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TRN-AVIA22-02 · Lesson 10 · 52 clock hours · lab

Flight Control Systems

Objective. Students will rig, inspect, and operationally verify primary and secondary flight control systems on a training aircraft to manufacturer travel limits and free-play tolerances.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Flight Control Systems: Rigging, Inspection, and Operational Verification

Flight control systems translate pilot inputs into precise aerodynamic responses. When cables stretch, turnbuckles slip, or hardware corrodes, control surfaces can exceed or fall short of their design travel limits — a direct airworthiness concern. The tasks in this lab follow the two primary references you will use throughout your career: the aircraft's Airplane Maintenance Manual (AMM) and AC 43.13-1B, the FAA's accepted means of compliance for aircraft inspection and repair.

Primary and Secondary Controls

Primary flight controls — ailerons, elevator (or stabilator), and rudder — directly command roll, pitch, and yaw. Secondary flight controls — flaps, trim tabs, spoilers, and slats — modify lift, drag, or pilot workload. This lab focuses on primary controls because errors there have immediate consequences on aircraft controllability.

Control inputs travel from the cockpit to the control surface through one of several mechanical paths: cable-and-pulley systems, push-pull tubes, torque tubes, or combinations of these. Cable-and-pulley systems are the most common on general aviation trainers, so cable tension management is the central skill here.

Why Cable Tension Matters

Steel aircraft control cables change length with temperature. A cable rigged to the correct tension on a cold morning will be tighter on a hot afternoon. Manufacturers publish cable tension charts in the AMM that account for outside air temperature at the time of rigging. You must record ambient temperature before taking tensiometer readings and look up the allowable tension range from the correct column in the chart. Never assume a single tension value applies at all temperatures.

Too little tension allows excessive free play — a condition where the pilot moves the control column without moving the surface. Too much tension overloads pulleys, fairleads, and swage fittings, accelerating wear and risking failure. Both conditions are rejectable.

Using the Tensiometer

A riser-type tensiometer (such as the Hoyt C-1 or equivalent) measures cable tension by deflecting the cable a fixed amount and reading the resulting force. Select the correct anvil and riser for the cable diameter stamped on the tool body or in the manufacturer's instructions. Place the tool perpendicular to the cable run, away from pulleys and fairleads. Take three readings per cable run and average them. Compare the average to the AMM temperature-corrected limit. Record your reading, the AMM limits, the temperature, and your go/no-go determination on the inspection form.

Rigging Aileron Travel

Control surface travel is measured in degrees of deflection from the neutral (faired) position. The AMM specifies separate limits for up and down deflection; these are not always equal. To rig aileron travel:

1. Place the aircraft on a level surface and verify the wings are level using a rigging level or reference points called out in the AMM.

2. Set the cockpit control wheel (or stick) to the neutral position and secure it with a rigging pin or fixture if specified.

3. Attach a digital inclinometer to the aileron surface at the location specified in the AMM — typically on the chord line near mid-span.

4. Zero the inclinometer with the surface at the neutral position.

5. Move the control to the full-travel stop in each direction and read the deflection angle.

6. Compare each reading to the AMM tolerance (for example, up travel within ± a stated number of degrees, down travel within its own tolerance).

7. If travel is out of tolerance, adjust turnbuckles. Turning the barrel in the direction that shortens the cable on the side being adjusted will increase surface deflection on that side. Small increments matter — make one-half turn adjustments, re-measure, and repeat.

8. Once within tolerance, safety-wire the turnbuckle per standard aviation practice: no more than three exposed threads on each shank, and safety wire installed so it prevents the barrel from unwinding (wire wraps so that rotation needed to loosen the barrel would tighten the wire).

Cable Inspection per AC 43.13-1B

AC 43.13-1B establishes the criteria for accepting or rejecting control cables. Inspect the full length of each cable under adequate lighting. Key rejection criteria include:

Classify each finding as airworthy, repairable, or replace and document it with a recommended corrective action. An incomplete or ambiguous inspection record is itself a discrepancy.

