Aircraft Maintenance: Tire trouble
Given that recent experience, I thought it appropriate to review the steps of proper and, more importantly, practical tire and tube replacement. The former can be found in a number of maintenance manuals; the latter comes from experience and the valuable insights of those great mechanics I’ve learned from over the years.
About six months ago, I decided it was time to retire the rubber on my main gear. Bonanzas use fairly large 700x6 main gear tires, which drives up the cost in itself. I’m typically a fan of retread tires and have had no issues in the past with them. I’ve found the quality to be outstanding and the service life has been excellent. That said, I decided to treat myself and my airplane to some new, premium treads. I was happy with the final result, but the path there was about as smooth as sandpaper.
The trouble started during the installation process itself. My friend, IA, and maintenance mentor Alan Brown made a point of reminding me to test-inflate and inspect the tubes outside of the tires before mounting them. I hadn’t done this before, but decided to follow his advice. So, I added just enough air to fill the tubes for a good inspection (NOT enough air to stretch them). Sure enough, one of the tubes had an obviously bad seam and was leaking air. Twenty-three years of maintenance and this was the first time I saw a tube fail out of the box prior to installation. Apparently, Alan "The Plane Whisperer" Brown knew something I didn’t. Time to order a new tube.
Next came all the usual steps for proper tire replacement (always use safety gear when working on a pressurized tire):
- Clean and inspect the wheel halves;
- Coat the tube liberally with tire talc;
- Fit the deflated tube inside the tire, then add a little air to round out the tube inside the tire and ensure there are no wrinkles;
- Align the balance marks for the tube and tire;
- Carefully fit the wheel halves together, ensuring that the tube is not pinched by the halves during assembly;
- Reassemble the wheel halves using new lock washers and torque the bolts to spec;
- Inflate the tube to full pressure. Deflate it to allow it to shift if required and inflate it again to the required tire pressure;
- Remount the wheel on the aircraft using new lock washers on the brake caliper bolts.
All was well until taxi time. The right wing loped up and down with every turn of the tire. Thinking it may have just been the result of sitting a bit, I checked everything visually and went for a series of taxi tests and a flight test. Unfortunately, the problem did not resolve. Back to the hangar.
I removed the wheel and inspected the offending tire. Most tires have a raised bead near the wheel that is used to identify whether the tire is mounted properly and not off-center to the wheel itself. I measured this carefully and everything was perfect. When I measured the outside of the tire, it was obvious that the tire was significantly out of round.
Off came the tires…both of them. The experience made me decide to switch brands to the “Brand B” premium tire. Fortunately, all went well with this new set. I am happy to report that, after many hours on these new tires, the fit, finish, durability, and ride quality of the new rubber have been excellent.
Fast forward a few months: I’m pulling up to the hangar after a long business trip from Atlanta to Boston. My boys and I hopped out of the airplane to the tune of a hissing tire. Sure enough, the leaking tube was the brother of the one that had failed during the initial inspection in the shop. Both tubes were bought together and probably made right next to each other. Call it overly cautious, but I should have considered replacing both tubes once I found a manufacturing defect in one of them. Upon disassembly, the tube failed at the same seam that its twin brother did (the retailer and manufacturer have been notified of the issue).
So, here we are today with a nice new set of tires and tubes, as well as a good story to go with them. Most importantly, I’m hoping there are a few good lessons in this story for some of you out there. Tire changes are a seemingly simple maintenance task that owners can do themselves as preventive maintenance according to Part 43, Appendix A of the federal aviation regulations. However, even the simplest of maintenance tasks can get complicated. So, follow the proper procedures and never assume that a part is truly airworthy just because it came in a box. Check for yourself because the world is an imperfect place despite the best intentions of everyone involved. Happy flying!
