Background

In July 2018, the ATSB received correspondence about the possibility of an increased number of engine issues involving helicopters, in particular Robinson helicopters fitted with Lycoming engines. It was suggested that the issues may have been related to the reduced lead content in aviation gasoline in northern Australia.

The Civil Aviation Safety Authority (CASA) had also received multiple reports from helicopter operators in northern Australia, including Katherine, Broome, Darwin and Alice Springs, of engine faults that the operators believed may be the result of reduced lead content.

The type of issues reported included premature cylinder removals, and a high rate of exhaust valve and guide wear. These issues were reported to occur more frequently in Lycoming engines fitted to Robinson helicopters conducting mustering operations.

CASA advised the ATSB that, in December 2015, the colour and branding of fuel supplied to the northern region of Australia changed, from green Avgas 100/130 to blue Avgas 100LL (low lead). Although the maximum permissible lead content reduced from 0.83 g/l to 0.56 g/l with this change, the actual lead content of the supplied Avgas 100/130 fuel had already been below the maximum permitted by the Avgas 100LL standard prior to this date. In addition, the same low lead fuel has been provided to other regions of Australia for some years without similar engine issues being reported.

ATSB occurrence database search

Search criteria

In response to the above reports, the ATSB reviewed their incident and accident (occurrence) data to explore the existence or extent of any increase in reported engine issues in northern Australia. As the change in fuel would have applied to all piston-engine aircraft, the search initially included all piston-engine aircraft types and then narrowed to look at Lycoming engines. The search of the ATSB’s database was based on the following criteria:

• A time period of 1 January 2008 to 30 June 2018 (the full year 2018 results were estimated by multiplying the known 2018 data by two, which is graphically presented by a broken line – no seasonal effects were identified for Lycoming engines between January to June compared to July to December in previous years).
• All piston-engine aviation gasoline-powered aircraft (including fixed-wing and rotary-wing).
• Occurrences where an engine failure or malfunction was reported; those where only an abnormal engine indication was reported were excluded.
• The occurrences identified were the result of a number of different failure mechanisms.

Limitations

The ATSB acknowledges that limitations exist in the analysis of occurrence data in the manner presented here; in particular, it highlights the following:

• The results are based on the number of occurrences only and do not take into consideration flying activity, aircraft or operational factors, or seasonal and environmental influences.
• The analysis is based on occurrences reported to the ATSB as per the requirements of the Transport Safety Investigation Act and Regulations (2003). The initial correspondence to the ATSB identified that the issue was being observed, in part, during maintenance, which is not required to be reported to the ATSB. Therefore, the results contained herein are likely to under represent an accurate number of instances.
• The analysis is based on the location of the reported engine failure or malfunction. This does not necessarily represent the location where the aircraft was last refuelled.
• The details of the fuel used, including the grade and provider, for each occurrence were not known.

Results

All piston engines (2008 – 2018)

The search results were grouped by location to allow for a comparison between ‘northern’ Australia (Western Australia, Northern Territory and Queensland), the areas most affected by the 2015 change to Avgas 100LL, and ‘southern’ Australia (remaining states and territory). However, it should be noted that the southern regions of Western Australian and eastern Queensland had previously transitioned to Avgas 100LL.

The results presented in Figure 1 show:

• The total number of reported piston-engine related failures or malfunctions remained relatively stable over the reporting period.
• With the exception of 2011, the number of occurrences recorded in northern Australia remained less than that observed in southern Australia. Overall, there was no substantial deviation in trend between the two regions.
• The number of occurrences recorded in northern Australia was similar between 2013 and 2017, with a slight increase observed in 2015 (n=86).

Figure 1: Engine failures or malfunctions involving piston-engine aircraft, 2008 – 2018

Note: 2018 estimate has been extrapolated from 6 months of data

Northern Territory (2008 – 2018)

The majority of the area identified by CASA as being affected by the fuel supply change was within the Northern Territory. As such, a search was conducted for occurrences within the Northern Territory only.

