Cold Hangar, Warm Rigging Chart: Elevator Cable Tension
You have replaced a damaged elevator control cable in a light twin and completed initial rigging. Using a calibrated tensiometer, you measure elevator cable tension at 203 lb. The rigging chart specifies 200 lb, plus or minus 10 lb, at 70 degrees F. The hangar is unheated and the ambient temperature is 20 degrees F. The maintenance manual carries a note for this aluminum structure: indicated cable tension decreases about 1 percent of the chart value for each 10 degrees F below 70 degrees F. A second mechanic looks at your numbers, says '203 is inside 200 plus or minus 10,' and tells you to safety-wire the turnbuckles and sign it off. The aircraft is due out for a morning departure.
1. Compute the temperature-corrected target tension and decide whether the current rig is acceptable.
Read the worked answer
The chart value applies at 70 degrees F; the hangar is 50 degrees F colder.
- 50 degrees F / 10 degrees F = 5 increments
- 5 x 1 percent = 5 percent reduction of the 200 lb chart value = 10 lb
- Corrected target = 200 - 10 = 190 lb, acceptable band 180 to 200 lb
The measured 203 lb is 13 lb above the corrected target and above the top of the corrected band. It is not acceptable; the cable is over-tensioned for the conditions and must be adjusted down.
Also confirm the tensiometer is in calibration and that the reading was taken with the system in the rigging condition the manual specifies (rig pins installed, control surfaces in neutral, no loads on the system).
2. After you adjust the turnbuckle, what must be verified before this can be approved for return to service?
Read the worked answer
At minimum:
- Turnbuckle thread engagement within the manual/AC 43.13-1B limits - threads must be visible through the inspection hole per the applicable requirement, not screwed in so far that engagement is inadequate.
- Safety wiring correctly double-wrapped and tensioned per AC 43.13-1B practice.
- Cable path: cable seated in pulley grooves, fairleads and pressure seals intact, no chafing on structure, pulley guards in place.
- Rigging: rig pins or rigging marks per the manual, control travel and stops correct in both directions, no binding through the full range.
- Recheck tension after cycling the controls several times, since a new cable seats and stabilizes; then record the final tension and the temperature at which it was measured.
A second person verifying full, unobstructed travel is good practice on a dual-cable system before sign-off.
3. Explain why the '203 is inside 200 plus or minus 10' argument is wrong, in terms the other mechanic can check.
Read the worked answer
It compares a cold-weather reading against a limit written for 70 degrees F. On this aluminum structure, tension rises as the airframe warms: a 203 lb reading at 20 degrees F corresponds to roughly 213 lb at 70 degrees F, which is above the 210 lb upper limit.
So the reading is not merely 'a little high for now' - at standard temperature it is out of tolerance in the over-tensioned direction, which loads pulleys, fairleads, and the bellcrank bearings and can cause binding or accelerated wear.
The correct method is to convert the measured value to the chart's reference temperature (or convert the chart limit to the ambient temperature) before comparing. Ignoring the note produces a false pass. Record the ambient temperature at the time of measurement so the next person can audit the decision.