A Light-Sport Aircraft Repair: Come Behind the Scenes
By Carol Carpenter, EAA 678959
Any aircraft owner will tell you that owning an aircraft is a wonderful, exhilarating experience, while having that aircraft stuck in a maintenance shop is a miserable one. In fact, it’s often the most frustrating part of aircraft ownership. For a special light-sport aircraft (S-LSA) owner, the experience can be even more frustrating since few pilots understand what is involved. While pacing in our living rooms, we can’t figure out what in the world is taking so long. This story starts with a mandatory service bulletin (SB) and a Flight Design CTsw.Let’s look behind the scenes at the process.
The owner, a local pilot, asked us to look at an SB he had received and questioned the requirement to send his aircraft to one of the few approved Flight Design Service Centers in the United States. The closest was 700 miles away. After we read the SB, it was clear that only a manufacturer-approved service center was allowed to perform the work – even though we have a full-service maintenance facility for general aviation and light-sport aircraft here at Rainbow Aviation. This wasn’t surprising, since the repair required specialized composite repair experience, would be made to the stabilator, and involved an S-LSA.
Flight Design CTsw in for mandatory service
To perform the repair, we would need specific authorization from Flight Design, the manufacturer of the S-LSA. We already had a good working relationship with Tom Peghiny of Flight Design, so a simple call revealed that the prerequisites were well within our expertise. Flight Design was controlling the distribution of the individual SB kits required for the repair in order to ensure that the experience and knowledge prerequisites were met. We agreed to send a resume of our experience for evaluation. Within a week, we had that required authorization for this one SB repair.
Our customer was elated and apparently promptly posted this information on an Internet users group – the calls began to come in. Within the first week, we had a request to comply with the SB on four aircraft. The SB kits arrived within the same week that they were ordered, so we were ready to begin the first repair.
Now here’s the thing: Most customers are eager to get their aircraft into and out of the shop. They don’t understand the process required to complete most repairs, let alone a composite repair. This was evident when several of our SB customers commented that they hoped to fly in and wait while the repair was made, thinking they would be able to fly home on the same day. (Keep that comment in mind as you read on.) In addition, anytime you take your aircraft in for maintenance, there are some unknowns that can occur. Discrepancies found, parts that need to be ordered. Not only can these unplanned items kill a budget in a heartbeat, but for the owners, these things also have several other effects such as inconvenience, frustration, and annoyance. As with anything that is a source of frustration in our lives, it’s always best to step back and look at the situation realistically. So let’s begin.
We started with compliance of the SB by removal of the stabilizer trim tab. This involved working with very small wrenches to disconnect the stabilizer trim tab pushrod tubes and then drilling out all 24 rivets in the eight hinges on the stabilator. We discovered that three different types of rivets had been used during the previous installation including some aluminum and Monel CherryMax rivets and some of the stainless-steel pop rivets as actually required by the maintenance manual. Only three of the CherryMax rivets had been properly installed. Anyone familiar with Cherry Max rivets will tell you what a pain they are to remove compared to a standard pop rivet.
After removing all the rivets, we found that three of the rivet holes had been elongated. This is abnormal, and since it wasn’t addressed in the maintenance manual, it would require another factory approval for a repair. We reread the SBs, and in particular, the area addressing cracks in the rear stabilator spar area, because it was evident upon initial inspection that this particular stabilator did indeed have cracking around the support bracket attachment. Not only were there cracks in the rear spar area, but it was obvious that the hinge reinforcement had been completed incorrectly. The previous technician hadn’t complied with the directions on proper installation of the hinge support brackets. We would need to identify what repairs had been previously completed and what specific sections of the SB would need to be addressed.
The horizontal stabilizer trim tab had previously been repaired, and some changes had been made, including cutouts of the stabilator trim tab balance weights. There were additional changes on the outboard section of the stabilator, and cutouts to the bar web to allow stiffeners to the outboard hinge location. We took pictures of the damaged area and e-mailed them to Flight Design for input.
Next, we prepared the horizontal stabilizer for repairs, masking off all of the painted surfaces around the area where any work was to take place to protect all of the surfaces from damage, epoxies, and dust. This was when we realized that the rivets that came with the SB kits weren’t actually the rivets required to reinstall the hinges on the horizontal stabilizer, but rather were meant only for holding the ribs in place while the epoxy cured. So we checked to see if we had the rivets required to reinstall the hinges. We had 13 boxes of rivets, three boxes of stainless-steel pop rivets, but none of the specific size called out in the SB.
The next hour was spent making phone calls searching for rivets. Our options: $50 for overnight shipping or a two-hour round-trip drive to pick them up. After a quick call back to make sure that the supplier would be open when we got there, we drove over. Concerned we would get back and not have one or two rivets we might need, we just asked for “50 of every size you have in the store.” Eighty dollars later, we drove back home. By then it was 7 o’clock at night, and we still needed to get the hinge support brackets glued in place. These were the hinge support brackets that we spent four hours manufacturing the night before (after obtaining the manufacturer’s authorization). However, once properly installed on the aircraft for a test fit, we discovered that the brackets needed to be modified.
Then it was back to the milling machine to get clearance for the hinge. Good thing we checked the fit prior to gluing them in place. It would have been nearly impossible to modify them after they were glued and riveted to the rear spar. Next was one more trial fit. It looked good, so then we mixed the epoxy, prepped the surfaces, mixed the flox with the epoxy, and carefully installed the hinge support brackets. We clecoed it in place and riveted it to the rear spar web. Finally, we carefully cleaned the outer edges and the excess epoxy from any surfaces.
The next day, the epoxy was cured, so it was time to build a tent around the repair area and heat for another 12 hours. Once the heating tents have been set up and temperature regulated, it was time to start pulling all of the hinge mechanism off of the aircraft so that we could balance the flight controls. We reread the manual on balancing procedures and determined we would have to come up with some kind of balancing stand. This was a good excuse to build something using our computer numeric control router. We took some quick measurements, and 60 minutes later, voila, a quick press-fit balancing stand specially made for this stabilizer. We disassembled the heating tents and started final assembly; we crossed our fingers and hoped everything would go well. We checked the alignment of pushrod tubes, inserted all the hinges with clecos, and installed the rivets into the hinges. Sure enough, four rivets needed to be longer than we anticipated. Good thing we got those extra rivets. We installed the hinge assembly on the stabilator, hooked up all the control systems, and installed the stabilator on the balancing fixture. Filled the balance weight cavity with lead shot until the stabilator was perfectly balanced, mixed the lead shot with epoxy slurry, and double-checked the balance. If everything goes well, we should be able to have this installed the next day.
As the project continues, your mechanic is doing his best to complete the repair. He’s dealing with the multiple steps required for him to do his job right. There’s always so much more involved in an S-LSA repair than aircraft owners realize. If you’re appreciative, he’ll be rewarded for his late nights and hard work. A little appreciation will go a long way toward making your mechanic feel like he’s valued, and it will give him an incentive to do his best work for you. Maybe you could even bring brownies.
About the Author
Carol Carpenter, coauthor of Sport Pilot Airplane: A Complete Guide and A Professional Approach to Ultralights,is a sport pilot instructor, and she’s an instructor for both the FAA Light-Sport Repairman-Inspection and maintenance courses. Carol and Brian Carpenter operate Rainbow Aviation in Corning, California. Contact them at www.RainbowAviation.com.