Cockpit Voice Recorder — Page 501, Lesson 598

Let’s start with the big picture. The Cockpit Voice Recorder, the CVR, exists for one principal reason: to preserve vital information in the event of an air accident, so that it can be recovered and used by the Accident Investigation Branch — the AIB. That is its entire purpose. It is not a convenience device; it is an accident-investigation tool. Now, what does it actually record? The CVR automatically records the last 30 minutes of communications and conversations on the flight deck. On some aircraft, that recording window is extended to 2 hours. So you have a rolling recording — it keeps the most recent 30 minutes, or 2 hours on those other aircraft, and overwrites older material as it goes. When is it operational? The CVR is operational whenever three conditions are met: when 115 volts AC power is applied to the aircraft, when any engine is running, or when the aircraft is airborne. Note that these are alternatives — any one of those conditions makes the system live. So if the aircraft is on the ground with no engines running but 115 volts AC is applied, the recorder is running. If an engine is running, it is running. If the aircraft is airborne, it is running. The system itself comprises four main units: a tape recorder, a control unit, a monitor display, and an area microphone. The control unit is what the flight crew interacts with, the monitor display shows system status, and the area microphone captures the ambient sound of the flight deck. Their locations are shown in Figure 37.1. Now let’s talk about what the recorder is required to capture. In accordance with the OPs Regulations — the Operations Regulations — the recorder must record from before the aircraft is capable of moving under its own power, until it is no longer able to do so. That is the legal requirement window. But it should also record pre-start procedures and post engine shut-down procedures. So the practical recording window is wider than the regulatory minimum — it captures the pre-start checks and the post-shutdown actions as well. The parameters recorded are specifically listed. First, voice communications transmitted from or received on the flight deck — that is, radio traffic. Second, the aural environment of the flight deck — the ambient sounds, which can be very informative in an investigation. Third, voice communication of flight crew members using the aeroplane’s interphone system — the internal intercom between crew stations. Fourth, voice or audio signals introduced into a headset or speaker — so anything that comes through the crew’s headsets or the flight deck speakers. And fifth, voice communication of flight crew members using the PA system — the public address system, when the crew addresses the cabin or passengers. Now, the physical recorder itself. The tape recorder is located inside a crash-proof metal box that is painted red or orange. It is normally placed at the rear of the aircraft, often adjacent to the flight data recorder — the FDR. The high-impact case is designed to withstand shock, high temperature, and fire. That is the crash survivability requirement — the case must protect the recording through the very accident it is meant to document. On the front of the unit is fitted an underwater locating device — the ULD. This device emits a continuous series of ultrasonic pulses to help locate a submerged CVR. So if the aircraft goes into water, the ULD pings continuously so search teams can find the recorder. The unit is automatically activated by water — it does not need a crew member to switch it on — and the battery will last several days. That battery life is the search window: several days of continuous ultrasonic pinging to guide recovery. So, to tie it together: the CVR is a crash-survivable, rolling recorder of the last 30 minutes to 2 hours of flight deck audio, powered by 115 volts AC, an engine running, or being airborne. It captures radio, interphone, PA, headset audio, and the ambient sound of the deck. It lives in a red or orange crash-proof box at the rear of the aircraft, with an underwater locating device that activates on water contact and pings for several days. That is the complete system as defined here.