1.1 History of the Flight

On December 18, 2006, at 1554 Pacific standard time, a Beech D95A (Travel Air), N144PG, descended uncontrolled into an open wastewater treatment tank at the South County Regional Wastewater Authority treatment facility in Gilroy, California. The airplane was destroyed. The certified flight instructor (CFI), the private pilot undergoing instruction (PUI), and private certificated passenger sustained fatal injuries. The airplane was owned and operated by California In Nice Inc., doing business as Nice Air, as a local instructional flight under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed and no flight plan was filed. The flight departed Reid-Hillview Airport of Santa Clara County, San Jose, California at 1330.

The local authorities received a call of a downed airplane at 1555. The wreckage was located by plant personnel at 1707 and reported to the local police.

According to the operator, the purpose of the flight was for the CFI to teach the students multi-engine operations. At some point during the flight, the instructor would have landed at a local airport for the students to switch positions (one in front left seat and one in back seat). The airplane was scheduled to return to Reid-Hillview by 1700.

1.1.1 Witness Information

A witness was flying in his airplane at an altitude of 3,500 feet on a heading of 320 degrees when he observed a multi-engine airplane in a spin and descending to the ground. He estimated the airplane was at an altitude of 2,500 to 3,000 feet and approximately 1 mile from his position when he first observed it. The airplane continued its vertical descent into an open sewage tank. He did not observe any other aircraft in the area at the time and he did not see any smoke emitting from the airplane. After the airplane disappeared into the open tank, he reported the incident to air traffic control. The controller requested that the pilot fly lower and report his observations to ATC. He descended to 1,000 feet and could not detect any wreckage or damage to the facility. He continued to circle the site for approximately 30 minutes, and then he notified air traffic control that he was going to depart the area.

An additional witness, who was a CFI at Nice Air, reported that she and her flight student were in a Cessna 152. They were flying over Gilroy at an altitude of approximately 4,000 feet on a north heading when she saw the multi-engine airplane spinning. The witness believed that the airplane was spinning to the left but was not certain. After 5 seconds, the airplane descended into what appeared to be a factory.

The witness further stated that on December 16, the accident CFI had flown with the same students on a similar mission. They departed Reid-Hillview about 1330 and the first student performed takeoffs and landings. Then, they flew to Hollister Municipal Airport, Hollister, California, where the students switched positions. The CFI and student then practiced maneuvers in the practice area, prior to returning to Reid-Hillview. The witness overheard the CFI speaking with his students the day prior to the accident and they indicated that the flight itinerary for December 18 would be the same as December 16. The witness also indicated that she spoke with the PUI and he stated that he would be practicing Vmc demonstrations as well as takeoffs and landings.

1.1.2 Radar Information

A Safety Board air traffic control specialist reviewed the radar data pertinent for the flight. Radar data was obtained from the FAA's Northern California Terminal Radar Approach Control (NCT) located in Sacramento, California. The radar data used for this report came from an ASR-9 radar site located near Moffett Field, California.

NCT supplied a video file containing a replay of the accident airplane's flight, beginning shortly after departure from San Jose. The airplane was initially radar identified, but subsequently terminated radar service, changing to transponder code 1200. Review of the data showed that the identified track was isolated from all but one unidentified aircraft near the point where radar contact was lost. The second aircraft passed within approximately 1/2-mile of the presumed accident airplane's track, in the opposite direction and at the same altitude. The track showed the presumed accident airplane's departure from San Jose, in a general south-southeast direction. The track proceeded into one turn to the right, and then continued in a south-southeast direction. At the last radar target, the airplane was established at 4,400 feet mean sea level.

1.2 Other Damage

The South County Regional Wastewater Authority plant sustained damage to the hand railing that surrounded the tank impact area. In addition, several cosmetic scratch marks were noted on the inner concrete walls and tank partition.

1.3 Personnel Information

1.3.1 Certified Flight Instructor

The CFI held a certified flight instructor certificate and was authorized to conduct single-engine, multi-engine, and instrument instruction. He held a first class medical that was issued in July of 2006. It contained no limitations or waivers.

The operator reported that the CFI's total time was about 2,000 hours, with approximately 200 hours of multi-engine time. Of the 2,000 hours, about 1,800 hours were accrued while giving instruction, and 150 hours of the 200 hours of multi-engine time were accrued while giving multi-engine instruction.

1.3.2 Pilot Undergoing Instruction

The PUI held a private pilot certificated and with an instrument rating. He held a second class medical that was issued in March of 2006. It contained the limitation that he must wear corrective lenses.

The PUI obtained his private pilot certificate on June 14, 2006, and his instrument rating on December 7, 2006. The pilot was undergoing instruction to obtain a multi-engine rating and had accrued 2.7 hours of total multi-engine flight hours, all within the accident airplane make and model and with the accident CFI.

