What happened
No accident details were available in the provided source material. The document consists of an AAIB bulletin header, contact information, and a comprehensive glossary of aviation abbreviations, but it lacks a substantive narrative regarding a specific flight occurrence, aircraft registration, or event sequence.
The investigation
The provided text does not contain any information regarding an investigation into a specific incident or accident. It serves as a template or a collection of technical definitions used within the Air Accidents Investigation Branch documentation.