N70216Thrush Aircraft S2R-T34 · 2011

On July 18, 2011, at 0555 mountain daylight time, N70216, a Thrush Aircraft Incorporated S2R-T34, sustained substantial damage after a loss of power on final approach to the Kit Carson County Airport (ITR), Burlington, Colorado. The commercial pilot was not injured. The airplane was registered to and operated by Stratton Equity Corporation, Stratton, Colorado. Visual meteorological conditions prevailed and no flight plan was filed for the local agricultural spraying flight conducted under 14 Code of Federal Regulations Part 137. The flight originated at ITR at 0520.

The pilot stated that he was returning back to the airport and was on a two mile final when the engine "just died." He said it got "real quiet" and the control column got "heavy." The pilot said he did not look at the engine gauges and there were no aural warnings. However, he did cycle the fuel control lever. Due to the low altitude, the pilot established a glide and subsequently landed hard in a field. The airplane bounced and came to rest about 15 yards from where it first landed.

The pilot also said that before the flight, he performed a preflight inspection, which included only draining the header tank for several seconds; however, he did not drain the fuel into a clear jar to check for water or debris. The pilot reported that the airplane was kept in a hangar and it had been washed the day before the accident.

The pilot held a commercial pilot certificate for airplane single-engine land. His last FAA second class medical was issued on May 12, 2011. He reported a total of 2,302 total flight hours, of which, 178 hours were in the same make and model as the accident airplane. The pilot also reported that he had flown 221 hours in the last 90 days.

A review of the engine logbooks revealed that the Pratt & Whitney PT6A-34AG (750 hp) turbo-prop engine was manufactured in April 2010. At the time of the accident, the engine had accrued a total of 171.3 hours since new and 172 cycles.

On August 1, 2011, the investigator-in-charge (IIC) performed an examination of the airframe and engine along with a representative of Pratt & Whitney Canada. The firewall was wrinkled and each wing sustained leading edge impact damage. The engine was still installed on the airframe and the three-bladed propeller had been removed. All three propeller blades were bent aft about 90 degrees and appeared feathered.

An external examination of the engine did not reveal any mechanical problems with the power turbine, compressor turbine or compressor assembly. The exhaust case sustained impact damage, which resulted in the power turbine blades contacting the shroud and preventing the power turbine disk and gearbox from rotating. The P3 and Py pneumatic lines were secure at all connection points.

The linkages to the fuel control unit (FCU) and the propeller governor were intact and moved freely without binding.

The firewall sump (engine side) was drained and approximately four fluid ounces of straw colored fuel (consistent with Jet-A fuel) was inside. A trace amount of debris was noted in the fuel and absent of water. The filter was disconnected and the filter screen had a very light trace of debris. Straw colored fuel was drained from the main fuel line from the sump to the engine. There was a light trace of debris (silicone) observed in the fuel.

The engine fuel filter was removed and the bowl was filled with approximately two fluid ounces of straw colored fuel that was absent of debris or water.

According to the company that recovered the airplane, approximately 77 gallons of fuel was drained from the airplane’s wings and approximately 8 gallons of fuel was drained from the header tank. The fuel was absent of debris and water.

The engine was removed and sent to Dallas Airmotive, Dallas, Texas, where a teardown examination was performed on September 16, 2011, under the supervision of the IIC. After the engine was removed from the sealed crate and placed on a test stand, the lines attached to the fuel control unit (FCU) and the propeller governor were tested for proper installment. The Py line to the propeller governor was slightly loose where it attached to the unit. Shop air was then blown through the line and a soap/water solution was sprayed externally on the line. No leaks were noted. Air was also blown into the P3 line and no leaks were noted. The P3 filter was disassembled and the bowl was absent of debris. The internal components of the filter were absent of debris.

The engine driven fuel pump’s metal filter was removed and examined. A trace amount of debris was found on the bottom of the screen.

The FCU, compressor bleed valve assembly, and the flow divider and dump valve were removed and bench tested while at Dallas Airmotive. The units operated to standard test specifications and no anomalies were noted.

The propeller and over speed governors were also removed and sent to Pratt & Whitney Canada for testing. The units were tested under the supervision of the Transportation Safety Board (TSB) on September 28, 2011.

A review of the Pratt and Whitney Accessories Accident Report revealed that the propeller governor was original to the engine when it was delivered. The driveshaft turned freely by hand. The speed setting lever, beta-valve clevis and reset arm moved freely over the full ranges and returned under the influence of their springs. The unit was tested in accordance with Woodward specification TSP-810 Rev. AH. Four of the test points were slightly out of test specifications, indicative of rigging adjustments made in the field after the unit was delivered.

The overspeed governor was not on the engine at initial engine delivery. The driveshaft turned freely by hand. There was orange anti-tamper paint on the pilot valve stop screw. The inside of the electrical connector was clean and dry. Lockwire was present at all locations. The unit was tested in accordance with Woodward drawing A210507. Two of the test points were slightly out of test specifications, indicative of rigging adjustments made in the field.

An examination of the airframe, available fuel supply, engine, and accessories revealed no pre-mishap anomalies or mechanical deficiencies that would have precluded the engine from operating at the time of impact. The source of the power loss could not be determined.