Here is a scary story about an upright bass player's ax that got damaged by TSA, who apparently did not follow their own rules.

Here is the text of the regulation, quoted from the article above:

The TSA?s own guidelines state: "Owners should be present when an instrument is removed from its case for screening? We encourage you to stay with your instrument while security officers screen it to make sure it is repacked properly." However, Patitucci has confirmed he was not allowed to stay present while they inspected his bass. The TSA also claim that "Security officers will handle musical instruments very carefully and will allow you to be as involved as possible in any physical screening." Clearly the agents that handled this instrument failed in their duty to protect the often precious property that is placed in their care for inspection.