Flight Recorder – CVR – FDR – ULB

Black box; A mandatory item on every aircraft, it is a flight recorder unit in its internationally used form. All information about the flight is recorded in the flight recorder with a specific algorithm. Thus, it makes flight data accessible to the authorities when needed. Black boxes, resistant to the most extreme situations and crashes. They are one of the most special tools of the aviation research industry.

An aircraft’s flight recorders are an invaluable tool for investigators in identifying the factors behind an accident. Recorders usually comprise two individual boxes: the Cockpit Voice Recorder (CVR) and the Flight Data Recorder (FDR). Popularly known as ‘black boxes’, these flight recorders are in fact painted orange to help in their recovery following an accident.

Flight Recorder

The Cockpit Voice Recorder (CVR)

The CVR would be better named the ‘cockpit audio recorder’ as it provides far more than just the voices of the pilots. In fact, it creates a record of the total audio environment in the cockpit area. This includes crew conversation, radio transmissions, aural alarms, control movements, switch activations, engine noise and airflow noise.

The Flight Data Recorder (FDR)

 The FDR records flight parameters. The data recorded varies widely, depending upon the age and size of the aircraft. The minimum requirement, however, is to record a basic group of five parameters: » pressure altitude » indicated airspeed » magnetic heading » normal acceleration » microphone keying. Microphone keying (the time radio transmissions were made by the crew) is recorded to correlate FDR data with CVR information. This basic requirement has existed since the 1960s. Today, modern jet aircraft far exceed this, and are fitted with FDRs that can record thousands of parameters covering all aspects of the aircraft operation. The FDR retains the last 25 hours of aircraft operation and, like the CVR, operates on the endless-loop principle. As FDRs have a longer recording duration than CVRs, they are very useful for investigating incidents and accidents.


Flight recorders are designed to survive both high-speed impact and post-impact fire. They are, however, not invulnerable and are sometimes destroyed. The recorder is designed to ensure that data, rather than the recorder itself, survives an accident. The data storage medium (tape or microchips) is mounted inside an impact-resistant and fire-resistant container.

The crashworthiness standards of flight recorders was revised in 2003 by the European Organisation for Civil Aviation Equipment (EUROCAE) committee, an international body on which the ATSB was represented. The recorder’s memory module is now required to withstand:

– An impact producing a 3,400-g deceleration for 6.5 milliseconds (equivalent to an impact velocity of 270 knots and a deceleration or crushing distance of 45 cm)
– A penetration force produced by a 227 kilograms (500 pounds) weight which is dropped from a height of 3 metres (10 feet)
– A static crush force of 22.25 kN (5,000 pounds) applied continuously for five minutes
– A fire of 1,100 degrees Celsius for 60 minutes.

The Underwater Location Beacon

Each recorder is fitted with battery-powered Underwater Location Beacon (ULB) to aid underwater recovery. When the ULB is immersed in water, it will begin to radiate an acoustic signal which can be received and transformed into an audible signal by a receiver. The ULB is sometimes called a ‘pinger’ due to the audible signal created by the receiver.

Source: Australian Transport Safety Bureau

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