CB70500-001- Boeing OEM Elevator Feel Computer

CB70500-001 – Boeing 737 Elevator Feel Computer

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Overview

The CB70500-001 is a flight-critical avionics Line Replaceable Unit (LRU) that functions as the Elevator Feel Computer for the Boeing 737 Classic and Next Generation series aircraft. In the B737's fully-powered hydraulic flight control system, pilots are isolated from the natural aerodynamic forces acting on the elevator. This computer's essential safety function is to synthetically recreate this crucial tactile feedback. By calculating and commanding a precise resistive force to the pilot's control column, it ensures predictable handling characteristics and prevents potentially dangerous over-control situations, especially at high airspeeds.

This computer is the computational core of the pitch feel system. It continuously processes inputs of computed airspeed and stabilizer position, applying a certified control law to determine the correct "feel" for any given point in the flight envelope. The result is a seamless and intuitive control response that mimics the feel of a conventional aircraft, providing pilots with the feedback necessary to fly the aircraft safely and accurately while protecting the airframe from exceeding its structural load limits.

Key Features

• Calculates Realistic Control Forces: Implements a sophisticated control law to provide artificial control column forces that are proportional to airspeed and adjusted for stabilizer trim.

• Dual-Channel Architecture: The system utilizes two feel computers for redundancy, ensuring fail-operational capability and meeting the highest safety standards for a critical flight control system.

• Processes Critical Flight Data: Interfaces directly with the aircraft's Air Data Computers (ADCs) and stabilizer position sensors to gather the necessary parameters for its calculations.

• ARINC 429 Data Bus Interface: Receives primary airspeed and Mach data via the industry-standard ARINC 429 digital data bus for high-integrity communication.

• Robust Avionics Construction: Housed in a standard ARINC form factor, this LRU is designed and tested to withstand the rigorous vibration, temperature, and electrical environments of a transport category aircraft.

• Core Component of 737 Pitch Feel: Serves as the central processing unit for the elevator feel and centering system, a fundamental component of the B737's certified handling characteristics.

Technical Specifications

• Part Number: CB70500-001

• Component Type: Elevator Feel Computer / Flight Control Computer

• OEM Design Authority: Boeing

• Typical Manufacturer: Crane Aerospace & Electronics (Eldec Corporation)

• Primary Inputs: Computed Airspeed (CAS)/Mach Number (via ARINC 429), Stabilizer Position.

• Primary Output: Analog electrical command signal to the Elevator Feel and Centering Unit.

• Material (Case): Standard aerospace-grade aluminum alloy.

Aircraft Compatibility

This computer is a standard component across two major generations of the world's most produced commercial jetliner.

• Aircraft Application:

  • Boeing 737 Classic: -300, -400, -500

  • Boeing 737 Next Generation: -600, -700, -800, -900, BBJ

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft's Illustrated Parts Catalog (IPC) and Aircraft Maintenance Manual (AMM) to confirm part number eligibility for a specific aircraft serial number.

Applications

• Sole Application: Pitch Axis Artificial Feel Computation. This computer's only role is to calculate the appropriate resistive force for the elevator control system, ensuring the pilot's control column forces are proportional to the aircraft's speed and configuration.

Why Choose CB70500-001?

Correct elevator feel is not a matter of comfort; it is a certification requirement and a cornerstone of flight safety. A malfunctioning feel computer can lead to dangerously light control forces at high speed (risking structural overstress) or excessively heavy forces during approach (risking a stall). Choosing the genuine OEM CB70500-001 ensures that the unit contains the correct, Boeing-certified software and hardware, guaranteeing that the aircraft's handling qualities are maintained as designed. The use of unapproved or improperly repaired parts introduces an unacceptable risk into a primary flight control system.

In the Boeing 737's hydraulically actuated, irreversible flight control system, the direct mechanical link that provides natural aerodynamic feedback is severed. The CB70500-001 computer re-establishes this critical human-machine interface synthetically. It continuously solves a pre-programmed polynomial control law where the primary independent variable is dynamic pressure (qc​), which is derived from the computed airspeed received from the air data computers. This ensures the feel force applied to the control column varies approximately as the square of the airspeed (Force∝V2), mimicking natural aerodynamic behavior. A secondary input, stabilizer position (δstab​), biases this primary calculation to compensate for changes in aircraft trim and pitching moment. The computer's output is a precise electrical signal to a torque motor in the hydromechanical feel and centering unit, which in turn modulates hydraulic pressure to generate a resistive force, thus ensuring the aircraft's handling qualities comply with the pitch control force requirements of 14 CFR §25.143.

Note: This is a flight-critical avionics Line Replaceable Unit (LRU) that directly affects the aircraft's handling qualities. Installation, removal, and testing must be performed by certified avionics technicians in strict accordance with the Aircraft Maintenance Manual (AMM). Post-installation system tests are mandatory to verify correct communication with input sources and proper response of the feel system before the aircraft is returned to service.

Documentation

No public-facing OEM or regulatory documentation was located for this part. All technical data, installation procedures, and maintenance specifications are proprietary to Boeing and are contained within the official Aircraft Maintenance Manual (AMM) and Component Maintenance Manual (CMM).