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Guide to Aircraft Airworthiness

Table of Contents

Importance to Members

14 CFR 91.7 prohibits any person from operating an aircraft that is not in an airworthy condition. What, exactly, is airworthiness An aircraft that is flyable is not necessarily airworthy. Many aircraft owners might be surprised to find that there are multiple violations for flying an aircraft that is not airworthy.

FAR 3:5(a) Statements about products, parts, appliances and materials provides a definition of "airworthy" as follows: (a) Definitions. The following terms will have the stated meanings when used in this section: Airworthy means the aircraft conforms to its type design and is in a condition for safe operation. With this definition in mind, it is important to understand who is responsible for determining the airworthiness of the aircraft prior to flight. This subject report will discuss this and other information relating to aircraft airworthiness.


The FAA is very clear in its intent that only airworthy aircraft should be operated. The regulation places responsibility on the pilot in command by stating, "The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur."

It is important to note that the responsibility for determining airworthiness does not stop here. 14 CFR 91.407 places additional responsibility on the operator by stating, "No person may operate an aircraft that has undergone maintenance, preventative maintenance, rebuilding, or alteration unless: (1) It has been approved for return to service by a person authorized under 43.7 of this chapter; and (2) The maintenance record entry required by 43.9 or 43.11 , as applicable, of this chapter has been made." Most owners and operators rely on maintenance facilities to perform required inspections and repairs along with ensuring all airworthiness directives, maintenance, and inspections are logged and signed off properly. Many owners and operators do not check for proper endorsements, which approve the aircraft for return to service and state that the aircraft is airworthy if a 100-hour or annual inspection was performed.

The condition of the aircraft is important but not the only factor in determining airworthiness. If you are an aircraft owner or operator, remember to review the logbooks after the aircraft is returned from maintenance. Ensure that the proper inspections, repairs, and airworthiness directives are completed and logged, and the logbooks contain a statement approving the aircraft for return to service.

Technical Information

Regulatory Requirements

FAR 91.7(a) requires that, "no person may operate a civil aircraft unless it is in an airworthy condition." Subsection (b) of the same section provides that the pilot in command [PIC] of an aircraft is responsible for determining that the aircraft is in a condition for safe flight, and that the PIC must discontinue the flight when the aircraft encounters unairworthy mechanical, electrical, or structural conditions. FAR 3:5(a) Statements about products, parts, appliances and materials provides a definition of "airworthy" as meaning the aircraft conforms to its type design and is in a condition for safe operation.

What is conformity to type certificate? The FAA's attitude has been that an aircraft must be in just about factory-new condition (if it was factory built), plus the alterations must be in the same condition as that when completed in accordance with a supplemental type certificate (if the craft was altered), plus the aircraft must be in compliance with any applicable airworthiness directives.

It is often debated whether the guidance offered to pilots in FAA publications such as the Aeronautical Information Manual (AIM) should be considered regulatory. That is, do you need to know and follow these publications just as you are required to know and comply with the federal aviation regulations?  A good means to end this debate is an FAA issued description of the scope of the AIM, and other such publications. “This publication, while not regulatory, provides information which reflects examples of operating techniques and procedures which may be requirements in other federal publications or regulations. It is made available solely to assist pilots in executing their responsibilities required by other publications.”  Such a statement expresses that although they should be taken as guidance and not requirements, a competent pilot in command would adhere the guidance recommended in the AIM.

Registration and Re-Registration Requirements

The first thing a first-time aircraft owner must do is register the aircraft in his name with the FAA. FAR 47.31 states no one can operate an aircraft until it's registered. FAR 47.31 tells how to apply for a certificate of registration, and specifies that when the FAA sends the permanent registration, the owner must keep the document in the aircraft.  As the registered owner of an aircraft, FAR 91.403 makes you responsible for maintaining the aircraft in an airworthy condition. This includes complying with all FAA airworthiness directives (ADs) issued for your aircraft, engine, and equipment. Also, aircraft owners must notify FAA of any change in permanent mailing address, the sale or export of the aircraft, or the loss of eligibility to register an aircraft (see FAR 47.41).


Effective October 1, 2010, aircraft owners are required to re-register their aircraft every three years. The plan calls for the re-registration of all U.S. civil aircraft  by December 31, 2013. The FAA re-registration fee is $5.00. The FAA will cancel the N-numbers of aircraft that are not re-registered or renewed. To ensure that their aircraft do not slip through the cracks, owners should check the FAA website now and make sure the FAA has accurate information regarding their aircraft.

How re-registration works

Here is how the re-registration process works. All aircraft owners will receive a notification from the FAA, which includes an online re-registration code (to be used for electronic filing), 180 days before the expiration of their current registration. The notice will give a three-month time frame (see chart below) in which the aircraft owner is able to log onto the FAA website and renew the registration using the re-registration code included in the notice. Note: The online option is available only if no changes need to be made. Owners have to re-register during the specified three-month window in order to use the electronic option. If an online application has not been processed at FAA by the deadline, an 8050-1 (paper registration application) will need to be completed and mailed to FAA.

