ACS Airframe Systems & Structural Maintenance 3 — Questions and Answers
Question 1: Which NDT method is BEST suited for detecting subsurface delaminations in a composite honeycomb sandwich structure?
- Dye penetrant inspection
- Magnetic particle inspection
- Tap test or ultrasonic through-transmission (Correct answer)
- Eddy current inspection
Correct answer: Tap test or ultrasonic through-transmission
A coin tap test or ultrasonic through-transmission is used to detect subsurface delaminations in composite honeycomb panels, while dye penetrant only finds surface defects and magnetic particle requires ferrous material.
Question 2: What is the correct procedure when stop-drilling a crack in aluminum aircraft skin?
- Drill the hole through the center of the crack tip
- Drill the hole just ahead of the visible crack tip (Correct answer)
- Drill the hole 1/2 inch behind the crack tip
- Drill two holes, one at each end, through the crack tips
Correct answer: Drill the hole just ahead of the visible crack tip
The stop-drill hole must be placed just ahead of (beyond) the visible crack tip to eliminate the stress concentration at the crack tip and arrest crack propagation.
Question 3: When replacing aircraft transparent enclosures (acrylic), the fastener holes should be:
- The same size as the fastener diameter
- Drilled undersized and reamed to final dimension
- Oversized to allow for thermal expansion of the acrylic (Correct answer)
- Sealed with silicone sealant after fastener installation
Correct answer: Oversized to allow for thermal expansion of the acrylic
Acrylic plastic has a high coefficient of thermal expansion, so fastener holes must be oversized to prevent cracking as the material expands and contracts.
Question 4: Which statement about aircraft control cable tension is correct?
- Cable tension should remain constant regardless of ambient temperature
- Cable tension must be set at the highest expected temperature and checked cold
- Tension must be set at the temperature specified, with correction applied for ambient temperature using a rigging chart (Correct answer)
- Cables should always be tensioned to the maximum allowable to prevent flutter
Correct answer: Tension must be set at the temperature specified, with correction applied for ambient temperature using a rigging chart
Control cable tension varies with temperature; a rigging chart must be used to apply temperature corrections so final tension is correct across the operating temperature range.
Question 5: A mechanic finds exfoliation corrosion on an aluminum alloy wing spar cap. What action is required?
- Treat with Alodine and apply primer immediately
- Remove the spar cap and replace it
- Clean, treat, and determine if remaining material meets minimum thickness per SRM (Correct answer)
- Polish smooth, apply zinc chromate, and return to service
Correct answer: Clean, treat, and determine if remaining material meets minimum thickness per SRM
Exfoliation corrosion causes layer-by-layer material loss; the mechanic must clean, treat, measure the remaining material, and compare it to the SRM minimum thickness allowable to determine airworthiness.
Question 6: What is the minimum bend radius for aluminum alloy sheet when forming a repair part?
- Equal to the material thickness
- As specified in the aircraft SRM or manufacturer's structural repair data (Correct answer)
- At least 10 times the material thickness for all alloys
- Determined solely by the forming tool diameter
Correct answer: As specified in the aircraft SRM or manufacturer's structural repair data
Minimum bend radius depends on alloy type, temper, and thickness, and must be obtained from the aircraft SRM or manufacturer's structural repair data, not a universal rule.
Question 7: When bonding a composite repair patch using a heat blanket cure, what is a critical parameter to monitor throughout the cure cycle?
- Ambient relative humidity only
- Resin pot life at room temperature
- Temperature uniformity across the repair area and pressure applied by vacuum bag (Correct answer)
- Color change of the prepreg material
Correct answer: Temperature uniformity across the repair area and pressure applied by vacuum bag
Uniform temperature distribution and adequate bag pressure (typically 25–30 inHg vacuum) are critical during heat-blanket cure to ensure proper resin flow, consolidation, and adhesion throughout the patch.
ACS Airframe Systems & Structural Maintenance 3
Which NDT method is BEST suited for detecting subsurface delaminations in a composite honeycomb sandwich structure?