1.3.3 Passenger

The passenger was also obtaining instruction for a multi-engine rating. He held a private pilot certificate. His first class medical certificate was issued in September of 2006 and contained no limitations or waivers. Records obtained from the operator showed that the passenger had accrued approximately 8.3 hours in multi-engine training in the accident airplane make and model, all with the accident CFI.

1.4 Airplane Information

The airplane was a Beech D95A (Travelair). Two Textron Lycoming IO-360-B1B engines powered the airplane and were equipped with Hartzell HC-C2YK-2CUF propellers. The last annual inspection was completed on June 10, 2006, at an airframe total time of 5,834.9 hours and a tachometer time of 209 hours. On November 30, 2006, the airplane underwent a 100-hour inspection at a tachometer time of 309 hours. The date of the accident, the airplane was dispatched with a tachometer time of 324.3 hours and a Hobbs meter time of 484.9 hours. No airframe total time was noted on the dispatch log.

According to the Beech Model D95A Owner's Manual, the best single-engine rate-of-climb speed with the landing gear and flaps retracted is 108 miles per hour (mph) (94 knots). The minimum control speed is 80 mph (69.5 knots). The power on stall speed with the landing gear and flaps retracted in level flight is 61 mph (53 knots). The power off stall speed in the same configuration is 85 mph (73.5 knots).

Information obtained from the operator and the airplane manufacturer indicated that the airplane weight (estimated) at the time of the accident was 3,692 pounds, with a center of gravity (CG) of 81.5 inches. The CG range of the airplane at 3,600 pounds is between 75 and 86 inches aft of the datum. The maximum weight of the airplane is 4,200 pounds.

1.5 Meteorological Information

An aviation automated routine weather report (METAR) was issued for Watsonville Municipal Airport, Watsonville, California, at 1554. The airport is located about 11 nautical miles west-southwest from the accident site. The following conditions were reported: sky condition, clear; visibility, 10 statute miles; altimeter, 30.23 inches of Mercury; temperature, 50 degrees Fahrenheit; dew point, 27 degrees Fahrenheit; wind from 240 degrees at 3 knots.

1.6 Wreckage and Impact Information

The National Transportation Safety Board investigator and inspectors from the San Jose Flight Standards District Office responded to the accident site. The site was at 36 degrees 58.991 minutes North latitude by 121 degrees 31.870 minutes West longitude. The elevation was approximately 150 feet mean sea level.

The plant consisted of varying levels of above-grade (raised) treatment tanks, which were surrounded by walkways lined with handrails. According to the plant project manager, the wreckage came to rest in a post anoxic tank located in the middle tank of a series of tanks. The footing foundation thickness was 20 inches and the perimeter wall thickness was 16 inches. The nitrification of toxic ammonia-nitrogen occurred in the oxidation ditch, which was directly north and south of the post-anoxic tank. Denitrification followed in the subject post-anoxic basin, where nitrates were biologically converted to nitrogen gas and released freely to the atmosphere. A reareation basin located directly next to the post anoxic tank, diffused oxygen into the wastewater, which was oxygen deficient following the nitrogen removal process. Wastewater was then directed to the secondary clarifiers, located approximately 100 feet from the post anoxic tank.

The center treatment tanks and walkways (which included the reaeration basin) were a total of about 260 feet in length and 37 feet wide. The post anoxic tank was 160 feet in length and 40 feet wide, with an overall basin depth of 18 feet (water depth of 13.2 feet). However, within the tank, concrete partitions separated the main area into smaller sections, connected through a common channel that ran through the center floor. The damage to the plant was confined to the immediate impact area and surrounding handrails.

The tank area that confined the main wreckage was about 18 feet long by 19 feet wide. The empennage section was broken from the main structure and lying next to the wreckage. The 5-foot section of handrail immediately aft of the main wreckage and to the right of where the empennage came to rest was torn away and located in the tank. A 10-inch wide by 14-foot high wing wall that ran perpendicular to the concrete partition, extended outward from the partition wall about 3 feet, in an area just aft of the fuselage. The top surface of this wall contained scratch marks and the concrete outboard edge was damaged. On the left horizontal stabilizer, a 10-inch wide rectangular-shaped impact was noted on the leading edge and the skin was pulled aft to the rivet line. A left wingtip and outboard 4 feet was lodged in a damaged handrail; the remainder of the left wing, stayed connected to the fuselage. The left engine had separated from the firewall and was twisted inboard. The right wing and right engine were found in an adjoining tank, separated by a concrete partition from the tank with the main wreckage. The wing separated at the fuselage structure. The propellers remained attached to their respective engines.