If an owner does not want to utilize the electronic option or if changes need to be made, he can instead use a new re-registration form (8050-1a) and mail it to the FAA Registry in Oklahoma City. The 8050-1a must be on file at the FAA before the current registration expires, so, be sure to mail it early enough in the cycle (allow 6 - 8 weeks for processing) to ensure it is received and filed at FAA before the registration expiration date. An N-number search has been added to the FAA home page, where owners can verify their applications have been received by the FAA.

Aircraft operators need to wait to fly their aircraft until they have received their new certificate from the FAA (the pink slip will not qualify as a temporary registration, as it does with a new purchase.)

After you've re-registered

Once owners have transitioned to the new registration, the new certificates will expire three years from the month in which re-registration was accomplished. For example, if an owner whose registration expired March 31, 2011, renewed in November, 2010, the three-year registration will display an expiration date of November 30, 2013.

Read more in AOPA's Regulatory Brief.

Federal, State and Local Regulations

In addition to the FAR requirements, aircraft owners must comply with state, county, and local regulations for sales, use, and property taxes, including payment of federal excise tax in the event the aircraft is used for commercial operations. The FAA requires a lot from owners, but it offers help in FAA Handbook 8083-19A.

Inspection Requirements

Under FAR 91.409(a), an aircraft must undergo an annual inspection every 12 calendar months to be legal to operate. If an aircraft is used to carry passengers for hire or is operated for hire (as in flight instruction), it also must have either an annual or 100-hour inspection within the preceding 100 hours of time in service. It's important to remember that while an annual can serve as a 100-hour inspection, a 100-hour inspection will not substitute for an annual. Remember that for an annual, the period of 12 calendar months extends from any day of any month to the last day of the same month in the following year.

Other inspections are required for the instruments and equipment installed in the aircraft. However, some of these inspections are only required if the aircraft is operated under instrument flight rules. For example, another inspection you should be aware of is the altimeter system and altitude reporting system test and inspection. This inspection, described in FAR 91.411(a), is required if the aircraft is operated in controlled airspace under IFR. It mandates that within the preceding 24 calendar months, each static pressure system, each altimeter instrument, and each automatic pressure altitude reporting system must have been tested and inspected and found to comply with appendix E of Part 43.  Automatic pressure altitude reporting system is just a fancy name for the mode c transponders altitude encoder.

An example of an equipment inspection you should be aware of is the emergency locator transmitter (ELT) entry required by FAR 91.207. This regulation says that the ELT must have been inspected within 12 calendar months after the last inspection. The ELT is checked for proper installation, signs of any battery corrosion, the operation of the controls and crash sensor, and the presence of a sufficient signal radiated from its antenna.

Finally, in order to operate under IFR using the VOR system of radio navigation, the VOR equipment of that aircraft has to have been operationally checked within the past 30 days in accordance with FAR 91.171.

In conclusion in order to be legal and safe to fly, an aircraft must have a current annual, a 100-hour inspection if used to carry passengers for hire or operated for hire, and all applicable ADs must have been complied with. Depending on how the aircraft is operated, it should also have static system and altimeter, transponder, ELT, and VOR equipment checks.

Flight School Requirements

A recent decision by the FAA administrator reminds us that a flight school has an independent responsibility to track when maintenance is due, and in particular, when compliance with airworthiness directives (ADs) is due--and to make sure the maintenance is completed and the ADs are complied with on time, before operating the aircraft in flight training activities. The flight school may not simply rely on its repair station to ensure that applicable ADs are complied with before using the airplane for flight training. The federal aviation regulations place the primary duty on the flight school--as the operator of the aircraft--to ensure AD compliance or risk a violation, including an FAA charge that the aircraft were operated in a careless or reckless manner.

Aircraft Aging

There are many factors affecting an aging aircraft and subsequently the airworthiness of an aircraft, these factors can be categorized as genetic, and non-genetic. Genetic factors are those that cannot be easily controlled, and conversely non-genetic factors can be controlled. To some degree, exposure to acids, salts, and other contaminants from airborne pollution is genetic. These factors hasten the onset of corrosion. Other genetic factors for each airplane include the normal fatigue cycles that are part of every taxiing, takeoff, cruising, and landing operation.

Non-genetic aging factors include poor maintenance and high loads and stresses connected with the spectrum of maneuvers encompassed in the operation of the airplane.

The Air Safety Institute has an informative online course on Aging Aircraft.

Also, a booklet titled The Best Practices Guide for Maintaining Aging GA Aircraft, endorsed by AOPA, is helpful to owners of GA aircraft built before 1974. Download the 26-page guide as a pdf.

Aircraft Modifications

The rule governing replacement parts for installation on a type-certificated airplane is FAR 21.303. This rule says that all parts for installation on certified products such as an airplane or engine must be produced by a company that holds a parts manufacturer approval (PMA). There are four additions to this rule.

Parts built by a type certificate holder such as Cessna, Piper, Mooney, Cirrus, Lancair, Teledyne Continental, Textron Lycoming, Hartzell, or McCauley do not have to be PMA parts because these companies hold type certificates and/or production certificates. These certificates permit the production of parts for their airframes, engines, and propellers, as appropriate.

