The Australian Transport Safety Bureau (ATSB) is leading a sea floor mapping and underwater search for missing Malaysia Airlines flight MH370 in the southern Indian Ocean. Geoscience Australia(Opens in a new tab/window) is providing advice, expertise and support to the ATSB.
The search comprises two planned phases. Phase one, a bathymetric survey providing a detailed map of the sea floor topography of the search area and phase two, an underwater search using side scan sonar.
Bathymetric survey
Bathymetry is the study and mapping of sea floor topography. It involves obtaining measurements of the ocean depth and is equivalent to mapping topography on land. The bathymetric survey undertaken in the search for MH370 has resulted in a map that charts the contours, depths and hardness of the ocean floor.
Prior to the bathymetric survey, very little was known about the sea floor in the MH370 search area, as few marine surveys have taken place in the area. Existing maps of the sea floor were coarse, having been derived from satellites and only providing a general indication of water depth.
Figure 1: Coarse three-dimensional model of sea floor terrain
Figure 1: This model of the sea floor terrain was based on coarse pre-existing data, which was derived from satellite gravity measurements and ocean passage soundings. The MH370 bathymetric survey was undertaken to gather more detailed and higher resolution data in preparation for the underwater search phase.
Figure 2:
Figure 2: The image on the left shows data at around 3400-metre resolution (data acquired predominantly by satellite altimetry), while the image on the right shows data with a combination of 250-metre and 50-metre resolutions (data acquired by bathymetric surveys from a vessel). The higher resolution data on the right more accurately reveals seabed features. This figure is for illustrative purposes only and does not show data from the search area.
The survey vessel Fugro Equator and the Chinese survey vessel Zhu Khezhen collaborated on the bathymetric survey, using multibeam sonar to gather data. That data—which was reviewed, corrected and analysed by experts at Geoscience Australia— revealed many seabed features for the first time. Newly discovered sea floor features include:
seamounts (remnant submarine volcanoes),
ridges (semi-parallel) up to 300 meters high, and
depressions up to 1400 metres deep (compared to the surrounding seafloor depths).
The data also revealed finer-scale seabed features that were not visible in the previous low-resolution, satellite-derived bathymetry data.
Figure 3: Detailed three-dimensional model of sea floor terrain
Figure 3: A three-dimensional model of the sea floor terrain in the MH370 search area was developed from high resolution (90-metre resolution) data from the bathymetric survey and revealed many seabed features for the first time.
Over 200,000 square kilometres of the sea floor were surveyed. The data collected in the bathymetric survey was used to build a comprehensive map of the sea floor in the search area, to be used in navigation for the underwater search. The ATSB also used the data when planning for search timings, methods, procedures, safety precautions and priority areas for each vessel to search.
While initial bathymetric survey operations have been completed and phase two has begun, further bathymetric survey work may recommence if the need arises.
Data collected as part of the bathymetric survey will be publicly released by Geoscience Australia in due course.
Visualisation of Sea Floor Terrain
Before the underwater search for MH370 could begin, it was necessary to accurately map the sea floor to ensure that the search is undertaken safely and effectively. Bathymetry survey vessels spent months at sea, scanning the sea floor with multibeam sonar to gather detailed, high-resolution data. The data has revealed many seabed features for the first time. This computer-animated ‘flythrough’ shows a visualisation of some of the sea floor terrain in the search area.
The Aviation Short Investigation Bulletin covers a range of the ATSB’s short investigations and highlights valuable safety lessons for pilots, operators and safety managers.
Released periodically, the Bulletin provides a summary of the less-complex factual investigation reports conducted by the ATSB. The results, based on information supplied by organisations or individuals involved in the occurrence, detail the facts behind the event, as well as any safety actions undertaken. The Bulletin also highlights important Safety Messages for the broader aviation community, drawing on earlier ATSB investigations and research.
Issue 33 of the Bulletin features 10 safety investigations:
At the request of the Malaysian Government, Australia is leading the search for missing Malaysia Airlines Flight MH370 in the Indian Ocean. The search is a complex operation that involves vast areas with only limited data and aircraft flight information available.
