Flight data recorder
A flight data recorder (FDR) (also ADR, for accident data recorder) is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraftperformance parameters. Another kind of flight recorder is the cockpit voice recorder (CVR), which records conversation in the cockpit, radio communications between the cockpit crew and others (including conversation with air traffic control personnel), as well as ambient sounds. In this both functions have been combined into a single unit. The current applicable FAA TSO is C124b titled Flight Data Recorder Systems.
The data recorded by the FDR is used for accident investigation, as well as for analyzing air safety issues, material degradation and engine performance. Due to their importance in investigating accidents, these ICAO-regulated devices are carefully engineered and stoutly constructed to withstand the force of a high speed impact and the heat of an intense fire. Contrary to the "black box" reference, the exterior of the FDR is coated with heat-resistantbright orange paint for high visibility in wreckage, and the unit is usually mounted in the aircraft's empennage (tail section), where it is more likely to survive a severe crash. Following an accident, the recovery of the FDR is usually a high priority for the investigating body, as analysis of the recorded parameters can often detect and identify causes or contributing factors.
Modern day FDRs receive inputs via specific data frames from the Flight Data Acquisition Units (FDAU). They record significant flight parameters, including the control and actuator positions, engine information and time of day. There are 88 parameters required as a minimum under current U.S. federal regulations (only 29 were required until 2002), but some systems monitor many more variables. Generally each parameter is recorded a few times persecond, though some units store "bursts" of data at a much higher frequency if the data begins to change quickly. Most FDRs record approximately 17–25 hours worth of data in a continuous loop It is required by regulations that an FDR verification check (readout) is performed annually in order to verify that all mandatory parameters are recorded.
This has also given rise to flight data monitoring programs, whereby flights are analyzed for optimum fuel consumption and dangerous flight crew habits. The data from the FDR is transferred, in situ, to a solid state recording device and then periodically analyzed with some of the same technology used for accident investigations. In other cases the data is downloaded from the aircraft's Quick Access Recorder (QAR), either by transfer to a portable solid state recording device or by direct upload to the operator's headquarters via radio or satellite.
FDRs are usually located in the rear of the aircraft, typically in the tail. In this position, the entire front of the aircraft is expected to act as a "crush zone" to reduce the shock that reaches the recorder. Also, modern FDRs are typically double wrapped in strong corrosion-resistant stainless steel or titanium, with high-temperature insulation inside. They are usually bright orange. They are designed to emit an ultrasonic "ping" from an underwater locator beacon for up to 30 days and can operate immersed to a depth of up to 6,000 meters (20,000 ft).
Cockpit voice recorder
Both side views of a cockpit voice recorder, one type of flight recorder
A cockpit voice recorder (CVR) is a flight recorder used to record the audio environment in the flight deck of an aircraft for the purpose of investigation of accidents and incidents. This is typically achieved by recording the signals of the microphones and earphones of the pilots' headsets and of an area microphone in the roof of the cockpit. The current applicable FAA TSO is C123b titled Cockpit Voice Recorder Equipment.
Where an aircraft is required to carry a CVR and utilizes digital communications the CVR is required to record such communications with air traffic control unless this is recorded elsewhere. As of 2008 it is an FAA requirement that the recording duration is a minimum of two hours.[18]
A standard CVR is capable of recording 4 channels of audio data for a period of 2 hours. The original requirement was for a CVR to record for 30 minutes, but this has been found to be insufficient in many cases, significant parts of the audio data needed for a subsequent investigation having occurred more than 30 minutes before the end of the recording.
The earliest CVRs used analog wire recording, later replaced by analog magnetic tape. Some of the tape units used two reels, with the tape automatically reversing at each end. The original was the ARL Flight Memory Unit produced in 1957 by Australian David Warren and an instrument maker named Tych Mirfield.
Other units used a single reel, with the tape spliced into a continuous loop, much as in an 8-track cartridge. The tape would circulate and old audio information would be overwritten every 30 minutes. Recovery of sound from magnetic tape often proves difficult if the recorder is recovered from water and its housing has been breached. Thus, the latest designs employ solid-state memory and use digital recording techniques, making them much more resistant to shock, vibration and moisture. With the reduced power requirements of solid-state recorders, it is now practical to incorporate a battery in the units, so that recording can continue until flight termination, even if the aircraft electrical system fails.
