F80055-36 – Trammel Bar Assembly for Stabilizer Trim Actuators

The Boeing F80055-36 Trammel Bar Assembly is a precision measurement tool used to verify that the horizontal stabilizer trim actuator is correctly rigged during functional testing on Boeing 737 aircraft. The stabilizer trim actuator controls the angular position of the horizontal stabilizer, which is the primary means of adjusting aircraft pitch trim in flight. Accurate rigging of this actuator is critical to longitudinal stability, autopilot performance, and safe handling characteristics across all flight regimes — making this trammel bar one of the most safety-significant measurement tools in the 737 flight controls tooling inventory.

Aircraft Applicability

• Boeing 737-100 / 737-200 (Original)
• Boeing 737-300 / 737-400 / 737-500 (Classic)
• Boeing 737-600 / 737-700 / 737-800 / 737-900 (NG)
• Boeing 737-8 / 737-8200 / 737-9 / 737-10 (MAX)

Purpose & Function

The horizontal stabilizer trim system on the 737 uses a jackscrew-driven actuator to position the entire horizontal stabilizer — not just a trim tab — through a range of nose-up and nose-down positions. The Boeing AMM specifies precise rigging positions that the actuator must achieve at defined reference points. The F80055-36 trammel bar assembly spans between fixed airframe reference points and the actuator mechanism, providing a direct physical measurement of actuator extension that confirms the trim system is correctly calibrated. During functional testing, technicians use the trammel bar to verify that actuator travel limits, neutral positions, and cutout switch settings all fall within Boeing-specified tolerances.

Key Features

• Precision trammel bar calibrated to measure horizontal stabilizer trim actuator rigging positions per Boeing AMM procedures
• Verifies actuator extension at defined reference points to confirm correct trim system calibration
• Supports functional testing of trim system travel limits, neutral positions, and automatic cutout switch settings
• Covers the complete 737 family — Original, Classic, NG, and MAX variants
• Referenced in Boeing AMM Chapter 27 (Flight Controls) stabilizer trim system rigging and testing procedures
• Also referenced under Boeing SPL-1677 supplemental tooling designation

Typical Maintenance Applications

• Horizontal stabilizer trim actuator rigging verification
• Stabilizer trim system functional testing after actuator installation or replacement
• Trim actuator travel limit verification (nose-up and nose-down stops)
• Automatic trim cutout switch position verification
• Post heavy-check stabilizer trim system re-rigging (C-check, D-check)
• Stabilizer trim runaway test setup and verification
• Compliance testing following Airworthiness Directives (ADs) related to horizontal stabilizer trim

Supersession & Related Part Numbers

The Boeing F80055 trammel bar family includes multiple dash numbers that have evolved over the 737 production history. The F80055-36 is the current-production configuration. Related and alternate part numbers include:

• F80055-1 – Earlier trammel bar configuration
• F80055-10 – Alternate trammel bar (also covers 707 and 727 in addition to all 737 series)
• SPL-1677 – Boeing supplemental tooling list designation for this tool

Why This Tool Matters

The horizontal stabilizer trim system is one of the most safety-critical flight control systems on any commercial aircraft. An incorrectly rigged trim actuator can result in out-of-trim conditions, reduced pitch authority, autopilot disconnect events, or — in the worst case — uncommanded stabilizer movement. Following multiple high-profile incidents involving 737 stabilizer trim systems, the industry and regulators have placed heightened scrutiny on the accuracy and documentation of trim system rigging procedures. The F80055-36 trammel bar gives A&P mechanics and MRO technicians the Boeing-approved measurement tool to confirm that trim actuator rigging meets exact AMM specifications — supporting airworthiness, regulatory compliance, and safe flight operations across the entire 737 fleet.