Over-water searches
Over-water aircraft accident locations are usually found by conducting a broad-area aerial search. The search area is generally determined by a combination of:
Position information from ground-based radar systems (maximum range is generally 250 NM)
Position information automatically transmitted from the aircraft at regular intervals
Position reports from the crew
Re-tracing the planned flight route
Eye-witness reports (possibly located on the shore, on other aircraft or on ships)
Uncertainty in the position of an accident location increases with time from the aircraft’s last known position (fix) so the search area will expand accordingly as the position data becomes ‘stale’.
Once floating wreckage is observed, reverse-drift techniques can be used to help determine the aircraft impact location. Only a small-area underwater search is then required to locate the wreckage and map the wreckage field. This underwater search can be aided by the underwater locator beacons fitted to flight recorders. As the beacons have a limited duration of nominally 30 days and to minimise the inaccuracies of the reverse-drift calculations, it is important that an aerial search is commenced as soon as possible and the floating debris is found quickly.
In the case of MH370:
The aircraft departed Kuala Lumpur at 1641 UTC
The final automatically transmitted position from the aircraft occurred at 17:07 UTC
No radio communications were received from the crew after 17:19 UTC
The final ATC (secondary) radar fix occurred at 17:22 UTC
At 17:25 UTC the aircraft deviated from the planned flight route
The final primary radar fix occurred at 18:22 UTC
The satellite communications log indicated the aircraft continued to fly for another 6 hours
No confirmed eye-witness reports were received
The search in the Australian search and rescue zone commenced on 18 March (10 days after the aircraft went missing)
As a result, the search area for MH370 has remained very large. A useful comparison is the search for Air France Flight 447 (AF477), which crashed in the Atlantic Ocean on 1 June 2009. The AF447 aircraft was programmed to send its position automatically every 10 minutes, there were a number of fault messages transmitted via satellite during the last few minutes of flight and it was following the planned flight route. The search for the aircraft began on 1 June and the first surface wreckage was discovered on 6 June, 5 days after the accident. Given the relative accuracy of the aircraft’s last known position, a circular search area of 40 NM was defined (17,240 km²). After a search effort involving five separate phases, the aircraft wreckage was located on the ocean floor almost two years later.
As none of the traditional sources of data could be used to locate the aircraft wreckage from MH370, it has been necessary to use novel sources of data and analysis techniques. This has led to a larger than typical search area; and there have been changes to its location as validation and calibration checks have been performed and the analysis is refined.
Determining the search area for MH370
The flight path of MH370 has three distinct sections; one under secondary radar in which the aircraft transponder was operational and ACARS messages were being transmitted, a primary radar section during which the aircraft was being tracked solely by air defence radar systems and the final stage for which the only information available was the satellite communications log data.
ACARS and radar data
The final ACARS transmission was at 17:07 UTC and provided location reports from the initial stage of the flight as well as a recording of the aircraft fuel remaining. The final secondary radar point was at approximately 17:22 UTC. The final primary radar point was at 18:22 UTC. Figure 1 shows the first and second sections of the flight.
Figure 1: MH370 Flight path derived from Primary and Secondary radar data
Source: NTSB/Google
Satellite communications (SATCOM) data
Following the loss of primary radar, the only available information was from satellite signalling messages, also referred to as ‘handshakes’, between the ground station, the satellite and the aircraft’s satellite communication system.
For each transmission to the aircraft, the ground station recorded the burst timing offset (BTO) and the burst frequency offset (BFO).
Figure 2: Satellite communications schematic
Source: Inmarsat
Burst Timing Offset (BTO)
The BTO is a measure of the time taken for a transmission round trip (ground station to satellite to aircraft and back) and allows a calculation of the distance between the satellite and the aircraft. Based on this measure, a possible location ring can be mapped on the surface of the earth (Figure 3). An analysis of SATCOM system parameters showed that the accuracy of the rings was ± 10 km. This analysis was validated using recorded BTO values from the initial stage of the flight when the aircraft’s position was known.
Figure 3: Satellite ring derivation Source: Inmarsat
There were 7 handshakes between the ground station and the aircraft after the loss of primary radar data. The location rings calculated from the recorded BTO values are shown in figure 4.
Figure 4: MH370 timing (UTC) with corresponding rings arrowed
Source: Inmarsat/Boeing /Google
The information from the BTO places the aircraft somewhere on each ring at the corresponding time. By taking the maximum speed of the aircraft into account, the rings can be reduced in length to arcs – there are some areas of the rings it simply could not have reached.
