The 30-day Inspection

Which is safer: a well-used rental airplane flown by dozens of pilots, from students to high-timers; or a personally owned airplane, flown regularly by only one, certificated pilot?

Popular logic suggests the personally owned airplane is usually in better shape, and therefore safer. It may be, though, that a personal airplane develops squawks that aren’t discovered before they become costly to repair… if not downright dangerous.

THIS IS ONLYA TEST: Conduct a complete preflight inspection of the airplane you intend to fly. Then, pull out the preflight inspection checklist from the airplane’s Pilot’s Operating Handbook (POH) — you remember there’s one in there, don’t you? Chances are excellent that there’s at least one item on the POH checklist you’ve forgotten to look at this time around. It’s simply human nature to miss things sometimes … which is why the checklist is there. Use it.

Rental airplanes usually fly a lot. Often several different sets of eyes and hands inspect a given rental airplane every day. Most of them (students) are using the checklist. If Pilot A misses something on his preflight inspection (and assuming it doesn’t affect the safe outcome of his flight), Pilot B may catch it on hers. Hence, rental airplanes will tend to get repeated thorough — and often complementary — preflight inspections.

Personal airplanes may go days, or even weeks, between flights. Often the owner is the only person that gives the airplane preflight inspections. That’s fine if he/she consistently gives the airplane a complete once-over with fresh eyes. BUT, if he or she tends to miss one item or another, then that item may go completely un-inspected between required checks (more on these in a moment). And, if the owner misidentifies the severity of a “squawk” found during an inspection, then he/she might as well have never seen the glitch at all. And no one will see it differently.

REQUIRED INSPECTIONS Depending on the airplane’s use, certain inspections are required under the Federal Air Regulations (FARs):

  • Annual inspection. All U.S. civil airplanes must receive a thorough inspection at least every 12 months. The “annual” is in effect a conformity check, to verify the airplane still meets the mechanical requirements of its Type Certificate (TC). Although the Airworthiness Inspection the airplane received when it was new never expires, the Airworthiness Certificate is not considered valid unless the airplane has a current annual inspection. Not just any licensed aviation mechanic can “sign off” an annual inspection; the technician verifying the airplane meets its TC standards must hold a special Inspection Authorization — an “IA.”

NOTE: Builders of “homebuilt” airplanes licensed as “experimental” can get Federal authorization to conduct annual inspections on the airplane they built. This authorization is valid only for the specific airplane he/she built, and is not transferable to a new owner if the airplane is sold.

  • 100-hour inspection. Airplanes operated “for hire,” including rental airplanes, must receive an inspection every 100 operating hours. The “100-hour” usually covers everything inspected in an annual inspection, but unlike an annual the 100-hour may be “signed off” by any licensed mechanic, not necessarily an IA.
  • 50-hour inspection. Most airplanes in charter service must receive an abbreviated inspection every 50 flying hours. The “50-hour” may also be signed off by a mechanic, not necessarily an IA.

How It Works: The philosophy is that a privately operated airplane must receive a good once-over at least annually. If the airplane is offered “for hire” to the public, but will be rented to pilots who should “know what to look for” to determine airworthiness, then it is held to a higher standard and must have additional (100-hour) inspections. When airplanes are operated with the “unknowing public” aboard, such as a charter operation, then the Feds dictate the airplane be inspected even more regularly.

Since a number of persons — each one with different lapses and areas of emphasis — inspect them much more frequently, and because they’re inspected by professionals much more frequently, it can be said that the rental airplane may indeed be “safer” than the personally owned aircraft. If you own your own airplane you can, of course, compensate for this by using the preflight inspection checklist, and performing what I call the “30-day inspection.

If you’re like me, you’re always in a rush when time comes to make a flight. You may be traveling on business, and have a schedule to keep. It may be cold or wet outside, hardly conducive to a lengthy preflight. The family may be loaded up for a vacation flight, baking inside the plane and anxious to get off the ground. You may simply be distracted by friends or other airplanes milling about the airport. Any or all of these make it tempting to skimp on the preflight inspection.

