Honeywell TFE731 N2 Monopole Improvement: SB Updates & Troubleshooting

March 2025

Honeywell has developed an N2 transducer that incorporates internal enhancements and improves the durability of the N2 transducer. The improved N2 monopole design includes:

• Larger wire & improved wrapping
• Weld improvement
• Vibration dampening (internal potting)
• Improved connector

SB (Service Bulletin) 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 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. SB72-3731 covers the installation of the proper engine harness. 

Troubleshooting N2 signal issues

When troubleshooting N2 signal issues, verify the P/N of the N2 monopole installed. Resistance values have been updated in the LMM via Temporary Revision. An EEI download containing an Event can be a valuable tool for troubleshooting these issues. In instances when resistance values are within limits, installation shimming should be checked prior to N2 monopole replacement.

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 those listed in the LMM. Refer to Service Information Letter D200808000038 for the correct values.

Preventive Maintenance

Apply waterproofing to N2 monopole connector. This may be accomplished if repeated intermittent fuel computer trips, attributed to N2 faults, are encountered.

For any technical questions about your TFE731 engines, I can be contacted at +1 308.249.6633 or via email at Shane.Mack@DuncanAviation.com.