Airframe and Powerplant

Log Role

February 1, 1999

Get involved with your logbooks

Maintaining good logbooks ranks right next to degreasing the belly and springing for an unexpected engine overhaul on the list of aircraft ownership's grand rewards. Logs tend to be handled like an eccentric uncle — at arm's length. As a result, the logs tend to travel in some sort of paperwork limbo from one maintenance facility to the filing cabinet, returning to yet another shop. And while the logs are certainly considered valuable — an airplane with complete, original logs brings a premium on the used market and can save its owner money at every annual — many owners are loathe to open the books during the 11 months of the year during which the annual is not foremost in their mind.

Too bad for that. It's really in the owner's best interests to become involved in the upkeep of the logbooks because leaving the work entirely to the maintenance personnel — who, in all fairness, have a lot of other things to do — will usually result in what might be considered strictly legal but hardly helpful log entries. According to FAR 91.417, the aircraft owner is responsible for keeping "records of the maintenance, preventive maintenance, and alteration and records of the 100-hour, annual, progressive, and other required or approved inspections, as appropriate, for each aircraft (including the airframe), each engine, propeller, rotor, and appliance of an aircraft."

For your airplane, you should have a veritable mountain of paperwork, including logs for the airframe, engine, and prop. Although it's not required, many owners keep a separate, detailed log of avionics work performed; the major components of these entries would, of course, appear in the airframe log. You should also have a full complement of service letters and work orders. Truly maintenance-involved owners also have their own copies of the airframe service and parts manuals, as well as the operator's and overhaul manuals for the engine.

If you haven't done so yet, take the time to peruse your logbooks; the principal advantage is that your familiarity will help to keep tabs on your maintenance facility — incidentally, that's not the same as second-guessing them. And when the FAA sends you the inevitable airworthiness directive (AD) papers, you'll be able to make a snap determination of whether the note will cost you a thick stack of greenbacks, and, if so, how long you'll have to dig them out of the mattress.

Look through your logs for cryptic entries such as "work performed i/a/w [in accordance with] manufacturer's specifications" and "see parts listing on work order 999662." You need not keep the work orders in the same logbook case as the main books, but it's a good idea to have them accessible. Also, for those entries that reference a manufacturer's spec, try to determine exactly what those are. (Here's where those airframe and engine parts, service, and overhaul manuals really pay for their place on the bookshelf.) There's nothing wrong with copying the work order and stapling it into the logbook page accompanying the entry noting the work performed.

References, please

Organization is the critical part of keeping good logs, and one of the most powerful tools is a master reference sheet. It's easy for owners of new airplanes who have just one of each logbook for the engine, airframe, and prop, but owners of older airplanes have a more daunting task. You should take a rainy weekend afternoon and pore over the books, carefully numbering them chronologically, and construct a cheat sheet to help you find the big items such as major damage repair or engine overhaul entries. Take this list of major items and place it near the front of the logbook folder for easy reference.

While you're doing this bit of frontal-lobe-intensive gruntwork, also come up with an equivalence sheet to help you determine the total time of the major components on the airplane. Chances are good that your tach's been replaced somewhere along the line; and so it doesn't jibe with the engine's total time, nor is it in synch with the airframe's number of hours. Go back to the beginning and double-check the math. It's extremely common for one mistake to be repeated through years and years of log entries. Also keep in mind that over time the tach and Hobbs values will diverge — the result of the tach's reading a one-to-one ratio only at a certain engine speed — while the Hobbs runs true clock time whenever (usually) the engine's running.

Pay particular attention to airframe total time, engine time since overhaul, times since top-end work, and the prop's total time or time since major (note also any inspections for AD or service bulletin compliance). Next to the total times for these major components, jot down their serial numbers — listed in the logs or on tags stapled within. At the next inspection, take this list to the airplane and double-check those serials. You might be surprised that, say, a magneto replacement or swap-out took place without a logbook entry. It happens.

Do the AD shuffle

An airworthiness directive list should be present in the logs. In recent years, maintenance facilities have come to rely on computerized AD and SB databases, so it's likely that one of the most recent annuals will have generated a printout of ADs that apply to your airframe, engine, prop, and various appliances such as ignition switches, magnetos, ELT, brakes, and oil filters. If you don't have one of these printouts, cozy up to your local shop and see if you can get one made. Note the ADs that require repetitive inspections and/or replacement parts; some of these repetitive ADs can be terminated by installing newer components. If the logbook entries are unclear as to the method of compliance, you may end up undergoing unnecessary inspections. A short form of the AD list describing the repetitive items and their next due times should be in your daily flight log for quick reference.

Here's a good example of how a cursory log entry can confuse. On my Beech P35 Bonanza, there's an AD on the ruddervator control horns; the original magnesium horns are subject to 100-hour repetitive inspections for cracks and corrosion, while replacement aluminum horns are not. At the last annual — the first for me with this airplane — we couldn't tell if fittings had been replaced. I spent more than an hour with the logs during the annual and poring through work orders before discovering that one of the horns had in fact been changed.

Squawk check

Pitot-static and transponder checks seldom seem to line up with the annual inspection, so be sure to keep a running tally handy — say, in that daily flight log. Might as well keep a log of your monthly VOR checks if you fly IFR, too.

Field frustrations

If poor logbook form makes persnickety owners crazy, it's almost enough to drive the conscientious A&P mechanic to distraction. According to a thumbnail survey of working wrenches, the list of logbook annoyances is long and familiar, starting with penmanship that would make your average prescription look like the product of a laser printer. This is evident even to owners — making whatever work old Rusty did back in the 1960s something of a mystery. The advent of computer-generated forms and stick-on labels has been a tremendous boon to owners everywhere.

As bad as these nearly useless, superficial entries, according to A&P mechanics, are those so detailed that every step of the annual, including coffee breaks and donut consumption, is chronicled. There is a happy middle ground, but with the feds becoming ever more interested in documentation and so-called pedigree of everything on the airplane, chances are that you'll see more detail today than ever. Pet peeves of the maintenance types are entries with no attribution at all. It's on their heads — and certificates — to determine whether that work was done correctly.

Your handwriting's in there, too

It's not just the licensed mechanic's script you should find in the logs. Any owner-performed maintenance allowed by the FARs has to be noted in the logbooks.

It's not heavy, or is it?

The FARs require a current weight and balance to be aboard the airplane, figures that include the empty weight of the airplane. But is that number accurate? How long ago was your airplane weighed? Do you have years of calculations based on an empty weight taken right after the airplane was built? Although everyone from airframe repairers to avionics technicians tries to be careful with the numbers, there will be the inevitable weight creep. Many new radio installations, for example, fail to take into account the weight of the new wiring laid atop the old stuff. Again, it will be worth your while to double-check the calculations. Better yet, have your airplane reweighed.

In the end, your efforts to organize and annotate your airplane's documentation will pay off. You'll be time and goodwill ahead on your annual because it won't take the IA half a day to make sense of the logs. It's true that an evening spent with your airplane's logbooks is a bit like settling down to a Michael Crichton novel with all the verbs cut out, but it'll be educational drudgery nonetheless.