recordings are scanned for "events", an event being a significant deviation from normal operational parameters. This allows operational problems to be detected and eliminated before an accident or incident results. A flight-data acquisition unit (FDAU) is a unit that receives various discrete, analog and digital parameters from a number of sensors and avionic systems and then routes them to the FDR and, if installed, to the QAR. Information from the FDAU to the FDR is sent via specific data frames, which depend on the aircraft manufacturer. Many modern aircraft systems are digital or digitally controlled. Very often, the digital system will include built-in test equipment which records information about the operation of the system. This information may also be accessed to assist with the investigation of an accident or incident. Specifications The design of today's FDR is governed by the internationally recognized standards and recommended practices relating to flight recorders which are contained in ICAO Annex 6 which makes reference to industry crashworthiness and fire protection specifications such as those to be found in the European Organisation for Civil Aviation Equipment documents EUROCAE ED55, ED56 Fiken A and ED112 (Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems). In the United States, the Federal Aviation Administration (FAA) regulates all aspects of US aviation, and cites design requirements in their Technical Standard Order, based on the EUROCAE documents (as do the aviation authorities of many other countries). Currently, EUROCAE specifies that a recorder must be able to withstand an acceleration of 3400 g (33 km/s2) for 6.5 milliseconds. This is roughly equivalent to an impact velocity of and a deceleration or crushing distance of . Additionally, there are requirements for penetration resistance, static crush, high and low temperature fires, deep sea pressure, sea water immersion, and fluid immersion. EUROCAE ED-112 (Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems) defines the minimum specification to be met for all aircraft requiring flight recorders for recording of flight data, cockpit audio, images and CNS / ATM digital messages and used for investigations of accidents or incidents. When issued in March 2003 ED-112 superseded previous ED-55 and ED-56A that were separate specifications for FDR and CVR. FAA TSOs for FDR and CVR reference ED-112 for characteristics common to both types. In order to facilitate recovery of the recorder from an aircraft accident site they are required to be coloured bright yellow or