3070800-42 - Honeywell Aerospace Turbine Engine Main Fuel Control Assembly

3070800-42 – Honeywell Aerospace Main Fuel Control (MFC) Assembly

Available now through the AirParts Aero marketplace.

Overview Section

The Honeywell 3070800-42 is a high-performance Main Fuel Control (MFC) unit, also known as a Fuel Control Unit (FCU). It is a critical hydro-mechanical "analog computer" designed for the Honeywell TFE731 turbofan engine series. The -42 dash number is a specific calibration optimized for high-thrust variants, providing the refined fuel scheduling required for modern transcontinental business jets.

This assembly is the central intelligence for engine power management. It continuously calculates the optimal fuel-to-air ratio by monitoring pilot input via the Power Lever Angle (PLA) and cross-referencing it with two vital environmental signals: Compressor Discharge Pressure ($P_3$) and Inlet Temperature ($T_2$). The 3070800-42 ensures the engine remains within its certified performance envelope, protecting against compressor surges and over-temperature events.

Key Features Section

• Precision Hydro-Mechanical Logic: Utilizes a complex system of internal cams and bellows to translate pneumatic and mechanical inputs into precise fuel metering.

• Refined Acceleration Schedules: Features an advanced internal cam profile that allows for rapid throttle advances while maintaining a safe margin from the engine's surge line.

• Dual Speed Governing: Incorporates internal mechanical flyweights to maintain stable $N_2$ speeds, preventing RPM "hunting" and providing overspeed protection.

• Altitude and Temperature Compensation: Automatically adjusts fuel flow as air density changes with altitude or temperature, ensuring consistent thrust and preventing "rich blowout."1

  
  

  
  

• Ruggedized Aerospace Construction: Housed in a high-strength aluminum alloy casing designed to withstand the vibration and thermal loads of the Accessory Gearbox (AGB) mounting.

• Service Bulletin (SB) Maturity: As a mature configuration, the -42 variant often includes hardware refinements that improve the service life of internal bellows and drive-train components.

Technical Specifications Section

Aircraft Compatibility Section

The 3070800-42 is a primary fuel management component for several high-performance aircraft in the AirParts Aero inventory:

• Dassault Falcon 50EX / 900 / 2000: Critical for the engine synchronization and fuel efficiency required for long-range missions.

• Hawker 800XP / 850XP / 900XP: Essential for the reliability of the TFE731-5BR and -50R powerplants.

• Learjet 40 / 45 / 45XR: Provides the crisp, linear throttle response characteristic of the Learjet flight envelope.

• Gulfstream G100 / G150: Utilized for precise thrust management and operational reliability.

Technical Applications & Safety

The MFC operates as a closed-loop feedback system. It senses the actual work the engine is performing (via $P_3$ compressor air) and compares it to the pilot's request. If the $P_3$ sensing line is restricted by carbon buildup or moisture, the 3070800-42 will sense an artificial "low air" condition and limit fuel, preventing the engine from reaching takeoff power.

Safety Warning: Installation requires a mandatory "Part Power Trim" procedure. This is a safety-of-flight task performed on the ground to synchronize the FCU to the engine's specific Interstage Turbine Temperature (ITT). Failure to correctly rig the 3070800-42 can result in "Hot Starts" or over-temperature events that can cause permanent, multi-million dollar damage to the turbine's hot section.

Technical Engineering Insight

The engineering value of the 3070800-42 lies in its Signal Dampening Architecture. In high-pressure turbofans, the $P_3$ air can be highly turbulent. The -42 variant utilizes internal dampening orifices to smooth these pressure pulses before they reach the sensitive bellows. This ensures a rock-steady power setting even in turbulent flight conditions, which is vital for the accuracy of modern autothrottle systems.

By sourcing a certified 3070800-42 through AirParts Aero, you ensure that the unit has been bench-tested to verify its Steady-State and Transient Schedules match the Honeywell master engineering curve, protecting your engine from surge-induced flameouts.

Installation & Maintenance Addendum

1. $P_3$ Line Integrity: Always blow out the $P_3$ sensing line and install a new $P_3$ air filter when replacing the MFC.

2. Drive Spline Lubrication: Apply the specified high-pressure anti-seize lubricant to the drive splines to protect against "fretting," which can lead to a mechanical failure of the drive input.

3. Preservation: If the unit is removed for storage, it must be filled with MIL-PRF-6081 (Grade 1010) preservation oil. If left dry, the internal steel bellows can become brittle, leading to a loss of calibration.