Safety Requirements for This Lab

Key terms9

Cable tensionThe load, measured in pounds, applied along the length of a control cable; must fall within AMM-specified limits corrected for ambient temperature.
TensiometerA hand-held instrument that measures cable tension by deflecting the cable a fixed amount and reading the resultant force; the correct anvil and riser must match the cable diameter.
Control surface travelThe angular deflection of a control surface from its neutral position, measured in degrees; the AMM states separate up and down travel limits for each surface.
TurnbuckleA threaded adjusting device used to vary cable tension or control surface travel; must be safety-wired after final adjustment to prevent unwinding.
Free playMovement of the cockpit control input with no corresponding movement of the control surface, caused by insufficient cable tension, worn bearings, or loose linkage.
AC 43.13-1BFAA Advisory Circular that provides accepted methods, techniques, and practices for aircraft inspection and repair, including rejection criteria for control cables.
Swage fittingA terminal pressed (swaged) onto the end of a control cable to form a permanent, load-bearing connection; inspected for cracks, proper length, and absence of wire fraying at the cable entry.
Digital inclinometerAn electronic angle-measuring instrument placed on a control surface to read deflection in degrees; used during travel rigging to verify AMM limits.
Go/no-go determinationA documented pass/fail judgment that compares a measured value to the applicable specification limit and states whether the condition is acceptable for return to service.

Worked examples4

1. The AMM aileron cable tension chart shows an allowable range of 30–40 lb at 70 °F. The ambient temperature in the hangar is 70 °F. Your three tensiometer readings on the right aileron cable are 28 lb, 29 lb, and 27 lb. What is the average tension and what is your go/no-go determination?
  1. Add the three readings: 28 + 29 + 27 = 84 lb total.
  2. Divide by the number of readings to find the average: 84 ÷ 3 = 28 lb.
  3. Compare the average (28 lb) to the AMM range at 70 °F (30–40 lb).
  4. 28 lb is below the minimum limit of 30 lb.
Answer: Average tension is 28 lb, which is below the AMM minimum of 30 lb at 70 °F. The determination is NO-GO. The cable must be tensioned by tightening the appropriate turnbuckle(s) until the average reading falls between 30 and 40 lb, then re-measured and safety-wired.
2. The AMM specifies left aileron up travel as 20° ± 1° and down travel as 15° ± 1°. After rigging, the digital inclinometer reads 21.5° up and 14.2° down. Which readings are within tolerance and which are not?
  1. Up travel tolerance: minimum 20 − 1 = 19°, maximum 20 + 1 = 21°.
  2. Compare 21.5° to the range 19°–21°: 21.5° exceeds the maximum of 21°. OUT OF TOLERANCE.
  3. Down travel tolerance: minimum 15 − 1 = 14°, maximum 15 + 1 = 16°.
  4. Compare 14.2° to the range 14°–16°: 14.2° is within limits. WITHIN TOLERANCE.
Answer: Up travel of 21.5° is out of tolerance (max allowed is 21°). Down travel of 14.2° is within tolerance. The up-travel stop or cable tension must be adjusted to bring up travel to 19°–21° without disturbing the down travel, then re-measured.
3. After safety-wiring a turnbuckle, you count 4 threads exposed on one shank. The standard requires no more than 3 exposed threads per shank. How many turns must you adjust the barrel to bring that shank into compliance, and in which direction?
  1. Each full turn of the turnbuckle barrel advances or retracts each shank by one thread pitch (one thread per turn).
  2. You need to reduce exposed threads on that shank from 4 to 3, so the shank must thread further into the barrel by 1 thread.
  3. Thread the barrel onto that shank by rotating the barrel one full turn in the direction that draws that shank in (the direction that shortens the exposed length).
  4. Verify both shanks now show 3 or fewer exposed threads, confirm cable tension is still within AMM limits, then re-apply safety wire.
Answer: Rotate the turnbuckle barrel one full turn in the direction that draws the over-exposed shank inward. Re-check that both shanks show no more than 3 exposed threads, re-verify cable tension against the AMM chart, and re-safety-wire the turnbuckle.
4. During cable inspection you find: (1) two broken wires in a 10-inch span of cable well away from any fitting, (2) a kink in the rudder cable, and (3) light surface discoloration on the elevator cable that produces no powder when flexed. Using AC 43.13-1B criteria, classify each finding.
  1. Finding 1 — Broken wires away from fittings: AC 43.13-1B provides rejection limits based on the number of broken wires per length of cable for the cable construction type. Two broken wires in a span may or may not meet the rejection threshold depending on cable diameter and construction; document the count, location, and cable specs, then compare to the specific table in AC 43.13-1B for that cable type. If within the allowed limit, classify as AIRWORTHY with continued monitoring noted; if at or beyond the limit, classify as REPLACE.
  2. Finding 2 — Kink: A kink permanently deforms the wire lay. AC 43.13-1B states kinked cables must be rejected regardless of wire-break count.
  3. Finding 3 — Light surface discoloration, no powder when flexed: If flexing produces no reddish-brown powder and the discoloration can be cleaned with a lint-free cloth and approved solvent revealing no pitting, the cable may be AIRWORTHY; document the finding and recommended monitoring interval.
Answer: Finding 1: Compare broken-wire count to the AC 43.13-1B rejection table for that cable construction — record as AIRWORTHY or REPLACE accordingly. Finding 2: REPLACE — a kink is an automatic rejection. Finding 3: AIRWORTHY with documented notation for re-inspection, provided cleaning reveals no corrosion pitting.

