ANNUAL vs. 100 hr.
ANOTHER MISCONCEPTION
Second Edition Vol. 1
The subject of this month’s article is to try to clarify the debate over the age old confusion between the Annual Inspection and the 100 hour inspection. I know what some of you old timers are saying. But, Chuck. They’re the same thing. No, they’re not. And I’ll explain why. First, we must go back to a time when our aircraft flew for much more than the customary twenty to thirty hours a year they’re flown nowadays. Back then, 100 hours came twice maybe three times a year and the 100 hour inspection was due at each of those intervals. The aircraft still needed to be re-licensed so to speak each year to be airworthy. We don’t necessarily “re-license” aircraft anymore, it’s now called “return to service”, and is returned to service after the 100 hour or Annual Inspection, whichever is appropriate at that time. When I worked at an FBO, we maintained the aircraft for the three flight schools that were on the field. We were always busy performing 100 hour and Annual Inspections on these aircraft. So, what’s the difference? Well, hold on, I’m getting there. Obviously each inspection is exactly what it says it is. For example, a Cessna 150 that is for hire via a Part 135 Operator, must have the 100 hour inspections performed, you guessed it, every 100 hours. This time limit can be extended for up to 10 hours, but then that time must be subtracted from the next 100 hours of flight time before the next 100 hour inspection. This means that if the aircraft flew 106 hours since the last 100 hour inspection, then the next 100 hour inspection is due at 94 hours. This same aircraft must have an Annual Inspection performed as well within the preceding twelve calendar months since the last Annual Inspection. Follow me so far? Now, here’s’ the rub. In scope and detail they’re supposed to be the same inspection, but the general consensus is that typically at an Annual, you would check for any new or recurring A.D. Notes. O.K., but what about A.D 87-20-03R2, now 11-10-09. It states the following.
I. For airplanes operating for hire:
- (A) For airplanes having less than 1,000 hours time-in-service (TIS) on the effective date of this AD, accomplish the AD requirements prior to the accumulation of 1,100 hours TIS;
- (B) For airplanes having 1,000 or more hours TIS on the effective date of this AD, accomplish the AD requirements within the next 100 hours TIS;
- (C) Following the actions of (A) or (B) above, repeat the inspection requirements of this AD at each 100 hours TIS. These inspections can be accomplished at the next scheduled inspection or the next 100 hours, whichever is later.
So, if you only checked for A.D.’s at the “Annual” then when would have to comply with this A.D.? The answer is simple. At the 100 hour inspection interval. I don’t know how many times I have seen this A.D., as well as others, not complied with at the 100 hour inspection on a Part 135 aircraft. They only seem to be complying with this A.D. at the “Annual Inspection”. Now let’s re-cap. If your Cessna 150 is on lease back, or your Flight School owns this aircraft, then it needs to have the 100 hour Inspection performed each and every 100 hours flown, and when the Annual Inspection is due, you have to comply with that inspection requirement also. FAR §91.409 states;
§91.409 Inspections.
(a) Except as provided in paragraph (c) of this section, no person may operate an aircraft unless, within the preceding 12 calendar months, it has had —
(1) An annual inspection in accordance with part 43 of this chapter and has been approved for return to service by a person authorized by §43.7 of this chapter; or
(2) An inspection for the issuance of an airworthiness certificate in accordance with part 21 of this chapter.
No inspection performed under paragraph (b) of this section may be substituted for any inspection required by this paragraph unless it is performed by a person authorized to perform annual inspections and is entered as an “annual” inspection in the required maintenance records.
(b) Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person (other than a crewmember) for hire, and no person may give flight instruction for hire in an aircraft which that person provides, unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection and been approved for return to service in accordance with part 43 of this chapter or has received an inspection for the issuance of an airworthiness certificate in accordance with part 21 of this chapter. The 100-hour limitation may be exceeded by not more than 10 hours while en route to reach a place where the inspection can be done. The excess time used to reach a place where the inspection can be done must be included in computing the next 100 hours of time in service.
(c) Paragraphs (a) and (b) of this section do not apply to —
(1) An aircraft that carries a special flight permit, a current experimental certificate, or a light-sport or provisional airworthiness certificate;
(2) An aircraft inspected in accordance with an approved aircraft inspection program under part 125 or 135 of this chapter and so identified by the registration number in the operations specifications of the certificate holder having the approved inspection program;
(3) An aircraft subject to the requirements of paragraph (d) or (e) of this section; or
(4) Turbine-powered rotorcraft when the operator elects to inspect that rotorcraft in accordance with paragraph (e) of this section.
So, let’s use this same Cessna 150. The common misconception and big question on everybody’s mind is doesn’t the 100 hour Inspection replace the Annual Inspection? The answer is NO! I can’t remember how many times I have seen logbooks for an aircraft that the IA returned the “airframe” to service after performing an Annual Inspection, but only performed a 100 hour Inspection on the “engine”. How can this be you ask? Good question when FAR §91.409 (a) (1) states;
(a) Except as provided in paragraph (c) of this section, no person may operate an aircraft unless, within the preceding 12 calendar months, it has had —
(1) An annual inspection in accordance with part 43 of this chapter and has been approved for return to service by a person authorized by §43.7 of this chapter; or
The “airframe” and the “engine” constitute an “aircraft”. You can’t perform an Annual Inspection on one and not the other. A 100 hour Inspection is not a substitute for an Annual Inspection. Nor are the two terms interchangeable. Although they’re basically the same inspection in scope and detail, they’re fulfilling two different regulatory requirements.
