ERA15FA016

The partial loss of engine power due to the undetected blockage of the inlet and outlet ports of the manifold valve by an organic compound of an unknown source.

The flight instructor and private pilot were conducting an instructional flight. A witness reported that, when the airplane about 400 ft above the ground, he heard a "surging" sound coming from the engine and observed pitch and roll oscillations occurring; he then lost sight of the airplane. A video provided by the fixed-based operator showed the airplane take off and begin to climb. Shortly after, it recorded a radio call on the common traffic advisory frequency indicating that an emergency existed and that the airplane was returning to the airport. Another witness reported seeing the airplane's landing gear barely clear a building as it flew toward the airport. He added that, as the airplane neared power lines, the airplane pitched up, likely in an attempt to avoid them. The airplane then collided with a telephone pole and unmarked transmission lines, which ruptured the fuel tank, and then struck the ground. A postcrash fire ensued that nearly consumed the cockpit, cabin, and both wings. Examination of the flight controls and heat-damaged engine revealed no evidence of preimpact failures or malfunctions. Examination of the manifold valve revealed that the inlet and outlet ports were blocked to varying degrees. Analysis of the blockage material determined that it was an organic polymer material consistent with polyester; however, the source of the contamination could not be determined. Although the blockages of the inlet and outlet ports precluded postaccident flow testing of the manifold valve, it is likely that the blockages resulted in the surging reported by the witness and the subsequent loss of engine power. The blockages likely would not have created a condition that would have been detectable to the pilots during the pretakeoff engine run-up. Although the fuel vent lines of both wings were found blocked with organic material consistent with insect nest material, the accident flight was very short and, therefore, it is unlikely that these blockages affected the engine operation. The blockages of the fuel vents were located in an area that would not have been visible to the pilots during the preflight inspection of the airplane.

