The horizontal tail group — comprising the horizontal stabilizer and the elevator — is the primary pitch-control system on virtually every fixed-wing aircraft. When an AMT rigs these components, the goal is to ensure that the control surfaces move through their correct range of travel, that neutral positions are properly established, that all hardware is correctly torqued and safetied, and that the completed assembly produces predictable, harmonious control response throughout the flight envelope. Rigging errors in the pitch axis have been implicated in serious accidents, making this one of the most consequential tasks on an airframe technician's checklist.
This article walks through the theory, procedural logic, and specific checks involved in elevator and stabilizer rigging, grounded in FAA guidance and the general practices described in the Aviation Maintenance Technician Handbook — Airframe (FAA-H-8083-31). Always supplement this material with the manufacturer's aircraft maintenance manual (AMM), which is the authoritative source for model-specific travel limits, hardware torque values, and rigging sequences.
Understanding the Horizontal Tail Group
The horizontal stabilizer provides a fixed (or in some aircraft, adjustable) aerodynamic surface that counteracts pitching moments generated by the wing and powerplant, maintaining trim equilibrium. On most light aircraft it is bolted rigidly to the fuselage structure at a fixed incidence angle. On heavier or more complex aircraft it may be an adjustable stabilizer (also called a stabilator or trimmable horizontal stabilizer) that pivots through a small arc to trim the aircraft, with the elevator then providing additional pitch authority on top of that trim position.
The elevator is a movable control surface hinged at the trailing edge of the horizontal stabilizer. Cockpit input through the control column or stick is transmitted via a system of push-pull tubes, bellcranks, cables, and pulleys — or on fly-by-wire systems, electrical signals — to rotate the elevator about its hinge line, changing the camber and lift of the tail group and thereby pitching the aircraft nose-up or nose-down.
Pre-Rigging Preparation
Before touching any rigging hardware, the technician must complete several preparatory steps. First, consult the specific AMM for the aircraft. Rigging data — travel limits, neutral positions, cable tensions, torque values — is entirely aircraft-specific and cannot be assumed from generic values. Second, place the aircraft in its rigging position: typically level laterally and longitudinally as confirmed with a calibrated spirit level or electronic inclinometer placed on specified structural reference points called rigging datum points. Third, verify that all structural attachments are secure — hinge bolts, stabilizer attach fittings, and control horn attach points — before measuring or adjusting travel.
Inspect every component in the control path for wear, corrosion, and deformation. Rod-end bearings (rose joints), cable ferrules, turnbuckles, and pulleys must all be in airworthy condition before rigging. A correctly rigged system built on worn components is still an unsafe system.
Establishing the Neutral Position
The neutral position (also called the streamline position or rigging neutral) is the reference point from which all travel measurements are taken. For the elevator, neutral is typically defined in the AMM as the position in which the elevator chord line is aligned with the stabilizer chord line — in other words, the elevator trailing edge sits flush or at a specified small offset relative to the stabilizer, producing a smooth, continuous aerodynamic surface. Some designs specify a slight built-in offset at neutral to account for aerodynamic download requirements.
A rigging pin or jig provided by the manufacturer (or fabricated to AMM specifications) is inserted through alignment holes in the control horn or bellcrank to physically lock the surface at its neutral position while the technician adjusts cable tensions and push-pull tube lengths. Using the correct rigging pin is critical — substituting an undersized pin or improvising can introduce angular errors that are difficult to detect without a protractor check.
Setting Control Cable Tension
On cable-operated systems, cable tension must be set within the range specified in the AMM, corrected for ambient temperature. FAA guidance in FAA-H-8083-31 emphasizes that cable tension changes with temperature: cables contract in cold weather (tension rises) and expand in warm weather (tension drops). A tensiometer matched to the cable diameter is used to measure tension. Most AMMs provide a tension-versus-temperature chart or table so the technician can interpolate the correct tension for the shop temperature on the day of rigging. Cables that are too loose allow excessive control free play and may jump pulleys; cables that are too tight create high control forces and may over-stress structural attach points or control horns.
After setting tension on one cable run, check that the opposing cable tension is within spec as well. Because elevator cables typically run as a pair (one for up-elevator, one for down-elevator), adjusting one turnbuckle affects both. Adjust incrementally and recheck both sides. Once final tension is confirmed, safety all turnbuckles with approved locking wire or clip-type safety devices per AC 43.13-1B.