What about the propeller(s) you ask? Are they “annualed”? You betcha! So are the magnetos, the carburetor, and every other component attached to the engine and airframe. These items are most likely included in the manufacturers Maintenance Manual and give either the inspection criteria for it, or refer you to the specific component(s) Maintenance Manual for inspection criteria. The propeller manufacturer has, most of the time, an inspection checklist specifically for each model of propeller each manufacturer builds. These documents are far more easily obtained today than fifteen or so years ago so there is no excuse not to keep up on the current inspection documents. What about other components you ask? What about them? All component’s inspections are covered somewhere, in some publication. You have to look for them.
In the case of the magneto’s, (and I discussed this briefly last month), the manufacturer of each brand of these “spark generators” lists the procedure and criteria as well as the T.I.S. interval the inspection is due. These inspections are not optional as the common misconception alludes to. It has to be complied with. Period. The 500 hour inspection is due at 500 hours T.I.S., and every 500 hours thereafter. These inspections are mandatory whether you’re flying under FAR Part 135 or FAR Part 91. Why you ask? Because it’s part of the Instructions for Continued Airworthiness as stated in the relative Maintenance Manual for the component in question. Besides, it’s the engine’s freakin’ ignition system for Pete’s sake. Why would one elect to neglect such an import aspect of the engine(s) performing well, or even performing at all?
What about checking and adjusting the unmetered fuel pressures on your fuel injected Continental engine? Very rarely have I seen this task ever mentioned in the logbook for the either the engine or the airframe. Why? I don’t know. It’s part of the engine inspection and is listed in the Engine Inspection checklist. There’s even a TCM Service Bulletin out that explains how and when to accomplish this task and it even gives you the values for every fuel injected Continental engine made. Again, it’s the engines freakin’ fuel delivery system for Pete’s sake. Why ignore it?
What about the brake disc thickness? The Cleveland Wheel & Brake Division of Parker-Hannifin Corporation publishes a Maintenance Manual for all of their products, including most McCauley products. Appendix “A” (A1 &A2), list the minimum thickness for every part number pad and disc made. Even a tolerance for the old drum style brakes typically found on the Piper Tri-Pacer is given. I have seen many brake discs that were so beyond limits that the disc had begun to curve because of the constant replacement of the brake friction pads, that the disc is now so thin, the heat has essentially warped the disc surface. Once again, it’s the freakin’ brakes. Isn’t their performance important?
O.K., I kind of gotten off topic a little, but you see my point. Some of these tasks are to be accomplished each 100 hours, while others are to be accomplished at each Annual Inspection, or some other interval. The inspection needed is dictated by the interval, which is dictated by the T.I.S. or Calendar time since the last inspection of whatever type, or whatever the Maintenance Manual dictates. The aircraft Maintenance Manual will always give some sort of instruction on when something is to be inspected, re-built/overhauled or replaced.
I mentioned “Scope & Detail” earlier and by that I mean the intensity of the respective inspection. Our eyes and our ears are the most important inspection tools we have as Aircraft Maintenance Technicians. Being able to identify problems accurately comes with experience and can’t be taught in a classroom environment. It is something that comes from experience and the drive is born from within oneself. You have to have a knack for finding problems. You could spend an eternity going over every square inch of every part on an aircraft looking for any discrepancy and still not find everything. Plus, where do you draw the line? Do you start removing cylinders to see if the correct part number pistons were installed at the last engine overhaul? Hell no. Unfortunately, you’re “assuming” that the chucklehead(s) before you, did their job correctly, and you won’t have to look at every single replaced part, installed STC, Major Repair or Alteration, or every other task that someone else performed before you got the aircraft, was performed correctly. Some things are easy to spot, other’s not so much. Would you check a component that was replaced years ago, that gave no signs of being incorrect, and functioned properly? In a perfect world, YES! But, we are sometimes not offered the luxury to spend as much time on an aircraft that we would like. Well, me anyway. Checking every light bulb, every antennae connector, every oleo strut valve core for the correct part, is just out of the question. If one were to do this, the inspection would cost more in time than the aircraft is worth. Plus, this inspection time and intensity would increase every year as maintenance was performed and parts replaced. There is a certain level of trust in assuming that the A&P/IA(s) before you, did their job correctly so you won’t have to dismantle the whole aircraft down to the last nut and bolt assembly to be certain that it’s all correct and airworthy regardless of the type of inspection you’re performing.
Now if you’re just a greasy “mechanic” then you might be able to get away with “pencil whipping” it for a while, but it will eventually catch up to you and subsequently, the owner. If you’re one of these types, should aspire to be better at your job and look closer at the aircraft you’re inspecting. Look closer at the installed components. Take a closer look at the required manuals while you’re at it. Take the time to look everything over thoroughly and most of all, make sure you perform the correct inspection and endorse it as so.