1.7 Medical and Pathological Information

The Santa Clara County Medical Examiner-Coroner completed autopsies on the occupants of the airplane. The FAA Civil Bioaeronautical Research Laboratory completed toxicological testing on specimens of the CFI and PUI. The tests were negative for carbon monoxide, cyanide, and tested drugs. The CFI's test was negative for volatiles. The PUI's volatiles test was positive for 12 (mg/dL, mg/hg) ethanol, which was detected in muscle, but not in his liver. Putrefaction was noted on the toxicology report.

1.8 Tests and Research

On December 21 and 22, 2006, the National Transportation Safety Board investigator, two inspectors from the San Jose Flight Standards District Office (FSDO) and technical investigators from Raytheon Aircraft Company, Hartzell Propeller Incorporated, and Textron Lycoming examined the wreckage at Plain Parts, Pleasant Grove, California.

1.8.1 Airframe

Impact forces destroyed the airframe. The main fuselage structure was vertically collapsed downward and to the left. During the collision sequence, the right wing separated from the fuselage structure at the root. The empennage section also separated and was found within several feet of the main wreckage. All control surfaces and balance weights were accounted for.

The left wing remained attached to the main fuselage structure and was separated 20 inches outboard of the wing root. The flap and aileron separated. The left main gear remained attached to the wing and was stowed. The auxiliary fuel cap remained attached to the fuel tank and the o-ring was pliable. The left engine was displaced 90 degrees inboard to the fuselage. Impact forces destroyed the engine cowling. The left flap actuator measured 1.5 inches, which according to the airframe representative, was consistent with the flaps in the retracted position.

The right wing was separated from the fuselage. The flap had separated and the aileron remained attached by its outboard hinge. The aileron separated from the bellcrank pushrod, but the aileron flight control cable remained attached to the bellcrank. The wing tip was attached. The flap actuator measured 1.5 inches.

The fuel selector handles were in the aux position at the cockpit fuel selector, as well as the fuel selector valves. All fuel tanks were breached.

The empennage control surfaces remained attached, excluding the left outboard elevator and right elevator counterweight. The missing portions of elevator were later identified within the recovered wreckage from the tank. The left stabilizer sustained leading edge impact damage 28 inches from the stabilizer root. A 10-inch wide section was torn up and aft to the main spar. The stabilizer was bent forward 28 inches from the stabilizer root. Approximately 43 inches of the left elevator remained attached. The outer portion was separated at the middle elevator hinge. The elevator control horn was displaced 3 inches aft into the tail cone. The elevator trim tab remained attached to the elevator. The actuator measured 1 3/8 inches or 5 degrees tab down. The elevator push rod separated from the actuator.

The right elevator remained attached by the middle and outboard hinge and the trim tab pushrod. The elevator counterweight separated. The trim actuator measured 1 7/8 inches or 25 degrees tab down.

The rudder was attached to the vertical stabilizer at the hinge points and moved freely at both hinge points. The rudder moved freely to both stops. The rudder flight control cables were manipulated 3 feet forward of the separated empennage. The rudder control surface responded appropriately. The rudder trim actuator measured 1.6 inches or 4 degrees tab left. According to the airframe manufacturer, all of the trim cable separations exhibited stress overload.

The left and right fuel selector valves were unobstructed and attached to the wing. The strainer screens were unobstructed.

The fuselage was turned onto its back and further visual documentation of the control cables was obtained, as well as access to the rudder control system. The rudder pedals were both separated on the left side. The right rudder pedal on the right side was missing; the left pedal was fractured. The rudder pedal bellcrank was intact, as well as the pushrods and cables that connected to it.

The front seats were removed and the seat tracks were documented. According to the airplane manufacturer, there was no evidence of hole elongation or seat slippage.

1.8.2 Left Engine

The left engine, serial number L8846-51A, was examined. The accessories were removed which included the fuel pump, magnetos, propeller governor, fuel injection servo, vacuum pump, and thermostatic bypass valve. The left engine crankshaft was rotated via the propeller. Thumb compression was obtained on all cylinders, and the valves produced similar movement. Investigators noted that the thumb compression on cylinder number 2 was weaker than the other cylinders. When the cylinder was borescoped, it was noted that sludge had accumulated around the intake valve seat. The magnetos were coated with sludge and attempts to spark them were unsuccessful. Fuel was present in the flow divider, fuel pump, and fuel control servo. The flow divider was examined, the gaskets were intact, and no perforations or holes were found. Disassembly and examination of the engine revealed no evidence of abnormal wear or failure of internal components.