The next application is parts built to a technical standard order, or TSO. TSOs are minimum standards for the design and production of common parts and accessories. Altimeters, compasses, instruments, tires, seat belt assemblies, autopilots, aircraft-covering fabric, wheels, and many avionics are examples of TSO-approved items.

When a product alters an airplane enough for the change to be considered a major change in the type design, but not enough to require a new type certificate, the change is accomplished under the provisions of a supplemental type certificate, or STC. Most popular modifications fall under the STC category. Vortex generators, engine and propeller upgrades, STOL (short takeoff and landing) kits, strobe lighting kits, engine analyzers, and wheel and brake upgrades are examples of typical modifications that are approved by the STC process.

The final addition to the rule is “Owner Produced Parts” According to a rules interpretation; the owner must control or participate in at least one of the following functions for the part to be considered owner-made. He must a) provide the manufacturer with the design or performance data to make the part; b) provide the manufacturer with the materials to make the part; c) provide the manufacturer with fabrication processes or assembly methods to make the part; d) provide the quality-control procedures to make the part; or e) personally supervise the manufacture of the part. The owner can hire someone, even his mechanic, to manufacture the part if he fulfills the conditions mentioned in the previous paragraph.

Concern Process

The Airworthiness Concern Process (ACP) is a cooperative information-sharing initiative between industry and the FAA intended to increase industry participation in the development of airworthiness issues before (or in lieu of) a proposed or final airworthiness directive (AD) for an aircraft. The ACP has been successfully employed for airframe-related concerns for years. As a result of AOPA's efforts, the ACP was expanded to include engine- and propeller-related airworthiness issues. An important element of this official FAA process is AOPA's Advocacy efforts, which serves as a "central hub" for distribution of airworthiness concern sheets to aircraft type clubs, and submittal of type club comments to the FAA.

Airworthiness Directives (ADs)

One way the FAA keeps owners, mechanics, and pilots current on required maintenance issues is with the Airworthiness Directive, or AD. It's important and has its own part in the FARs, which usually isn't included in commercial compilations of the regulations. Briefly, Part 39 says that we can't operate an aircraft to which an AD applies unless we comply with the requirements of that AD.

ADs differ significantly. Some require a one-time inspection or modification. Others require a periodic inspection or part replacement. An AD might apply to all aircraft of a certain make or model, or only certain aircraft within a range of serial numbers. It may apply to all aircraft that have a certain component, such as a particular engine, propeller, or accessory. The point is, just because an aircraft has a valid annual inspection doesn't mean it's airworthy today. For example, if the deadline for a recurring AD passes without compliance six months after the airplane's annual inspection, the airplane isn't airworthy.

Checking an airplane's compliance with its ADs isn't something a pilot normally does, especially if renting airplanes. But it's not a bad idea to confer with the owner or a mechanic about ADs that apply to the aircraft you fly periodically. Often, an AD compliance table is part of the aircraft maintenance records, and you can get an idea about when recurring ADs are due by studying the table. Many flight schools keep a table that lists the required inspections, maintenance, and ADs, when they were completed - and when they are due - in their aircraft

You can search the FAA lists of all ADs issued from 1943 to present.

Minimum Equipment List (MEL)

A minimum equipment list is a user-friendly, black-and-white way to determine whether problems affect the safety and legality of a flight. As the name implies, an MEL lists the minimum equipment and instruments that must properly operate before an airplane can legally fly. MELs are aircraft-specific right down to a registered aircraft and its owner. In other words, an MEL for Cessna Skyhawk 12345 cannot be used on Skyhawk 67890.

An MEL identifies the aircraft's equipment and instruments individually, and specifies each item that may be inoperative for various combinations of day and night VFR and IFR operations. If an item isn't required by the MEL for the intended operation, the airplane may be legally flown if the item is either removed, or deactivated and placarded.

Talking with an inspector at the local FAA Flight Standards District Office (FSDO) is the first step in getting an approved MEL for an aircraft. You don't create an MEL from scratch. The FAA has make-and-model-specific Master MELs (MMELs) for many multiengine aircraft and a generic single-engine MMEL. You customize the applicable MMEL to the specific equipment requirements for your airplane.

Items on the MMEL that are not installed in your aircraft are deleted. Equipment in your aircraft but not on the MMEL are added to the list. When this task is completed, you submit the MEL with a request to the FSDO. The request is usually evaluated by FAA representatives specializing in operations, airworthiness, and avionics. Once the MEL is agreed upon, you and the FAA sign a letter of authorization, which enables you to use the MEL.

Additional Resources

Airworthiness Concern Process Guide
Small Airplane Directorate: Airworthiness Directives Manual Supplement

Airworthiness Directives

Aviation Maintenance Alerts

AOPA Regulatory Brief: Airworthiness Concern Process
The issue: The Airworthiness Concern Process (ACP), is a cooperative
information sharing initiative between Industry and FAA.

FAA's Supplemental Type Certificate Database