3 TIPS FOR MONITORING HELICOPTER ENGINE POWER
In the helicopter world, it’s a given that engine performance will change over time. Routine power assurance checks will help you know when you need to take action.
1. SEE TRENDS WITH FREQUENT POWER ASSURANCE CHECKS
Helicopter operators use power assurance checks (PACs) to better understand turboshaft engine performance in real time. This data becomes even more beneficial if operators trend PAC results over time to gain a better understanding of changes in the engine’s condition.
This is known as Engine Condition Trend Monitoring (ECTM) or Helicopter Engine Condition Trend Monitoring (HECTM) for helicopters. Routinely reviewing trend data allows you to keep a close watch on your engines, recognize significant trend changes as soon as they begin and take prompt action. For that reason, regular PACs are highly recommended, as Pat DiRico, P&WC Customer Engineering, Turboshaft Engines, explains.
Although there are specified intervals for PACs in the Rotorcraft Flight Manual, we know that the more frequently PACs are done for trending purposes, such as every 10 hours, the better. This allows you to identify the early onset of cold or hot section deterioration.
The process can be greatly simplified with P&WC's FAST™ solution for engine health management. Available on PT6C-67C-powered Leonardo AW139 helicopters, FAST captures, analyzes and wirelessly transmits data relating to power and a host of other engine and aircraft parameters after each flight, within minutes of engine shutdown. For helicopter operators, it also enables automatic power assurance checks with a display in the cockpit – reducing pilot workload and potential for human error.
2. MONITOR THE TRENDS
Two engine parameters are recorded and evaluated during PACs. One is the Inter Turbine Temperature (ITT) or, depending on the engine model, Measured Gas Temperature (MGT). The other is compressor rotor speed, also known as Ng.
The specification (“spec”) engine values for these parameters—commonly referred to as thresholds—are determined based on the outside air temperature (OAT) and pressure altitude (PAlt) on the day the PAC is performed. The PAC charts in the Rotorcraft Flight Manual include performance curves that represent the engine parameter characteristics over a wide range of ambient pressures and temperatures.
“Most operators tend to use the PAC as confirmation that they have some margin remaining from the threshold,” says Pat. “In other words, as long as there is still some margin, the engine is considered good to go. While this may be true over the life of the engine, any rapid change in margin, such as a 10-degree or 1.5% change in the past 50 hours, indicates a possible engine issue that needs to be investigated.”
If the performance values are running close to the recommended threshold, or if a shift is observed from the last PAC, it is an indication that follow-up work should be done.
The follow-up action might be to repeat the PAC (because, for instance, the customer bleed was not turned off), do a compressor performance recovery wash or perform a borescope or hot section inspection.
3. PERFORM TROUBLESHOOTING BASED ON TREND RESULTS
The specific engine parameter margin shift can be used to determine whether you need to address a cold section (compressor) issue, a hot section (turbine section) issue or simply an indication issue. For example, if there is a shift in the ITT/MGT margin and no shift in the Ng margin, it may be an indication issue.
With the knowledge provided by HECTM, you can concentrate on the real problem instead of wasting time and resources looking elsewhere. What’s more, if there’s work that needs to be done, you can plan around it. In other words, HECTM allows you to proactively decide when to do maintenance rather than being unexpectedly grounded due to performance issues.
The Engine Maintenance Manual’s power plant fault isolation chapter (chapter 71-00-00) includes all the recommendations and fault isolation procedures you may need for performance-related issues. Most can be carried out at the operator’s facility. If required, you may also call your P&WC Field Support Representative or the CFirst Centre for assistance.
Want more advice from our experts? Read our article on 4 Must-Haves for Helicopter Engine Line Maintenance.