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On December 25, 2001, at 1503 Pacific standard time, a Cessna 172N, N738BC, lost engine power and ditched in the Pacific Ocean about 1/4-mile offshore from San Clemente, California. Security Aviation was operating the rental airplane under the provisions of 14 CFR Part 91. The private pilot sustained serious injuries, one passenger sustained fatal injuries, and one passenger is missing and presumed to be deceased. The airplane was destroyed. The personal cross-country flight departed McClellen/Palomar Field (CRQ), Carlsbad, California, at 1449, en route to Hawthorne (HHR), California. Visual meteorological conditions prevailed, and no flight plan had been filed. The primary wreckage was at 33 degrees 20.02 minutes north latitude and 117 degrees 30.26 minutes west longitude.
The Hawthorne based operator reported that the pilot scheduled the airplane for a flight on Tuesday, December 25, between the hours of 1000 and 1400. The pilot came in on Monday to get the keys.
The National Transportation Safety Board investigator-in-charge (IIC) interviewed the pilot. The pilot stated that he had flown this route frequently. He experienced no problems with the airplane or engine on the flight from Hawthorne to Palomar. He stayed on the ground at Palomar about 1 hour.
On the way to Palomar, the pilot stated that he had the right tank selected; however, when he set up for landing, he placed the fuel selector in the "BOTH" position. He left it there through landing and takeoff, and had not moved the fuel selector at the time of the accident.
The pilot stated that he completed a preflight inspection at both Hawthorne and Palomar. He visually checked the fuel level and drained fuel. He did engine run ups prior to both takeoffs, and noted no anomalies.
At Palomar, the pilot rotated about 65 knots, and thought that takeoff performance was similar to previous takeoffs with passengers on board.
The pilot said that he transitioned from climb to cruise at 4,500 feet. He had just established the airplane at an airspeed of 90 knots on an airway about 7 miles from the shoreline. He established 2,200 revolutions per minute (rpm) and leaned for cruise.
Immediately thereafter, the rpm dropped. The pilot stated that the engine speed dropped to 1,000 rpm. He did not recall any loud noises; he just noted the loss of engine rpm. He thought that he had leaned it too much so he richened the mixture. The engine did not respond, and he attempted to diagnose the problem. He adjusted the carburetor heat, but it had no effect. He leaned it a little bit, but that didn't work so he went full rich. The propeller began to slow and then stopped.
The pilot received flight following on all of his flights. Southern California Terminal Radar Approach Control (SCT) provided the airplane with flight following. He notified SCT that he was having engine problems and simultaneously made a turn towards the shore. He asked for vectors and SCT told him that Oceanside was at 110 degrees. He set up for an emergency landing at 60 to 65 knots, and then tried to restart the engine. The engine started for about 2 seconds; it went to a low rpm setting and then stopped. He started the engine again; it was on for about 2 seconds and then died. He told SCT that he wasn't going to make it to shore, and was going to make a water impact. He felt that the controllers were very helpful. They talked to him all the way until the airplane dropped off radar. He estimated that occurred about a minute prior to impact. He also stated that he left the master switch in the "ON" position.
The pilot landed the airplane about 300 yards offshore. The pilot and the passengers exited the airplane before it sank in 70 feet of water. Local authorities rescued the pilot and recovered one victim. Search and rescue units located the wreckage on Wednesday, December 26, and a recovery agent retrieved the wreckage onto a barge on December 27.
The operator reported that the pilot held a private pilot certificate with a rating for airplane single engine land. The pilot held a third-class medical certificate issued on March 9, 2000. It had no limitations or waivers. His total flight time was 133 hours. He logged 3.5 hours in the last 30 days. He had 14.6 hours in this make and model.
The airplane was a Cessna 172N, serial number 17269840. The operator reported that the airplane had a total airframe time of 6,168 hours. The tachometer read 6,169.3 when examined; the Hobbs hour meter read 2,819.2. It had an annual inspection on July 17, 2001. The last 100-hour inspection occurred on November 20, 2001, at a total time of 6,101 hours. A 50-hour inspection occurred on December 14, at a total time of 6,154.7.
The engine was a Textron Lycoming O-320-H2AD, serial number L-5692-76T. At the last 100-hour inspection, total time since a factory major overhaul was 1,569 hours, and time since major overhaul was 1,369 hours.
The operator's records showed that the previous flight occurred on Sunday, December 23. That flight lasted 0.7 hours, and the last pilot refueled the airplane with 3.56 gallons of fuel, which he said filled the tanks. The IIC interviewed the pilot, who reported that he did not observe any discrepancies with the airplane or engine.
The airplane was in contact with SCT.
