In March 1994, the pilot began flying the MU-2 airplane. As of March 10, 2001, the pilot had accumulated 112.2 hours total flight time in the 12 months prior to the accident. Approximately every 90 days during the 4 years prior to the accident, the pilot attended recurrent training at the facilities of Flight Safety International, Houston, Texas. From February 5, 2001, to the date of the accident, the pilot had accumulated 26.2 hours total flight time in the accident airplane. The pilot's most recent Mitsubishi recurrent simulator training was accomplished in April 2001 at the facilities of Flight Safety International, Houston. This training consisted of 15 hours of ground school and 6 hours of flight simulator time. According to these training records, dated April 26, 2001, the pilot had accumulated 2,839.1 hours total flight time of which 1,108.0 hours were in the Mitsubishi airplane (555.9 hours in N16CG). Further, the training records indicated that the pilot had satisfactorily completed the training and testing requirements to act as pilot-in-command (PIC) of a Mitsubishi MU-2B-40 for CFR Part 91 operations. At the time of the accident, the pilot was returning from his latest recurrent training to his home base of operations. The Flight Safety personnel described the pilot as safety minded with good situational awareness, excellent checklist utilization, and professionalism in the piloting of the MU-2 airplane. They further stated that the pilot had good system and operational knowledge of the MU-2 airplane. Interviews with immediate family members and acquaintances disclosed no evidence of any activities that would have prevented the pilot from obtaining sufficient rest in the 72 hours before the accident. AIRCRAFT INFORMATION Aircraft Registration Review In July 1979, Mitsubishi MU-2B-40, serial number (SN) 418SA, was issued registration number N140MA (changed to N16CG on November 11, 1979). The FAA Standard Airworthiness Certificate was issued on November 9, 1979. At the time of the accident, the airplane was configured to carry seven passengers and one pilot. The airplane history indicates that on September 24, 1981, the airplane was involved in a wing-to-wing ground collision in which substantial damage was incurred to the right wing from the wing-to-fuselage attachments and fuselage bell frames to the right tip tank. The aircraft was repaired and returned to service. On January 4, 1991, the airplane was deregistered from the United States Civil Aircraft Registry for export to Caracas, Venezuela. Subsequently, the airplane was entered on the Venezuela registry as YV-11CP. On December 21, 1995, the airplane was deregistered from the Venezuelan Register, imported to the USA, and re-entered on the United States Civil Aircraft Registry. On February 23, 1996, the FAA airworthiness certificate was re-issued for the aircraft, and it was purchased by Aberg, LTD, Rockford, Illinois. In October 1997, the airplane was purchased by Anaconda Aviation Corporation, Boca Raton, Florida. The airplane was registered to the current owners on October 23, 1997. Maintenance Records Review The FAA aircraft records, insurance records, pilot's computer records, and available maintenance records were reviewed by the respective manufacturer's representatives and the NTSB IIC. Installed in each engine nacelle was a Honeywell (formerly Garrett) TPE331-10-511M engine. In 1989, the right engine, SN P37159, had accumulated 2,647.6 hours time since new (TSN), and the left engine, SN P36383C, had accumulated 864.8 hours TSN. According to engine service records, at the manufacturer's facility in Phoenix, Arizona, dated September 28, 1989, engine SN P-36383C received hot section and gearbox inspections at an engine time of 864.8 hours time since new (TSN) and 959 cycles since new (CSN) In December 1989, both engines were installed at zero time in the airplane by Intercontinental Jet, Inc., at Tulsa, Oklahoma. In June 2000, the 6 month, 12 month, 2 year, 100 and 500 hour inspections were performed at an accumulated airplane time of 2,439.1 hours. In February 2001, the left engine had accumulated 2,104.3 hours TSN (1,239.5 SMOH), and the right engine 3,887.1 hours TSN (1,239.5 SMOH). Both engines had the Hartzell propeller model HC-B4TN-5 with LT10282NSB-5.3R blades installed. Prior to March 2001, the left propeller hub was SN CDA3189, and the right propeller hub was SN EAA1209M1. In February 1996, the blades for the right propeller were shot peened. Airworthiness Directive (AD) 83-08-01 (Service Instructions No. 140A) for torque sequence of bolts was complied with in July 1999, and the propellers balanced. In February 2001, the left propeller and the right propeller were overhauled and re-installed on the respective engines. In March 2001, at a total aircraft time of 2,481.9 hours, the propellers were removed and reinstalled on the opposite engines such that EAA1209M1 was installed on the left engine and CDA3189 was installed on the right engine. Pilot Computer Records Review According to the pilot's computer records in part: In February 2001, "right prop blades [were] installed wrong causing [a] bad vibration." In March 2001, "reset blades in hubs (they were installed wrong) also weighed prop saddle weights found 1 weighed 1 ounce more than the other three. Repositioned blade pitch with bender to near zero error prop[eller] balanced with very little vibration. Switched left prop[eller] to right engine to verify vibration was in the right [propeller] and not in the right engine. The vibration moved to the left engine when the right prop[eller] was installed on the