CEN14FA057

The flight instructor's failure to maintain airspeed following a partial loss of engine power for reasons that could not be determined during postaccident examination, which resulted in an aerodynamic stall and subsequent loss of airplane control.

The purpose of the night instructional flight was to in remain in the airport traffic pattern and practice touch-and-go landings. According to air traffic control data, during the initial climb following the second touch-and-go landing, the flight instructor told the tower controller that the airplane was experiencing "engine problems" and requested to make an immediate 180-degree turn back to the airport for landing. Based on available radar data, the airplane was likely less than 250 ft above the ground when the flight instructor reported the engine problem. A witness reported that, while the airplane was on the downwind leg for the first landing, the engine sounded abnormal and that the engine continued to run roughly while the airplane was on initial climb following the second landing. Several witnesses reported seeing the airplane in a steep left turn before it entered a near-vertical descent into terrain. A postaccident airframe examination did not reveal any malfunctions or failures that would have precluded normal operation. The carburetor heat control was found in the "off" position. Control cable continuity was confirmed between the carburetor heat box and the cockpit control; however, impact damage to the carburetor air box precluded a determination of whether the carburetor heat was activated at the time of the accident. Although the weather conditions at the time of the accident were conducive to the formation of carburetor ice at reduced engine power settings, the investigation was unable to determine to what extent carburetor ice might have formed during the accident flight. Additionally, disassembly of the carburetor revealed that one of its two hollow polymer floats was flooded with fuel, which would reduce the buoyancy of the float and could result in poor idle power performance and/or possible flooding of the carburetor. During the 5 years preceding the accident, the carburetor manufacturer issued multiple service bulletins (SB) that acknowledged that the hollow polymer float design had known issues with fuel leaking into the float through a welded seam. The carburetor manufacturer specified that all affected carburetors should be inspected within 30 days and then at 30-day intervals until the affected floats were replaced with an updated solid-epoxy float design that was impervious to flooding. Owner/operator compliance with the service bulletins was considered optional under FAA regulations. According to maintenance documentation, the accident carburetor had not been inspected as specified by the SBs. Ultimately, the root cause for the partial loss of engine power could not be identified because the investigation was unable to determine to what extent carburetor icing, the flooded float, or a combination of the two conditions could have contributed to the loss of engine power. Following the partial loss of engine power, it is likely that the flight instructor failed to maintain airspeed during the turn back to the airport, which resulted in an aerodynamic stall.

