This US AOPA article highlights a common practice where A&Ps write out a 337 for just about everything and it gives everybody a warm feeling. It’s usually going to be completely wrong, not least because a 337 has to be backed by an STC or Field Approval related documents.
The info on the definition of changing weight and balance is particularly interesting. You might need to do a new W&B check after an alteration without having affected weight and balance limits, and therefore not having made a major alternation by that definition.