The math in this lesson2

Learners average three tensiometer readings to 28 lb and compare to the 30–40 lb AMM range.
S-ID.2N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Using a protractor rigging board and tensiometer, measure aileron, elevator, and rudder cable tension; compare readings to AMM limits at the stated temperature; record readings and make a go/no-go determination for each cable run. · Rig aileron travel to AMM-specified up and down deflection angles using a digital inclinometer; adjust turnbuckles in the correct direction, safety-wire to standard aviation practice, and verify final travel is within tolerance. · Inspect control cables for corrosion, broken wires, kinks, and proper swage-fitting attachment per AC 43.13-1B criteria; classify each discrepancy and record results on an inspection report with a recommended action for each finding.
Materials: Training aircraft, cable tensiometer, digital inclinometer, rigging protractor board, turnbuckle tool, safety-wire and pliers, torque wrench, AC 43.13-1B, aircraft AMM, inspection report forms, PPE
Check: Cable tension measurements recorded correctly and within AMM limits; aileron travel within AMM tolerance after rigging (checked with inclinometer by instructor); safety-wire meets standard inspection criteria; cable inspection report complete with correct classifications—minimum satisfactory rating on all three activities

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Airframe Systems — Flight Controls
1. When measuring control cable tension with a tensiometer, which factor must be recorded before comparing readings to the AMM tension chart?
Airframe Systems — Flight Controls
2. According to standard aviation practice, a turnbuckle is considered correctly safety-wired when:
Inspection — Acceptable Methods, Techniques, and Practices
3. A kink is found in an elevator control cable during inspection. Per AC 43.13-1B, what is the correct action?
Airframe Systems — Flight Controls
4. The AMM specifies aileron up travel as 18° ± 1°. A digital inclinometer reads 19.8° at full up deflection. What is the correct determination?
Safety — General Maintenance Practices
5. Before moving cockpit controls during a flight control rigging check, the technician should:
Airframe Systems — Flight Controls
6. Which instrument is used to measure control surface deflection angle during a rigging check?
Inspection — Acceptable Methods, Techniques, and Practices
7. During cable inspection, flexing a cable produces a reddish-brown powder. This indicates:
Airframe Systems — Flight Controls
8. A technician adjusts a turnbuckle to increase aileron up-travel. After adjustment, what must be done before the aircraft can be returned to service?
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