Burst Frequency Offset (BFO)
The BFO is the measure of the difference between the expected frequency of the transmission and the frequency received at the ground station. This difference is attributed to various sources including the Doppler Effect from the motion of the satellite and the aircraft, as well as some processing effects. Once the known components that contribute to the BFO are resolved, the remainder can be used to estimate the speed and direction of the aircraft. There are a large number of speeds and headings that can be consistent with a BFO recording. These are limited, however, by the operational constraints of the aircraft.
Candidate paths of different speeds were created which met the BTO ring location/time constraints and the predicted BFO values of these paths have been compared with the recorded values. The better the match, the higher the probability that the path was close to that of MH370.
Final handshake message at 00:19 (7th arc)
The 00:19 signalling message (7th arc) was a logon request from the aircraft. This is consistent with the satellite communication equipment on the aircraft powering up following a power interruption. The interruption in electrical supply may have been caused by fuel exhaustion.
Note on the satellite communication
The satellite’s normal function is essentially communication and it was never initially intended to have the capability to track an aircraft. Following the Air France 447 accident, Inmarsat engineers began recording the BTO in order to provide another potential means of geo-locating aircraft in the event of a similar accident.
Aircraft Performance Calculations
Estimates of fuel consumption were calculated from the time of the last recorded fuel quantity, using a range of flight paths and speeds. The results of these calculations were consistent with fuel exhaustion occurring close to the 7th arc.
Validation
Several teams independently provided both satellite communications and performance analysis as part of the validation process. The location of 9M-MRO on previous flights as well as the locations of other aircraft in the air at the same time were all used to validate the techniques.
Other information
Surface search
An international air and maritime force conducted a surface search of drifted regions along the 7th arc from 18 March to 28 April 2014. A drifted region is created by modelling the movement of an area of water over the time period when the surface search is conducted. During this time, no debris was identified to be likely from MH370.
Underwater search
Acoustic detections possibly related to underwater locator beacons were made by two vessels in the refined probability area from 5 - 8 April 2014. To further investigate these signals, a search of the ocean floor around the detections was performed by a number of vessels. To date no further sign of MH370 has been detected.
Hydrophones
Low frequency hydroacoustic signals present in the Indian Ocean are being examined to determine whether they can provide any information to help define the search area. These signals are recorded by hydrophones as part of the United Nations Comprehensive Nuclear-Test-Ban-Treaty Organisation (CTBTO) or the Integrated Marine Observing System (IMOS).
Use of waypoints
Comparison of possible flight paths with tracks using waypoints is also under consideration.
Air Routes
There is only one published north-south air route in the south-eastern Indian Ocean. Air route M641 connects Cocos Island to Perth and has four waypoints. The air route crosses the area where the four acoustic signals were detected.
Shape of the search area
At the time MH370 reached the 7th arc, the aircraft is considered to have been descending. A study completed after the Air France 447 accident concluded that the majority of aircraft in loss of control accidents were found within 20 nautical miles (32 km) of their last known position. This provides a reasonable limitation for the size of the search area across the arc.
The ATSB has been advised that the hours flown data provided by the Bureau of Infrastructure, Transport and Regional Economics (BITRE) and used for the calculation of occurrence rates by aircraft type, may have been under-reported for some aircraft types used in charter operations. The ATSB is awaiting new hours flown data from BITRE and will update the reports accordingly when this data is available.
Why the ATSB did this research
This is the first in a series of research investigations looking at technical failures reported to the ATSB between 2008 and 2012. This report reviews power plant problems reported to the ATSB affecting turbofan-powered aircraft, and the types of incidents they are associated with.
By summarising power plant-related occurrences across all operators, this report provides an opportunity for operators to compare their own experiences with others flying the same or similar aircraft types, or aircraft using the same engines. By doing so, the ATSB hopes that the wider aviation industry will be able to learn from the experience of others.
What the ATSB found
Despite the complexity of modern turbofan engines, their reliability is evidenced by the remarkably low rate of power plant occurrences. With a combined total of over five and a half million flight hours for turbofan engine aircraft between 2008 and 2012, there were only 280 occurrences relating specifically to the power plant systems (or approximately one occurrence every 20,000 flight hours). Additionally, the vast majority of these (98%) were classified as being a low risk rating occurrence with a low or no accident outcome. Only four were classified as medium risk, two as high risk and one as very high risk. None resulted in injury to passengers or crew.
