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TFE731 Improved N2 Monopoles

September 2009

Honeywell has introduced new N2 monopoles with internal enhancements that improve N2 monopole durability. Service Bulletin (SB) 77-3023 covers all TFE731-2/3/4/5 engine models and replaces N2 monopole P/N 3070722-3 with P/N 3070722-10.

Hawker Exceptions

The above SB does not apply to the TFE731-5BR-1H engine (Hawker 800XP). Instead, this engine utilizes SB 77-3022 which replaces N2 monopole P/N 3070722-3 with P/N 3070722-9. The Hawker 800XP application also requires a specific engine harness when upgrading to the improved N2 monopole. Engine harness P/N verification is necessary. If the improper harness is used, the N2 monopole will not fit correctly and could result in intermittent N2 signal loss. SB 72-3731 covers installation of the proper engine harness.

Troubleshooting N2 signal issues

When troubleshooting N2 signal issues, verify the P/N of N2 monopole installed. Resistance values have changed and the LMM does not reflect the correct resistance values for improved N2 monopole. Always refer to Service Bulletins for correct resistance values.

Spare Parts Bulletin

TFE731-20/40/50/60 engines also have an improved N2 monopole introduced through a Spare Parts Bulletin. N2 monopole P/N 3070722-8 replaces P/N 3070722-7. Also, when troubleshooting N2 signal issues, always verify the P/N of N2 monopole installed. The resistance values are different than listed in the LMM. Refer to Service Information Letter D200808000038 for the correct values.

Please contact a Duncan Aviation Turbine Engine Tech Rep for more information.