WRECKAGE AND IMPACT INFORMATION
The airplane came to rest in 70 feet of water in an upright position.
The pilot stated that nearing the water the nose dropped a little, and he flared during the landing. The airplane touched down in a fairly level attitude, and the airspeed was about 40 knots when it hit the water. He did not brief the ditching, and neither he nor the male passenger in the front seat unlatched their doors prior to touchdown. Both occupants in the front seats had their lap belts and shoulders harnesses secured. The female passenger in the left rear seat only had a lab belt, and she had it secured. There were no injuries, and everyone exited the airplane under their own power. At first, the pilot couldn't open his door because of water pressure. He opened the window and was then able to open his door. The pilot and the rear seat passenger exited through the left door. The front seat passenger had no difficulties opening his door, and exited through it. They were on the top of the airplane for about a minute before it sank.
The swells were high, and the water was cold. The pilot said that his clothes were water soaked and heavy. He was wearing boots as well as a sweater/sweatshirt. His passengers were wearing casual clothes. With each swell, the distance increased between the pilot and his passengers. The female was closer to him, and he tried to grab her hand. He thought that she was having difficulties. He kept going under water, and when he resurfaced, he noted that he was farther away from both of them. He lost sight of them, and then tried to swim towards the shore.
The pilot flipped over onto his back and watched the way the clouds moved for reference. While in the water he tried to get his boots off, but he was unable to do so. He was struggling and exhausted, but fought hard to keep his head above water. He stayed determined that he was not going to give up.
An airplane flew overhead, and the pilot thought that it was a Baron. Some time later, he heard the sheriff's helicopter overhead. He heard them say something to him over a bullhorn. He was very tired and due to the condition he was in, he didn't know what they were saying. He looked to his left and saw a life vest. He swam over to it, put it on, and then passed out. The next thing he remembered was being in the hospital.
The pilot felt that his training helped him stay focused on getting the airplane down safely. Most of his training had been at the same flight school where he rented the airplane. Their instruction area was offshore; however, they did not carry flotation devices. He had practiced landing emergencies, but not water landings. He had read books about determining the wind and observing the swells, and had some discussions about how to do water landings during his training. He was confident that if the event had happened over land, everything would have been fine.
The pilot did not know if the school made flotation devices available to its renters; he had never heard anyone mention them. He did not consider getting flotation devices. From this experience, he would recommend flotation devices.
SCT directed a pilot in a Mooney toward the stricken airplane. The Mooney pilot saw the 172 before it hit the water. He said that it hit the water at 1503. He saw a big splash, and noted that the tail pointed out to sea. He orbited over the airplane between 1,000 and 2,000 feet. He saw movement on top of the wing, but could not tell haw many people were on board. He saw the nose go under water, and noticed splashing as people swam away. He thought that it was three people in a 15- by 15-foot triangle. He heard that a police helicopter was coming out, and provided vectors to it. He thought that it took about 15 to 20 minutes for the helicopter to arrive.
Personnel in the sheriff's helicopter noted a woman face down in the water; a big brown or black jacket was about 10 feet from her. They dropped an inflatable life ring to the pilot. Surfers also paddled from shore to assist.
The Pilot Operating Handbook for the 172N provided a procedure for ditching. It recommended an approach speed of 65 knots with flaps up or 60 knots with flaps at 10 degrees. It directed pilots to unlatch the doors, and touch down in a level attitude. For evacuation, it stated that it might be necessary to open the window and flood the cabin to equalize the pressure so that the doors could be opened.
The fuselage did not exhibit a loss of volume. The front seat tracks were intact, and the seats remained attached to the tracks. The front seat belts and shoulder harnesses remained attached to the airframe structure. Both the left and right front seat belts were unlatched; the left front shoulder harness remained attached to the left seat belt link. The rear seat remained attached to the airframe structure, and the seat back remained attached to the bottom. The rear lap belts remained attached, and both left and right belts were unlatched.
TESTS AND RESEARCH
The Federal Aviation Administration (FAA), Cessna, Textron Lycoming, and Teledyne Continental Motors (TCM), who manufactured the magnetos, were parties and to the investigation. All parties except TCM examined the wreckage on shore next to the recovery barge on December 28, 2001.
The IIC instructed the recovery agent to rinse the engine with fresh water, drain water from the engine and cylinders, and apply a lubricant inside the cylinders and magnetos as soon as he recovered the airplane onto the barge.
A portion of the front windshield was broken out. The front left and right metal skin on the lower fuselage exhibited some deformation.