Although the rates were low for the turbofan engine aircraft group as a whole, there were large differences between individual aircraft models. Three aircraft types in particular, the Boeing 747 classic, the Fokker F28/F100 and the British Aerospace BAE 146/Avro RJ, had far greater rates of power plant occurrences between 2008 and 2012 than any other aircraft in this study. Although these three aircraft types represented some of the older fleets, there were other fleets of aircraft of similar ages with far lower rates of occurrences.
Safety message
The small number of high and very high risk power plant occurrences between 2008 and 2012 remind us that even highly sophisticated modern power plants can, and do, fail. Timely and vigilant reporting of all technical problems is therefore strongly encouraged to ensure as much information as possible is collected to better understand these problems. Of particular importance in technical occurrences are the follow-up reports from engineering inspections. These are often the only way that the root cause of the problem can be determined. The more comprehensively these are reported to the ATSB, the more insightful and useful reports like this become.
The Aviation Short Investigation Bulletin covers a range of the ATSB’s short investigations and highlights valuable safety lessons for pilots, operators and safety managers.
Released periodically, the Bulletin provides a summary of the less-complex factual investigation reports conducted by the ATSB. The results, based on information supplied by organisations or individuals involved in the occurrence, detail the facts behind the event, as well as any safety actions undertaken. The Bulletin also highlights important Safety Messages for the broader aviation community, drawing on earlier ATSB investigations and research.
Issue 32 of the Bulletin features 10 safety investigations:
The Aviation Short Investigation Bulletin covers a range of the ATSB’s short investigations and highlights valuable safety lessons for pilots, operators and safety managers.
Released periodically, the Bulletin provides a summary of the less-complex factual investigation reports conducted by the ATSB. The results, based on information supplied by organisations or individuals involved in the occurrence, detail the facts behind the event, as well as any safety actions undertaken. The Bulletin also highlights important Safety Messages for the broader aviation community, drawing on earlier ATSB investigations and research.
Issue 31 of the Bulletin features 10 safety investigations:
At the request of the Malaysian Government, Australia is leading the search for missing Malaysia Airlines Flight MH370. All the available data indicates the aircraft entered the sea close to a long but narrow arc of the southern Indian Ocean.
The underwater search is a complex operation that will involve a range of vessels, equipment and expertise to cover 60,000 square kilometres of ocean floor—roughly the size of Tasmania.
The intensified underwater search
The Australian Transport Safety Bureau (ATSB) is coordinating the continuous underwater search phase for MH370. This is expected to take up to 12 months to complete a search area of up to 60,000 square kilometres. The aim of the search is to locate the aircraft and any crucial evidence (such as aircraft wreckage and flight recorders) to assist with the Malaysian investigation.
As part of the search, the ATSB will contract experts to localise, positively identify and map the debris field of MH370 which is a Boeing 777 aircraft, using specialist equipment.
The ATSB will use data obtained from a comprehensive bathymetric survey of the search area to identify and prioritise areas of the search zone. The bathymetric survey – currently underway – will essentially provide a map of the search zone, charting the contours, depths and hardness of the ocean floor. (The ATSB factsheet Mapping the ocean floor—bathymetric survey provides greater detail on the survey operations).
Search equipment
The equipment used during the underwater search will be capable of mapping and photographing any aircraft debris and operating at depths of at least 6,000 m. It will likely include:
a towed sonar
an Autonomous Underwater Vehicle with mounted sonar
optical imaging equipment with sufficient resolution to identify the aircraft or a debris field from the aircraft.
The equipment will be deployed from a vessel(s) capable of operating in the search area for up to 12 months.
Contracted services
The ATSB will contract the services of a specialist organisation (preferably a prime contractor), to conduct the underwater search. The contractor will provide the expertise, equipment and vessel(s) to search the 60,000 square kilometre search zone, identified as being the most probable location of the missing aircraft. The vessel(s) being utilised by the prime contractor may also be coordinated, in consultation with the ATSB, with other vessel(s) also undertaking search activities in the search zone on behalf of other countries.
More information
The following ATSB factsheets, available at www.atsb.gov.au/mh370 help explain the steps involved for the underwater search:
The Australian Transport Safety Bureau (ATSB) is leading the underwater search for missing Malaysia Airlines flight MH370. All the available data indicates the aircraft entered the sea close to a long but narrow arc of the southern Indian Ocean.