Like the FDR, the CVR is typically mounted in the rear of the airplane fuselage to maximize the likelihood of its survival in a crash.
Combined units [edit]
With the advent of digital recorders, the FDR and CVR can be manufactured in one fireproof, shock proof, and waterproof container as a combined digital Cockpit Voice and Data Recorder (CVDR). Currently the CVDR is manufactured by L-3 Communicationsas well as other manufacturers.
Additional equipment [edit]
Since the 1970s, most large civil jet transports have been additionally equipped with a "quick access recorder" (QAR). This records data on a removable storage medium. Access to the FDR and CVR is necessarily difficult because of the requirement that they survive an accident. They also require specialized equipment to read the recording. The QAR recording medium is readily removable and is designed to be read by equipment attached to a standard desktop computer. In many airlines, the quick access recordings are scanned for 'events', an event being a significant deviation from normal operational parameters. This allows operational problems to be detected and eliminated before an accident or incident results.
Many modern aircraft systems are digital or digitally controlled. Very often, the digital system will include Built-In Test Equipment which records information about the operation of the system. This information may also be accessed to assist with the investigation of an accident or incident.
Specifications
Cockpit voice recorder module of PR-GTD, a Gol Transportes AéreosBoeing 737-8EH SFP, found in theAmazon in Mato Grosso, Brazil.
After the crash of Gol Transportes Aéreos Flight 1907, Brazilian Air Forcepersonnel show the recovered flight data recorder
The design of today's FDR is governed by the internationally recognized standards and recommended practices relating to flight recorders which are contained in ICAO Annex 6 which makes reference to industry crashworthiness and fire protection specifications such as those to be found in the European Organisation for Civil Aviation Equipment]documents EUROCAE ED55, ED56 fiken A and ED112 (Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems). In the United States, the Federal Aviation Administration (FAA) regulates all aspects of U.S. aviation, and cites design requirements in their Technical Standard Order, based on the EUROCAE documents (as do the aviation authorities of many other countries).
Currently, EUROCAE specifies that a recorder must be able to withstand an acceleration of 3400 g (33 km/s²) for 6.5 milliseconds. This is roughly equivalent to an impact velocity of 270 knots (310 mph) and a deceleration or crushing distance of 450 cm. Additionally, there are requirements for penetration resistance, static crush, high and low temperature fires, deep sea pressure, sea water immersion, and fluid immersion.
EUROCAE ED-112 (Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems) defines the minimum specification to be met for all aircraft requiring flight recorders for recording of flight data, cockpit audio, images and CNS / ATM digital messages and used for investigations of accidents or incidents. When issued in March 2003 ED-112 superseded previous ED-55 and ED-56A that were separate specifications for FDR and CVR. FAA TSOs for FDR and CVR reference ED-112 for characteristics common to both types.
In order to facilitate recovery of the recorder from an aircraft accident site they are required to be coloured bright yellow or orange with reflective surfaces. All are lettered "FLIGHT RECORDER DO NOT OPEN" on one side in English and the same in French on the other side. To assist recovery from submerged sites they must be equipped with an underwater locator beacon which is automatically activated in the event of an accident.
Regulation
In the investigation of the 1960 crash of Trans Australia Airlines Flight 538 at Mackay (Queensland) the inquiry judge strongly recommended that flight recorders be installed in all airliners. Australia became the first country in the world to make cockpit-voice recording compulsory.[24][25]
The United States first CVR rules were passed in 1964 requiring all turbine and piston aircraft with four or more engines to have CVRs by 1 March 1967.[26]
As of 2008 it is an FAA requirement that the CVR recording duration is a minimum of two hours,[18] following the NTSB recommendation that it should be increased from its previously-mandated 30-minute duration.[27]
As of 2014, flight data recorders and cockpit voice recorders are only required on US aircraft that have 20 or more passenger seats, or those that have six or more passenger seats, are turbo-charged, and require two pilots.
For US air carriers and manufacturers, the National Transportation Safety Board (NTSB) is responsible for investigating accidents and safety-related incidents. The NTSB also serves in an advisory role for many international investigations not under its formal jurisdiction. The NTSB does not have regulatory authority, but must depend on legislation and other government agencies to act on its safety recommendations.