1.8.3 Left Propeller

The left propeller, hub serial number AU8876B, was removed for further examination. The blade model was FC7666C-4 and blade L1 was serial number J07017, blade L2 was serial number J07014. The L1 blade was at extreme low pitch and the blade counterweight had contacted the hub. Investigators were unable to cycle the propeller. The air valve retained its charge. The cylinder was gouged by the L1 counterweight and was cut for disassembly. The low pitch stop contained an impression mark. The feather stop did not contain any marks. The start lock was intact and operable. The L1 preload plate had light burnishing from normal operation from opposing knob. There was slight deformation from knob impact. The L2 preload plate contained a gouge in the area of opposing knob contact at low pitch due to an undetermined cause. The L1 pitch change knob fractured and contained a gouge in the knob side that matched with the position of the preload plate.

Blade L1 was bent aft 70 degrees. Blade L2 was intact and unremarkable. There was no evidence of leading edge gouging or chordwise striations. The blades were both located at the low pitch stop. The manufacturer's representative stated that the blade damage was consistent with a low or no power condition.

1.8.4 Right Engine

The right engine, serial number L-6537-51A, was examined. The spark plugs were removed and investigators noted that excluding the numbers 1 and 4 spark plugs from the top, all spark plugs contained sludge and water. The cylinders also were filled with a similar material. The electrode wear was similar. The fuel injectors were removed and all of the screens appeared clear. The number 3 injector cover could not be removed so the entire screen was not visually examined. The oil screen was removed from the sump and it was free of contaminants. The fuel injection servo screen was removed and no blockage was evident. The servo throttle and mixture control arms were in place and secured to the fuel injection servo. The propeller governor turned and was coated with oil. The control arm moved by manual activation. The magnetos were also coated with sludge and attempts to spark them were unsuccessful. Fuel was present in the flow divider, fuel pump, and fuel control servo. The flow divider was examined, the gaskets were intact, and no perforations or holes were found. The crankshaft was rotated and thumb compression was obtained on all cylinders. The valves produced similar movement. The examination of the engine revealed no pre-impact mechanical anomalies.

1.8.5 Right Propeller

The right propeller, hub serial number AU8873B, was removed from the engine for further examination. The blade model was FC7666C-4 and the R1 blade was serial number J06908, the R2 blade was J06910. The spinner did not have any frontal crushing. The propeller cycling was not attempted. The air valve retained its charge. The spring guide was worn and fractured. The spring was intact. The low pitch stop contained an impression mark. The feather stop did not. The start lock was intact and operable. According to the manufacturer's representative, the hub assembly sustained internal damage due to inward movement of the blades and preload plates. The R1 preload plate contained scuffing at the low-lower pitch from the fork bumper. The R2 preload plate had light scuffing that according to the manufacturer was due to contact from the opposing pitch change knob (normal wear). The R1 pitch change knob was intact. The R2 pitch change knob was bent and cracked at the base.

Blade R1 outer 1/3 was curled forward approximately 180 degrees and twisted toward high pitch. Rotational scoring was evident on the flat side with leading edge damage on the outer 4 inches of blade. The R2 blade was bent aft 90 degrees at the 2/3 radius. The outer 6 inches of the blade tip was curled forward greater than 90 degrees. An abrasion was present on the tip and leading edge outer 3 inches of the tip. Rotational scoring was present on the flat side. According to the propeller manufacturer, the blade damage was consistent with a mid to high power range at the time of impact.

1.9 Additional Information

1.9.1 Vmc Demonstration

According to the Airplane Flying Handbook (FAA-H-8083-3A), Vmc is the minimum control speed with the critical engine inoperative. To perform a Vmc demonstration maneuver, the handbook indicates, in part, to reduce power on the left engine to idle, as the right engine power is advanced to a takeoff setting. As the airplane slows, a bank toward the operating engine is established and rudder pressure is used to maintain directional control. According to the handbook, "The moment the pilot first recognizes the uncontrollable yaw, or experiences any symptom associated with a stall, the operating engine throttle should be sufficiently retarded to stop the yaw as the pitch attitude is decreased."

1.9.2 Performance Study

A performance engineer utilized winds aloft, radar, and weight and balance data to calculate performance data using a Safety Board computer program. The calculations showed that the target was generally established at 4,200 feet msl, with slight variations between 4,100 and 4,400 feet msl, in a south-southeasterly direction. The calibrated airspeed was 134 knots, which continually decreased to 86 knots from 1548:00 to 1549:35, and the target showed a rate of descent of approximately 700 feet per minute (fpm). From that time, the calibrated airspeed increased to 122 knots and the rate of climb increased to about 500 feet per minute, until 1550:37. Near the end of the radar track, the airspeed then decreased to 110 knots calibrated airspeed, and the descent rate was approximately 400 fpm, with the last two recorded radar targets showing a track to the left.

1.9.3 Wreckage Release

The aircraft wreckage was released the aircraft's insurance company on June 19, 2007.

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