An aircraft’s cockpit voice recorder (CVR) records the audio communication and environment in the cockpit between crew members and others, including air traffic control, as well as other ambient sounds. Better known as the “black box,” it is used to investigate accidents or other incidents that involve the aircraft.
Although a CVR is not relevant for flight, it is a required piece of equipment for safety and could ground an aircraft if it fails. The FAA requires all aircraft that are equipped with a CVR to perform a functional test of the CVR before the first flight of each day. A failed CVR will not necessarily ground an aircraft, as the FAA allows for operations of an aircraft with an inoperative CVR provided that repairs are made within the time frame noted in the aircraft operator's Minimum Equipment List (MEL). This is normally three days.
Duncan Aviation repairs and overhauls two main types of CVRs: Digital and Tape.
The Fairchild / L-3 GA100, A100() is a CVR that relies on tape to record cockpit communications. The water packs inside these units are used to protect the tapes and have a shelf life of only 10 years. Once they reach their useful life, they will need to be replaced.
Water packs also have a weight tolerance. During inspection if the water packs have not expired, they get weighed. All water packs have a weight stamped on them from the day they were manufactured. If their current weight is 45 grams or more off of that weight, they have to be replaced.
When a tape CVR fails the self-test, a common cause for failure is that the heads on the internal board have become corroded and worn.
The Universal Avionics CVR-30B and CVR-120 are digital CVRs. They are solid-state units using digital technology to record audio of the pilot and copilot.
Common squawks result from the electrolytic capacitors in the power supply becoming corroded, causing intermittent failures. These capacitors begin to emit the electrolytic fluid and begin to corrode the power supply board.
Tape recording is old technology and tape CVRs are no longer manufactured. This makes parts often difficult to find and replace. However, Duncan Aviation maintains a large supply of parts for these units.
All CVRs, when they arrive at Duncan Aviation, are given an initial function test to evaluate the unit and identify the failure. Most CVR internal boards are in stock and units can typically be fixed and turned in one day.
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