N204BF

HISTORY OF FLIGHTOn October 22, 2019, about 1950 mountain daylight time, a Czech Sport Aircraft Sportcruiser airplane, N204BF, was substantially damaged when it was involved in an accident near Holden, Utah. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that during a night flight, the airplane was at 11,000 ft mean sea level when the engine sputtered and then experienced a total loss of power. She noted that the propeller was not windmilling, and her attempts to restart the engine were unsuccessful. Due to the dark night conditions, the pilot could not identify a safe forced landing area, so about 700 ft above ground level, she deployed the airplane's ballistic recovery system (BRS). She stated that the parachute jolted the airplane up and to the left and then to the right before impact with the ground. AIRCRAFT INFORMATIONThe airplane was a single-engine, all metal, low-wing monoplane of semi-monocoque construction with two side-by-side seats. It was equipped with a fixed tricycle undercarriage with a castering nosewheel. The airplane was powered by an American Society for Testing and Materials-compliant, 4-cylinder, horizontally opposed, 100-horsepower, Rotax 912 ULS 2 engine. The engine used a single central camshaft with hydraulic tappets. The cylinder heads were liquid cooled, and the cylinders were ram air cooled. The oil system was a dry sump, forced lubrication system. The engine used a reduction gearbox to drive the three-bladed, ground-adjustable, composite Sensenich propeller.

According to maintenance records, the airplane was manufactured in 2017. The airplane’s most recent 100-hour inspection was completed on October 4, 2019. At the time of the inspection, the airplane had accrued 1,689.8 hours of operation. During the 100-hour inspection, the oil filter was opened and examined; no contaminants were found in the oil filter. AIRPORT INFORMATIONThe airplane was a single-engine, all metal, low-wing monoplane of semi-monocoque construction with two side-by-side seats. It was equipped with a fixed tricycle undercarriage with a castering nosewheel. The airplane was powered by an American Society for Testing and Materials-compliant, 4-cylinder, horizontally opposed, 100-horsepower, Rotax 912 ULS 2 engine. The engine used a single central camshaft with hydraulic tappets. The cylinder heads were liquid cooled, and the cylinders were ram air cooled. The oil system was a dry sump, forced lubrication system. The engine used a reduction gearbox to drive the three-bladed, ground-adjustable, composite Sensenich propeller.

According to maintenance records, the airplane was manufactured in 2017. The airplane’s most recent 100-hour inspection was completed on October 4, 2019. At the time of the inspection, the airplane had accrued 1,689.8 hours of operation. During the 100-hour inspection, the oil filter was opened and examined; no contaminants were found in the oil filter. WRECKAGE AND IMPACT INFORMATIONExamination revealed that the airplane sustained substantial damage to the left wing and left aileron. The left-rear metal suspension cable for the BRS parachute fractured and separated near the cockpit canopy’s left hinge retention bolt. The cable separation exhibited a frayed or broom-straw appearance consistent with overload separation from contact with the hinge retention bolt. The right-rear metal suspension cable and the two forward suspension straps remained intact. According to the manufacturer, the BRS performed as expected. No other anomalies were found with the airframe that would have precluded normal operation.

Examination of the engine, serial number (S/N) 9569290, revealed the No. 2 cylinder intake valve spring retainer had fractured into two pieces, which were found in the rocker box along with fragments of the intake valve guide. The No. 2 valve spring shim exhibited a worn appearance with a groove visible around the shim. The No. 2 intake valve had fallen into the cylinder, and it was bent into an “S”shape and embedded in the top of the cylinder head. The top of the No. 2 piston was damaged. The No. 2 piston wrist pin had separated from the piston and lodged between the crankshaft and the No. 2 cylinder bore. According to the engine manufacturer, BRP-Rotax GmbH & Co. KG (BRP-Rotax), worn valve spring shims are a clear sign of an engine operating with air in the oil system. Figure 1 is an illustration of the valvetrain components.

Figure 1. Illustration of components of the engine valvetrain.

Examination with an electron microscope by BRP-Rotax revealed the fracture area of the No. 2 intake valve spring retainer had a fatigue break with pronounced vibration stripes. The breakage exit area was close to the upper edge (outer bore), but the exact breakage exit was in a destroyed or damaged condition. See Figure 2.

