Aviation Safety Letter 3/2004

Fibreglass in Amateur-built and Ultralight Aircraft

Kolb Sport in Flight FrontFibreglass has been used in amateur-built aircraft for over forty years. Since the early 1980s, with the advent of modern aircraft designs such as the Vari EZ, Long EZ, the Cozy, the Velocity, the Glassair, the Seawind and many others, the use of fibreglass has become quite common. It is a composite material that is light, strong, somewhat flexible and can be shaped into many useful aircraft structures. It is made of two or more components: glass fibre (glass fibre reinforced plastic — GRP) and an epoxy or polyester resin. A catalyst is used to create the chemical reaction that will bond the two parts. Over time, composite parts are affected by cyclic variations in temperatures, weathering, rain, snow, moisture absorption, ultraviolet (UV) radiation and other factors. The initial methods and care of fabrication will influence the longevity of the part. Many believe that composite parts are free from maintenance, but this is not the case. Here are two stories that recount the importance of having an inspection schedule for these parts in order to ensure continuing airworthiness.

The amphibious amateur-built aircraft was made of fibreglass and had been sitting at a local airport for several years, when it was put up for sale. An aircraft mechanic purchased it, inspected the structure as best he could, made repairs, and put it up for re-sale. He soon found a buyer who was hoping that the amphibious abilities of the aircraft would allow him to fly from his home airport to the numerous good fishing spots that abounded in the northern region of Canada, where he lived. The aircraft was ferried successfully to the new owner's home-base where an inspection was carried out and the transaction completed. The new owner was given flight instructions and later went off by himself to do a fly-by. During this flight, one of the wings failed and the aircraft plummeted to the ground, killing him. Investigation by the Transportation Safety Board (TSB) revealed that one of the wing's integral fibreglass fuel tanks had delaminated and allowed fuel to seep through and weaken the wing spar to a point where failure occurred. This construction flaw had gone unnoticed for some time and the wing deteriorated and failed.

In another instance, two pilots were ferrying an amateur-built aircraft from their home strip to a nearby airport. The aircraft was of a design that had been around for over twenty years. The cabin and fuel cells were made of fibreglass and the wings were made of metal. Fifteen minutes into the flight, the engine failed and a forced landing was initiated on a provincial highway. There would not have been any damage if oncoming traffic had not compelled the pilot to veer off into a four-foot ditch. Fortunately, there were no casualties. In order to transport the aircraft, the wings were disassembled and it was noted that the cabin header tank was empty. A check of the fuel line of the wing tanks revealed that it was blocked. Blockage was found to be due to fibreglass debris in one of the fuel tanks. A vent pipe was also found blocked by a nest of mud wasps.

Fibreglass parts need care in order to ensure continued airworthiness in service. Your inspection schedule has to take into consideration these composite parts and if you are unsure of how to proceed, communicate with a licensed aircraft maintenance engineer (AME) for assistance. Be especially careful with fuel cells, which are an integral part of a wing structure, as wings flex and may increase the risk of delamination. Commercial airliners today are proof that the use of composites is very safe. They can represent up to 30% of the total weight of a commercial airliner. In helicopters, they represent 60-80% and in today's fighter aircraft, close to 50%. It is a very efficient material, but it needs care too. Inspect and repair, as necessary. Happy flight.

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