Aircraft Electrical System 1

Md. Nur AlamCorse code/Batch: FENDA 09Student ID 33
Task: 01 (a)
Parameters of modern aircraft recording system:
A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of an aircraft accident or incident. For this reason, flight recorders are required to be capable of surviving the conditions likely to be encountered in a severe aircraft accident. They are typically specified to withstand an impact of 3400 g and temperatures of over 1,000 °C (1,832 °F) (as required by EUROCAE ED-112). There are two common types of flight recorder, the flight data recorder (FDR) and the cockpit voice recorder (CVR). In some cases, the two recorders may be combined in a single FDR/CVR unit.
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.
The FDR rule change effected by the FAA in late 1997 will require operators of airplanes flying under FAA rules to make sure the FDRs on their airplanes can record several additional parameter groups. The compliance date for these airplanes depends on their date of manufacture. [1]
Mandatory parameters selected
In the selection of the mandatory parameters for crash investigation purposes, the objective is to obtain, either directly or by deduction from the recorded data, the following information:
The aircraft's flight path and attitude in achieving that path;
The basic forces acting on the aircraft, e.g., lift, drag, thrust and control forces;
The general origin of the basic forces and influencing factors, e.g., status of such systems as primary and secondary flight controls, hydraulic power supply, cabin pressurization, electrical power, and navigation.
The mandatory parameters are specified in national regulations for civil aircraft operation and generally relate to the following:
Time (GMT or elapsed);
Indicated altitude;
Indicated airspeed;
Vertical (normal) acceleration;
Magnetic heading;
Pitch attitude;
Roll attitude;
Flap position;
Engine power.
Optional parameters selected
Total air temperature
Lateral acceleration
Longitudinal acceleration
Horizontal stabilizer position
Pitch control surface position (elevators)
Lateral control surface position (aileron)
Yaw Control surface position (rudder)
Engine thrust (N1)
Flaps and slats
VHF keying
HF keying
Engine reverse thrust (unlocked and deployed)
Mach number
Maximum allowable airspeed
Glide slope deviation
Radio altimeter
Localizer deviation
Spoiler position
Autopilots engage.
Because most airplanes recorded only six parameter groups, nearly all operators were required to retrofit the FDRs in their airplanes. In response to this requirement, many FDR manufacturers developed crash-survivable FDRs that did not require flight data acquisition units to replace the first-generation foil FDRs, and that accommodated the 11 required parameter groups for airplanes with up to four engines. Airplanes such as the 737 that have these FDRs can accommodate up to 18 parameter groups, as they have only two engines for which data must be recorded. [2]
http://en.wikipedia.org/wiki/Flight_recorder
http://www.skybrary.aero/index.php/Flight_Data_Recorder_(FDR)
Task: 01 (b)
Block diagram of Aircraft Integrated Data System (AIDS):
An integrated data system (AIDS) is a method of improving flying safety and operating efficiency. Data recorded in flight are processed on a ground-based digital computer, and instances of operation outside established operational envelopes are identified. Positive information is available to guide corrective action directed toward improving training programs, operating procedures, or performance by individual crewmen.

Figure: block diagram of Aircraft Integrated Data System
On the other hand AIDS (Aircraft Integrated Data System) is an aircraft system that allows the airline to record and/or monitor all available parameters which are on the aircraft buses. Some Aircraft like the Airbus A320 have an AIDS print button which, when programmed over the MCDU, allows paper data reports, DAR recordings, or ACARS transmissions of a select amount of parameters to be printed. [3]
Accident data recording system
Typical data output to the DFDR comprises a continuous stream of digital data formed into frames. Each frame is divided into four sub-frames, typically of one-second duration each; the sub-frame
is formed by 64 12-bit words. The first word in each sub-frame is a synchronizing word; the other three contain data. Each word contains 12 bits of digital information; the total number of bits in a sub-frame is therefore 768. Various formats are used to form the digital bits of logic one and logic zero, these formats include:

non-return-to-zero (NRZ)
bipolar-return-to-zero return-to-zero (RZ)
Harvard bi-phase format. [4]

Non-return-to-zero (NRZ) logic one is formed by a 5 V DC level; logic zero is indicated by 0 V DC. The two logic levels are therefore represented by one of two significant conditions, with no other neutral or
rest condition. A clock waveform is required to distinguish between bits. Two wires are used to carry the signal, together with a third wire for a clock reference. Bipolar-return-to-zero return-to-zero (RZ) describes a code in which the signal drops (returns) to zero between each pulse. This takes place even if a number of consecutive logic zeros or ones occur in the signal. Logic one is indicated by a 0.5 V DC level, and logic zero by a _ 0.5 V DC level. The signal returns to 0 V DC in the second half of each bit. The signal is self-clocking; therefore separate clock pulses are not required alongside the signal. In the Harvard bi-phase format, each bit changes state at its trailing edge; either from high to zero or [5]

Data recovery analysis:

Figure: Digital data formed into frames

Zero to high independently of its value. A logic one is indicated by a mid-bit change of state; a logic zero is indicated by no mid-bit change of state. The 64th word of 16 consecutive frames is combined into a super-frame. These words are formed in binary coded decimal (BCD) format; each word comprises four bits, used to represent the denary numbers zero to nine. This illustrates how binary numbers and then BCD represent the denary (or decimal) numbers 0–20. The advantage of BCD is that it allows conversion to decimal digits for printing or display and faster decimal calculations. This is particularly useful where a numeric value is to be displayed, e.g. recording [6]


 Tooley, Mike; Tooley, Michael H. (2007). Aircraft digital electronic and computer systems: principles, operation and maintenance. Butterworth-Heinemann. pp. 75–76. ISBN 978-0-7506-8138-4.
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM,Page-329,330
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM,page-330,332
Task: 02
Operation of modern aircraft engine health monitoring system:
With an electrical system connecting all the equipment with power, the control system controlling all the actions of the system, a monitoring system is needed to log the actions, performance and status of the components in these systems.
Monitoring systems technologies log the actions, performance a status of the components in the electrical and control systems. They collect data from various components, sub-systems or a system, which is then used to draw certain conclusions, based on algorithms programmed into the collection system. The monitoring collection system can be ground-based, while monitoring systems flying in the air, floating on the sea, or generating electricity on another continent.
All monitoring systems work on the simple basis of:
Sense - Acquire - Transfer - Analyze - Act.
The aim of a monitoring system is to maximize reliability and availability. A monitoring system will not stop a system from malfunctioning, but will log system data from which system characteristics can be deduced. This provides our customers with advanced data on the status of their system and data to plan maintenance schedules around.
The monitoring system collects data from all over the system and provides feedback at a specific location, this location can either be the control room on a ship or the control room on land receiving feedback signals from a fleet of aircraft, which are currently flying, or the generator set situated in on an oilrig.
The monitoring systems provides us with the freedom of knowing what our system is doing, how well it is doing it and will help predict how it will react next time we run it.
Rolls-Royce is improving its capability continuously to improve its monitoring capability and providing its customers with a higher level of in-service support
The achieving procedures are collected from Rolls Royce as follows:
Engine health management
Rolls Royce uses Engine Health Management (EHM) to track the health of thousands of engines operating worldwide, using onboard sensors and live satellite feeds.
A corporate EHM team covers Civil, Defense, Marine and Energy which enables the Group to develop technologies and best practice across all business sectors. In the Civil market for example, the Trent family of engines is supported by a comprehensive Rolls-Royce EHM capability operated in conjunction with Optimized Systems and Solutions (OSyS), a Rolls-Royce company, and accessible as appropriate by the airlines involved.
EHM is a pro-active technique for predicting when something might go wrong and averting a potential threat before it has a chance to develop into a real problem. It is especially useful in industries such as aerospace where the results of a technical failure could prove very costly. EHM covers the assessment of an engine's state of health in real time or post-flight and how the data is used reflects the nature of the relevant service contracts. Essentially, EHM is about making more informed decisions regarding operating an engine fleet through acting on the best information available.
The evolution of EHM and the revolution in its use has significantly reduced costs by preventing or delaying maintenance, as well as flagging potentially costly technical problems. New assets will incorporate EHM capability, and techniques will, where possible, be retrofitted to existing equipment. Broader engineering disciplines can benefit from the growing reservoir of supporting data. As operational profiles of technical performance are revealed in ever more detail – from individual components to whole engines – so engineers can develop more thorough and cost-effective maintenance schedules, and designers can feed higher reliability features into the engine products of the future.
Sense
EHM uses a range of sensors strategically positioned throughout the engine to record key technical parameters several times each flight. The EHM sensors in aero engines monitor numerous critical engine characteristics such as temperatures, pressures, speeds, flows and vibration levels to ensure they are within known tolerances and to highlight when they are not. In the most extreme cases air crew could be contacted, but far more often the action will lie with the operator's own maintenance personnel or a Rolls-Royce service representative in the field to manage a special service inspection.
The Trent engine can be fitted permanently with about 25 sensors. The figure below shows the typical parameters measured for EHM. 