Proposed requirements
The NSTB recommended in 1999 that operators be required to install two sets of CVDR systems, with the second CVDR set being "deployable or ejectable". The "deployable" recorder combines the cockpit voice/flight data recorders and an emergency locator transmitter (ELT) in a single unit. The "deployable" unit would depart the aircraft milliseconds before impact, activated by sensors. The unit is designed to "eject" and "fly" away from the crash site, to survive the terminal velocity of fall, to float on water indefinitely, and would be equipped with satellite technology for immediate location of crash impact site. The "deployable" CVDR technology has been used by the U.S. Navy since 1993.[29] The recommendations would involve a massive retrofit program. However, government funding would negate cost objections from manufacturers and airlines. Operators would get both sets of recorders for free: they would not have to pay for the one set they are currently required by law to carry. The cost of the second "deployable/ejectable CVDR" (or "Black Box") was estimated at $30 million for installation in 500 new aircraft (about $60,000 per new commercial plane).
In the United States, the proposed SAFE Act calls for implementing the NTSB 1999 recommendations. However so far the SAFE ACT legislation failed to pass Congress in 2003 (H.R. 2632), in 2005 (H.R. 3336) and in 2007 (H.R. 4336).[30] Originally the "Safe Aviation Flight Enhancement (SAFE) Act of 2003" was introduced on June 26, 2003 by Congressman David Price (NC) and Congressman John Duncan (Tennessee) in a bipartisan effort to ensure investigators have access to information immediately following commercial accidents.[29] On July 19, 2005, a revised SAFE Act was introduced and referred to the Committee on Transportation and Infrastructure of the U.S. House of Representatives. The bill was referred to the House Subcommittee on Aviation during the 108th, 109th, and 110th congresses.
The NTSB has also asked for the installation of cockpit image recorders in large transport aircraft to provide information that would supplement existing CVR and FDR data in accident investigations. They also recommended image recorders be placed into smaller aircraft that are not required to have a CVR or FDR.[34] The rationale is that what is seen on an instrument by the pilots of an aircraft is not necessarily the same as the data sent to the display device. This is particularly true of aircraft equipped with electronic displays (CRT or LCD). A mechanical instrument is likely to preserve its last indication, but this is not the case with an electronic display. Such systems, estimated to cost less than $8,000 installed, typically consist of a camera and microphone located in the cockpit to continuously record cockpit instrumentation, the outside viewing area, engine sounds, radio communications, and ambient cockpit sounds. As with conventional CVRs and FDRs, data from such a system is stored in a crash-protected unit to ensure survivability.[34]Since the recorders can sometimes be crushed into unreadable pieces, or even located in deep water, some modern units are self-ejecting (taking advantage of kinetic energy at impact to separate themselves from the aircraft) and also equipped with radioemergency locator transmitters and sonar underwater locator beacons to aid in their location.
After Malaysia Airlines Flight 370
On March 12, 2014 in response to the missing Malaysia Airlines Flight 370, David Price re-introduced the SAFE Act in the House of Representatives.[35]
The disappearance of Malaysia Airlines Flight 370 demonstrated the limits of the contemporary flight recorder technology, as physical possession of the flight recorder device is necessary to help investigate the cause of an aircraft incident. Considering the advances of modern communication technology commentators called for flight recorders to be supplemented or replaced by a system for "live streaming" data from the aircraft to the ground.[36][37] Furthermore commentators called for the battery life of the underwater locator beacons to be extended from 30 to 90 days, the range of the locator to be increased and additionally for the outfitting of civil aircraft with deployable flight recorders, which are commonly used in military aircraft. Previous to MH370 the extension of the battery life has been suggested as " rapidly as possible " by investigators of the Air France Flight 447 crash – the AF447 crash happened in 2009, however it took until 2011 to recover the flight recorders.[38]
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to electrical substations located near demand centers. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. Transmission lines, when interconnected with each other, become transmission networks. The combined transmission and distribution network is known as the "power grid" in the United States, or just "the grid". In the United Kingdom, the network is known as the "National Grid".
A wide area synchronous grid, also known as an "interconnection" in North America, directly connects a large number of generators delivering AC power with the same relative phase, to a large number of consumers. For example, there are three major interconnections in North America (the Western Interconnection, the Eastern Interconnection and the Electric Reliability Council of Texas (ERCOT) grid), and one large grid for most of continental Europe.