This is in NO WAY a suggestion to replace or hurry through a good preflight inspection, but it WILL help you keep tabs on some special airworthiness items, and help protect you if you inadvertently let conditions dictate the thoroughness of your preflight. If you own your own airplane, you may find it valuable to budget an hour or so to do a complete aircraft inspection, when you are alone and under no pressure to make a flight — or not even going flying at all. In other words, go out to the airport about once a month when you do not plan to make a flight, and give the airplane a “30-day inspection.

In addition to the POH-style preflight inspection, review:


  • Inspection status. Double-check that the annual (and any other required) inspection will not come due in the next month (it’s amazing how sometimes pilots can forget such things). Or if it does come due the next month, go ahead right then and schedule the inspection.
  • Transponder check. Whether an airplane is flown VFR or IFR, if it has a transponder installed, that transponder must be operationally checked every 24 months. Make sure the date of the check doesn’t come due within the next month or, if it does, go ahead and schedule the check.
  • IFR checks. If your airplane is certified for instrument flight, its altimeter and static system must be certified every 24 months. If it’s due before your next scheduled “30-day inspection,” go ahead and get an appointment to recertify your airplane for instrument flight.
  • Airworthiness Directives. Reference your airplane’s Airworthiness Directive (AD) Log (specific to the individual airplane) and see if any ADs must be complied with within the next month (given your expected number of flying hours in the upcoming month). Remember, some ADs specify repetitive inspections as frequently as every 50 flying hours. Other, low-frequency AD work (sometimes measured in calendar years, or thousands of flying hours) may be overlooked on an annual inspection, so double-check this as well. Schedule any work that may be required soon, so you won’t have to delay a flight later.

Insider’s Tip: Owner/pilots commonly make a marker board for the hangar (or a notebook to leave in the airplane, if the airplane is tied down outside), listing the tachometer reading or date when each required check will come due. Such a record will make it very easy for you to check this airworthiness status before a flight.


  • Oil changes. Determine when the next oil change is due, and make plans to change the oil and/or filter (or schedule a shop to do it for you) if an oil change will likely come due in the next month.
  • VOR accuracy checks. If your airplane is certified for instrument flight, you must log a VOR accuracy check within 30 days prior to a flight on an instrument flight plan — even if you use GPS or some other method of navigation. Leave yourself a note on the instrument panel to make and log the check on your next flight (if you can’t check it on the ground at your home airport). Remember, you can’t launch IFR unless the most recent VOR accuracy check is logged “somewhere” in the airplane.
  • GPS database updates. Check that any GPS databases are updated as required. Order updates if they’ll come due before your next 30-day inspection.
  • Complex systems. If your airplane has retractable landing gear or other complicated systems, spend extra time looking them over carefully during your 30-day inspection.
  • Trim. Adjustable trim systems have a “safe” range for takeoff, marked on indicators in the cockpit. In some airplanes, the cockpit indicators may “slip,” indicating something other than what the actual trim setting may be. During your 30-day inspection, set the cockpit trim indicators to the “zero,” or neutral position, then look at the actual trim tabs on the control surfaces. If the indicator is “Zero’d out” in the cockpit, trim tabs should be flush with the control surfaces. Consult a mechanic experienced with your type of airplane if you find anything different, before attempting a flight.
  • Lubrication. Take this time to grease up fittings and otherwise lubricate your airplane, per the servicing instructions in the POH or in the airplane’s maintenance manuals.
  • Tire pressures and strut inflation. Check tire pressures and add (or remove) air as necessary. If your airplane has pneumatic landing gear struts, check for proper inflation; get it adjusted if needed.

There are likely a lot of other things you should check on your 30-day inspection, but you get the idea. Make your own checklist, and update it as you discover new things to check or particular to your aircraft during your “30-day Inspection.

Whether you’re flying a rental airplane or one of your own:

  • Always conduct a thorough preflight inspection.
  • When you’ve completed your inspection, reference the POH Preflight Inspection checklist to make sure you didn’t miss checking anything.
  • Bring any questionable items to a mechanic or other knowledgeable person’s attention before you fly.

If you’re fortunate enough to own your own airplane, then:

  • Recognize that yours is the only safety check the airplane gets between scheduled inspections … and that nobody’s perfect.
  • Consider making the “30-day Inspection” part of your airplane ownership plans.