The Cockpit Voice Recorder captures all flight-deck voice traffic - crew conversations, interphone calls, and radio messages - and keeps the final two hours available for investigation. A January-2022 regulation requires that newly-built transports above 27,000 kg must carry a 25-hour CVR. After landing, the tape can be wiped in seconds if the aeroplane is on the ground, the parking brake is set, the GND CTL switch is ON and the ERASE button is held for two seconds.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What are the Cockpit Voice Recorder requirements?
The requirements for a Cockpit Voice Recorder include that it must retain at least the last 2 hours of recorded information using a recorder that meets the standards of TSO-C123a or later revision.
All multi-engine, turbine-powered airplanes and rotorcraft that seat six or more passengers and require two pilots must be equipped with an approved Cockpit Voice Recorder that operates continuously from the pre-flight checklist to the final checklist at the end of the flight. Recorders installed in aircraft manufactured on or after April 7, 2010 must retain at least the last two hours of information using equipment that meets TSO-C123a and receive electrical power from the bus that provides maximum reliability without jeopardizing required or emergency loads. Each unit must have an independent power source that provides 10 minutes of back-up power, an aural or visual pre-flight check, and be housed in a separate bright-orange or bright-yellow container with reflective tape and an approved underwater locating device secured so it is not likely to be separated during crash impact. The container must be located as far aft as practicable, but not where aft-mounted engines will crush it, and the microphone must be positioned to maximize intelligibility. Aircraft with a maximum certificated take-off mass exceeding 27,000 kg (59,524.8 lbs) manufactured after January 1, 2021 must carry a 25-hour CVR, and all new U.S.-registered aircraft manufactured after May 16, 2025 must be similarly equipped, with existing aircraft retrofitted by 2030.
What must a Cockpit Voice Recorder record?
A Cockpit Voice Recorder must capture four separate channels of audio information. The first channel is from each microphone, headset, or speaker used at the first pilot station, the second channel is from each microphone, headset, or speaker used at the second pilot station, the third channel is from the cockpit mounted area microphone, and the fourth channel is from each microphone, headset, or speaker used at the station for the third and fourth crewmembers, or from any microphone on the flight deck used with the passenger loudspeaker system if its signals are not picked up by another channel.
The recorded audio must include all voice communications transmitted from or received in the airplane by radio, voice communications of flightcrew members on the flight deck using the airplane's interphone system, voice or audio signals identifying navigation or approach aids introduced into a headset or speaker, and all datalink communications using an approved data message set if datalink communication equipment is installed. All sounds received by the listed microphones must be recorded without interruption irrespective of the position of the interphone transmitter key switch. No person operates a large turbine engine powered airplane manufactured after October 11, 1991, unless it is equipped to record the uninterrupted audio signal received by a boom or mask microphone.
What is a Cockpit Voice Recorder panel?
A Cockpit Voice Recorder panel is the flight-deck interface that groups the controls for the cockpit voice recorder (CVR) and the digital flight data recorder (DFDR). It carries a VOICE RECORDER switch, a TEST switch, a STATUS light and a HEADPHONE jack, giving the crew direct access to the recorder's basic functions. The panel hosts the GND CTL ON switch: when this switch is set to ON, the CVR and DFDR erase circuits are armed and the DFDR is energized on the ground.
The CVR circuit-breaker is the dedicated protective device in the panel. Pulling it removes electrical power from the CVR, satisfying the erase requirement before maintenance and assuring the recorder cannot operate when the aircraft is unattended.
Can pilots turn off the Cockpit Voice Recorder?
The Cockpit Voice Recorder is not provided with a pilot-accessible OFF switch. As a rule, the pilot cannot turn off the black box. Regulation 14 CFR 91.609 permits the operator to conduct an airworthiness flight test during which the CVR is turned off, and the holder of an air carrier operating certificate ferries an aircraft with an inoperative CVR from a place where repair cannot be made to a place where it can be made. If the unit becomes inoperative after take-off, the operator continues the flight as originally planned. On the ground, an operator other than an air carrier operates the aircraft for not more than 15 days while the Cockpit Voice Recorder is inoperative provided the maintenance records contain an entry that indicates the date of failure and a placard is located in view of the pilot to show that the CVR is inoperative.
What is the purpose of the erase button on the Cockpit Voice Recorder?
The ERASE button on a CVR (Cockpit Voice Recorder) is provided so that the flight crew can erase the recording after a safe landing and no incident has occurred. The switch only works when the aircraft is on the ground, the parking brake is on, and the GND CTRL button is on; these interlocks prevent inadvertent erasure in flight.
