During 2018 CASA was made aware that some operators of R22 and R44 helicopters were experiencing high replacement levels and low installation lives on engine cylinders primarily due to exhaust valve seat degradation and exhaust valve chipping resulting in a loss in valve seat sealing and cylinder compression on carburetted engines.
In most cases this loss of compression did not occur at once but over time. This would then lead to a gradual loss of power that is observable. CASA issued AWB 85-024 to advise owners, registered operators, pilots, maintenance organisations and Licensed Aircraft Maintenance Engineers of the R22/R44 exhaust valve issue.
CASA AWB 85-024: image of exhaust valve seat degradation
CASA AWB 85-024: image of exhaust valve chipping
However, there have also been less frequent occurrences with R44 helicopters and intake valve and vale seat distress, which can result in an induction backfire, engine power loss and a sudden momentary left airframe yaw. CASA issued AWB 85-025 to advise owners, registered operators, pilots, maintenance organisations and Licensed Aircraft Maintenance Engineers of the R22/R44 intake valve issue.
Robinson helicopters also released Service Letter SL-78 asking R44 operators to complete the intake valve survey, including differential compression test, per Lycoming Service Instruction (SI) 1577.
CASA AWB 85-025: combustion chamber view on intake valve crescent-shaped burn
CASA AWB 85-025: combustion chamber view on uneven heating at valve edge
CASA reviewed the aircraft defect database to establish if it had received previous reports of this loss of power through loss of cylinder compression. There was limited data available and CASA was not able to find a link or causal connection between incidents and a loss of cylinder compression.
As a result of the loss of compression some in the industry have expressed the view that these issues were related to the change in grade of the AVGAS being used which had higher levels of aromatics and a reduced lead content.
To address ongoing concerns and access more data CASA formed a stakeholder working group, consisting of Lycoming, Viva Energy, Brisbane Aero Engines, several affected operators, and CASA representative. This stakeholder working group met on several occasions and agreed to a range of cooperative measures to better understand the R22/R44 exhaust and intake valve issues. The potential contributing factors identified for follow up were:
- Aircraft/Engine Operating Conditions - Installation of Engine Data Monitoring kits (5 helicopters). The in aircraft operating data collected by AHIA and CASA were contradictory. CASA issued Airworthiness Bulletins AWB 85-024 and 85-025 provide guidance on Operating Procedures and Limitations
- Aviation Fuel - Independent Fuel Sampling (Intertek Nov 2018), Vopak Darwin fuel samples complied with the American Society for Testing and Materials (ASTM) specifications
- Lubricating Oils - Ongoing
- Engine Cool Down Procedures - Robinson Helicopters issued a specific Hot Climate Cool Down Procedure as an addendum to the Pilot’s Operating Handbook (POH) in February 2019. CASA issued Airworthiness Bulletins AWB 85-024 and 85-025 provide guidance on Operating Procedures and Limitations
- Engine Component Quality - Ongoing
Regular contact with Robinson Helicopters, Lycoming Engines, the Federal Aviation Administration (FAA) and the Australian Helicopter Industry Association (AHIA) has been maintained as CASA attempts to get a better understanding of what is influencing the change in R22/R44 durability.
The AHIA commissioned a report that investigated the R22/R44 engine durability concerns and whilst not conclusive in its findings the report did acknowledge that there was not a single contributing factor to the R22/R44 engine durability issues. The report did maintain the perception that the timing of the emergence of the durability issues (2018) aligned with when Avgas 100LL was introduced in Australia (2015). The report also acknowledged that the Air Transport Bureau (ATSB) safety information bulletin issued in November 2018 concluded that they did not identify a link between the introduction of Avgas 100LL in December 2015 and the reported engine-related occurrences in northern Australia. A recommendation from the report was to undertake further work to ore fully characterise the thermal and operational performance of aviation gasolines.
In addition to the measures identified by the stakeholders working group, CASA requested that Lycoming Engines conducted independent engine testing using the Avgas fuel grades available in Australia (Viva 100LL, Warter Fuels 100/130) and the United States (Phillips 66 Sweeny 100LL) at various test points including hot conditions at cylinder head, oil temperature and induction air limits. The testing was conducted using a stable workhorse engine in a controlled environment, oversighted by FAA and remotely witnessed by FAA, Robinson Helicopters and CASA.
Lycoming has recently provided the results of the engine fuel testing, via Lycoming Service Letter No. L282 dated December 11, 2020. Lycoming Engine’s conclusion of this testing was
“The results of the test showed negligible changes in engine operating characteristics between each fuel tested other than slight differences in exhaust gas temperature. There is no evidence that the differences in exhaust gas temperature exhibited during this test will have an impact on engine durability.”
CASA is satisfied with the independent testing conducted by Lycoming Engines and oversighted by the FAA and does not intend at this time to pursue any further review of the Aviation fuels used by R22/R44 operators.
CASA is in dialogue with the AHIA regarding establishing two working groups i.e. R22/R44 Operators and R22/R44 Maintainers at the beginning of 2021 to gather additional relevant data on the R22/R44 engine durability issue. CASA will continue to liaise with the relevant type certificate holders and State of Design National Aviation Authorities on this issue. CASA continues to be interested in obtaining additional information that will assist in making data driven assessments and decisions going forward.