When an operator asks for an infrared inspection on a bonded composite panel, the first question a Level III should answer is not which camera to use. It is which document the inspection is being performed to, and whether the technique has been qualified for the part in front of you. For a lot of general aviation and transport work that document chain starts with AC 43.13-1B and runs into the OEM nondestructive testing manual, often the 55-40-50 series for empennage and flight control surfaces. This is where an AC 43.13 thermography inspection earns its place as an accepted method rather than a convenient one.
What AC 43.13-1B actually says about thermography
AC 43.13-1B, Chapter 5, lays out acceptable methods, techniques, and practices for inspecting aircraft structure, including the advanced and special NDI methods. Infrared thermography sits in that advanced category alongside bond testing and ultrasonics. The advisory circular is not a procedure. It does not tell you the pulse duration for a flash on a Nomex core panel or the frame rate for a lock-in sequence on a CFRP skin. What it does is establish that thermography is an acceptable method when the technique is properly developed, the operator is qualified, and the results are interpreted against known reference standards. The detail comes from the OEM manual.
That distinction matters in a Part 145 shop. We do not perform thermography because AC 43.13 permits it in general. We perform it because the rudder or elevator manual, frequently the 55-40-50 block for stabilizer and control surface composite structure, calls out an infrared technique with an acceptance basis. The advisory circular is the floor. The NDT manual is the floor plan.
Active thermography on bonded and honeycomb structure
The defects that drive most of this work are familiar to anyone who maintains composite control surfaces: skin to core disbonds, core crush, delamination between plies, and trapped water in honeycomb cells. Active thermography puts a controlled pulse of energy into the surface and watches how heat moves back out. A disbond or a water pocket changes the local thermal diffusivity, so the cooling curve over a flaw looks different from the cooling curve over sound structure. Flash thermography handles thin skins well. Lock-in and step heating reach deeper into thicker laminates and sandwich panels where a single flash does not penetrate far enough.
The strength of the method is coverage. A thermal camera images a wide area in seconds, which is why it pairs so well with large bonded panels. We cover the theory and method selection in depth in our complete guide to infrared thermography for composite inspection, and the broader bonded structure picture lives in the composite and honeycomb inspection guide.
Qualifying the technique, not just owning the camera
Here is the part that gets shops in trouble during an audit. A thermal camera does not make an inspection compliant. The technique has to be qualified on a reference standard that represents the part: the same skin lay-up, the same core, the same bondline, with engineered flaws at known locations and depths. We confirm that the technique detects the smallest required indication before any production part is touched. That reference standard, the heating parameters, the camera settings, and the acceptance criteria all get written into a procedure, and the procedure is what the inspection records point back to.
Personnel qualification follows NAS 410. The technician running an infrared inspection holds the appropriate level for the method, and interpretation against the OEM acceptance basis is a Level II or Level III call. None of this is optional. It is the difference between a thermal image and a defensible inspection result that an operator can sign off on.
Where thermography fits, and where it does not
Thermography is fast and it is excellent for first pass screening of large bonded areas. It is not a tap hammer and it is not a cure all. Deep flaws under thick skins can fall outside its reliable depth range, and edge effects near fittings and fasteners need careful handling. That is why we treat it as one tool in a method stack. When a thermal indication needs confirmation we resolve it with ultrasonics or a bond test, and we explain the tradeoffs in our breakdown of thermography versus tap test for composite bond inspection. For control surface core damage specifically, see our field notes on honeycomb core damage in flight control surfaces.
Records and the regulatory chain
Every inspection produces a record that ties the technique to the manual reference, the reference standard used, the equipment and settings, the operator and level, and the disposition of each indication. When an inspection supports an airworthiness directive or a repair return to service, that record is the evidence. We walk through how NDT satisfies regulatory requirements in the guide to FAA airworthiness directive NDT compliance, and the full picture of inspecting an airframe by zone and method is in the ultimate guide to aircraft NDT inspection.
Baron NDT performs thermographic inspection of composite and honeycomb structure under our FAA Part 145 repair station certificate, to AC 43.13-1B and the applicable OEM NDT manual. If you have a bonded panel, a control surface, or a repair that needs an accepted infrared inspection with records that hold up, call us at 904-304-2907 or reach out through baronndt.com.