To activate the erase sequence the crew pushes the recessed button for two seconds and erasing is then indicated by an audio tone. The CVR erase function does not delete the recording but, as in the original patent, the hardware scrambles the audio file's address, preventing quick access in the same way a quick-format of a hard disk leaves latent data blocks.
Accordingly, recordings can still be recovered by non-normal copying or replay techniques. Bulk erasure inside the unit does not permanently obliterate the information. The erase button therefore offers privacy protection by assuring that personal and operationally irrelevant conversations are expunged before they are mis-used, yet it is not a guarantee that the file is irretrievably lost.
What rules apply to erase Cockpit Voice Recorder recordings?
The rules for a CVR erase include that information recorded 30 minutes earlier can be erased and erasing can be done anytime during operation. Some other regulations state that recordings can be erased after 15 minutes. Regardless of when the erase command is given, the device must still retain the most recent 30 minutes (or 15 minutes, depending on seating capacity) of recorded information, satisfying 121.359 and 135.151.
Practical use of the erase feature is allowed only under specific conditions: the aircraft must be on the ground and the parking brake must be set. These restrictions keep the crew from deleting data while the aircraft is in motion or still subject to investigative interest. If a bulk-erase function is employed, EUROCAE Document ED-112 (referenced by ICAO Annex 6) ensures that the recording is modified to prevent retrieval by any normal replay or copying technique. This permanent-deletion standard was prompted by the 1979 TWA Flight 841 incident and ensures that once data is erased it is truly unrecoverable.
Whenever an accident or incident occurs, the operator must keep the recorded information for at least 60 days, and the NTSB will request that the data be preserved for a longer period. Erasure is prohibited once an event has triggered an official investigation.
How is a CVR test performed on an aircraft?
The CVR test is activated when the crew pushes and holds the TEST pushbutton, provided the CVR is energized and the parking brake is ON and the same conditions apply to every activation. A low-frequency tone is then heard through the cockpit loudspeakers, and, if a boomset is plugged into the BOOMSET jack, the flight crew will hear the same low-frequency signal. During cruise or any other lull in activity one crew member turns the intercom ON and states “This is the beginning of the CVR Flight Test for aircraft” while the Captain's and First Officer's intercom tests 1-2-3-4-5 are spoken in turn. When both intercoms are OFF the area microphone is selected. The entire in-flight portion will take no longer than fifteen minutes. If the test is not successful the ECAM triggers a RECORDER CVR FAULT alert five seconds after the pushbutton is pressed. If a test gets interrupted the crew must pull the CVR circuit breaker and reset once ready to commence the test.
After the flight, the CVR recording inspection is performed by an audio specialist analyst who examines the audio recording files of the CVR. The inspection verifies that all the data required to be recorded by the CVR is recorded, that the audio quality is sufficient for analysis and investigation purposes, and that the recorder operates correctly for the nominal duration of the recording. It checks that the signal is acceptable on each of the four audio channels - captain's mic, co-pilot's mic, cockpit-area mic, and public address - and that the required input sources are connected to the CVR system. It confirms that adequate signal-to-noise ratio exists for all input signals, that recorded levels and signal quality are acceptable on each channel, that signal levels are reasonably balanced between the channels, and that a mixed track is present. The inspection detects any inoperative cockpit area microphone. These steps guarantee serviceability of the CVR systems and are repeated at regular time intervals.
After I verified the cockpit was in a secure, powered level, I examined the connected circuit and the CVR itself. The first measure required a complete examination; I introduced a sequence of calibrated check inputs into each of the aircraft sound communications and confirmed the registered outputs corresponded to the known reference standards. The concluding portion of the exam was the deletion confirmation, guaranteeing the positioning brake was firmly specified and the recorder ready for continued service.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
Who are the manufacturers of Cockpit Voice Recorders?
Today's CVR market is dominated by Curtiss-Wright and Honeywell, which jointly developed the Honeywell Connected Recorder 25 providing both cockpit voice and flight data recording. KR has been type-certified for many Boeing 737/767/777 fleets and for Airbus equivalents and is offered on new hulls as well as retrofits. Equally active are Smiths Industries (VADR product line) and Hensoldt and L3Harris Technologies, whose combined recorders power large civil and military fleets. These suppliers add features like Rugged solid-state storage, a lithium-free underwater locator beacon, and a flight-data-acquisition-unit (FDAU) that meets MIL-STD-810, MIL-STD-461 and MIL-STD-704.