Honeywell HTF7000 and HTF7350 Engine Inspection Intervals

The Honeywell HTF7000 (AS907-1-1A) and HTF7350 (AS907-2-1A) propulsion engines are used on the Bombardier Challenger 300 and Bombardier Challenger 350 aircraft, respectively. As with most modern turbofan engines, the HTF family of propulsion engines do not have mandatory scheduled overhauls or HSI (Hot Section) teardown inspections. Instead, they follow an on-condition maintenance program where the engine stays on wing until an issue arises during a scheduled inspection, an unscheduled event occurs, or an engine component reaches its life limitation. This makes budgeting engine maintenance costs more challenging, unless the engines are covered under a maintenance service program such as Honeywell’s MSP program.

Inspection requirements for the AS907-1-1A and AS907-2-1A engines are listed in Chapter 5 of both the applicable Airframe and Engine Maintenance Manuals (MM).

Honeywell and Bombardier have been collaborating on a program to extend the HTF periodic inspection intervals. That program recently completed a major milestone with the release of Chapter 5 revisions to both the Airframe and engine MMs in January of this year. Among the more significant changes are a 20% increase in the major periodic borescope inspection intervals, from the previous 4200 and 8000 hours for the turbine and compressor section borescope inspections respectively, to 4800 and 9600hrs.

Below is a summary of the more significant inspection requirements and applicable SBs (Service Bulletins). Please note that Chapter 5 of the applicable Airframe and Engine MMs should be consulted when determining engine maintenance requirements, and the below information should be considered reference only.

400 & 800 Hour Inspections

• SB (Service Bulletin) AS907-72-9084: Oil filter replacement and analysis requirement is now in the 150-250 hour range.

Airframe 4800 & Engine 4000/8000 Hour Inspections

• Bombardier has released Temporary Revisions 5-3-60 through 5-3-70 for longer engine inspections intervals. 4200 hour is extended to 4800 hour; 8000 hour is extended to 9600 hour.
• Engine SB requirements on all the tasks for the longer intervals are listed in the Engine MM in tables 8011 and 8012. The Bombardier Manual lists these bulletins for specific tasks as noted below:
  • SB AS907-72-9001: Installation of O-rings on the unison ring pins. Bombardier Temporary Revision 5-3-67 only requires this bulletin for the General Visual Inspection of the Compressor Guide-Vane Actuator System (Task 75-31-09-201). Best time to complete is at the 2000 hour when the engine is accessed on-wing.
  • AS907-72-9044: Replaces the engine combustion chamber assembly. Most engines are already in compliance. Bombardier Temporary Revision 5-3-63 only requires this bulletin for the Special Detailed Inspection of the Engine Combustor Module (Task 72-40-00-202). Not applicable to Challenger 350 (AS907-2-1A)
  • AS907-72-9048: Replacement of non-conforming spinner inner ring. Only applies to a few serial numbers. Not applicable to Challenger 350 (AS907-2-1A)
  • AS907-73-A9004: Replacement of non-conforming fuel controls. Applies to 13 engine SNs. Bombardier Temporary Revision 5-3-65 only requires this bulletin for the General Visual Inspection of the Engine Fuel System Components and Tubing (Task 73-10-00-201. Not applicable to Challenger 350 (AS907-2-1A)
  • AS907-76-9021: Application of sealant to prevent water entry into the ECU (electronic control unit). Most engines are already in compliance. This is applicable to AS907-1-1A, S/N P-136416 and before.   
  • SB AS907-72-9045/AS907-72-9080: Honeywell has a special program for replacement of the #4 bearing at the 4200 or 4800 hour inspection, as applicable. MSP will cover this cost. There is a discounted price for non-program engines. 
  • Engines with 8000 hours or more on the LPT2 blades require compliance with SB AS907-72-9067 per Bombardier Temporary Revision 5-3-63 to extend to the 9600 hour interval. This is specific to the Special Detailed Inspection of the Engine LP Turbine Module (Task 72-50-00-205). The Engine Manual does not list this SB in Chapter 5.

8000/9600 Hour Inspections

If an engine is in compliance with the SBs listed on the 4000/4200/4800 section and has completed the LPT2 blade z-form inspection per SB AS907-72-9067, as applicable, then the 8000 hour CSBI interval can be extended to 9600 hours.