Each aircraft manufacturer has obtained a type certificate for the aircraft it produces for sale to the general public. To obtain the type certificate, the manufacturer must supply engineering data and test results to the agency issuing the type certificate.
The airworthiness certificate carried in the aircraft indicates that the aircraft met the applicable design and construction requirements, and was considered airworthy on the date the certificate was issued. As the aircraft is beyond the manufacturer's control once it leaves the factory, additional requirements are placed on the aircraft's operator to maintain the aircraft in an airworthy condition. The same requirements apply after the aircraft leaves a repair station after a 100 hour or annual inspection.
Each manufacturer publishes a document that may be called Maintenance Manual, Manual for Continued Airworthiness, or something similar. This manual must be available in any repair station that is certified to work on a specific brand of balloon. The manuals vary considerably in size and content, ranging from just a few pages for some early brands, to binders several inches thick for one large manufacturer.
Different balloon systems vary in construction methods and acceptable repair techniques. The manuals set forth the maximum damage a balloon may sustain while remaining airworthy. These limits are listed in the maintenance manual under the heading, "Acceptable Damage."
Each pilot or trained crew member must be aware of the acceptable damage limits (or allowances) for the particular balloon model being flown. Damage as described below will normally be visible during packup after a landing in which the envelope is laid across a sharp object (barbed wire fence, square street light, sharp brush) or stepped on when spread over rocks or pavement. It may not be discovered until the next inflation attempt.
Below is a summary of the limits for several of the more common brands flown in the United States and the UK. Owners of brands not listed here should obtain the appropriate maintenance manual from the manufacturer. The following summaries are listed alphabetically by manufacturer. This information is in summary form for this article. It is believed to be correct, and is provided so you will not fly a non-airworthy or questionable balloon. If you have a specific question, please contact your local repair station, refer to the appropriate manual, or contact the manufacturer's engineering department.
Aerostar (Raven)
Aerostar has two different limits for fabric damage. The two categories are "less than 100 hours AND less than 3 years old with 250 degree tell-tale unturned," and "all other balloons." The damage dimensions are measured as the distance across the "crisp" fabric around a burn hole, the length of a straight tear, or the sum of the horizontal and vertical parts of an "L" shaped tear.
Allowable Damage Limitations
Location Low Time All Other Balloons
Above first horizontal band below equator 1 in. 3/8 in.
Below first horizontal band below equator and 2 in. 1 in.
above six feet from mouth
Withing six feet above mouth 18 in. 12 in.
Envelope Skirt Damage may not exceed ten percent of the total skirt area.
The owner/operator is allowed to make temporary repairs to damaged areas not exceeding the above limits, using adhesive patches. At the next annual inspection, larger patches must be made permanent by a repairman.
Cameron Balloons
Cameron's limits for allowable damage cover many items. This table summarizes the more common types of damage encountered in normal operation. If the system has suffered a particularly rough landing, a thorough inspection using the inspection checklist is in order.
Allowable Damage Limitations
Location Damage
Above 10 feet Less than 3/4 inch in the longest direction
Lowest 10 feet above throat No limit unless load tape is damaged
Vertical load tapes Up to two broken filaments in one load tape, with no other verticial load tape damage
Horizontal load tapes Fewer than 25% of filaments damaged
Envelope Skirt or Scoop Damage must not interfered with burner operation or pilot's visibility
Suspension cables, One strand broken - tape to prevent envelope damage stainless steel
Suspension cables, kevlar Polyester cover not brittle enough to crack, no kevlar fiber exposed
Suspension cables, basket Maximum 19 broken strands below thimble, 38 broken strands above ferrule near thimble. Plastic tubing must be undamaged or wrapped with 1/16 inch thick electrical tape one inch beyond damage in each direction
Fuel System Hoses may show small cracks or abrasion marks in rubber covering, providing the braided steel reinforcement is not exposed.
Burner Piezoelectric ignitor(s) may be inoperable, main burner lets may be mising (owner replaceable).
Head Balloons
Acceptable Damage Limitations
Location Damage
Above equator Less than 1/2 inch in the longest direction
Below equator to six feet above throat Less than one inch in the longest direction
Lowest six feet above throat Less than 12 inches in the longest direction
Vertical and horizontal load tapes above Up to 10% damaged filaments in any six inches of load tape webbing.
Horizontal load tape around throat Fewer than 20% of filaments damaged in any six inches of load tape webbing.
Suspension cables, steel No strands broken, cable not overheated - must be replaced if any strands broken, or cable overheated.
Lindstrand Balloons
Acceptable Damage Limitations
Location Damage
More than 13 feet above throat No fabric damage
Lowest 13 feet above throat Less than 12 inches in the longest direction
Load tapes No damage
Carabiners No distortion, screw gate operates smoothly
Deflation System Parachute line not frayed, pulley not worn, deflation locks undamaged
Suspension cables No strands broken, cable not kinked - must be replaced if any strands broken, or cable kinked
Basket Suspension No damage to basket wires or swaged ends,< no load frame distortion, no abnormal wickerwork distortion, no large holes in wicker
The Balloon Works (Firefly, Galaxy, Barnes)
Acceptable Damage Limitations
Location Damage
Above equator Less than 3/8 inch in the longest direction if more than 12 inches apart, and more than 12 inches from a seam, and no more than 4 in one panel
Below equator Less than one inch in the longest direction, if more than 12 inches apart, and more than 12 inches from a seam, and no more than 4 in one panel
Load cords Less than 10% cross section damage
Carriage suspension ropes Up to 25% cross section damage except for 10% within 10 inches from the tie plate under the floor
Thunder & Colt
Acceptable Damage Limitations
Location Damage
Envelope Less than one inch in the longest direction, if more than 3/4 inch from a load tape.