a major alteration is any alteration not listed in an aircraft, engine, or propeller specifications that might appreciably affect weight, balance, structural strength, performance, power plant operation, flight characteristics, or other qualities affecting airworthiness or that is not done according to accepted practices or cannot be done by elementary operations.

Simply put, a major alternation is any change in original type design that, if not accomplished in accordance with FAA-approved data, could lead to a loss of life. When focusing on the word appreciably, it’s definition is understood to be noticeable. Therefore, if a person can notice a difference between the original design and an altered design, it becomes by definition a Major Alteration.

a major repair is a repair that, if improperly done, might appreciably affect weight, balance, structural strength, performance, power plant operation, flight characteristics, or other qualities affecting airworthiness, or that it is not done according to accepted practices or cannot be done through elementary operations.

Always remember that a repair by definition restores a product to its original type design condition. To determine whether or not you are involved with a repair or an alteration, you must decide whether the work to be done restores it or changes it?