JT15D Engines Fall 2000

• JT15D-5A/5D High Idle Setting Reference Service Information Letter JT15D-010R1
• Test Flight Requirements

JT15D-5A/5D High Idle Setting Reference Service Information Letter JT15D-010R1

JT15D-5A/5D operators often ask for the recommended Idle Setting to be used in ground operation. Service Information Letter 7077 was issued in 1994; it recommended that the High Idle setting be used wherever possible during ground operations to reduce the carbon build-up in the old style “duplex” fuel nozzles. After the introduction of the new style “hybrid” fuel nozzles, one of their advantages is the ability to resume ground operations in the Low Idle setting.

The “hybrid” fuel nozzle has shown an improvement in performance over the earlier “duplex” nozzle; however, field experience has indicated that the new “hybrid” design can also be susceptible to carbon build-up. The carbon build-up forms in the primary nozzle tips and the fuel passages of the nozzle adapters. This causes an increase in time-to-idle during the start process. In some cases, particularly in cold weather, start times have exceeded limits resulting in the removal of the nozzles for refurbishment.

Due to the continuation of carbon build-up in the new style “hybrid” fuel nozzles, Pratt & Whitney has recommended the following in order to minimize the occurrence of fuel nozzle contamination:

1. Continuation and reinforcement of the use of the High Idle setting for ground operations, whenever conditions allow. In conditions that demand a minimum thrust setting, Low Idle should be selected after the ITT has fully stabilized.
2. The recommended idle time prior to engine shut-down must be observed, as per the Aircraft Flight Manual, to minimize the amount of heat “soak-back” which aids in the formation of carbon build-up.

For detailed information on this subject reference Pratt & Whitney Service Information Letter JT15D-010R1 and/or contact Ken Kuchenreuther in BTL at 800.525.2376 or contact Doug Alleman in LNK at 800.228.4277.

Test Flight Requirements

Following specific maintenance events on the JT15D, operators should expect to complete functional flight check requirements to ensure correct engine operation before continued service. These events include, but may not be limited to, an engine replacement, engine overhaul, fuel control unit replacement or fuel control adjustment.

Some of the checks completed verify engine idle and acceleration settings. These checks are done at 14,000 feet and are the only way to verify correct fuel control settings. If the fuel control settings are not correct, operators may experience a variety of discrepancies during engine operation.

As always, be sure to consult the Pratt & Whitney and Airframe Manufacturers maintenance manuals for proper procedures.

For more information, please contact Ken Kuchenreuther in BTL at 800.525.2376 or Doug Alleman in LNK at 800.228.4277.

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