left engine. The right prop[eller] after installation on left engine was balanced .16 at 70% torque and .20 at 100% torque. The left prop[eller] after being installed on the right engine balanced to .08." Maintenance Personnel Interviews The president of Brit International Aviation, Inc., at Conroe, Texas, reported to the NTSB IIC that during a flight on February 5, 2001, the airplane had a substantial vibration, and the vibration subsided when the right engine was pulled back. During the flight, he observed the right rear engine nacelle was vibrating. Following the flight, a maintenance check of the propeller revealed that the right propeller was out of track. The pilot was informed of the discrepancy, and that the propeller shop wanted to look at the propeller. The pilot stated that the airplane had a vibration ever since he had purchased the airplane. The pilot flew the airplane back to Alamogordo, and about two weeks later, flew the airplane to the propeller shop for further evaluation/maintenance repair. The manager of Millennium Propeller (formerly Dallas Propeller), at Lancaster, Texas, reported to the propeller manufacturer's representative that both propellers were overhauled in February 2001. There had been a vibration problem on the left side for several years, and the vibration did not improve after the overhaul. In March 2001, the left propeller (CDA3189) was disassembled, checked, and one blade counterweight was modified to make all the blades the same weight. The propellers were dynamically balanced and checked. The work reduced approximately 75 percent of the vibration. The aircraft mechanic at Alamogordo reported to the aircraft manufacturer's representative that the airplane had a vibration on the right propeller following the overhaul in March 2001, at Lancaster. Two to three weeks later, the mechanic flew with the pilot to the propeller shop at Lancaster where both propellers were checked. During the disassembly of the right propeller, it was found that one blade was at the maximum allowable and the opposite blade was at the minimum allowable balance which, according to the mechanic, "gives an out of track condition and a low frequency vibration." Following the repair (dynamic balance of the hub, blades, and clamps) of the right propeller, it was installed on the left engine, and the left propeller was installed on the right engine. According to the pilot's mechanic, during the return flight to Alamogordo, there was a vibration. The president of Brit International Aviation, Inc., reported that he flew the airplane with the pilot on the morning of the accident, and the vibration was a lot better, but there was still a vibration. A change in power settings and speed did not seem to change the frequency of the vibration. The flight returned to Conroe where the airplane was refueled. When the pilot performed the checklist procedures for the pre-start and start items, everything checked "good" prior to the departure for Alamorgordo. Weight and Balance Weight and balance data for the airplane dated February 17, 2001, indicated the maximum gross weight of the airplane was 10,470 pounds with a basic empty weight (BEW) of 7,000.10 pounds. Prior to the flight, the airplane was refueled with the main fuel tanks and outer tanks topped and 60 gallons added per side to the tip tanks. According to the manufacturer's representative, the gross weight at the time of the accident was 10,391.7 pounds. The Jet A fuel truck and fuel farm fuel were checked for water contamination (ppm), flow rate, and specific gravity. The fuel was found to be within specifications. METEOROLOGICAL INFORMATION An NTSB Meteorologist derived the following information from his review of National Weather Service (NWS), National Centers for Environmental Prediction (NCEP), National Climatic Data Center (NCDC), Center Weather Service Unit (CWSU), Aviation Weather Center, Geostationary Environmental Satellite-8 (GOES-8), and air traffic control (ATC) data. A Surface Analysis chart prepared by the NWS NCEP indicated a ridge of high pressure over the southeastern United States. The chart showed a weak area of high pressure over the northern Gulf of Mexico. Finally, the charts indicated a weak trough of low pressure over northeastern Texas. At 1153, the NWS surface observations for Conroe indicated scattered clouds at 2,800 feet and 3,900 feet; visibility 10 statute miles; temperature 78 degrees Fahrenheit; dew point 64 degrees Fahrenheit; wind from 150 degrees at 10 knots; altimeter 30.04 inches of Mercury. A Center Weather Advisory (CWA) issued by Houston CWS, issued at 1250, stated in part: Developing area level 2-3 showers/isolated thunderstorms... 15 nautical miles wide...moving from 150 degrees at 5 knots. Tops generally FL200-250 locally to FL300. A review of the AFSS weather briefing for the pilot indicated that the flight route was dominated by a high pressure area with southwesterly flow. There were a couple of radar echoes south of the planned flight route; however, there were no thunderstorms or radar echoes for the remainder of the flight. A pilot report (PIREP) indicated tops to the west were 6,000 feet. There were no known in-flight weather advisories in effect for the time and location of t
The pilot's failure to maintain airplane control following a loss of right engine power, which resulted in impact with terrain in an uncontrolled descent. A contributing factor was the loss of right engine power as a result of the fatigue failure of the propeller shaft coupling.
Source: NTSB Aviation Accident Database
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