The results presented in Figure 2 show:

• While overall the figures fluctuated, the number generally declined in the Northern Territory, with 23 engine failure or malfunction occurrences recorded in 2008 and 10 in 2017. It was unknown if the overall variance was attributed to the small number of occurrences recorded, was representative of changing flying activity, or was influenced by other unknown factors.
• The increase for northern Australia in 2015 as shown in Figure 1 (and below in Figure 3) is not present in Northern Territory data.
• The number of engine failures or malfunctions recorded in 2015 and 2016, around the reported time of the introduction of Avgas 100LL, were similar or slightly lower than average compared to previous years. This does not support a hypothesis that a change in the fuel supply at this time has had an overall effect on engine failures or malfunctions. However, it should be noted that problems identified during maintenance were not required to be reported to the ATSB, and are not included in these figures.

Figure 2: Engine failures or malfunctions involving piston-engine aircraft in the Northern Territory, 2008 – 2018

Note: 2018 estimate has been extrapolated from 6 months of data

Lycoming piston engines (2012 – 2018)

The search was refined to look at occurrences where Lycoming was identified as the engine manufacturer. As engine manufacturer information was not accurately available prior to 2012 in the ATSB database, the search was limited to occurrences after 1 January 2012.

The results presented in Figure 3 show:

• Occurrences of engine failure or malfunctions involving Lycoming piston engines in northern Australia fluctuated between 2012 and 2017, with a peak in 2015 (n=44). Preliminary data for 2018 suggests that occurrences will be at a similar level to that observed in 2012.
• An increase in the total number of reported occurrences was observed in 2015. This was largely influenced by the increase in northern Australia. However, while the total number remained high in 2016, this was largely due to an increase in southern Australia.

Figure 3: Engine failures or malfunctions involving Lycoming piston engine aircraft, 2012 – 2018

Note: 2018 estimate has been extrapolated from 6 months of data

Helicopters with Lycoming piston engines (2012 – 2018)

While the introduction of Avgas 100LL in December 2015 affected the supply for all piston-engine aircraft, the reports of engine issues received by ATSB and CASA specifically related to helicopters powered by Lycoming piston engines. Based on this, the search was modified to consider only helicopters fitted with Lycoming engines.

The results presented in Figure 4 show:

• Due to the low number of occurrences of engine failure or malfunction in Lycoming engined helicopters, the results of figure 4 should be treated with caution.
• There was an increase in occurrences in northern Australia from 2014 (n=3) to 2017 (n=6), although these numbers have fluctuated over the years. Between January and June 2018, five occurrences were reported to the ATSB.
• The total number of reported occurrences of engine failures or malfunctions in helicopters with Lycoming engines from 2012 to June 2018 was higher in northern Australia (n=35) compared to the south (n=9). There were no occurrences in southern Australia for 2014-2016.
• As flight activity data was not available by region, it was not possible to identify if northern Australian occurrences were disproportionately high.

The results were not limited to Robinson helicopters and included helicopters from other manufacturers fitted with Lycoming engines. Of the 35 occurrences reported in northern Australia, 11 and 20 involved Robinson R22 and R44 helicopters respectively, the remaining four involved helicopters from other manufacturers.

Figure 4: Engine failures or malfunctions involving helicopters with Lycoming piston engines, 2012 – 2018

Note: 2018 estimate has been extrapolated from 6 months of data

As discussed earlier, the results above present all reported instances of engine failure or malfunction. A further search was conducted in order to gain an appreciation of the failure mechanism precipitating the engine failure or malfunctions of helicopters fitted with Lycoming engines.

