Composite Complexities

A non-pilot recently asked me if 14 years since new was old for a Cirrus. I didn’t have to pause when answering that it certainly is not. But after thinking about it for a while, it occurred to me that while the modern composite design of a Cirrus—or Diamond or Columbia—may still seem new even after 14 years, the earlier models in the fleet are indeed aging. When these mass-production composites came to market, there was much speculation on how the airframes would hold up and how difficult they would be to service when they break. Owners of earlier models are now finding out.

When fiberglass airframes gained popularity, one sales pitch was that the design would be cheaper to maintain because compared to all-metal designs, corrosion is mostly a non-issue. It was also said that fiberglass airframe structures are simpler than their metal counterparts, which means there is less to disassemble and inspect during annual inspections. That may be true, however, it’s false to say that a fiberglass airframe isn’t susceptible to corrosion because there are plenty of metal parts inside the structure, including critical flight control components.

When one of the first new Cirrus models ended up in my local maintenance hangar for an oil change, I remember a seasoned mechanic shaking his head and chiding its owner to trade it in before its composite structure needed even basic repairs. Those were, and still are the sentiments of many old-school airframe mechanics. I’ve always thought this was a narrow-minded outlook on progress, but there’s no arguing with the reasoning that it wouldn’t be difficult to find a shop that could fix airframe damage on an all-metal Beechcraft or Piper, to name a couple. That’s not the case with a composite airframe, even these days when airport ramps are littered with composite models.

In our March 2014 issue, we reported on the CIES digital fuel level sensors and electronic fuel quantity gauge retrofit that was accomplished on a first-gen Cirrus SR22. The retrofit doesn’t require any modification of the composite structure in and around the fuel tanks since the new digital fuel senders bolt in where the original analog senders did. But while accomplishing the installation, the shop found that the sealed mounting nut plate—that’s the metal assembly that the fuel sensor attaches to—was broken, likely the result of someone overtorquing it. It went from bad to worse because once the nut plate was removed, it was revealed that the composite flange at the upper portion of the fuel tank was warped. Since the composite flange is sandwiched between the metal nut plate, whatever or whoever broke the nut plate also damaged the surrounding composite. The metal portion of the repair, which includes riveting and sealing a new nut plate in place, is relatively easy and inexpensive. For parts and labor, the total repair is around $150. But repairing the damaged composite was another matter.

Since the technical folks at Cirrus Aircraft never encountered this type of damage to that area of the structure, there wasn’t an approved repair technique or replacement part in inventory. That meant that Cirrus had to engineer a replacement flange assembly. To the aircraft owner’s surprise, he had to pay for these factory engineering costs. Like it or not, that’s not uncommon with major composite repair work on certified aircraft, and you should understand this when considering the purchase of a used composite model.

While this early-gen SR22 was serviced within the Cirrus authorized repair network for most of its life, it’s obvious that someone either didn’t understand the consequences of overtorquing the nut plate or was careless in doing so. Regardless, it’s an example that repairing and maintaining a composite aircraft could be more complex than a metal one. —Larry Anglisano