The search is a complex operation that will involve a range of vessels, equipment and expertise to cover 60,000 square kilometres of ocean floor.
Bathymetric survey
During the first stage of the search, the ATSB is tasking a Chinese PLA-Navy ship to undertake a bathymetric survey of the 60,000 square kilometre search area. A contracted commercial vessel with join the survey in June. The bathymetric survey will provide a map of the underwater search zone, charting the contours, depths and hardness of the ocean floor.
While the ocean depth of the search zone is understood to be between 1000 m and 6000 m, we currently have very limited knowledge of the sea floor terrain facing the underwater search operation. The information we receive from the bathymetric survey will give us crucial data to plan and conduct the intensified underwater search.
How the survey’s done
The operation will involve a ship surveying the ocean floor using multi beam sonar, which is capable of collecting high quality data to water depths of up to 6,000 m.
Multibeam sonar is a common offshore surveying tool that uses multiple sound signals to detect the seafloor. Due to its multiple beams it is able to map a swath of the seabed under the ship, in contrast to a single beam sonar which only maps a point below the ship. Different frequencies are used to map different water depths, with higher frequencies (>100kHz) used for shallow water and low frequencies (<30 kHz) for deep water.
Generally, the multibeam sonar transducer is mounted rigidly to the hull of the survey vessel and its position can be calculated very accurately. Other parts of the multibeam system include auxiliary sensors such as motion-sensing systems and Global Positioning Systems (GPS) to ensure accurate positioning, motion sensing and sound speed measurement system.
A modern multibeam sonar transducer typically uses the Mills Cross telescope array. The sound is transmitted from transducers that are perpendicular to the survey track. Consequently, the sound pulses forms a transmit swath that is wide across-track and narrow along-track. The returning sound pulses, which are mainly recording the impedance contrast and seafloor topography, are received by the receivers which are mounted parallel to the survey track. These return beams are narrow across-track. Unlike the sidescan sonar which commonly produces only acoustic backscatter data (i.e. hardness), the multibeam sonar generates both water depth and seafloor hardness data concurrently.1
How many vessels will be involved in the survey
The Chinese PLA-Navy ship Zhu Kezhen (872) is already in the search area conducting a bathymetric survey of an area provided by the ATSB. A contracted survey vessel will arrive in the search area in early June.
How long it will take
It is expected that the bathymetric survey will take around three months to complete, but this will depend on a number of factors, such as weather conditions, during the survey operations.
The underwater search will begin when we have enough data from the bathymetric survey to start searching. This means that the underwater search will begin while the survey is still being completed.
The ATSB’s website www.atsb.gov.au/mh370 and the Joint Agency Coordination Centre website also provide information about the overall search effort for MH370.
The Aviation Short Investigation Bulletin covers a range of the ATSB’s short investigations and highlights valuable safety lessons for pilots, operators and safety managers.
Released periodically, the Bulletin provides a summary of the less-complex factual investigation reports conducted by the ATSB. The results, based on information supplied by organisations or individuals involved in the occurrence, detail the facts behind the event, as well as any safety actions undertaken. The Bulletin also highlights important Safety Messages for the broader aviation community, drawing on earlier ATSB investigations and research.
Issue 30 of the Bulletin features 12 safety investigations:
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.
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.
Older CVRs retain the last 30 minutes of an aircraft’s 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.
Cockpit Voice Recorder
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
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.
Memory chip recording medium (left) and recording medium (right)
Installation
On 10 June 1960, an accident occurred in which 29 people died in a Fokker F27 aircraft landing at Mackay in Queensland. The subsequent board of inquiry was unable to come to any definite conclusions as to what had caused the accident and recommended that all airliners be fitted with flight recorders. The Federal Government implemented this recommendation the following year.
Australia was one of the first countries to introduce this requirement. Today, all aircraft on the Australian register with a maximum take-off weight less than or equal to 5,700 kg, and which are pressurised and turbine-powered by more than one engine are required to carry a cockpit voice recorder (CVR).
All Australian-registered aircraft with a maximum take-off weight greater than 5,700 kg and turbine powered are required to carry both a CVR and FDR.
Flight recorders are normally located near the aircraft’s tail, as experience has shown that this area generally suffers the least damage during an accident.
