N499AGKevin Allen Rehm AG-915 SPARTAN · 2022

On September 27, 2022, about 1015 central daylight time, an Airgyro AG915 Spartan gyroplane, N499AG, was destroyed when it was involved in an accident near Yankton, South Dakota. The pilot sustained fatal injuries. The gyroplane was operated as a Title 14 Code of Federal Regulations Part 91 flight test.

According to the pilot’s family members, the purpose of the local area flight was to build flight time and to obtain 40 flight hours on the experimental gyroplane. The gyroplane was based out of a hangar at the Chan Gurney Municipal Airport (YKN), Yankton, South Dakota. The gyroplane departed from runway 31 at YKN and traveled to the west for the flight.

One witness observed the gyroplane, about 400 ft above ground level (agl), with “heavy black smoke” emitting from the gyroplane. The gyroplane appeared to be flying to the west, but then made a “quick” turn toward the south; it went “straight down, nose first,” and impacted the ground. The witness did not see any fire emitting from the gyroplane while it was it was flying.

A second witness observed the gyroplane flying to the west, about 350 ft agl. He observed “a lot of black smoke” emitting from the gyroplane, but he did not see any fire emitting from the gyroplane while it was flying. The witness observed the gyroplane turn toward the south and the gyroplane then went “straight down, nose first” into the ground.

The gyroplane impacted a flat grass field on private property. The accident site was located about 2.3 nm northwest from the departure end of runway 31 at YKN.

According to the pilot’s family, this was the pilot’s first time building an aircraft and he was self-taught about the gyroplane build process. The pilot did not report any mechanical concerns about the gyroplane to family members. A review of Federal Aviation Administration (FAA) records did not show the pilot held a mechanic or a repairman certificate, nor was he required to.

The pilot’s logbook was not available for review.

According to a pilot and mechanic who administered a builder’s assistance program for experimental aircraft, the pilot was at his facility for about 6 weeks in Paris, Texas, with the gyroplane. He classified the pilot as an “excellent craftsman” while building the gyroplane and stated that he performed “very good” work.

According to FAA gyroplane airworthiness records and the gyroplane maintenance records, the pilot was the builder of the gyroplane.

Listed as a repairman, the pilot performed maintenance work on the gyroplane several days before the accident. The maintenance records showed that at the last two work entries, on September 24, 2022, the gyroplane had accumulated 37.8 flight hours. The first work entry consisted of the pilot replacing the engine oil drain plug and checking for oil leaks. The second work entry consisted of servicing the engine oil, replacing the engine oil filter, and checking for oil leaks. An examination of the gyroplane’s maintenance records revealed no evidence of any uncorrected mechanical discrepancies with the airframe or the engine.

The gyroplane weight and balance records were not available for review.

In the program letter to accompany the application for airworthiness to the FAA, the pilot had YKN listed as a geographical area for flight testing. The gyroplane flight manual was not available since the gyroplane had not completed the required 40 flight test hours.

The experimental engine installed in the gyroplane was partially configured for a constant speed propeller but required additional components, including a propeller governor. The Rotax Aircraft Engines factory installs a protective flange cover on the propeller governor pad, which is intended for delivery purposes only and must be removed before flight since it is not intended for operational use.

The governor flange cover, as listed in Rotax Aircraft Engines Service Instruction PAC-002 Governor Flanger Cover and Installation/Use of Governors for Rotax Aircraft Engines, serves as a protective cover during transportation with the 915iS3 version, but is not considered part of the engine type design. This document, published on December 27, 2019, discusses that before engine operation, the governor flange cover must be replaced with a functional governor, or the engine is to be converted to a 915iS2 version.

Rotax developed two versions of the Rotax 915 iS engine: the iS2 version, designed for usage without a governor, and the iS3 version, intended for usage with a governor. The iS3 version is delivered without a governor but includes a flange where a governor can be installed. During the end-of-line testing at the factory, an aluminum cover is mounted on the governor flange to protect the connection area from foreign object debris. The Rotax Aircraft Engines 915 Series Engine Installation Manual (61-00-00) states that this cover is not suitable for flight operations.