The results presented in Figure 5 show:

• Northern Australia was dominated by occurrences where the failure mechanism was either ‘unknown’ (34 per cent) or was related to a magneto or electrical issue (31 per cent). Actual or suspected carburettor icing was also observed, accounting for 14 per cent of the occurrences. Three occurrences of interest relating to internal engine failures (valve, cylinder or crank assembly issue) were identified, although the first two occurred before the date of the introduction of Avgas 100LL:
  • 10 January 2013: A Robinson R44 helicopter lost power during cruise. The crew heard a loud bang accompanied by a loss of power and abnormal engine indications. The crew conducted a precautionary landing in the nearest clearing. An engineering inspection revealed metal shavings in the oil filter indicative of internal engine failure (ATSB reference number: 201300292).
  • 28 February 2015: An Enstrom 280 helicopter departed Caloundra Airport, Queensland on a private fight to Redcliffe. During the cruise, the engine failed and the pilot conducted a forced landing. A subsequent maintenance inspection found damage to the number three cylinder and piston, consistent with detonation (ATSB reference number: 201500662).
  • 4 February 2016: After take-off at Headingly, Queensland, the Robinson R22 helicopter lost power and the pilot conducted a forced landing. An engineering inspection revealed heavy carbon deposits suspected to be from excessive unburnt fuel in the engine intake valves (ATSB reference number: 201600161).

• A disproportionate number of the engine failures where the failure mechanism remains unknown (9 out of 12) in northern Australia occurred between 2016 and June 2018, after the introduction of Avgas 100LL in December 2015. Symptoms of some of the failures and subsequent power loss were reported by pilots to include:
  • reporting a loud bang
  • suspected magneto or governor failures
  • a noticeable yaw developing at the time of failure.

Figure 5: Failure mechanism for engine failures or malfunctions involving helicopters with Lycoming piston engines, 2012 – 2018

Industry action

Northern Fuels Stakeholder Investigation Group

In July 2018, a working group was formed, with representatives from operators, maintainers, the primary affected engine manufacturer, the fuel supplier and CASA, to discuss the fuel concerns. The group noted that Avgas fuel quality was one area of inquiry and that no conclusions had been made at this stage regarding a potential fuel-related issue.

Airworthiness bulletin (AWB) 85-024 Issue 1 – 2 August 2018

In August 2018, CASA issued an airworthiness bulletin (AWB) in relation to piston engine exhaust valve and valve guide distress. The purpose of the AWB was to advise of an ‘increasing incidence of premature exhaust valve and valve guide wear, due to elevated combustion temperatures’. This AWB identified the affected population as Robinson helicopters fitted with Lycoming engines located in the northern regions of Australia.

The AWB also identified that, ‘it has not been conclusively determined that changes in the fuel composition is the source of the engine problems’ and that ‘the described problem is not limited to Lycoming products… with Continental engines installed in fixed wing aircraft also having similar occurrences’.

CASA also encouraged operators to ‘Report all instances of premature exhaust valve and guide wear to CASA via the DRS system available on the CASA website’. CASA’s defect reporting service (DRS) is a mechanism of reporting and recording of problems identified during maintenance. As discussed earlier, problems identified during maintenance are not necessarily reported to the ATSB, and CASA’s DRS data was not included in the ATSB’s analysis.

Conclusions

A review of the ATSB’s occurrence data found that:

• There has been no discernible increase in reported engine failures or malfunctions in northern Australia after the introduction of Avgas 100LL in December 2015.
• There was an increase in reported occurrences of engine failures or malfunctions in helicopters with Lycoming piston engines since 2014, largely dominated by northern Australia. However, occurrence numbers are low so some year-to-year variation from chance alone is expected. Additionally, the increase did not align with the introduction of Avgas 100LL in December 2015.
• A disproportionate number of helicopter engine failures or malfunctions where the failure mechanism could not be identified occurred after the introduction of Avgas 100LL in December 2015. Although it could not be identified what these failures were at the time of publication, the possibility that new factors may exist contributing to engine failures in northern Australia cannot be eliminated.
• Overall, the review did not identify a link between the introduction of Avgas 100LL in December 2015 and reported engine-related occurrences in northern Australia. However, taking into account the data limitations, the small number of occurrences, and the proportion of unknown failure mechanisms, it was not possible to draw any absolute conclusions.