Crashworthiness
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.
Cockpit voice recorder received by the ATSB showing accident damage
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 5 minutes
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.
Underwater Location Beacon
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 detected by a receiver under the surface of the water. The maximum 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.
ATSB capability and facilities
The ATSB’s central office in Canberra includes an audio laboratory and an FDR laboratory. ATSB investigators use these laboratories to perform CVR and FDR readouts for occurrences in Australia and overseas.
Australia is one of a few countries in the Asia-Pacific region to possess these types of labs. The ATSB offers its services and expertise to international investigators. In the past, the ATSB has assisted regional neighbours such as New Zealand, Indonesia, Singapore, Taiwan and Bangladesh with investigation readouts.
The ATSB also uses the labs to certify new recorder-type/aircraft-type combinations.
In addition to its recorder readout capability, the ATSB has advanced computer graphics software which allows data obtained from all available sources to be combined to create a graphical reconstruction or animation of an accident or incident.
These data sources include FDR, CVR, ground-based radar recorders, eye-witness reports, air traffic service communications and wreckage analysis. Videos can also be produced from the computer graphics. Computer graphics are a powerful tool for investigators, being an excellent means of explaining accident scenarios to people unfamiliar with aviation, and also providing a valuable educational tool for pilots and other aviation professionals.
If an accident occurred at night in a remote area or at sea, the flight recorders may be the main, if not only, means of establishing the sequence of events immediately preceding the accident. At the very least, CVR and FDR data can save an investigation team many days or weeks of delay as the team examines the wreckage.
Many accidents have involved aircraft without flight recorders, and despite thorough investigation, the factors underlying these occurrences can remain inconclusive or unknown. As well, accidents leaving very little recoverable aircraft wreckage have, many times, been resolved once the flight recorders were found.
Flight recorders are also useful for cases in which evidence is transitory, e.g. occurrences involving windshear. In such instances, flight recorders will reveal the sudden effects of windshear upon an aircraft’s flight path. The evidence available from flight recording indicates that, prior to flight-parameter recording, the effect of the wind in many aircraft accidents was underestimated.
Flight recorder data recovery
Accident animation
On 22 March 2010, an Embraer S.A. EMB-120ER Brasilia aircraft (EMB-120) crashed moments after take-off at Darwin Airport, Northern Territory. Both pilots died in the accident. The purpose of the flight was to revalidate the command instrument rating of the pilot under check. The aircraft was under the command of a training and checking captain, who occupied the copilot’s seat. The take-off included a simulated engine failure.
The aircraft was equipped with a CVR and an FDR which provided crucial evidence for the investigation. A computer graphics animation was produced based on the FDR data. The investigation report AO-2010-019 and animation are available at: www.atsb.gov.au
Picture of a computer graphics animation
Different types of recorders
Deployable recorders
Deployable recorders incorporate the functions of the Cockpit Voice Recorder, the Flight Data Recorder and an Emergency Locator Transmitter (ELT) into a package that is automatically deployed (released) from the aircraft at the start of an accident sequence.
The deployable package possesses capabilities that enable it to deploy and rapidly establish a flight trajectory that clears the airframe during the accident sequence. The deployable package is designed to float on water after deployment. After deployment, the deployable package starts transmitting an emergency signal that can be detected by satellite and search aircraft/ships.
Deployable recorders are mainly installed on helicopters operating over water as well as military aircraft. Commercial aeroplanes have not adopted deployable recorders.
Combined recorders
Combined recorders incorporate the functions of the Cockpit Voice Recorder and the Flight Data Recorder in one box. When combined recorders are used on an aeroplane, two combined recorders are required. One is installed near the cockpit and one installed towards the rear of the aircraft. The forward-mounted recorder has the advantage of shorter cable distances between the cockpit area and the recorder, reducing the chance of the wires being breached during an in-flight fire or breakup. Traditional rear mounted recorders maximize impact survivability.
Image recorders
Image recorders record images of all flight crew work areas including instruments and controls. The image recorder supplements existing information recorded by the Cockpit Voice Recorder and the Flight Data Recorder.
A general view of the cockpit area, instrument and control panel displays provides an insight into the cockpit environment, serviceability of displays and instruments, crew activity, and the human/machine interface.
Image recorders have not been widely adopted due to crew privacy issues and they are not installed in commercial airliners.
