N144PG

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...