Aircraft Part Overhauls

Why are so many aircraft owners and A&P mechanics "spring-loaded to the overhaul position"? I think the word "overhaul" might be the most overused and misunderstood word in the lexicon of aircraft maintenance.Last week, I was talking to a friend who had just put his airplane in the shop for its annual inspection. I asked him if he'd submitted any squawks for the shop to fix. He replied, "My nose strut hasn't been feeling right and it's been weeping fluid, so I had them overhaul it."I pointed out to my friend that I was sure the shop hadn't really "overhauled" his leaky nose strut. The shop would have disassembled the strut, cleaned it, replaced the O-ring seals with new ones, then reassembled the strut and serviced it hydraulic fluid and compressed nitrogen. That's a "reseal" or a "repair" but not an "overhaul."

What's An Overhaul?

It may sound like I'm nit-picking here, but the distinction is important. The word "overhaul" is a term-of-art that has a very specific meaning under the FAA regulations. This is set forth in 14 CFR Part 43, the section of the regs that deals with maintenance:

43.2 Records of overhaul and rebuilding.(a) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being overhauled unless ---(1) Using methods, techniques, and practices acceptable to the Administrator, it has been disassembled, cleaned, inspected, repaired as necessary, and reassembled; and(2) It has been tested in accordance with approved standards and technical data, or in accordance with current standards and technical data acceptable to the Administrator, which have been developed and documented by the holder of the type certificate, supplemental type certificate, or a material, part, process, or appliance approval under 21.305 of this chapter.

Note that two requirements must be met before something can be properly called "overhauled":

The thing must be inspected and repaired as necessary; and
The thing must be tested and certified to be within service limits as set forth in the manufacturer's overhaul manual.

Bill O'Brien, the FAA's top-ranking A&P mechanic, has a marvelously simple way of explaining to mechanics the difference between an overhaul and a repair:

"If you used a micrometer, it was an overhaul; if you didn't, it was a repair."

Bill's explanation is obviously an oversimplification, but it gets the essential point across very well. For something to be overhauled, each part must be measured and certified to be within service limits as set forth in an applicable overhaul manual.In resealing the leaky nose strut, the shop would certainly have met requirement #1 by disassembling, cleaning, inspecting, repairing as necessary (by replacing the O-rings and so forth), and reassembling the strut. But it almost certainly would not have met requirement #2 (testing and certifying that the strut meets service limits). In fact, it might well have been impossible for the shop perform such testing because they probably didn't have an overhaul manual for the nose strut, and such service limit data doesn't normally appear in the regular airplane service manual.A mechanic can legally "repair" almost anything on an airplane if he has the service manual for that airplane. But a mechanic cannot legally "overhaul" anything unless he has the applicable overhaul manual (unless the service limits are documented in the service manual).Frequently, the overhaul manual requires that certain parts be replaced at overhaul on a mandatory basis. For example, when an air-driven gyro instrument is overhauled, it's SOP to replace all the bearings (and they aren't cheap).Another related term that's often misused is "rebuild" ... as in, "I asked the shop to rebuild my nose strut." This usage is even further off the mark than "overhaul." Here's the applicable reg:

43.2 (b) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being rebuilt unless it has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to the same tolerances and limits as a new item, using either new parts or used parts that either conform to new part tolerances and limits or to approved oversized or undersized dimensions.

In other words, an aircraft component can only properly be called "rebuilt" if it has been overhauled to new limits.