Historically, transmission and distribution lines were owned by the same company, but starting in the 1990s, many countries have liberalized the regulation of the electricity market in ways that have led to the separation of the electricity transmission business from the distribution business.[1]
System[edit]
Most transmission lines are high-voltage three-phase alternating current (AC), although single phase AC is sometimes used in railway electrification systems. High-voltage direct-current (HVDC) technology is used for greater efficiency at very long distances (typically hundreds of miles (kilometers)), or in submarine power cables (typically longer than 30 miles (50 km)). HVDC links are also used to stabilize and control problems in large power distribution networks where sudden new loads or blackouts in one part of a network can otherwise result in synchronization problems and cascading failures.
Electricity is transmitted at high voltages (120 kV or above) to reduce the energy losses in long-distance transmission. Power is usually transmitted through overhead power lines. Underground power transmission has a significantly higher cost and greater operational limitations but is sometimes used in urban areas or sensitive locations.
A key limitation of electric power is that, with minor exceptions, electrical energy cannot be stored, and therefore must be generated as needed. A sophisticated control system is required to ensure electric generation very closely matches the demand. If the demand for power exceeds the supply, generation plant and transmission equipment can shut down, which in the worst case may lead to a major regional blackout, such as occurred in the US Northeast blackout of 1965, 1977, 2003, and other regional blackouts in 1996 and 2011. It is to reduce the risk of such failure that electric transmission networks are interconnected into regional, national or continent wide networks thereby providing multiple redundant alternative routes for power to flow should such equipment failures occur. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line (ordinarily less than its physical or thermal limit) to ensure spare capacity is available should there be any such failure in another part of the network.
Overhead transmission[
Overhead power line
High-voltage overhead conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Copper was sometimes used for overhead transmission but aluminum is lighter, yields only marginally reduced performance and costs much less. Overhead conductors are a commodity supplied by several companies worldwide. Improved conductor material and shapes are regularly used to allow increased capacity and modernize transmission circuits. Conductor sizes range from 12 mm2(#6 American wire gauge) to 750 mm2 (1,590,000 circular mils area), with varying resistance and current-carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to the skin effect, that causes most of the current to flow close to the surface of the wire. Because of this current limitation, multiple parallel cables (called bundle conductors) are used when higher capacity is needed. Bundle conductors are also used at high voltages to reduce energy loss caused by corona discharge.
Today, transmission-level voltages are usually considered to be 110 kV and above. Lower voltages such as 66 kV and 33 kV are usually considered subtransmission voltages but are occasionally used on long lines with light loads. Voltages less than 33 kV are usually used for distribution. Voltages above 230 kV are considered extra high voltage and require different designs compared to equipment used at lower voltages.
Since overhead transmission wires depend on air for insulation, design of these lines requires minimum clearances to be observed to maintain safety. Adverse weather conditions of high wind and low temperatures can lead to power outages. Wind speeds as low as 23 knots (43 km/h) can permit conductors to encroach operating clearances, resulting in a flashover and loss of supply.[2]Oscillatory motion of the physical line can be termed gallop or flutter depending on the frequency and amplitude of oscillation.
Bulk power transmission
A transmission substationdecreases the voltage of incoming electricity, allowing it to connect from long distance high voltage transmission, to local lower voltage distribution. It also reroutes power to other transmission lines that serve local markets. This is the PacifiCorpHale Substation, Orem, Utah, USA
Engineers design transmission networks to transport the energy as efficiently as feasible, while at the same time taking into account economic factors, network safety and redundancy. These networks use components such as power lines, cables, circuit breakers, switches and transformers. The transmission network is usually administered on a regional basis by an entity such as a regional transmission organization or transmission system operator.
Transmission efficiency is greatly improved by devices that increase the voltage, (and thereby proportionately reduce the current) in the line conductors, thus allowing power to be transmitted with acceptable losses. The reduced current flowing through the line reduces the heating losses in the conductors. According to Joule's Law, energy losses are directly proportional to the square of the current. Thus, reducing the current by a factor of 2 will lower the energy lost to conductor resistance by a factor of 4 for any given size of conductor.
The optimum size of a conductor for a given voltage and current can be estimated by Kelvin's law for conductor size which states that the size is at its optimum when the annual cost of energy wasted in the resistance is equal to the annual capital charges of providing the conductor. At times of lower interest rates Kelvin's law indicates that thicker wires are optimal, while when metals are expensive thinner conductors are indicated: however power lines are designed for long-term usage so Kelvin's law has to be used in conjunction with long-term estimates of the price of copper and aluminum as well as interest rates for capital.
