JT15D Engines Winter 1999
JT15D ITT Ground Fluctuations
Occasionally, operators need to monitor ITT at take-off power on the ground to evaluate engine performance. On Citations incorporating JT15D-4,-4B and -5A engines, a 30 to 40 degree ITT fluctuation may be noticed on the left hand engine while at power.
The Pratt & Whitney JT15D engine ITT indication is a combination of several computations. T6 (exhaust temp.) is measured and added to 3 times the rise in the fan bypass temperature. As inlet air passes through the fan and is compressed, there is a rise in temperature. The rise in fan bypass temperature is measured by 2 probes in the fan bypass duct. One in front of the fan and one in the rear of the duct. This calculation is then standardized by use of a variable resistor and shown on the cockpit ITT Gauge.
Due to the position of the left engine on the airframe and the absence of any RAM effect on the inlet, a vortex of cool air is intermittently drawn over the fan bypass probe causing fluctuations in indicated ITT. As a result of the probe cooling down with no change in the fan bypass duct outlet temperature, the ITT indication increases.
When recording left engine ITT at take-off power on the ground, always record the lowest indicated ITT during the fluctuation. Provided the aircraft is not on a take-off roll or in flight, this will be the most accurate ITT indication for the left engine.
Remember to observe all precautions while running engines at power on the ground.
JT15D Active Commercial Support Programs
Programs available from Pratt & Whitney to provide financial support for inspection, replacement or modification of specific components.
Program # |
Close Date |
Description |
| C91075R2 | 12/31/99 | Pre SB7187 Impeller Replacement |
| A940 16R2 | 12/31/00 | Diffuser Pipe Replacement |
| A94023 | 11/30/00 | Intermediate Case Replacement |
| A95023 | 1/31l/00 | Fuel Line Support Strut |
| A95024 | 6/30/00 | Outer By-pass Duct Rear Flange Crack Repl |
| A96007 R1 | 6/30/00 | HT Blade Lean Inspection |
| A96029 | 11/30/00 | Rear Inner Compressor Assy (Booster) Mod |
| C87006Rl | 12/31/00 | Gas Gen. Case Replacement (Deep Drawn) |
| A98039 | 12/31/01 | Hot Section Improvement |
| A96023 | 6/30/01 | Introduction Of New #2 & #3 LRC Bearings |
JT15D ITT Oil Leaks
Engine oil leaks have always been a concern for aircraft operators. Learning about the causes of leaks and corrective actions, may help when a puddle of oil is found under an engine.
Many leaks on the JT15D are discovered the day after a trip or a few hours after engine shutdown. The first step in troubleshooting the problem is to remove the cowling and ensure that the engine does not have an external oil leak (a loose fitting, defective hose ect...). Next, determine if oil is dripping out of the breather tube or an accessory drain line. Oil dripping from either of these areas for a short time after shutdown usually indicates a stuck oil check valve or a defective o-ring in the check valve itself.
Oil dripping from these areas after a few days to a week can mean a defective oil pump or an internal leak. Troubleshooting a defective oil pump or an internal engine leak requires 12 to 24 hours to obtain accurate results.
Oil leaks are not always as serious as they first appear and can often be corrected with little downtime, but they should always be addressed before further operation.
Be sure to maintain proper oil levels and consult the maintenance manual for approved procedures.
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