Figure: showing different sensor areas and parts of an engine from where information collected
Many of these are multi-purpose as they are used to control the engine and provide indication of engine operation to the pilot as well as being used by the EHM system. These are selected to make the system as flexible as possible.
The main engine parameters – shaft speeds and turbine gas temperature (TGT) – are used to give a clear view of the overall health of the engine. A number of pressure and temperature sensors are fitted through the gas path of the engine to enable the performance of each of the main modules (including the fan, the intermediate and high pressure compressors, and the high, intermediate and low pressure turbines) to be calculated. These sensors are fitted between each module, except where the temperature is too high for reliable measurements to be made.
Vibration sensors provide valuable information on the condition of all the rotating components. An electric magnetic chip detector is fitted to trap any debris in the oil system that may be caused by unusual wear to bearings or gears. Other sensors are used to assess the health of the fuel system (pump, metering valve, filter); the oil system (pump and filter); the cooling air system and the nacelle ventilation (nacelle is the cover housing – separate from the fuselage that holds engines, fuel, or equipment on aircraft). As engine operation can vary significantly between flights (due to day temperature or pilot selection of reduced thrust), data from the aircraft to provide thrust setting, ambient conditions and bleed extraction status is also used.
Acquire
Most modern large civil aircraft use an Aircraft Condition Monitoring System (ACMS) to acquire the data for EHM. This captures three types of reports:
The first are snapshots, where the sensor data listed above is captured and collected into a small report. This is carried out during take-off, during climb and once the aircraft is in cruise.
The second type is triggered by unusual engine conditions. Examples might be if an engine exceeded its TGT (Turbine Gas Temperature) limits during a take-off. These reports contain a short time-history of key parameters to enable rapid and effective trouble-shooting of the problem.
The final type is a summary, which is produced at the end of the flight. This captures information such as maximum conditions experienced during the flight, and power reductions selected during take-off and climb.
The Trent 900 is the first engine to be fitted with a dedicated Engine Monitoring Unit as well as the ACMS. This engine-mounted system places a powerful signal processing and analysis capability onto the engine. A fan -mounted EMU is shown below:

Figure: A fan -mounted engine monitoring unit (EMU).
This is used to look in more detail at the vibration spectrum, which helps to pick up problems with bearings or rotating components. It also provides a flexible computing platform so new EHM software can be rapidly deployed to detect specific problems.
Transfer
A critical aspect of the EHM system is the transfer of data from aircraft to ground. Aircraft Communications Addressing and Reporting System (ACARS) digital data-link systems are used as the primary method of communication. This transmits the Aircraft Condition Monitoring System (ACMS ) reports via a VHF radio or satellite link whilst the aircraft is in-flight.
A worldwide ground network then transfers this data to the intended destination. The positive aspect of this system is its robust nature and ability to distribute information worldwide. On the other hand, the Airplane Condition Monitoring Function (ACMF) reports are limited to 3kB, hence the acquisition systems need to work within this limitation. Future systems are being deployed to increase data volumes through wireless data transmission as the aircraft approaches the gate after landing. This will enable more data to be analysed, but will not be as immediate as ACARS, where data can be assessed well before the aircraft lands again.
In the Defence business, the transfer of data is controlled by the service requirement. Some EHM data requires a rapid in-theatre response; some, such as fleet trends, has a more long-term aspect. Some of the longer-term information can wait until the engines return to the UK, although Rolls-Royce can still provide 24/7 support through a combination of deployed service engineers and the Operations Centre in Bristol.

Analyze
As soon as the individual reports arrive at the specialist EHM analysts - OSyS (Optimized Systems & Solutions) they are processed automatically. The data is checked for validity and corrections applied to normalize them. The snapshot data is always 'trended', so that subtle changes in condition from one flight to another can be detected. Automated algorithms based on neural networks are used to do this, and multiple sensor information is fused to provide the most sensitive detection capability.
When abnormal behavior is detected, this is confirmed by an OSyS analyst based in the Operations Centre, before being sent to the aircraft operator and logged by the Rolls-Royce Technical Help Desk. Manual oversight is still an important part of the process, as false alerts can cause unnecessary maintenance actions to be taken by airlines and these need to be avoided. Trended data, and data from the other types of ACMS report, are also uploaded onto the Rolls-Royce Aero manager website, so that plane operators can easily view the health of their fleet of engines.
Act
The EHM signature will typically highlight a change in an engine characteristic. Expert knowledge is then used to turn this symptom into a diagnosis and usually a prognosis. This is done by using the skills of Rolls-Royce engineers working with the OSyS analysts, to assess the most likely physical cause of a particular signature, how an operator can confirm this and how urgently this needs to be carried out. For an engine that is showing gradual deterioration, for example, an inspection in several weeks time may be appropriate.
If a step change in performance has been observed, inspection within the next 2-3 flights might be recommended. The Technical Help desk will discuss the recommendations with the operator (to manage the best fit with their planned operation) and will then regularly liaise with them until the problem is understood and any risk to their service mitigated.
http://www.rolls-royce.com/about/technology/systems_tech/monitoring_systems.jsp








Reference/ Sources:
http://en.wikipedia.org/wiki/Flight_recorder
http://www.skybrary.aero/index.php/Flight_Data_Recorder_(FDR)
Tooley, Mike; Tooley, Michael H. (2007). Aircraft digital electronic and computer systems: principles, operation and maintenance. Butterworth-Heinemann. pp. 75–76. ISBN 978-0-7506-8138-4.
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM,Page-329,330
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM,page-330,332
http://www.rolls-royce.com/about/technology/systems_tech/monitoring_systems.jsp
Unit title: Aircraft Electrical System (84)
Assignment title: Function and operation of Aircraft Electronic System
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