A review of available ATC information indicated that the accident flight had received normal air traffic control services and handling. A transcript of the voice communications recorded between the accident flight and David Wayne Hooks Air Traffic Control Tower are included with the docket materials associated with the investigation. The David Wayne Hooks Memorial Airport (DWH) is a privately owned airport that is open to the public. The airport is located approximately 17 miles northwest of Houston, Texas. The airport field elevation was 152 feet msl. The airport is serviced by an air traffic control tower and ground control. The airport has three parallel runways: runway 17R/35L (7,009 feet by 100 feet, asphalt); runway 17L/35R (3,987 feet by 35 feet, asphalt); and a water runway 17W/35W (2,530 feet by 100 feet). Runway 17R incorporated a displaced threshold measuring 1,007 feet, a 4-light precision approach path indicator, runway end identifier lights, and high intensity runway edge lighting. According to air traffic control documentation, all runway lighting was functional at the time of the accident. On January 30, 2008, Precision Airmotive LLC, the manufacturer of the MA-3A carburetor, issued Mandatory Service Bulletin No. MSA-13 that required the replacement of brass and polymer hollow floats with a new solid-epoxy float design. According to the service bulletin, the installation of the new solid-epoxy float design would eliminate the known issues of hollow floats becoming flooded with fuel. Additionally, the service bulletin acknowledged that the polymer float design had known issues with fuel leaking into the hollow portion of the float through the welded seam. The service bulletin stated that a flooded float would reduce the buoyancy of the float, which could result in poor idle power performance and/or possible flooding of the carburetor. The service bulletin stipulated that affected carburetors be inspected within 30 days and then at 30 day intervals until the new solid-epoxy float was installed. The service bulletin stated that if the carburetor exhibited any signs of flooding, the float should be replaced immediately. Additionally, the service bulletin stipulated that all carburetors affected by the bulletin be overhauled every 10 years or at the specified engine time between overhaul (TBO), whichever occurred first. On July 18, 2008, Lycoming Engines issued Mandatory Service Bulletin No. 582 that required all Lycoming engines that were equipped with Marvel-Schebler, Facet, Precision Airmotive, or Volare carburetors to be in compliance with Precision Airmotive Mandatory Service Bulletin No. MSA-13. The Lycoming service bulletin stipulated that affected carburetors be inspected within the next 30 days and then at 30 day intervals until the new solid-epoxy float was installed. On February 1, 2009, Volare Carburetors LLC, who had acquired the Precision Airmotive carburetor line, issued Service Bulletin No. SB-2, which reiterated that hollow floats needed to be replaced with the newer solid-epoxy float design. The service bulletin stated that deteriorated, leaking, or broken floats can negatively affect engine performance. In conformance with the previously issued service bulletins, it stipulated that all affected carburetors be inspected within 30 days and then at 30 day intervals until the affected floats were replaced with the newer solid-epoxy float design. On April 2, 2009, Volare Carburetors LLC issued Service Bulletin No. SB-5, which superseded the older Mandatory Service Bulletin No. MSA-13. The updated service bulletin clarified that the new float design was made of a solid, blue epoxy material. Previous service bulletins had mistakenly identified the new float design as being made from foam. Service Bulletin No. SB-5 stipulated that affected carburetor floats should be inspected per the guidance contained in Service Bulletin No. SB-2. A review of maintenance records established that the carburetor was rebuilt and tested by Precision Airmotive on August 11, 2004, before being installed on the accident engine during a field overhaul completed on November 4, 2004. The engine overhaul documentation specified that the accident engine had a 2,400 hour TBO. At the time of the accident, the accident engine had accumulated 3,674.3 hours since its last overhaul. A review of available maintenance paperwork did not reveal any maintenance, repair, inspection, or overhaul of the carburetor since the last engine field overhaul. Additionally, the reviewed maintenance information did not contain any documentation that Service Bulletin Nos. MSA-13, 582, SB-2, or SB-5 had been complied with. On November 18, 2013, an autopsy was performed on the flight instructor by the Harris County Institute of Forensic Sciences, located in Houston, Texas. The cause of death was attributed to multiple blunt-force injuries that were sustained during the accident. The FAA's Civil Aerospace Medical Institute located in Oklahoma City, Oklahoma, performed toxicology tests on samples obtained during the autopsy. The toxicological test results were negative for carbon monoxide and ethanol. Atropine was detected in liver and blood samples. Atropine, often used in emergency resuscitation efforts, is a prescription anticholinergic agent and muscarinic antagonist. On November 19, 2013, an autopsy was performed on the student pilot by the Harris County Institute of Forensic Sciences. The cause of death was attributed to multiple blunt-force injuries that were sustained during the accident. The FAA's Civil Aerospace Medical Institute performed toxicology tests on samples obtained during the autopsy. The toxicological test results were negative for carbon monoxide, ethanol, and all drugs and medications. At 1853, the DWH automated surface observing system reported: calm wind, visibility 10 miles, sky clear, temperature 23 degrees Celsius, dew point 21 degrees Celsius, and an altimeter setting of 29.89 inches-of-mercury. The United States Naval Observatory reported that the sunset and end of civil twilight at DWH was at 1725 and 1751, respectively. The moonrise was at 1742 for the full-phase moon. The carburetor icing probability chart included in Federal Aviation Administration Special Airworthiness Information Bulletin No. CE-09-35, Carburetor Icing Prevention, indicated that the accident flight was likely operating in atmospheric conditions that were associated with a serious risk of carburetor ice accumulation while operating at reduced engine power settings. A postaccident investigation confirmed that all airframe structural components and flight controls were located at the accident site. The wreckage was located on the east side of the airport, north of taxiway hotel and east of taxiway mike. The initial impact point was determined to be where the right wing collided with the northwest corner of a hangar structure. The outboard 9 feet of the right wing separated during the initial impact and was found about 90 feet northwest of the initial impact point on taxiway mike. The main wreckage, located about 29 feet north of the initial impact, consisted of the left wing, fuselage, empennage, engine, and propeller. The forward fuselage, including the cockpit, exhibited impact damage that significantly reduced the cabin volume. The left wing remained partially attached to the fuselage. The left wing had impacted a structural post and a spiral staircase that was associated with a residential hangar. The aircraft wreckage was orientated on a 035 degree magnetic heading. The fuselage was found resting on its lower surface. There was no evidence of an inflight or postimpact fire. The first responders reported that there was a substantial fuel odor at the accident site. Flight control cable continuity could not be established due to multiple separations; however, all observed separations were consistent with overstress fractures. Both flaps had separated from