Converting an iS3 version to an iS2 version requires following instructions found in the Rotax Aircraft Engines 915 Series Maintenance Manual Heavy (72-10-00), that involves the replacement of the flange and other modifications. For the accident engine, it operated as an iS3 version without a governor and without the necessary conversions outlined in the Rotax Aircraft Engines 915 Series Maintenance Manual Heavy.

A review of the kit manual that the pilot used to build the gyroplane, created by MBL Classics – Gyroplane Department, revealed that it did not list any specific information about the governor flange cover needing to be removed and installing a funcional governor or converting the engine to a different version. However, the kit manual did reference the Rotax Aircraft Engines 915 Series Engine Installation Manual multiple times.

According to the pilot and mechanic who administered the builder’s assistance program that the gyroplane was involved with, he did not recall having any conversations or seeing any work done by the pilot regarding the governor flange cover or converting the engine to a different version.

According to FAA gyroplane airworthiness records and the gyroplane maintenance records, the pilot was the builder of the gyroplane.

Listed as a repairman, the pilot performed maintenance work on the gyroplane several days before the accident. The maintenance records showed that at the last two work entries, on September 24, 2022, the gyroplane had accumulated 37.8 flight hours. The first work entry consisted of the pilot replacing the engine oil drain plug and checking for oil leaks. The second work entry consisted of servicing the engine oil, replacing the engine oil filter, and checking for oil leaks. An examination of the gyroplane’s maintenance records revealed no evidence of any uncorrected mechanical discrepancies with the airframe or the engine.

The gyroplane weight and balance records were not available for review.

In the program letter to accompany the application for airworthiness to the FAA, the pilot had YKN listed as a geographical area for flight testing. The gyroplane flight manual was not available since the gyroplane had not completed the required 40 flight test hours.

The experimental engine installed in the gyroplane was partially configured for a constant speed propeller but required additional components, including a propeller governor. The Rotax Aircraft Engines factory installs a protective flange cover on the propeller governor pad, which is intended for delivery purposes only and must be removed before flight since it is not intended for operational use.

The governor flange cover, as listed in Rotax Aircraft Engines Service Instruction PAC-002 Governor Flanger Cover and Installation/Use of Governors for Rotax Aircraft Engines, serves as a protective cover during transportation with the 915iS3 version, but is not considered part of the engine type design. This document, published on December 27, 2019, discusses that before engine operation, the governor flange cover must be replaced with a functional governor, or the engine is to be converted to a 915iS2 version.

Rotax developed two versions of the Rotax 915 iS engine: the iS2 version, designed for usage without a governor, and the iS3 version, intended for usage with a governor. The iS3 version is delivered without a governor but includes a flange where a governor can be installed. During the end-of-line testing at the factory, an aluminum cover is mounted on the governor flange to protect the connection area from foreign object debris. The Rotax Aircraft Engines 915 Series Engine Installation Manual (61-00-00) states that this cover is not suitable for flight operations.

Converting an iS3 version to an iS2 version requires following instructions found in the Rotax Aircraft Engines 915 Series Maintenance Manual Heavy (72-10-00), that involves the replacement of the flange and other modifications. For the accident engine, it operated as an iS3 version without a governor and without the necessary conversions outlined in the Rotax Aircraft Engines 915 Series Maintenance Manual Heavy.

A review of the kit manual that the pilot used to build the gyroplane, created by MBL Classics – Gyroplane Department, revealed that it did not list any specific information about the governor flange cover needing to be removed and installing a funcional governor or converting the engine to a different version. However, the kit manual did reference the Rotax Aircraft Engines 915 Series Engine Installation Manual multiple times.

According to the pilot and mechanic who administered the builder’s assistance program that the gyroplane was involved with, he did not recall having any conversations or seeing any work done by the pilot regarding the governor flange cover or converting the engine to a different version.

A postimpact fire consumed the composite airframe. Due to thermal damage, flight control continuity and airframe to engine control continuity could not be established. Four round weights were found in the wreckage. Each weight weighed 10 pounds, for a total of 40 pounds of weights recovered. The two main rotor blades were accounted for but sustained impact damage. The main rotor head, with main rotor blade remnants, was found forward of the main wreckage location. The main rotor head was able to be rotated by hand with no binding or resistance. The engine sustained thermal damage and the propeller was destroyed from the thermal damage.

