ENGINES
• Minimum fuel fl ow stop setting too high – Replace the fuel control unit
• Fuel nozzle restriction – Check the fuel nozzles; if the spray pattern does not reach the igniters, this will cause a fl ame out
• Fuel manifold adapters in the wrong position – Confi rm proper position by referencing the installation manual
• Start control transfer valve stuck open – Remove valve, clean and polish
• Dump valve in fl ow divider stuck closed – Replace unit
• Defective N1 indicator – Reads high, which causes early entry of fuel; replace N1 indicator
Operating Problems
Compressor Overspeed (N1) • Sheared fuel control unit drive coupling – Replace the fuel control unit and coupling • Defective fuel control unit bypass diaphragm
– Replace fuel control unit
• Fuel control unit bypass valve stuck closed – Replace unit
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Vibration • The compressor is out of balance and causes a steady hum – Check for FOD – Check bleed valve for being stuck shut; this will cause a higher-than- normal ITT at idle
• The compressor is out of balance and causes an intermittent hoot – This condition is okay if hoot goes away by 60-percent N1 rpm; check turbine balance.
• The power turbine out of balance – Check power turbine for balance and failure
High N1 RPM • Check the indicating system – Replace the indicator as necessary
• The compressor is dirty – Perform a compressor wash
• Possible compressor FOD – Check the fi rst-stage blades for FOD/damage
• Compressor bleed valve(s) are open – This will give an accompanying high ITT; have the bleed valve(s) bench checked
• Excessive P3 air leaks – Check all gas generator gaskets for integrity and security
Uncontrolled Acceleration • The fuel control unit drive is sheared – Replace coupling and fuel control unit
• Fuel control unit bypass diaphragm is ruptured – Replace the fuel control unit
• Fuel control unit bypass valve is stuck closed
– Replace the fuel control unit
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22
HelicopterMaintenanceMagazine.com April | May 2014
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