The GVL Airport is equipped in part with runway 29, which is 4,001 feet in length and 100 feet wide. While the airport common traffic advisory frequency is not officially recorded, a fixed base operator on the field has security cameras that contain a portion of runway 29, and also record audio transmission from radio calls on the CTAF. A review of the provided video recording revealed that a portion of the takeoff was recorded, as well as a radio call from an occupant of the airplane. The video depicted the airplane when it was about 1/2 way down the runway in a normal climb attitude. The airplane went out of view of the camera, and a short time later, a radio call on the CTAF frequency was recorded by the FBO security system. The radio call indicated an emergency existed and advised the flight was returning runway 05. Approximately 2 seconds later, power to the video camera was shut off, which was attributed to impact to the power lines. Examination of the servo fuel injector revealed extensive heat damage which precluded operational testing. The fuel regulator plug which was safety wired was removed and the fuel diaphragm stem nut was observed to be in-place. Disassembly examination revealed the air diaphragm was heat damaged and the fuel diaphragm was destroyed. The plastic portion of the seat was destroyed, while the metal portion of the seat was in-place. Removal of the mixture control and fuel control section revealed ghost mark indicating the mixture was just off the full rich position. The clevis was broken to facilitate removal of the idle valve. Based on internal components of the servo, the throttle was in the wide open position. A detailed report concerning the servo fuel injector examination is contained in the NTSB public docket. Examination of the manifold valve revealed that the inlet fitting, inlet port and the ports of the valve body for each cylinder were obstructed to varying degrees by an unknown substance. Because of the obstructions, flow testing was not performed. Following removal of the cover from the bottom of the manifold valve, brown colored material was noted. The top cover of the manifold was removed and the fuel side of the diaphragm and housing were clean. The manifold valve was sent to the NTSB Materials Laboratory for analysis of the obstruction material. A detailed report concerning the manifold valve examination is contained in the NTSB public docket. According to the NTSB Materials Laboratory Report concerning the examination of the manifold valve, most of the portals had substance build-up that limited the openings to approximately half of the portal diameter or more. The blockages of each portal were estimated as follows: 45 percent and 75 percent for the inlet fitting and valve body opening, respectively; 60 percent for both the portal 'A' fitting and valve body opening; 70 percent for the portal 'B' valve body opening; 45 percent for the portal 'C' valve body opening; and 60 percent for the portal 'D' valve body opening. Samples of substances were taken from each port, along with the larger central opening of the back cover for testing by Fourier Transform Infrared (FTIR) spectrometer with a diamond attenuated total reflectance (ATR) accessory. Multiple FTIR analyses were performed on each portal sample, including the hard and soft areas of each sample, as well as areas of different colors for each sample. A spectral library search found the unknown material spectrum to be a very strong spectral match to several types of polyester-a type of organic polymer. Because the sample was degraded and the spectra for polyesters are so similar, it was difficult to differentiate between different types of polyesters. A copy of the NTSB Materials Laboratory Factual Report is contained in the public docket. The flight instructor seated in the left seat was transported to a hospital for treatment of his injuries, but died while hospitalized on November 10, 2014. Because of the length of hospital stay, a postmortem examination and toxicology testing by FAA Bioaeronautical Sciences Research Laboratory was not performed. A postmortem examination of the right seat occupant was performed by Forensic Medicine Associates, Inc., at the DeKalb County Forensic Science Center. The cause of death was listed as "Blunt Force Head Trauma." Forensic toxicology testing on specimens of the right seat occupant was performed by the FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. The toxicology report stated the results were negative for carbon monoxide, volatiles, and tested drugs, while testing for cyanide was not performed. The airplane crashed off airport; the main wreckage was located at 34 degrees 16.201 minutes North latitude and 083 degrees 50.226 minutes West longitude, or 0.28 nautical mile and 211 degrees from the departure end of runway 29. Examination of the accident site revealed the crash site was southwest of the intersection of Scott Street and Palmour Drive. Two powerline poles were broken; 1 pole immediately adjacent to the accident site and 1 pole near the intersection of Scott Street and Palmour Drive. The powerline pole immediately adjacent to the accident site was broken in three pieces (including a piece that was underground). Additionally, damage to unmarked 7200KV three phase electrical wires oriented on a magnetic heading of 035 degrees was noted; the pole and wires were repaired before NTSB arrival, but the damaged components were retained at the accident site. Examination of the broken powerline that was immediately adjacent to the accident site revealed it was approximately 40 feet long, and was set approximately 6 feet below the ground. The pole was fractured at ground level and also about 25 feet above ground level. Pieces of white paint with green color on the opposite side and gouges were noted on the upper 40 inches of the pole, consistent with contact by a portion of the airplane. Wiring from the left Aeroflash Signal Box was found hanging on a telephone wire to the northeast of the broken powerline pole immediately adjacent to the accident site. Nearby businesses were contacted to determine if either contained security video that captured the accident sequence; no video depicting the accident sequence was recorded. Further examination of the accident site revealed ground scars on the road 53 feet 6 inches from the pole contact location. With an estimated pole contact located 31 feet 8 inches above ground level, the descent path to the ground was calculated to be approximately 59 degrees. The ground scar was oriented on a magnetic heading of 068 degrees. Examination of the wreckage revealed the engine, cockpit, and wing carry-thru were inverted. A postcrash fire nearly consumed the cockpit, cabin, and both wings. The outer 4 feet of the left wing was initially found on the sidewalk in the area of the powerline pole, but subsequently moved closer to the main wreckage before NTSB arrival. Examination of the left wing revealed the outer 4 feet was separated; the upper and lower wing skins exhibited sawtooth type fractured oriented in a spanwise direction. The separated section contained the outer portion of the integral fuel tank, and fuel vent lines. The full span of the aileron remained connected, and the aileron counterweight was in-place. The main landing gear was fractured, and the wheel assembly was damaged. The aileron control cables were connected the aileron bellcrank adjacent to the control surface and the pushrod was connected to the bellcrank and the remaining portion of the aileron. Examination of the separated outer section of left wing revealed the fuel tank vent lines were detached at both fittings of the fuel vent scoop assembly; both openings of the fuel vent scoop assembly were free of obstructions. Examination of the ends of the flexible hoses attached to each of the vent lines revealed both were free of obstructions at the opening