Aircraft Composites — What They Are, Why They’re Used and Why NDT Matters

Modern aircraft are built from materials that barely existed half a century ago. Walk past a Boeing 787 or an Airbus A350 and you are looking at a structure that is more carbon fibre than aluminium. The shift from metal to composite has been one of the most significant engineering transitions in aviation history and it shows no sign of slowing down.

For engineers and inspection teams responsible for keeping those aircraft airworthy, that shift brings both opportunity and challenge.

What are aircraft composites?

A composite material combines two or more constituent materials to produce something with characteristics that neither could achieve alone. In aerospace, the most common configuration pairs a high-strength reinforcing fibre with a polymer resin matrix that holds the fibres in place and transfers loads between them.

The result is a material with an exceptional strength-to-weight ratio, the primary reason aviation has adopted composites so aggressively over the past four decades.

Carbon Fibre Reinforced Polymer (CFRP)

CFRP is the dominant structural composite in modern aerospace. Carbon fibres are laid up in specific orientations and bonded together with an epoxy resin, producing a material with higher specific strength than steel and higher specific stiffness than aluminium at a fraction of the weight.

Composites make up approximately 50 percent of the Boeing 787 by structural weight and around 53 percent of the Airbus A350. Fuselage, wings, empennage, doors and nacelles are all primarily CFRP on both platforms.

Glass Fibre Reinforced Polymer (GFRP)

Glass fibre composites were the first adopted in aerospace, appearing on the Boeing 707 in the late 1950s. They are cheaper than CFRP and electrically non-conductive, making them the material of choice for radomes, fairings and antenna covers. They are also widely used in helicopter rotor blades.

GLARE (Glass Laminate Aluminium Reinforced Epoxy)

GLARE alternates thin layers of aluminium alloy with glass fibre reinforced epoxy. Used most visibly on the Airbus A380 upper fuselage and also on the Airbus A321XLR fuel tanks, it offers excellent fatigue resistance, superior impact tolerance and better corrosion resistance than monolithic aluminium.

Aramid Fibre Composites

Kevlar and Nomex are used for their toughness and heat resistance rather than structural strength. Nomex honeycomb is a common lightweight core material in sandwich panel structures throughout modern aircraft.

Why are composites replacing metal in aviation?

Weight and fuel efficiency

Every kilogram saved in structural weight is a kilogram of additional payload or a reduction in fuel burn across the aircraft’s life. CFRP components typically weigh 20 to 30 percent less than equivalent aluminium parts. Boeing attributed approximately 20 percent better fuel efficiency per seat on the 787 partly to its composite-heavy construction.

Structural performance

Unlike isotropic metals, composites can be engineered to have different stiffness and strength in different directions. Fibres are laid up to match the load paths through a specific component, reducing material use while maintaining or improving performance. Composites also offer superior fatigue resistance and, in the case of CFRP, are largely immune to the corrosion that drives significant maintenance cost on metal airframes.

Design freedom

Composite components can be moulded into complex three-dimensional shapes that would require extensive machining and assembly if made from metal. A wing spar that would once have been hundreds of individual parts can be manufactured as a single integrated structure, reducing part count and potential failure points simultaneously.

Why is NDT inspection of aircraft composites so challenging?

The properties that make aviation composites so attractive also make them harder to inspect than traditional metal airframes.

Damage is hidden

A significant impact on an aluminium panel leaves a visible dent. The same impact on a CFRP panel may leave the surface almost completely unmarked while causing extensive internal delamination beneath. This is known as Barely Visible Impact Damage, or BVID, and it is the reason visual inspection alone is wholly inadequate for composite airframes. Hail strikes, tool drops and ground equipment impacts can all create subsurface damage that poses a serious structural risk without any surface indication.

Defects are varied

Aircraft composites are susceptible to delamination, disbonding, porosity, moisture ingress, foreign object inclusions and fibre misalignment — none of which can be detected through surface inspection. Each defect type has different characteristics and different implications for structural integrity.

The material itself creates inspection complexity

The layered, anisotropic structure of composite laminates behaves differently to metals under ultrasonic interrogation. Sound travels at different velocities in different directions, and the multiple interfaces between plies create complex reflection patterns that can mask or mimic defect signals.

Sandwich structures add further complexity. A typical aerospace sandwich panel bonds a composite face sheet (or skin) to a lightweight honeycomb core with another face sheet on the opposite side. Disbonds at the skin-to-core interface are difficult to characterise without spatial imaging capability.

GLARE is particularly demanding. The combination of aluminium and glass fibre in alternating layers creates an acoustic environment that differs significantly from either material in isolation and requires sophisticated signal processing to interpret accurately.

Geometry is rarely simple

Wings, fuselage sections, nacelles, leading edges and rotor blades all involve curvature, varying thickness and complex three-dimensional geometry. Maintaining consistent scan coverage and acoustic coupling across these surfaces is a persistent practical challenge for conventional inspection methods.

How the Dolphicam2 addresses these challenges

The Dolphicam2 uses Matrix Array Ultrasonic Testing, a 2D array of over 16,000 active elements, to produce full C scan, B scan and 3D imaging simultaneously from a single probe placement in real time.

Although the probe itself is physically a 2D array, it effectively operates as a 4D system, capturing data across X, Y and Z dimensions along with time. This enables live C scan imaging, allowing users to observe changes within the material as they happen.

Where conventional single-element UT produces one data point per position, the dolphicam2 produces a full two-dimensional map of the inspection area instantly. That difference in data density is what makes reliable detection and characterisation of porosity, BVID, delamination and disbonds in complex composite structures possible in a way that manual UT cannot match.

The system weighs 3kg, is operational in under 60 seconds, carries an IP66 rating and works across temperatures from minus 20 to plus 50 degrees Celsius. Inspections that would previously require component removal and laboratory turnaround can be performed directly on the aircraft.

Critically, the dolphicam2 is approved by both Boeing and Airbus — Boeing has authorised specific NDT procedures for the 787 using the system. Get in touch to find out more!