The CRJ family has been in revenue service long enough that the airplanes coming through our hangar are well into their fatigue lives. That changes what we look for. Early heavy checks were mostly about access and corrosion. The fleet we see now wants crack detection at the structural details that carry load every cycle, and a lot of that work lands on phased array ultrasonics. A good CRJ phased array inspection is less about owning a fancy scanner and more about reading the Bombardier source documents correctly and building a technique that actually matches the part.
Most of these inspections trace back to the Bombardier Structural Repair Manual and the CRJ NDT manual, and increasingly to airworthiness directives that mandate repeat ultrasonic checks at a fixed interval. The method callout is not a suggestion. When the document specifies a phased array technique with a defined wedge, frequency, and scan plan, that is the technique we qualify to, and any deviation has to be approved through the operator’s engineering. We work as a Part 145 repair station, so the inspection record has to show the document revision in effect, the calibration block used, and the personnel certification level behind the call.
Where PAUT earns its place on the CRJ
The structural areas that drive most of our CRJ phased array work are the wing lower skin and stringer runouts, the center wing and stub-beam attach fittings, the fuselage frame and shear tie details, and the empennage attach hardware. These are spots where conventional single-element ultrasonics struggle because the geometry is tight, the flaw orientation is unpredictable, and you cannot get a clean normal-beam shot at the suspect plane. Phased array lets us sweep a range of angles from one footprint, so a fatigue crack growing off a fastener hole bore or a fillet radius shows up whether it is favorably oriented or not.
The fastener-hole work is the clearest example. A crack initiating at a hole in a thick aluminum fitting can run in any direction, and a fixed-angle shear wave will walk right past it if the angle is wrong. A sectorial scan covering roughly 40 to 70 degrees gives continuous angular coverage across the bore wall, and the S-scan image makes the indication far easier to interpret than a flickering A-scan. We still keep the raw A-scan in view, because the image is only as honest as the calibration behind it.
Calibration and technique discipline
On aluminum airframe structure we run shear wave at 5 MHz for most of the thin-to-medium skins and step down in frequency on the heavier forgings where attenuation and grain noise start to fight you. The reference is a side-drilled hole or notch reflector in a block of the same alloy and thickness as the part, machined to the dimensions the NDT manual specifies. We set the reference level off that reflector, apply the TCG so amplitude holds across the sweep, and record the scan plan with the wedge, element aperture, and angular range documented. Encoded scanning is the default on any area where we have to show full coverage and come back to the same spot at the next interval. The encoder data is what lets the next inspector compare growth honestly instead of guessing.
Surface prep matters more on these airplanes than people expect. Paint, primer, and sealant under a fitting all change coupling, and a CRJ that has been flying for fifteen years carries plenty of all three. We document surface condition because it affects the technique and because the customer’s engineering will ask. Personnel are qualified to NAS 410, and the call on a rejectable indication comes from a Level II or III who can tie it back to the acceptance criteria in the controlling document, not just point at a bright spot on the screen.
Why operators move this work to PAUT
Two reasons, mostly. Speed and the record. A phased array sweep covers in one pass what used to take several manual scans at different angles, which matters when the airplane is on the ground burning money. And the encoded data file gives the operator a defensible record for the FAA and for their own continued-airworthiness tracking. When the same detail has to be re-inspected on a repeat-interval AD, having the prior scan to compare against turns a judgment call into a measurement.
The CRJ is a regional workhorse, and the structural inspections will only get more frequent as the fleet ages. Phased array is the method that keeps those checks fast, repeatable, and documented to a standard that holds up under an FAA records review. If you have CRJ structure coming due for ultrasonic inspection, the right move is to confirm the controlling document revision first, then build the technique to match, then scan. The order matters.
Baron NDT performs PAUT and conventional ultrasonic structural inspections on regional and transport aircraft as an FAA Part 145 repair station. For broader context, see our guide to aircraft NDT inspection and the deeper ultimate guide to ultrasonic testing. Related task work includes our phased array crack detection per the 737 NDT manual, PAUT of A220 buttstrap runouts, and the 737NG lap splice inspection under AD 2023-13-05. If you want the method-selection tradeoffs, our writeup on PAUT versus conventional UT covers the basics.