The increase in voltage is achieved in AC circuits by using a step-up transformer. HVDC systems require relatively costly conversion equipment which may be economically justified for particular projects such as submarine cables and longer distance high capacity point to point transmission. HVDC is necessary for the import and export of energy between grid systems that are not synchronized with each other.
A transmission grid is a network of power stations, transmission lines, and substations. Energy is usually transmitted within a grid with three-phase AC. Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors. In the 19th century, two-phase transmission was used but required either four wires or three wires with unequal currents. Higher order phase systems require more than three wires, but deliver little or no benefit.
Losses[edit]
Transmitting electricity at high voltage reduces the fraction of energy lost to resistance, which varies depending on the specific conductors, the current flowing, and the length of the transmission line. For example, a 100 mile 765 kV line carrying 1000 MW of power can have losses of 1.1% to 0.5%. A 345 kV line carrying the same load across the same distance has losses of 4.2%.[9] For a given amount of power, a higher voltage reduces the current and thus the resistive losses in the conductor. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the I 2 R losses by a factor of 100, provided the same sized conductors are used in both cases. Even if the conductor size (cross-sectional area) is reduced 10-fold to match the lower current the I 2 R losses are still reduced 10-fold. Long-distance transmission is typically done with overhead lines at voltages of 115 to 1,200 kV. At extremely high voltages, more than 2,000 kV exists between conductor and ground, corona discharge losses are so large that they can offset the lower resistive losses in the line conductors. Measures to reduce corona losses include conductors having larger diameters; often hollow to save weight,[10] or bundles of two or more conductors.
Transmission and distribution losses in the USA were estimated at 6.6% in 1997[11] and 6.5% in 2007.[11] By using underground DC transmission these losses can be cut in half.[ citation needed ] Underground cables can be larger diameter because they do not have the constraint of light weight that overhead cables have, being 100 feet in the air. In general, losses are estimated from the discrepancy between power produced (as reported by power plants) and power sold to end customers; the difference between what is produced and what is consumed constitute transmission and distribution losses, assuming no theft of utility occurs.
As of 1980, the longest cost-effective distance for direct-current transmission was determined to be 7,000 km (4,300 mi). For alternating current it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter than this.[7]
In any alternating current transmission line, the inductance and capacitance of the conductors can be significant. Currents that flow solely in 'reaction' to these properties of the circuit, (which together with the resistance define the impedance) constitute reactive powerflow, which transmits no 'real' power to the load. These reactive currents however are very real and cause extra heating losses in the transmission circuit. The ratio of 'real' power (transmitted to the load) to 'apparent' power (sum of 'real' and 'reactive') is the power factor. As reactive current increases, the reactive power increases and the power factor decreases. For transmission systems with low power factor, losses are higher than for systems with high power factor. Utilities add capacitor banks, reactors and other components (such as phase-shifting transformers; static VAR compensators; physical transposition of the phase conductors; and flexible AC transmission systems, FACTS) throughout the system to compensate for the reactive power flow and reduce the losses in power transmission and stabilize system voltages. These measures are collectively called 'reactive support'.
Subtransmission
Subtransmission is part of an electric power transmission system that runs at relatively lower voltages. It is uneconomical to connect all distribution substations to the high main transmission voltage, because the equipment is larger and more expensive. Typically, only larger substations connect with this high voltage. It is stepped down and sent to smaller substations in towns and neighborhoods. Subtransmission circuits are usually arranged in loops so that a single line failure does not cut off service to a large number of customers for more than a short time. While subtransmission circuits are usually carried on overhead lines, in urban areas buried cable may be used.
There is no fixed cutoff between subtransmission and transmission, or subtransmission and distribution. The voltage ranges overlap somewhat. Voltages of 69 kV, 115 kV and 138 kV are often used for subtransmission in North America. As power systems evolved, voltages formerly used for transmission were used for subtransmission, and subtransmission voltages became distribution voltages. Like transmission, subtransmission moves relatively large amounts of power, and like distribution, subtransmission covers an area instead of just point to point.[12]
Failure protection[edit]
Under excess load conditions, the system can be designed to fail gracefully rather than all at once. Brownouts occur when the supply power drops below the demand. Blackouts occur when the supply fails completely.
Rolling blackouts (also called load shedding) are intentionally engineered electrical power outages, used to distribute insufficient power when the demand for electricity exceeds the supply.
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