Figure 2. Image showing the number two valve spring retainer and the worn valve spring shim after removal from the engine. ADDITIONAL INFORMATIONAt the request of the NTSB, BRP Rotax reviewed its records and advised that they had identified a total of 18 production engine failures due to broken valve spring retainers for 900 series engines produced between February 2015 and February 2019.

The failures occurred with engines installed on multiple types of aircraft, and the failures occurred over a large spread in operating hours from as low as 7 hours to as high as 1936.6 hours. All components examined at the Rotax factory met their specifications. Not all the engines were affected by or complied with Service Bulletin SB-912 i-008 R1 / SB-912-070-R1 / SB-914-052 R1, which was originally issued due to deviations in the manufacturing process of the valve push-rod assembly that could result in partial wear on the rocker arm ball socket. This wear could lead to rocker arm cracking / fracture and subsequent malfunction of the valve train.

Icon Airplane Valve Spring Retainer Failure

On August 10, 2021, the NTSB was notified of another valve spring retainer failure on a Rotax 912S engine (S/N 7705135) that was installed in an Icon A5 airplane, N639BA. The engine was manufactured in 2021 and should have had all changes that were addressed in previous Rotax guidance materials complied with before being placed into service.

The airplane was in cruise flight at a power setting of about 5,350 rpm when the pilot felt the engine vibrating. The exhaust gas temperature (EGT) for cylinder No. 1 began to steeply drop, and the engine rpm dropped to 4,820 rpm without throttle reduction by the pilot. About 2 seconds later, the EGTs for cylinders Nos. 2 and 4 began to drop. Shortly thereafter, the engine lost total power. The pilot then tried twice to restart the engine without success. The pilot made an uneventful forced landing.

Post incident examination revealed that the No. 1 cylinder exhaust valve spring retainer was broken in half. Half of the valve spring retainer was discovered in the rocker box cover, and the other half was found jammed between the cylinder head and the exhaust rocker arm. The No.1 exhaust valve was found severed, and the No.1 piston was impact-damaged.

Corrective Actions

As a result of these occurrences, to increase safety, these organizations took the following actions:

BRP Rotax

o Revised Service Bulletin SB-912 i-008 R1/ SB-912-070 R1/ SB-914-052 R1 to include a specific venting procedure for the oil system. (Now SB-912 i-008R2/ SB-912-070R2/ SB-914-052R2.)

o Revised Service Instruction SI-915 i-003/ SI-912 i-004R1/ SI-912-018R2/ SI-914-020R2 to help preclude lack of proper oil purging after an engine had been first installed and /or an engine had been re-worked, and to help to prevent engine failures in the field, as air could be trapped in the valve tappets and cause valve train failure. (Now SI-916 i B-003/ SI-915 i-003R1/ SI-912 i-004R2/ SI-912-018R3/ SI-914-020R3.)

o All future instructions for continued airworthiness (service bulletins, service instructions, and alert service bulletins) will provide direct references to instructions found in other documents that pertain to the required procedures.

o Notified their distributers of the publication of Service Instruction SI-916 i B-003/ SI-915 i-003R1/ SI-912 i-004R2/ SI-912-018R3/ SI-914-020R3 and encouraged them to inform their customers proactively and to encourage original equipment manufacturers (OEMs) to also distribute the information relating to air in the lubrication system in documents issued by the OEM to significantly improve the chance to reach the end customer with the information. They also asked that their distributors ensure that all OEMs in their regions understand the importance of the revised service instructions, check their relevant instructions for continued airworthiness (ICAs) for possible checks and required changes, and have their aircraft customers, operators, and maintenance technicians made aware and informed about it. Additionally, they further asked their distributers to transmit the relevant ICAs to all their service centers, OEMs, retail sellers, flying schools, flying clubs, authorities, and press, for accomplishment or information.

o Began a process to improve the materials and dimensions of the valve spring retainers and cotters to make the valve train system more robust.

Rotech Flight Safety

o Distributed Service Bulletin SB-912 i-008R2/ SB-912-070R2/ SB-914-052R2 on the Rotax-owner website, advising that the new revisions included instructions on purging the oil system after the work was completed. A video clarifying purging of the lubrication system was also included.

o Distributed Service Instruction SI-916 i-003R1 / SI-915 i-003R2 / SI-912 i-004R3 / SI-912-018R4 /SI-914-020R4 on the Rotax-owner website to provide further guidance for the lubrication system with respect to purging and venting and to avoid air in the lubrication system. They also advised that the service in...