Overhaul Vs. IRAN

Did my friend really want or need to have his nose strut "overhauled" or "rebuilt"? Of course he didn't. All he wanted was for it to be fixed so that it didn't leak. Fortunately for him, that's in fact what the shop did to his strut: It "inspected and repaired as necessary" (known in the trade by the acronym "IRAN").Owners and mechanics are both guilty of using the terms "overhaul" and "rebuild" as if they were synonymous with "repair." As you've seen, they aren't. This is much more than just quibbling over words. There's often a huge cost difference between simply repairing something and overhauling or rebuilding it. Frequently, an aircraft owner can save big bucks by specifying that he wants an "IRAN" rather than an "overhaul."Case in point: Six years ago, one of the alternators on my 1979 Cessna T310R became intermittent. The problem rapidly got worse until it reached point where the alternator was not working more than it was working. The usual procedure would have been to replace my balky alternator with an overhauled one. However, my known-ice-equipped airplane uses big, 100-amp, gear-driven alternators, and the price of an overhauled exchange unit was about $1,000. Ouch! (That was in 1998; today, for some reason, the price has come down to about $750.)

These alternators normally go to engine TBO (1500-2000 hours), but mine had less than 400 hours on it. I decided it was worth troubleshooting the problem further, and ultimately discovered that the alternator had a bad brush/slip ring assembly that wasn't making good contact. My A&P and I considered trying to open up the alternator and see if we could fix the problem (this was before I earned my own A&P ticket), but concluded that doing so required special tools and skills that we didn't possess.I then decided to make some phone calls to see if I could find an accessory shop that would be willing to do an IRAN on my alternator. The first few I called said no -- they were only willing to do a full overhaul -- but eventually I found a shop that agreed to open up the alternator and just fix the problem with the brushes. I sent it out, and got it back less than a week later with an invoice for just $103 (including shipping). The difference between IRAN and overhaul: approximately $900.Another more recent example: Just last month, the Cessna 400B autopilot in my airplane developed a nasty case of "pitch bumps." I'd encountered this problem once before some years ago, and after taking the airplane to an autopilot specialty shop, the culprit turned out to be a noisy pitch-axis pickoff in my G-519B-1 attitude indicator. (The 400B autopilot obtains its pitch and roll information from this instrument.) I replaced the attitude indicator with an overhauled exchange unit that cost me $869 plus installation labor.

When the same problem occurred again last month, I was certain that the attitude gyro was once again the culprit. I considered ordering another overhauled exchange gyro, but the one in my airplane was a very low-time instrument with only about 75 hours time in service since overhaul. It seemed ridiculous to spend the money to overhaul it again so soon.I sent emails to various instrument shops asking if they'd be willing to do a simple IRAN of my gyro to repair the bad autopilot pickoff, and I got back an affirmative response from The Gyro House just north of Sacramento (Calif.), who said they'd repair the instrument for an estimated cost of $200 (2.5 hours of labor at $80/hour).That sounded better than $869, so I had them repair my gyro and they fixed me right up. The autopilot now flies like a dream; no more pitch bumps. My savings by choosing an IRAN rather than an overhaul: nearly $700.To paraphrase the late Everett Dirksen, if you can save $900 here and $700 there, pretty soon you're talking about real money.Speaking of real money, I spotted an interesting discussion today on the Beech owner's list in which various Bonanza and Baron owners were talking about problems they'd had with sticking needles (particularly the glideslope needle) on their King KI-525 Horizontal Situation Indicators. Several owners mentioned that they'd wound up having their HSIs overhauled to the tune of about $2,500. Then one particularly savvy owner (who also happened to be an A&P) chimed in to say that repairing the "sticky needle syndrome" in these instruments is relatively easy, and could be done on an IRAN basis for less than $200.I'm sure you get my point. If your airplane has an instrument or accessory that's long-in-the-tooth and plumb worn out, it certainly makes sense to have it overhauled or to exchange it for an overhauled unit. But don't be "spring-loaded to the overhaul position." Just because something isn't working right doesn't necessarily mean that it needs to be overhauled. Frequently a simple repair is all that's needed.In my experience, not every instrument or accessory shop is willing to do an "IRAN" because they make more money and believe they have less liability exposure if they confine their work to full-blown overhauls. You may have to call around (or the email equivalent) to find a shop willing to help you out. Your "type club" is often a great source of information about whom to call.My advice is to be careful how you use the terms "overhaul" and "rebuild," and to add the term "IRAN" to your vocabulary. It can save you a bundle.See you next month.