CHI08LA129

The airplane was on a visual approach to an airport when the engine stopped producing power. The pilot subsequently landed the airplane in a field, but struck trees at the edge of the field during the forced landing. Examination of the engine, engine fuel controls, and Power Analyzer and Recorder (PAR), provided evidence that the engine shut down during the flight. Further examination of engine and fuel system components from the accident airplane failed to reveal a definitive reason for the uncommanded engine shut-down.

History of flight

On May 9, 2008, at 2037 eastern daylight time, a Cessna 208B, N893FE, operated by CSA Air, Inc., and piloted by a commercial pilot, sustained substantial damage during a forced landing following a loss of engine power near Ada, Michigan. The airplane was on a visual approach to runway 26L at the Gerald R. Ford International Airport (GRR), Grand Rapids, Michigan. The Title 14 Code of Federal Regulations Part 135 cargo flight was operating in visual meteorological conditions and was on an instrument flight rules (IFR) flight plan. The pilot was not injured. The flight originated from the Cherry Capital Airport, Traverse City, Michigan about 2000.

Personnel information

The pilot held a commercial pilot certificate with airplane single-engine land, airplane multiengine land, and instrument airplane ratings. His most recent flight review was conducted on February 20, 2008, in the same make and model airplane as the accident airplane. His most recent second class medical certificate was issued on February 12, 2008. According to a report submitted by the pilot, he had accumulated 5,600 hours of total flight experience, including 3,450 hours in the same make and model as the accident airplane.

Aircraft information

The airplane was a 1990 Cessna model 208B airplane, serial number 208B0223, and was a fixed landing gear, strut braced high wing airplane. It was powered by a single Pratt & Whitney PT6-114A turboprop engine rated at 675 horsepower. The airplane was maintained under an approved airworthiness inspection program (AAIP), and had accumulated 8,625 hours time in service as of the last inspection on March 18, 2008. The airplane's engine had accumulated 8,836 total hours, 675 hours since overhaul, and 60 hours since the March 18, 2008 inspection.

Meteorological information

The recorded weather conditions at the GRR at 1953 were: winds 320 degrees at 9 knots; visibility 10 statute miles; few clouds at 6,000 feet above ground level; overcast clouds at 12,000 feet above ground level, temperature 15 degrees Celsius; dew point 3 degrees Celsius; altimeter setting 29.83 inches of mercury.

Communications

The airplane was on an instrument flight rules flight plan and was in contact with the GRR air traffic control tower using the identifier "iron air 7343". The airplane had been cleared for a visual approach to runway 26L at GRR. The GRR controller issued a traffic advisory and cleared the accident airplane to descend to 2,500 feet above sea level. The pilot later informed the controller that engine power was lost. When queried, the pilot informed the controller that there was one person and 800 pounds of fuel on board the airplane. No further transmissions were received.

Wreckage and impact information

The airplane touched down in a field of tall grass and impacted trees at the edge of the field. The left wing was separated from the fuselage at the wing root. The right wing was separated about mid-span. The nose landing gear had collapsed and the propeller blades were all bent rearward with little evidence of rotation. Some grass and dirt debris was visible in the cowling intakes. Examination of the airplane established that engine control continuity from the cockpit to the engine existed. Engine compressor and power turbine blades appeared intact. The compressor and propeller shafts rotated freely. Fuel was found within the fuel lines from the tanks to the engine fuel controls. Fuel samples were tested for water accumulation and tested negative. The fuel lines and vent lines were tested for obstructions and none were found. The engine and fuel boost pumps were retained for further examination at the respective manufacturer's facilities.

Examination of the fuel boost pump consisted of testing for compliance with the factory acceptance test procedure. The pump from the accident airplane passed the acceptance test within the specified parameters.

Examinations of the engine and fuel controls were conducted at the Pratt & Whitney facilities in Longueuil, Quebec, Canada. The compressor and power turbine shafts rotated freely. The engine fuel and pneumatic lines were tight. During initial examination, a crack was observed on the engine scavenge pump housing. Due to the presence of the crack, an engine run was not performed. It could not be determined if the crack existed prior to impact. The engine core was subsequently disassembled. The turbine blades and disc were intact and unburned grass was found within the gas generator case and combustor confirming the non-running state of the engine at the time of ingestion.

The fuel control unit (FCU) and fuel pump were tested as a unit on a test stand at the manufacturer's facility. Low speed testing of the units revealed pressure and fuel flow fluctuations that could not be reliably duplicated. The testing of the units revealed other test parameters that were outside of manufacturing tolerances; however, those test point discrepancies were noted to be due to permissible field adjustments and would not have resulted in a loss of engine power. The minimum pressurizing valve which regulates fuel pressure is not fully open at low speed and it was noted that a sticky FCU minimum pressurizing valve can slam closed during a deceleration, and could result in a flameout. The minimum pressurizing valve was disassembled and axial scoring of the plunger and housing were noted. Examination of the scoring on the valve and plunger revealed the presence of embedded silicon particles. Further examination of the scoring revealed that the depth of the scoring (0.00006 inches) relative to the valve radial clearance (0.0015" to 0.0025") was too small to make a positive determination that the valve stuck due to imbedded contamination.

Testing of additional fuel system components revealed no anomalies that would have resulted in a loss of engine power.

Tests and research

The airplane was equipped with a Power Analyzer and Recorder (PAR). Data downloaded from the PAR confirmed an engine shutdown near the time that the pilot reported the loss of power to air traffic control. No data was obtained from the PAR that indicated the reason for the power loss.