Cockpit Voice Recorder "Hot Mic", 14 CFR Parts 23, 25, 121, and 135
The NTSB indicates that the performance of CVR installations where the audio signal from the boom microphone of each flight crewmember is continuously recorded on a dedicated channel, often referred to as a "hot mic", to be far superior to the standard cockpit area microphone (CAM). This conclusion was reached after the NTSB investigated a number of accidents/incidents involving both U.S. and foreign registered airplanes equipped with CVR "hot mics". In fact, the "hot mic" has proven to be a most significant technological improvement in CVRs. This level of improvement far surpasses any technological improvement that could be achieved by state-of-the art recording or signal processing equipment.
In contrast, the quality of the audio signal recorded by the standard CAM can generally be described as poor because it requires considerable time and effort to produce a transcript. Frequently, the tape contains unintelligible dialogue that is important to the determination of causal factors. The high quality audio signal available from the "hot mic" should eliminate this problem for the most part, and at the same time, provide additional benefits, as follows:
(1) Positive crewmember identification,
(2) Redundant multichannel recordings,
(3) A potential for the evaluation of crewmember incapacitation by monitoring respiration rates, and
(4) Improved accuracy in determining which pilot was controlling the aircraft.
The Civil Aviation Authority (CAA) of the United Kingdom (UK) has required CVR "hot mic" since 1974. The UK Accident Investigation Branch's nearly 13 years of experience in analyzing CVR "hot mic" recording has prompted it to promote the adoption of standards by the international aviation community. As a result, both ICAO and EUROCAE have adopted CVR "hot mic" standards. In addition, the Board of Directors of the Air Line Pilots Association voted in May 1987 to adopt a resolution to promote the use of CVR "hot mics".
Although the benefits of CVR "hot mic" are numerous, the economic penalties are slight. In fact, most if not all major airplane manufacturers are now offering CVR "hot mics" as standard equipment, and wiring an existing microphone jack to a CVR is a relatively easy task. Therefore, a CVR "hot mic" requirement would not pose an economic penalty either for operators purchasing new equipment or retrofitting a CVR on an existing aircraft.
Cockpit Voice Recorders (CVR) and Flight Recorders