Measuring and Adjusting Control Travel
Control surface travel is measured with a protractor, inclinometer, or rigging board (a flat board with a pivot-mounted pointer and degree scale) placed on the surface. The measurement is taken from the neutral position to the full up-elevator stop and from neutral to the full down-elevator stop. Elevator travel limits are entirely aircraft-specific and are not standardized across designs — always use the exact figures published in the AMM or type certificate data sheet rather than any generic approximation.
Travel is limited by mechanical stops, which may be adjustable bolts located on the control horn, the bellcrank, or within the cockpit quadrant. Adjust the stop bolts so that the surface reaches — but does not exceed — the specified maximum travel before the stop contacts the mating surface. Do not accept a condition where the stop is reached before full cockpit input travel is reached (a rigging-short condition) or where full cockpit deflection does not contact the stop (an over-travel condition). Both are unairworthy.
Also verify that the elevator trim tab (if installed) moves in the correct sense: trim tab trailing edge up produces nose-up trim, and trailing edge down produces nose-down trim. The trim travel limits and neutral position are set separately, typically through the trim jackscrew or trim cable system, using the same protractor methodology.
Checking Friction, Free Play, and Binding
Once travel and tension are set, physically operate the system through its full range and back. The control should move smoothly with no binding (a sudden increase in resistance) and no stiffness at any point that is not present through the full arc. Binding typically indicates misalignment of a push-pull tube, a pulley that is not tracking in its groove, an over-tight rod-end bearing, or cable routing interference. Each symptom must be diagnosed and corrected before signing off the work.
Free play (also called backlash or slop) is checked by holding the surface still and moving the cockpit control: any movement at the cockpit input that does not result in immediate surface movement is free play. The AMM specifies maximum allowable free play, typically measured in fractions of an inch at a defined point on the control column. Excessive free play indicates worn bellcrank bushings, elongated cable attachment holes, or worn rod-end bearings.
Stabilizer Incidence and Symmetry Checks
For aircraft with a fixed stabilizer, verify that the stabilizer is mounted at the correct incidence angle as specified in the AMM. This is typically checked with a precision inclinometer placed on the upper surface of the stabilizer and compared to a reference reading on the wing or fuselage. If the stabilizer has been removed for any reason — damage repair, inspection, or component replacement — the incidence must be re-established and documented before return to service.
Stabilizer symmetry is checked by measuring from a fuselage centerline reference to equivalent points on the left and right stabilizer tips. A difference greater than AMM tolerance indicates that the stabilizer has been mounted asymmetrically (skewed), which can introduce yawing and rolling tendencies in addition to incorrect pitch response. Shim packs at the attach fittings are typically used to correct incidence and symmetry errors on designs that permit adjustment.
Key Numbers and Rules
- Always use the AMM — no generic travel limits exist; values are aircraft-specific.
- Cable tension must be temperature-corrected using the AMM tension-temperature chart and a calibrated tensiometer sized for the cable diameter.
- Turnbuckle safetying — inspect per AC 43.13-1B, Chapter 7 guidance on thread exposure at the barrel ends; safety with approved wire or clip-type locking devices, and always confirm exact thread-exposure criteria against the applicable AC 43.13-1B figure for the turnbuckle design in use.
- Rigging sequence — neutral position is always established before travel or tension adjustments.
- Trim tab travel must be verified separately from elevator travel and recorded.
- Free play limits — measured at the cockpit control input point; maximum values are AMM-specific.
- Documentation — all rigging data (measured travel, cable tension, temperature, date, technician signature) must be recorded in the maintenance record per 14 CFR Part 43.
Common Test Traps
- Confusing trim tab movement direction: The trim tab moves opposite to the elevator to generate an aerodynamic force that deflects the elevator — that is, trim tab trailing edge up drives the elevator trailing edge down, producing a nose-up trim effect. Candidates often reverse this relationship.
- Ignoring temperature correction for cable tension: Rigging a cable to the correct tension in a hot hangar and then flying in cold weather will result in over-tensioned cables. Always apply the temperature correction from the AMM chart.
- Using rigging pin substitutes: A rigging pin that is even slightly undersize introduces angular error at neutral; always use the manufacturer-specified pin or jig.
- Checking travel only in one direction: Both up and down travel must be measured and confirmed against AMM limits. A surface within limits in one direction may be out of limits in the other.
- Confusing an adjustable stabilizer with a conventional stabilizer: On aircraft with a trimmable horizontal stabilizer, pitch trim is achieved by moving the entire stabilizer, not just a trim tab. Rigging procedures for these aircraft are significantly different and more complex.