Your engine is designed for the cold. Like aircraft that fly at sub-zero, high-altitude temperatures, engines are
also built to handle cold weather operations. Harsh, icy conditions can cause some difficulties for aircraft
operators. Preparing the engine for cold can help.
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.
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
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
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.