ROTOR Magazine2019 WinterWork Safe

How Far Is Too Far?

By December 23, 2018March 26th, 2021No Comments

Preventive maintenance is always better than reactive maintenance.

Earlier this year, I was having maintenance challenges with an aircraft. Sometimes everything was perfect and nothing amiss, but other times, something wasn’t right. The plane would be hard to start but then would run perfectly. Other times, it wouldn’t start at all.

I read maintenance manuals, troubleshooting charts, and online blogs. I spoke to tech support people. I checked p-leads, spark plugs, fuel delivery, and the electrical system. I changed the ignition switch and installed a new carburetor. But I didn’t get to the root of the problem until the last maneuver of a biennial flight review, when the engine quit and the proverbial light came on.

What I had been experiencing all along was an intermittent magneto problem—a dual magneto problem at that!

A dual magneto failure. What are the chances? I hadn’t thought it possible. Our machines are redundant in so many ways. The electrical system is designed to make a dual mag failure very unlikely.

Here are some clues as to how this happened: Both magnetos were installed new at the same time during an engine overhaul. Both had 950 hours on them. Although both magnetos should have had 500-hour inspections, that never happened. At each annual inspection, the timing was checked, along with all items spelled out in FAR Part 43, Appendix D. Ops normal.

For Part 91 operations, the FAA allows us to continue to fly our aircraft if they pass the Part 43 annual inspection. We do not have to abide by the criteria for manufacturers’ recommended inspection or recommended time before overhaul.

This usually works out because much has been done in the past five decades to improve the equipment we fly. The machining process is better. The lubricants we use are a lot better. Parts are precision machined and last longer than components of yesteryear.

Many owners and pilots continue to fly beyond the recommended time limits. Is that a problem? It could be. You must ask yourself: If I do not use the manufacturer’s limit, then what is the limit? How far beyond the inspection criteria is too far?

When you fly that component to failure, you will know exactly how far is too far. But when you reach that point, where will you be? On the ground at your local airport or helipad? Or in the air, perhaps far from a hospitable forced-landing site?

A few days ago, I was in a different aircraft, out of town on a short flight of about 35 minutes each way. On the way back, I experienced an alternator failure. Not as big of a deal as the dual magneto failure, but still I had to do some higher-level math to determine how soon I needed to get the electric landing gear down with available battery power. I was certainly grateful to have an engine monitor, an electrical system monitor, and a navigation system with time-to-go displayed.

With a little brain power, I calculated I could get back to base with no problem. I chose to slow down and lower the landing gear at 11.7 volts to allow some juice to spare for radios. It worked out nicely. The gear went down, and the radios, autopilot, and transponder continued to work with the battery power I had.

Upon landing, I went through the logbooks. The alternator had been in service for 20 years and one month, or 1,756 hours. Kudos to the company who assembled such a robust alternator, but it should have been replaced or overhauled well before that day.

We have the right and authority to fly our machines beyond manufacturers’ recommended limits if we do not fly for compensation or hire. But we need to be smart about it and not put ourselves in a position where we fly them to failure. If you fly a component beyond the manufacturers’ recommendations, fine. But then whose recommendations will you follow?

Fugere tutum!

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Zac Noble

Zac Noble

Zac, HAI’s director of maintenance and technology, joined the association as its deputy director of flight operations and technical services after 11 years of flying in the air medical sector. A US Army veteran, Zac’s aviation career spans more than 35 years. He is a dual-rated ATP, a dual-rated CFII, and an A&P with IA privileges.