The airframe manufacturer's representative determined that the flap actuator was in the full up position. The cockpit flap indicator was in the 0 degree position, and the flap handle was bent down and to the right. The elevator trim measured approximately 1 inch, and he determined that this equated to approximately 10 degrees tab down. Control continuity was established from the left aileron, right aileron bellcrank, elevator bellcrank, elevator trim, and rudder to their respective cockpit controls. The right aileron push/pull rod separated; the rod was bent and the fracture surface was cupped and grainy.
The cockpit throttle was in the closed position; the mixture was full rich. The carburetor heat control was out about 3/4 inch. The primer was in and locked.
The fuel selector valve was slightly right of the both position. The fuel selector moved freely between its detents. Investigators disconnected the fuel line to the carburetor. They drained approximately 1 gallon of a murky blue fluid from the line before the fluid primarily turned to a milky color. They drained about 30 gallons of fluid from the wings; about half of the fluid was blue, and the rest was a milky color. With the fuel selector positioned to BOTH, investigators blew through the disconnected line and heard air enter the fuel tanks in both wings. They did not hear any air leaks coming from any of the connecting lines or fittings.
The propeller did not have any bending, and the spinner was not crushed.
Investigators removed the top spark plugs and did not observe any mechanical damage to them. The Lycoming representative inspected the interior of the cylinders with a borescope. He said that he did not observe any mechanical deformation on the valves or cylinder heads, and observed normal combustion deposits on the pistons. Investigators manually rotated the propeller and obtained thumb compression on all cylinders. They observed similar valve lift on all cylinders. The valve train moved freely, and the vacuum pump drive gear rotated.
The magneto was a Teledyne Continental Motors D-3000 series unit, serial number 1290002 GR. During engine rotation, investigators did not hear a strong click from the impulse coupling, and they could not obtain spark from the ignition leads. While looking into the magneto vent holes, the timing marks seemed to align in the area of the TC (top center) marks on the starter ring gear. The engine data plate indicated that the timing should be set to 25° spark advance. They removed the magnetos and observed that the magneto drive gear on the crankshaft rotated freely. They rotated the magnetos manually and noted that they rotated freely.
The IIC took the magnetos and ignition harness to an accessory shop for inspection. The repairman connected the magnetos and ignition harness to a test stand, and the magnetos did not fire. The repairman disconnected the harness from the magnetos and noted that the impulse coupling did not snap briskly when he manually rotated the magneto.
The repairman cleaned the magnetos and reconnected them to the test stand using a test harness. He observed flash crossover from the coil to ground. He separated the distributor block from the magneto and cleaned the unit. He removed the impulse coupling to set the timing and found a broken coupling spring. He felt that the broken spring would greatly affect the engine's timing; it would drastically retard it.
The repairman reassembled the magnetos without the impulse coupling, and reconnected them to the test stand. One magneto fired continuously on all four leads. The other magneto fired intermittently on three leads (the repairman pointed out that the fourth lead appeared to be defective and some corrosion remained on the contacts).
Materials Laboratory Report
The IIC submitted the magneto the Safety Board's Materials Laboratory. A specialist prepared a factual report, which is part of the public docket. Pertinent parts of the report follow.
The received components included a blue data plate that identified the magneto as a Teledyne Continental factory rebuilt unit. It was a D4RN-3000, part number BL-682555-14. The data plate was also marked with the letter "A" in the lower right quadrant.
The exterior surfaces of the housing were heavily corroded, as was the mounting area for the impulse coupling. The interior components and surface of the magneto showed areas of light corrosion with some deposits. The impulse coupling components were separate from the housing and exhibited some surface corrosion on the flyweight assembly and the spiral spring.
Initial examination found that the flat spiral spring of the coupling had fractured into three pieces. The outer two pieces of the spring were inside the coupling body. The innermost end of the spring separated from coupling. Referencing the D-3000 System Support Manual, the spring was wound in the clockwise direction, and was identified as part number 10-51324.
The spring fractured at two locations near the outer end. The specialist arbitrarily labeled the fractures "A" and "B" for identification. Fracture "B" was approximately 180 degrees of rotation from the outer spring end and fracture "A" was about 360 degrees from the outer end. The surfaces of both fractures showed light to moderate corrosion and red rust deposits. Fracture "A" was generally transverse across the width of the spring. He observed little or no plastic deformation adjacent to the fracture.
Scanning electron microscope examinations of the fracture surfaces, after acetone and replica tape cleaning, revealed three fracture planes with differing fracture features. A darker rippled band oriented generally perpendicular to the spring was adjacent to the inner surface and accounted for most of the fracture surface. A 45° slant fracture plane connected the rippled fracture area to the outer surface of the spring, and a small flat region occupied one end of the fracture. Both the rippled and flat end fracture regions contained mixed intergranular and transgranular features. Both regions also showed micro features of corrosion on the surfaces. These fracture areas appear consistent with stress corrosion cracking. The slant fracture region contained ductile dimples consistent with overstress shear lip formation and no indications of corrosion.
