By Paul Groves
Pratt & Whitney of Canada has developed many series of turboprop, turboshaft, and turbofan engines over the years. The most recent production series for corporate jet aircraft is the 530A/535A engines. The PW 530A engine was introduced in December 1995 on the Cessna Citation Bravo. This engine is a 3.24:1 high by-pass, twin-spool engine with a rated take-off thrust of 2,887 pounds. In June 1999, the PW 535A engine was introduced on the Cessna Citation Ultra/Encore. This engine is 8 inches longer than the 530A due to the addition of another compressor stage. This engine shares the same core as the PW 530A. It is rated at 3,360 pounds of thrust at take-off and has a 3.5:1 high by-pass ratio.
The new generation PW 530A/535A engines have their roots in the PW JT15D. Two special features set this engine series apart. The first is the use of an integrated blade rotor (IBR) design. The first stage rotor is milled from a solid block of titanium alloy. The second feature, the Axiam Inc. method, is the high precision, computerized stacking and balancing of the compressor and turbine rotating components.
As with any advanced engine, to effectively troubleshoot an engine problem, you must know the symptoms. We can compare troubleshooting to a trip to the doctor. If we visit the doctor and tell him, "I don’t feel well," the doctor could very well order many tests, costing thousands of dollars. Ineffective troubleshooting can result in excessive labor costs and unnecessary parts replacement costs. Getting detailed descriptions of the write-up is the starting point. If you receive a write-up that says, "The left engine is sluggish" and you have the pilot at hand, you can begin the interrogation. But if the pilot hands you the logbook and walks away – well, you have been there and so have I. Getting as much detail of the nature of the problem, and the circumstances surrounding it will make troubleshooting easier. Always refer to the maintenance manual and troubleshooting decision trees for assistance.
The left engine (opposite page) is the PW 530 engine. The right engine is the 535. As a matter of convenience, I will discuss a few basic troubleshooting tips by reference to the engine system.
Upon approaching the engine check the inlet cone for oil. Any oil present is an indication of a bad No. 3 seal and the engine is no go and requires overhaul.
The next inspection area is the integrated blade rotor (IBR). As this component is made of titanium alloy, do not touch it with your bare hands or with dirty gloves or rags. This will cause stress risers and could lead to corrosion of the rotor.
Remember to always keep lead away from titanium. Any damage to the IBR should be evaluated IAW the aircraft/Pratt & Whitney Maintenance Manual before flight is permitted.
Engine surging at cruise or a decrease in engine performance may indicate a malfunction in the bleed valve system. A malfunction of the bleed valve system will result in the compressor bleed valve control automatically going to a pneumatic backup mode. Also note that loss of the dedicated N2 speed signal to the bleed control valve will result in automatic reversion of the bleed off valve to the manual pneumatic backup mode.
If you experience higher than normal fuel flow you may have a degraded high pressure compressor.
If increases in T4.5 (Inter Turbine Temperature) and N2 are encountered, one should inspect the high-pressure compressor for foreign object damage, dirt, or erosion.
A gas generator case drain stuck open will result in high fuel flow, increasing ITT, and increasing N2.
An increase in T4.5 with increased fuel flow and decreasing N2 at a given power setting may indicate damage to the high pressure turbine vane ring airfoils or vanes (FOD, burning, or erosion). Also suspect damage to the high pressure turbine blades (FOD, burning, or erosion). Leaking or damaged sealing rings may also produce similar results.