Cockpit Voice Recorders
By Patrick Mondout
The Cockpit Voice Recorder (CVR) records the flight crew's voices, as
well as other sounds inside the cockpit. The recorder's "cockpit area
microphone" is usually located on the overhead instrument panel
between the two pilots. Sounds of interest to an investigator could be
engine noise, stall warnings, landing gear extension and retraction, and
other clicks and pops. From these sounds, parameters such as engine rpm,
system failures, speed, and the time at which certain events occur can
often be determined. Communications with Air Traffic Control, automated
radio weather briefings, and conversation between the pilots and ground or
cabin crew are also recorded.
A CVR committee usually consisting of members from the National
Transportation Safety Board (NTSB), Federal Aviation Administration (FAA),
operator of the aircraft, manufacturer of the airplane, manufacturer of
the engines, and the pilots union, is formed to listen to the recording.
This committee creates a written transcript of the tape to be used during
the investigation. FAA air traffic control tapes with their associated
time codes are used to help determine the local standard time of one or
more events during the accident sequence. These times are applied to the
transcript using a computer process which provides a local time for every
event on the transcript. More precise timing for critical events can be
obtained using a digital spectrum analyzer. This transcript contains all
pertinent portions of the recording and can be released to the public at
the time of the NTSB's public hearing.
The CVR recordings are treated differently than the other factual
information obtained in an accident investigation. Due to the highly
sensitive nature of the verbal communications inside the cockpit, Congress
has required that the Safety Board not release any part of a CVR tape
recording. Because of this sensitivity, a high degree of security is
provided for the CVR tape and its transcript. The content and timing of
release of the written transcript are strictly regulated: under federal
law, transcripts of pertinent portions of cockpit voice recordings are
released at a Safety Board public hearing on the accident or, if no
hearing is held, when a majority of the factual reports are made public.
See also: Flight
Source: National Transportation Safety Board (NTSB).
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