SAN ANGELO, TX, USA
N201QK
Mooney M20J
The airplane was en route cruising at 9,500 feet msl approximately 12 miles east of its destination, when the pilot reported a loss of engine power. At 2,200 feet msl, the pilot reported that he would not make the runway. During the off airport landing, the airplane struck a tree, the right wing separated from the airframe, the airplane descended into the water, and came to rest inverted in water 7 feet deep. Examination of the wreckage revealed engine oil in the single drive dual magneto and one of the rear case bearing retaining plate screws was broken. The magneto was removed from the engine and disassembled. A metallurgist found that screw failure was a result of delayed fracture from hydrogen embrittlement and the 'hydrogen was most likely picked up during the cadmium plating for corrosion resistance at original manufacture of the screw.' The magneto had accumulated 775.58 hours since last overhaul in 1993. At the last annual inspection, November 1998, the magneto points and timing were checked. Time since that annual inspection was 3.27 hours. Service Bulletin (SB) 643 dated 02/08/94 recommended magnetos be 'overhauled or replaced at the expiration of four years without regard to the accumulated operating hours since new or last overhaul.' No evidence was found that the SB had been accomplished; however, under 14 CFR Part 91 operations, compliance with the SB is not required.
On November 16, 1998, at 1845 central standard time, a Mooney M20J airplane, N201QK, impacted trees and water, during a forced landing following a loss of engine power near San Angelo, Texas. The airplane was owned and operated by a private individual under 14 Code of Federal Regulations (CFR) Part 91. The private pilot received minor injuries and the airplane sustained substantial damage. Visual meteorological conditions prevailed for the personal dark night cross country flight which departed Levelland, Texas, at approximately 1730, with a planned destination of San Antonio, Texas. The pilot received VFR flight following from the Midland Air Traffic Control facility. During personal telephone interviews, conducted by the investigator-in-charge (IIC), with local authorities, air traffic control personnel, the FAA inspector, and the pilot, the following information was revealed. The airplane was en route cruising at 9,500 feet msl approximately 12 miles east of San Angelo at 1841, when the pilot reported a loss of engine power. The pilot requested and received vectors to the San Angelo Mathis Field Airport (elevation 1916 feet). The pilot was given a heading of 280 degrees, an altimeter setting of 29.90, and cleared for the straight in approach to runway 27. A helicopter pilot kept the Mooney in sight as the flight tracked toward the runway. The Mooney was 8 miles east of the airport at 5,100 feet msl when the runway 27 lights were turned to full bright. Subsequently, the pilot reported the airport in sight and continued toward the runway. When the airplane was at 2,200 feet msl, the pilot reported that he would not make the runway. During the off airport landing, the airplane struck a tree, separating a wing from the airframe. The airplane descended into the tributary waters of Lake Nasworthy approximately 3/4 mile short of runway 27. The airplane came to rest inverted where the water depth was 7 feet. The pilot released his restraint system, exited the airplane through the cockpit door, and was rescued by boat. A review of the pilot logbook and the FAA records revealed that the private pilot held airplane single engine land and instrument ratings. He was issued a third class medical certificate on March 6, 1997. The pilot first flew the Mooney M20J on March 14, 1997. On the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) the pilot reported a total flight time of 385 hours of which 310 hours were in N201QK. The FAA inspector responding to the site reported that the airplane traveled approximately 100 feet at tree top level before descending into the water. The right aileron and right outboard wing tip were found lodged in a tree approximately 30 feet from the water. Upon removal of the aircraft from the water, the FAA inspector found that the right wing was separated near the inboard end of the aileron. The tachometer reading was 3,931.65 hours. Mixture, throttle, and propeller controls were full forward at the cockpit quadrant. The fuel selector was on the left tank and approximately 18 gallons of fuel was drained from the left fuel tank. Fuel was found in the engine supply line. The left fuel tank screen was clean. Flight control continuity was confirmed. The gear and flaps were in the retracted position. The pilot reported to the FAA inspector that following the last annual inspection, he noticed a change in the normal operating cylinder head temperature and exhaust gas temperature. He further stated that at 9,500 feet msl the tachometer was indicting 2,500 rpm and "just before the engine failed the engine was running smoothly then began to pop or backfire." The tachometer then indicated 1,200 to 1,500 rpm. Prior to the departure from Levelland, there were no discrepancies noted by the pilot. A review of the maintenance records by the FAA inspector, a NTSB investigator, and the IIC, revealed that the engine, a Lycoming IO-360-A1B6D, S/N L-22279-51A, was installed on the airplane on December 16, 1993, at a tachometer time 3,156.07, following a major overhaul by Lycoming. The major overhaul maintenance entry on November 5, 1993, stated that "All accessories as part of the type certificate are either new or newly overhauled." At the time of the accident, the total time on the engine was 4,836.98 hours with 775.58 hours since the major overhaul. On October 8, 1997, at tachometer time 3,745.4 hours, Airworthiness Directive (AD) 78-09-07 was complied with on the Bendix D4LN-3000 dual magneto, S/N 3050584, by inspection of the impulse coupling. A maintenance entry related to the magneto, dated November 13, 1998, at the last annual inspection at tachometer 3,928.38, stated "checked mag[neto] points and mag[neto] timing." Time in service since that annual inspection was 3.27 hours. Teledyne Continental (formerly Bendix) recommends in Service Bulletin SB643, issued February 8, 1994, that magnetos "must be overhauled or replaced at the expiration of four years without regard to the accumulated operating hours since new or last overhaul." There was no evidence found that the SB had been accomplished; however, under 14 Code of Federal Regulations Part 91 operations, compliance with the Service Bulletin is not required. A mechanic at the recovery facility reported that when the magneto's distributor cap was removed during engine preservation (authorized by the IIC), approximately 12 ounces of engine oil drained from the magneto. During an NTSB investigator's examination of the engine, the magneto was removed from the engine. The head and about 2/3rds of the shank of one of the four screws (P/N 10-382789) that retain the bearing, fell out of the rear case of the magneto. When the propeller was hand rotated with the magneto distributor cap removed, the magneto points were not opening. The plastic cam followers of both contact assemblies (P/N 10-382585) were melted where they rested against the cam. The point gaps were reset, and the magneto was re-installed on the engine. The engine was then started and run for approximately 20 minutes. Operation of the left side of the dual magneto was intermittent. The magneto was removed from the engine and disassembled. The lower 1/3 of the shank of the broken screw was found still screwed into the bearing retaining plate (P/N 10-382787). The plate was wet with oil in the vicinity of the broken screw. The bearing retaining screws and the plate from the magneto were forwarded to the NTSB Materials Laboratory for further examination. The NTSB Metallurgist found that all 4 screws had been threaded into the retainer, about 5 threads. The fracture location of the broken screw was generally in the thread root above the last thread in the retainer plate. Micro-hardness measurements were performed on the tail section of the fractured screw and on longitudinal sections through the other three screws. The hardness data for the fracture screw indicated a numerical average (HRC) of 45.4. HRC 45 equates to an approximate ultimate tensile strength of 211,000 psi. According to the metallurgist, socket head cap screws are typically manufactured from carbon steels heat treated to 160,000 psi minimum (HRC 36). See the enclosed metallurgical report for additional details. The airplane was released to the owner.
The total loss of engine power due to the magneto failure resulting from oil contamination when the bearing plate retainer screw fractured due to improper manufacturing. Factors were the lack of suitable terrain for the forced landing, and the dark night conditions.
Source: NTSB Aviation Accident Database
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