• Repairing upholstery and decorative furnishings of  the balloon basket interior when the repairing does  not require disassembly of any primary structure or  operating system or interfere with an operating system  or affect primary structure of the aircraft. • Replacing seats or seat parts with replacement parts  approved for the aircraft, not involving disassembly  of any primary structure or operating system. • Replacing prefabricated fuel lines. • Replacing and servicing batteries. • Cleaning of balloon burner pilots and main nozzles in  accordance with balloon manufacturers’ instructions. • Replacement or adjustment of nonstructural standard  fasteners incidental to operations. • The interchange of balloon baskets and burners on  envelopes when the basket or burner is designated  as interchangeable in the balloon Type Certificate  Data Sheet (TCDS), and the baskets and burners  are specifically designed for quick removal and  installation. 1.  Those of an emergency nature requiring immediate  compliance prior to further flight. 2. Those of a less urgent nature requiring compliance  within a specified period of time. the conditions under which the product may continue to be  operated. ADs may be divided into two categories: ADs are regulatory and shall be complied with unless a  specific exemption is granted. It is the aircraft owner or  operator’s responsibility to ensure compliance with all  pertinent ADs. 14 CFR part 91, section 91.417 requires  a record to be maintained that shows the current status of  applicable ADs, including the method of compliance; the AD  number and revision date, if recurring; the time and date when  due again; the signature; kind of certificate; and certificate  number of the repair station or mechanic who performed  the work. For ready reference, many aircraft owners have a  chronological listing of the pertinent ADs in the back of their  aircraft maintenance records.  Many companies manufacture balloons that are type- certificated by the FAA. A type-certificated balloon has passed  many tests, has been approved by the FAA, and conforms to  the manufacturer’s TCDS. Balloon size is rated by envelope  volume with categories defined in metric units.  Figure 2-16 illustrates the most popular size ranges in use today (volumes  are provided in cubic meters, as well as cubic feet). Repairs and alterations are classified as either major or minor.  14 CFR part 43, appendix A, describes the alterations and  repairs considered major. Major repairs or alterations shall  be approved for return to service on FAA Form 337, Major  Repair and Alteration, by an appropriately rated certificated  repair station, an FAA certificated A&P mechanic holding  an Inspection Authorization, or a representative of the  Administrator. Minor repairs and minor alterations may  be approved for return to service with a proper entry in the  maintenance records by an appropriately certificated repair  station or FAA certificated A&P mechanic. For modifications of experimental aircraft, refer to the  operating limitations issued to that aircraft. Modifications  in accordance with FAA Order 8130.2, Airworthiness  Certification of Aircraft and Related Products, may require  the notification of the issuing authority. Different balloon sizes offer different advantages. The size  of the balloon purchased should be determined according to  planned use(s). Most pilots think smaller balloons are easier to  handle, fly, and pack up. Bigger balloons use less fuel, operate  cooler, and last longer. Higher elevations or hotter climates or  passengers indicate a larger balloon. Balloon competitions and  sport flying require a smaller balloon.  [Figure 2-17] A primary safety function of the FAA is to require correction  of unsafe conditions found in an aircraft, aircraft engine,  propeller, or appliance when such conditions exist and are  likely to exist or develop in other products of the same design.  The unsafe condition may exist because of a design defect,  maintenance, or other causes. 14 CFR part 39, Airworthiness  Directives (ADs), define the authority and responsibility  of the Administrator for requiring the necessary corrective  action. ADs are the means used to notify aircraft owners and  other interested persons of unsafe conditions and to specify  2-14 Advantages of Balloon Sizes Airworthiness Directives (ADs) Repairs and Alterations Choosing a Balloon  Figure 2-16.  Popular balloon size ranges. AX5  900–1,200  1  31,779–42,372 AX6  1,200–1,600  1–2  42,372–56,372 AX7  1,600–2,200  2–4  56,496–77,682 AX8  2,200–3,000  4–7  77,682–105,930 AX9  3,000–4,000  6–10  105,930–141,240 FAI Category Cubic Feet Cubic Meters Number of People