My publications

Data Communication Standards Used In Avionics Applications: An Overview

(Published in International Aviation Symposium Proceedings held at SNIST in April 2009)

Abstract: The modern aircraft of today is equipped with different types of systems and subsystems which control all the major and minor aspects of flight right from take-off, cruise, landing and even mission management in case of fighter aircrafts. The equipments on board are capable of giving enormous amount of data to the flight crew and to the various systems controlling the various aspect of the flight. In order to accomplish the task this data needs to be transferred from one system to another system in a proper and speedy manner. This job is done with the help of data communication buses. These buses are the conductive path which provides a channel for data transfer between different systems and subsystems. But these communication buses are needed to be standardised. Standardisation is required to ensure interoperability, commonality, reliability, compatibility with logistics and various other factors so that an user does not face any problem during usage of the system. In order to standardise these buses various organizations like ARINC (Aeronautical Radio Incorporated) and US Department of Defence have published different communication standards for defence as well as civilian and space application purposes. In this paper an overview of some of the communication standards used for defence and military avionics applications has been discussed.  

Keywords: Interoperability, LAN, Ethernet, Manchester coding, Time Division Multiplexing.

THE DATA COMMUNICATION BUS: AN INTRODUCTION

A data communication bus is a channel for transferring data from one system to other. It ensures fast data transfer and fixed capacitive loading. A data communication bus for interconnecting a desired number of subsystems consists of an integrated circuit having a bus conductor of desired length and fixed number of ports for connecting the subsystems. Each port comprises of control and data terminals for a group of driver/receiver circuits. Each driver/receiver circuit is connected to a bus conductor. Each driver/receiver circuit consists of a driver circuit having address and data output latches and driver gates. The receiver circuit has address and data input latches. The buses make up the path over which information is transferred between different subsystems. The bus itself is just a conductor. The subsystems interface with each other through the bus with the help of an established communication protocol. This arrangement allows incorporation of additional subsystems. But as each subsystem is added, it results in the slowing down of the data transmission speed of the bus.

AVIONICS DATA BUSES

In an aircraft flying at an altitude of 35000 feet carrying a few hundred passengers or an aircraft which has been deployed for a combat mission, reliability is most important characteristics of any equipment or component onboard. So an avionics data bust must be fault tolerant, deterministic in behaviour and must have an option for redundancy. Most of the avionics buses are serial in nature. A serial bus using only a few sets of wire keeps the point to point wiring and weight down to minimum.

        The baseline operation of a bus is established by the avionics protocol and the capability limits are set by the data bus interface architecture. The capability and ease of use for the bus varies from application to application even if the same protocol is used. So while choosing a bus for a specific application the following points should be taken into consideration:-

• Host interface
• Number of channels and protocols
• Host involvement in protocol processing
• Host interaction with data
• Special features such as monitoring and time injecting
• Processing power available for the protocol and user application
• Hardware and software development tools and support
• Development and production cost

In the following sections of this paper we will be discussing about some of the widely used communication standards used for defence as well as civil avionics applications.

MIL-STD 1553

Military Standard (MIL-STD) 1553 is a serial data communication bus developed by the United States Department of Defence in the year 1973. The standard was first used in F-16 fighter jets. Now it is used by all branches of US military and has also been adopted by NATO. The standard provides an integrated, centralized system control and a standard interface for all equipments connected to the bus. The standard defines function of a serial data communication bus that interconnects multiple devices with the help of twisted shielded pair of wires. MIL-STD 1553 is referred as ‘1553’ with suffix A or B. The basic difference between 1553A and 1553B is that in the case of 1553B there is greater co-ordination between the hardware and the software. This is because the items in 1553b are already predefined. Thus the manufacturer need not develop a new design of hardware and software for every new application. The primary goal of 1553B is to provide flexibility without creating a new design for each new user. This has been accomplished by specifying the electrical interfaces explicitly so that compatibility between designs by different manufacturers can be assured. A single bus consists of a wire pair with an impedance of 75-80 ohms at a frequency of 1MHz. The transmitters and receivers are coupled to the bus using isolation transformers. This reduces the possibility of short circuits and ensures that the bus does not conduct current through the body of the aircraft. A Manchester code is used to represent data and clock on the same pair of wire and to eliminate DC component present on the signal. The data transmission rate (bit rate) is 1Mbps. The combined accuracy and long term stability of the bit rate is 0.1%. The peak-peak output voltage of a transmitter is 18-27V. The bus can be made doubly or triply redundant by using several independent pair of wires and then connecting all the devices to all the buses. There is also a provision to incorporate a new bus control computer in the case of failure of the current master controller.

In MIL-STD 1553 Manchester-II biphase type of data encoding is used.

• Logic one (1) is transmitted as a bipolar coded signal 1/0 i.e. a positive pulse followed by a negative pulse
• Logic zero (0) is transmitted as a bipolar coded signal 0/1 i.e. a negative pulse followed by a positive pulse.

A transition through zero occurs at the mid point of each bit, whether the rate is logic zero (0) or logic one (1).

  

MIL-STD 1553 is a Time-Division Command/Response multiplexed data bus. Multiplexing facilitates the transmission of information along the data flow. It also permits transmission of several signal sources through one communication system. Multiplexing also helps in reducing weight, increasing simplicity, flexibility and standardization.

                         Information is transferred through MIL-STD 1553 in the from of words. A word is in this case is a sequence of 20 bits- 3 bits time sync pattern, 16 bit data and 1 bit for parity check. The 1553 terminals add the sync and the parity bits at the time of transmission and remove it at the time of reception of information. There are three types of words namely command word, status word and the data.

