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2.2.1 The equipment shall provide appropriate local and remote alarm / status indications including an output to indicate the overall operational status of the equipment (1047).
2.2.2 The remote alarm / status indications shall not be affected by any loss and/or subsequent restoration of electrical power to the equipment (1048).
NOTE: Urgent and non-urgent alarms may be used to distinguish between problems which require immediate attention, such as failure of the recording equipment, and those which do not, such as an impending recording archival media change.
2.3 Time and Date Information
2.3.1 The equipment shall automatically record time (hours/minutes/seconds) and date (day/month/year) information (1049).
2.3.2 Co-ordinated Universal Time (UTC) in hours, minutes and seconds of the 24-hour day beginning at midnight shall be used (1050).
2.3.3 The time shall have an accuracy such that it can be maintained within plus or minus 2 seconds (UTC) (1051), except when data link communications are utilised, when the accuracy shall be plus and minus 1 second (UTC) (1052), within a reasonable period of time and at least for the duration of recording time on a single archival storage media.
2.3.4 The time shall have a resolution of 1 second (1053).
2.3.5 Where an external source is used to derive time and date information, the equipment shall incorporate an internal source to be used in the event of failure of the external source or temporary loss of signal from radio time code receivers (1054).
NOTE: The time and date information may be derived from an internal source or via an external interface with the ATC Unit Master Clock where this exists, another common reference source, or a radio time code receiver utilising terrestrial (e.g. MSF &, DCF77) or Global Positioning System signals.
2.4 Line Interface
2.4.1 Line interfaces shall be provided which are compatible with telephone connections made via the Public Switched Telephone Network or private lines (1055).
2.4.2 Line interfaces shall be provided which are compatible with radio connections made via the Public Switched Telephone Network or private lines to transmitter, receiver and associated control equipment at 2 Wire or 4 Wire level (1056).
NOTE: Optional modules to provide telephone connection Off-Hook and Ring Detect signals for the contact activation circuits may be incorporated into the line interfaces.
2.5 Recording Initiation
2.5.1 Voice Activation
2.5.1.1 Voice Activation or Voice Operated Switch (VOX) may be used to initiate recording of telephone signals or other ground-ground communications.
2.5.1.2 The sensitivity of the voice activation circuit shall be adjustable (1057).
2.5.1.3 An adjustable time delay shall be provided after the voice activation circuit releases before recording stops (1058).
2.5.1.4 An adjustable minimum time period shall be provided for the voice activation to prevent spurious responses to noise pulses (1059).
NOTE: Due to the inherent delay with the voice activation circuit responding to initial syllables of speech and delays due to the mechanical inertia in the magnetic tape transport system of analogue equipment, it is possible that initial syllables of speech may not be recorded. A circuit to buffer the signals to be recorded may be used to reduce this effect.
The setting of the voice activation sensitivity is more critical for varying input levels, such as radio signals, which may result in communications not being recorded.
Voice activation is not generally acceptable for radio signals due to these possible effects.
2.5.2 Contact Activation
2.5.2.1 Contact activation derived from on / off hook, ring detect or other signalling conditions, may be used to initiate recording of telephone signals or other ground-ground communications.
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CAP 670 Air Traffic Services Safety Requirements 2(3)
