Industry Study Details Best Paint Practices

Paint is the first thing people see when they approach an aircraft, but not many pause to give it a thought. However, they should, as “Paint serves a purpose that goes far deeper than a glossy exterior,” according to Aircraft Paint Expectations, a recent industry benchmark forum report detailing the best practices and frequently asked questions faced by experts in the MRO field.

Beyond the decorative, paint is “a thin protective shell that serves as an aircraft’s only line of defense against the elements.” The moment an aircraft leaves the hangar, that protective shell is under assault.  As aircraft are designed to flex, it is not surprising that the paint coating will soon develop microcracks, which will grow larger over time, exposure and usage if left untended. Another factor that will degrade paintwork is the extremes of skin temperatures to which it will be exposed, from more than 100 degrees F on the ground to -50 degrees F in flight, often in the span of minutes. Those environmental changes will cause expansion of aluminum, composites, the sealer coat and even the paint itself, leading to cracking. Maintenance and even normal operations can cause chipping and wear. In addition, basing the aircraft in a coastal area can be expected to diminish the paint’s lifespan from the normal five to seven years.The authors of the report suggest that for aircraft that spend much time in ambient corrosion areas—those with high humidity, pollution or salt air—owners apply a paint coating once a year to the aircraft exterior.

Like most systems on an aircraft, the exterior paint requires constant care, according to the experts. In a perfect world, the aircraft should be kept in a hangar and washed after every flight. The authors of the report acknowledge that this is likely not common practice for a majority of operators, but they emphasized that it is imperative to wash down the aircraft after every de-icing event, to remove any lingering de-icing fluid or salt from winter operations. Operators should inquire with their manufacturer as to what cleaning products are compatible with the paint surface. When viewed under a microscope, a smooth, glossy surface is flat, while a dull surface has peaks and valleys that can collect contaminants and lead to corrosion.

Chips and cracks in the exterior paint are unavoidable, and they should be touched up immediately; a quality touch-up job should be performed after every maintenance event. To ease that task, operators should avoid waxes that contain silicon, as they could interfere with the adhesion of the touch-up paint.

Practical Considerations

It is the rare aircraft that is not white, and the reason for that is twofold: white is easy to touch up after maintenance, and it reflects more heat when the aircraft is parked in the sun, keeping the cabin cooler than if the aircraft was painted a dark color. Likewise, dark-painted wings could increase the temperature in fuel tanks, causing fuel expansion and limit the amount held in the tanks. Yet, some owners and operators insist on custom paint schemes, and for them the experts advise consulting with the airframer about color restrictions. Metallic or pearlescent finishes can be difficult to match, and pearl coats are particularly troublesome because of the three-layer process, and their susceptibility to degradation from contact with fuel.

When it comes to the actual paint job, there may be no such thing as a perfect paint job on something as large as a business aircraft, and owners should expect some dirt specks to be present in the finished product. Before starting the job, the maintenance facility should furnish a guide detailing how much debris might reasonably be expected per area of the aircraft. If owners cannot live with the result, they can opt either to have the area repainted and hope for better results, or attempt to buff the debris out, which could present some long-term hazing or staining issues.

Composite areas tend to be especially prone to paint cracking, as they expand and contract more than aluminum surfaces. The report notes that “less is more” when painting these areas, and while the honeycomb texture of the composite material may be detectable after the paint dries, the result will wear better than a heavier coat, which will soon show excessive cracking.

Among the contributors to the report were Dassault Falcon, Duncan Aviation, Elliott Aviation, Jet Aviation, King Aerospace, StandardAero, Stevens Aviation and West Star Aviation.