Postaccident examination of the wreckage revealed that the composite components exhibited signs of thermal damage that did not appear to be related to a postimpact fire. In addition to the thermal damage, there was also evidence of fluid consistent with oil on both the interior and exterior of several fuselage and empennage pieces. The fluid on the exterior surfaces appeared in patterns consistent with being airflow-driven.

The main rotor mast exhibited thermal discoloration and heavy sooting up to and including the swash plate. The remaining main rotor blade sections showed no thermal damage or sooting.

The engine had an oil coating over a large area of the exposed surfaces. The governor pad was heavily coated in oil, with an area of coagulated oil directly beneath it.

The governor oil pressure feed line banjo bolt, a normally torqued fitting, was found finger tight. There was no evidence of torque paint/marking on the surface of the fitting or the adjacent area of the engine block. However, the torque paint may have been damaged or destroyed by thermal exposure.

During the examination, it was observed that a governor had not been installed on the governor pad and the governor flange cover was still in place. The cover plate bolts were found to be only finger tight, possibly a result of thermal exposure. Rotax Aircraft Engines does not provide a specific torque specification for the cover plate bolts, and a general torque specification was applied based on the size of the bolts.

The only area not covered with oil was near the turbocharger and two of the exhaust ducts. This area also exhibited thermal discoloration. Two aluminum valve covers (cylinders Nos.2 and 4) collocated in this area were melted along the bottom edge of the covers with evidence of dripping and material flow. The flow direction of the melted areas were consistent with the material having been in an upright (in-flight position) at the time the material started to flow.

The oil return connection flange on the engine block located above the turbocharger exhibited thermal damage with melting on the threads. The connecter from this flange was found separated from the engine. There was resolidified aluminum on the connector. The cold side of the turbocharger and other aluminum engine components were also melted.

Flight Testing

The FAA has published Advisory Circular 90-89C, Amateur-Built Aircraft and Ultralight Flight Testing Handbook. This handbook discusses the objectives of a flight test plan and states:

The objective of a flight test plan is to determine the aircraft’s controllability throughout all the maneuvers and to detect any hazardous operating characteristics or design features. You should use this data to develop a flight manual that specifies the aircraft’s performance and defines its operating envelope. Additionally, the plan should reference the use of checklists to assure that all relevant steps and elements are covered.

This handbook also discusses the time required for flight test and states:

Your original issued experimental certificate should be limited to operation within an assigned flight test area for a minimum of 25 hours when a type certificated (TC) engine/propeller combination is installed. A minimum of 40 hours is required when a non-TC’d engine, propeller, or engine/propeller combination is installed. Furthermore, if the TC’d engine, propeller, or engine/propeller combination installed has been altered in a way that differs from an approved type design in a Type Certificate Data Sheet (TCDS), a minimum of 40 hours will be required.

Build Errors

The Experimental Aircraft Association (EAA) published an article in the June 2023 edition of the EAA Sport Aviation Magazine. The article, titled, “The Top Five Build Errors,” discusses engine installation as a build error and provides the following guidance for experimental aircraft builders:

1. Follow directions to the letter, if there’s something that is confusing, get help.

2. Have other knowledgeable experts review your work.

3. Be patient and take time with the details.

4. Use checklists and then double-check the checks.

Lack of Knowledge

The FAA has published the Aviation Maintenance Technician Handbook – General FAA-H-8083-30B. This handbook discusses human factors with maintenance work but can also be applied to experimental aircraft building. This handbook discusses the “dirty dozen,” regarding a lack of knowledge, and states in part:

A lack of knowledge when performing aircraft maintenance can result in a faulty repair that can have catastrophic results.

All maintenance must be performed to standards specified in approved instructions. These instructions are based on knowledge gained from the engineering and operation of the aircraft equipment. Technicians must be sure to use the latest applicable data and follow each step of the procedure as outlined.

An autopsy of the pilot was performed by the Minnehaha County Coroner, Sioux Falls, South Dakota. According to the autopsy report, the cause of death was blunt force injuries and the manner of death was accident. No soot was found in the airways of the pilot.