An aircrafts flight recorders are an invaluable tool for investigators in identifying the factors behind an accident. Recorders usually comprise two individual boxes: the ****pit Voice Recorder (CVR) and the Flight D
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.
A typical FDR is 16 cm (6.3 in) in height, 12.7 cm (5.0 in) in width and 50 cm (19.6 in) in depth. It weighs 4.8 kg (10.6 lbs).
The FDR often tells accident investigators what happened during an accident sequence and the events leading up to it.
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.
Data storage
Older CVRs were analogue recorders which used magnetic tape as the recording medium. Modern solid-state CVRs, however, store the digitized audio information in memory chips.
Older FDRs were mostly digital recorders using magnetic tape as the recording medium. As with CVRs, modern solid-state FDRs store the digitized data in memory chips.
The ****pit Voice Recorder (CVR)
The CVR would be better named the ****pit 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 ****pit area. This includes crew conversation, radio transmissions, aural alarms, control movements, switch activations, engine noise and airflow noise.
Older CVRs retain the last 30 minutes of an aircrafts flight. A modern CVR retains the last 2 hours of information. The newest data records over the oldest data (endless-loop principle).
A typical traditional CVR is 16 cm (6.3 in) in height, 12.7 cm (5.0 in) in width and 32 cm (12.6 in) in depth. It weighs 4.5 kg (10 lbs).
Around 80 per cent of aircraft accidents involve human factors, which means that crew performance may have contributed to the events. As a result, the CVR often provides accident investigators with invaluable insights into why an accident occurred.
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.
The ULB must meet the following requirements:
- nominal operating frequency: 37.5 kHz
- size (typical): 9.95 cm long by 3.30 cm diameter
- operating depth: 0 to 6,096 metres (20,000 feet)
- automatic activation by both fresh and salt water
- minimum operating life of 30 days. The acoustic output will decrease as the battery voltage decreases. It may be possible to still detect the ULB after 60 or more days but the detection range will be decreased.
The ULB can only be dedected by a receiver under the surface of the water. The maxium detection range of a ULB is typically up to 2 to 3 kilometres but is dependent on:
- ULB acoustic output level
- receiver sensitivity
- whether the ULB is buried by debris (e.g. aircraft structure and mud)
- the ambient noise level (e.g. sea state, nearby boats, marine animals, gas and oil lines)
- water temperature gradients
- depth difference between the ULB and the receiver.
