NTSB Factual Report

On February 18, 2000, at 0748 Pacific standard time, an Ayres S2R-600 single engine airplane, N4011Y, sustained substantial damage during an off-airport forced landing following a loss of engine power after departing from Elko, Nevada. Charter Aviation, Inc., Williams, California, was operating the airplane under the provisions of 14 CFR Part 91. The commercial pilot, the sole occupant, sustained a minor injury. The positioning flight departed Elko 6 minutes prior to the mishap, and was en route to a landing strip to load the airplane with chemicals for an aerial application mission. Visual meteorological conditions prevailed, and a flight plan had not been filed.

According to the operator, two airplanes were transitioning to a job site when the second airplane observed the first airplane emit a puff of black smoke and execute a forced landing. A helicopter pilot, who was working nearby, observed the accident. He picked up the pilot and transported him to the hospital for observation.

According to the pilot's written statement, the airplane was climbing when he felt a loss of engine power. He made a forced landing on upsloping terrain covered with sage brush and juniper trees. The airplane remained on its belly and skidded to a stop within 40 yards.

The airplane sustained substantial damage to the landing gear, the left wing, and the propeller. The underspeed governor input shaft linkage fractured in the rod end's threaded section; however, its fracture surfaces displayed shear lips. The turboprop engine, a Honeywell (AlliedSignal/Garrett) TPE331-6-252M, serial number P-20426C, was shipped to the Honeywell Product Integrity facility in Phoenix, Arizona. Technicians from Honeywell examined the engine on June 16, 2000, under the supervision of the National Transportation Safety Board investigator-in-charge (IIC).

The technicians disassembled the engine and noted the following pertinent items:

-Dirt and debris were on the first and second stage compressor shrouds, within the first stage compressor diffuser, on the combustion chamber liner's outer wall, on the fuel nozzles, and within the combustion chamber plenum.

-Rotational score marks were on the first and second stage compressor impeller blades, along with corresponding rotational score marks on the first and second stage compressor shrouds.

-Rotational score marks were on the first stage turbine rotor blades along with corresponding rotational score marks on the first stage turbine rotor shroud.

-Rotational score marks were on the propeller shaft, along with corresponding rotational score marks on the forward end of the sun gear.

-Rotational score marks were on the aft sun gear nut, along with corresponding rotational score marks on the third direct drive fuel control (DDFC) gear retainer and torque sensor housing.

-The nuts securing the forward propeller shaft ball bearing mount studs were in the nose cone housing oil sump, with what appeared to be other metallic debris. The stud threads were deformed. The forward propeller shaft ball bearing mount studs, nuts, and metallic debris were submitted for Honeywell material analysis.

-The planet carrier mounting stud dowels, located in the intermediate gearbox assembly, were displaced.

-The second DDFC idler gear and associated retaining parts were in the gear case oil sump. It had separated from its retaining splined shaft. The splined shaft fractured forward of the forward splines and its teeth displayed rotational deformation. The gear was submitted for examination at the Honeywell materials analysis department.

-The compressor section's main drive torsional shaft was darkly discolored and sheared just forward of its aft spline section. It too was submitted for material analysis.

Review of the Honeywell material analysis report revealed that the main drive torsional shaft and the second DDFC idler gear splined shaft both failed as a result of torsional overload. In addition, microhardness measurements taken on the failed components revealed that they were within specified limitations. The forward propeller shaft ball bearing mount studs and nuts were stripped.

The fuel pump and fuel control unit (FCU) remained intact and in place. Technicians removed the fuel pump interstage fuel filter for examination, and it appeared to be uncontaminated. There was residual fuel in the fuel pump interstage fuel filter bowl. They reinstalled the interstage fuel filter in the fuel pump after examination and prior to functional testing. The fuel control functional test revealed that the underspeed governor minimum stop and maximum stop were set higher than the allowable limits. However, this would have resulted in increased fuel flow supplied to the engine during operation with the condition lever below the maximum position and at the maximum position, respectively. The FCU was operable. After the functional test, they again removed and analyzed the interstage fuel filter. They observed no anomalies. They submitted the residual fuel in the pump for testing and detected no anomalies.

The technicians examined the engine's lubrication system, and noted no anomalies. They observed residual oil on all components requiring lubrication, and observed no signs of obstruction. They took an oil sample from the nose cone oil sump and submitted it for oil analysis. They didn't identify any anomalies. The magnetic drain plug (chip detector) was undamaged, and had captured several metallic fragments. Material analysis determined that the debris was 4340 gear material.

Review of the engine maintenance records revealed that the engine underwent a 4,000-hour inspection on December 17, 1998, at an engine total time of 2,978.5 hours and 3,185 cycles. During the 4,000-hour inspection the engine components underwent various repairs and overhauls, was converted for agricultural use, and was returned to service. On May 1, 1999, maintenance personnel installed the engine on the accident airplane. On July 19, 1999, at an engine total time of 3,275.7 hours, they replaced the rear propeller shaft bearing. The last pre-accident oil sample test was on January 10, 2000. The test results were normal.

NTSB Probable Cause

the loss of engine power for undetermined reasons. A contributing factor was the lack of suitable terrain for the ensuing forced landing.