Fracture "B" formed a shallow "V" across the width of the spring. The fracture also contained multiple fractographic regions. These included a severely corroded region near one edge where corrosion completely obliterated the original fracture features. A second region containing mixed intergranular and transgranular separation (similar to that seen on fracture "A") occupied about 1/3 of the fracture adjacent to the corroded area. The remainder of the fracture displayed ductile dimples consistent with overstress separation. A small amount of bulk plastic deformation was visible adjacent to the overstress region at higher magnifications.
As a comparison to fractures "A" and "B", an overstress fracture was produced in a section of spring by reversed bending of a spring section. Examinations of the induced fracture face revealed 100 percent ductile dimples on the fracture surface and a small amount of plastic deformation adjacent to the fracture.
Optical and SEM examinations of the spring pieces uncovered many areas of corrosion and corrosion pitting on the spring surfaces. The corrosion pitting was particularly evident on the edges of the springs, but other corrosion areas were visible on the flat faces of the spring.
The specialist prepared a metallographic section of the longitudinal face of the spring adjacent to fracture "B". The selected area of the spring contained corrosion and pitting along one edge near the fracture and the specimen. After grinding and polishing, the section intersected corrosion pits in the edge. These pits measured 0.001 to 0.002 inch deep and 0.002 to 0.007 inch wide. As seen on the metallographic section, the fracture path displayed some intergranular intrusions into the adjacent material, but no significant amount of branching.
When etched with 2 percent Nital, the revealed microstructure was uniformly fine tempered martensite with no indications of segregation, decarburization, or a significant number of inclusions. The specialist noted a thin worked layer along one edge of the spring.
Engineering drawing 10-51324 requires the spring to be manufactured from AISI 1095 steel strip, 0.250 inch wide by 0.031 inch thick, heat treated to a hardness range of 30N67.5 to 71. Energy dispersive x-ray spectra acquired during SEM examinations were consistent with 1095 steel. Dimensional and hardness measurements made at representative locations on the spring were within the drawings requirements.
Inspections found that the flyweights were impression stamped "K062" and also "S" indicating that snap rings were installed on the flyweight axles in accordance with Service Bulletin 645. The specialist noted no polishing or wear of the flyweight heels, and the flyweight to stop pin clearances met the requirements of the Support Manual. He noted no damage or wear on the trip dogs or drive lugs of the coupling housing.
D-3000 Series Magneto
The D-3000 series magneto features two electrically independent ignition circuits in a single magnesium alloy housing. Magnetos generate and distribute high voltage, which is distributed to the spark plugs through a radio-shielded harness. This magneto incorporates an impulse coupling. The impulse coupling helps generate a better spark for starting, retards the spark during engine cranking, and acts as a drive coupling for the magneto.
A single four-pole magnet that rotates at engine speed has a cam connected to its contact assembly end. Polarity changes as the magnet turns, which produces flux reversals in the magneto coil core. The number of flux reversals during one complete revolution is four. With the contact assembly points closed, the flux reversals cause the primary winding in the magneto coil to generate a current. The flow of current through the coil produces a magnetic field around the coil. When the cam pushes the contact points assembly open, current ceases to flow. The magnetic field around the primary winding collapses, which induces a high voltage in the secondary winding of the coil. A capacitor, which is connected in parallel across the contacts to ground, suppresses arcing across the opening contacts. This provides a low impedance path to ground for the continuing induced primary voltage.
A carbon brush conducts the high voltage induced in the coil secondary winding to the distributor gear electrode. This ionizes the gap to one of the terminals in the distributor block. The energy jumps the gap, is conducted through the contact springs, and then flows through a lead to a spark plug.
A representative from TCM indicated to the IIC that a broken spring could retard the timing. It could retard it to TDC or after.
History of the Magnetos on this Airplane
The IIC reviewed the engine's logbooks. Maintenance technicians installed factory rebuilt magnetos on October 27, 2000, at a total airframe time of 5,404 hours. Airworthiness Directive (AD) 96-12-07 called for a repetitive inspection of the magnetos every 500 hours. Technicians replaced both point sets, both condensers, timed the magnetos internally and to the engine, and performed the AD at 5,567 hours on Jan 19, 2001. They replaced the right side points, timed the engine to 25° before top dead center (BTDC), and completed the inspection again at 5,702 hours on April 10, 2001. The next inspection was due at 6,202 hours; current time was 6,169 hours.
The IIC released the wreckage to the owner's representative on December 28, 2001.