What was the status of these aircraft when Inspector Destruction came on the scene? Were they in daily active service, RON, spare, etc?

The reason I ask is aircraft are not required to be secure at all times. If he was climbing on the TAT probe, then the cabin door was closed (I'd assume). If these aircraft were in active service and door closed, then this should not be an issue. If they were OTS or RON, then this is not an issue. An aircraft does not have to be observed 24 hours a day. That is one of the many reasons that we do security checks on first flight and after an aircraft has been left unattended.