Information transfer in the case of 1553 is of three types:-

• Bus controller to remote terminal transfer
• Remote terminal to bus controller transfer
• Remote terminal to remote terminal transfer

The typical transmission range of Mil-STD 1553 is 400ft (122m). In order to increase the range an extender system is used. The bus extender system enables log distance communication by use of specified media and compliant equipment while confirming to all 1553 specifications. The bus network can also insert simulated or table-driven data address to any bus controller or remote terminal/support area network combination.

ARINC 429

ARINC 429 is an avionics data bus standard widely used in the high-end commercial and transport aircrafts. ARINC 429 defines the physical and electrical interface of a two wire data bus and a data protocol to support the aircraft’s avionics local area network. ARINC 429 is application specific in nature. It uses a unidirectional data bus standard i.e. transmitter and receiver are connected to different ports. This standard is also known as Mark 33 Digital Information Transfer System (DITS). The connection is made with a twisted pair of wire. It also provides point to point wiring which ensures high reliability of data transmission. A transmitter can communicate with maximum of 20 receivers on a single wire pair. Each receiver continuously monitors for data applicable to it but it does not send any acknowledgement on reception of data. A transmitter requires acknowledgement from receiver when large amount of data has been transmitted. This handshaking is done using a particular word style. When this type of two way communication format is required two twisted pairs constituting two channels are necessary to carry information back and forth, one for each direction. ARINC 429 allows self clocking at the receiver side thus eliminating the requirement of transmitting a clocking signal. In case of ARINC 429, a word is of 32 bits of which 24 bits contain the actual data and the remaining 8 bits describe the data. The detailed description of the word format is as follows:-

·Bit number 1-8 contain the label and is expressed in octal format. They identify the type of data.

·Bits 9 and 10 are Source/Destination Identifier (SDI). These bits indicate the source of origination of the data and to where it is going.

·Bits 11-29 contain the actual data. They can either be in Binary Coded Decimal (BCD) or two’s compliment format.

·Bits 30 and 31 are the Sign/Status Matrix (SSM) and indicate whether the data in the word is valid.

·Bit number 32 is the parity check bit and is used for verifying that the word was not damaged during transmission.

ARINC 429 uses several physical, electrical and protocol techniques to minimize the radio and electrical interference from on board radio and other transmission cables. The transmission bus media uses a 78W shielded twisted pair of cable for preventing interferences. The shield is grounded at each end and at all junctions along the bus. The transmitting source output impedance should be maintained at 75W with a tolerance of 5W. The receiving sink must have an input impedance of minimum 8kW.

    ARINC 429 specifies two speeds for data transmission. Low speed operation is at 12.5 KHz with an allowable range of 12-14.5 Kbps. High speed operation is at 100 Kbps with a allowable tolerance of 1%. These two data rates cannot be used on the same transmission bus. Data is transmitted in a bipolar return-to- zero format. It is a tri-state modulation consisting of high, null and low states. Transmission voltages are measured across the output terminals of the source. Voltages present across receiver input is dependent on line length, stub configuration and the number of receivers connected. The following voltage levels indicate the three allowable states:-

• A high signal (1) is achieved with transmission signal going from null to + 10V for first half of the bit cycle and then again returning to zero or null.

• A low or zero (0) signal is produced by the signal dropping from null to -10V for the first half of the bit cycle and then returning to zero.

With a return to zero modulation format each bit cycle time ends with the signal level at 0V thus creating a self clocking signal and eliminating the need for an external clock.

     

SWITCHED ETHERNET

Avionics Full Duplexer Switched Ethernet (AFDX) is a data network for safety critical applications. It uses dedicated bandwidth while providing Quality of Service. AFDX is based on IEEE 802.3 Ethernet technology and uses commercial off the shelf components. The AFDX takes the Ethernet technology and by using switched Ethernet in full duplex mode forms a deterministic packet delivery and high integrity and high availability mechanism. In the Ethernet standard one physical layer describes the use of two pairs of wires to be used for transmitting and receiving. In one of the modes of operation called Carrier Sense Multiple Access with Collision Detection (CSMA/CD) each of the end systems monitor it’s receive port for knowing whether something has been transmitted or not. Prior to transmission such indications are used to avoid interfering with the ongoing transmission. During a transmission, any indication of another transmission indicates a collision which results in corrupted communication.

             The central points of an AFDX network are its virtual links.  Virtual links are unidirectional logic path from source end system to all the destination end system. Unlike the traditional Ethernet switch which routes packets based on Ethernet destination AFDX routes packets using a virtual link ID. The virtual link ID is a 16 bit unsigned integer which comes after the 32 bit field. The switches are designed to route an incoming frame from only one end system to a predetermined set of end systems. There can be more than one receiving end systems connected within each virtual link. Each virtual link is allocated dedicated bandwidth with the total amount of bandwidth defined by system integrator. There are sub-virtual links as well which are designed to carry less critical data. Sub-virtual links are assigned to a particular virtual link. Data is read in a round robin sequence among the virtual links with data to transmit. One problem with the sub-virtual links is that it does not provide guaranteed bandwidth or latency. Each switch can support up to 4096 virtual links. Thus in a network with multiple switches cascaded the total number of virtual links are limitless. There is no specified limit for the number of virtual links that can be handled by an end system but the number of sub-virtual links that can be created in a virtual link is limited to four.

       The deterministic aspect of AFDX is implemented by the architecture of the LAN configuration of the given aircraft. The controlled traffic that flows through the virtual links and the bounded transit time through the end systems and switches allows determining the maximum latency between the sender and the receiver. This allows the minimum bandwidth usage over any small interval of time. Traffic shaping is implemented in the end system and a policing function is implemented in the switch in order to maintain the deterministic delivery of message frames across the LAN. The integrity of each packet is checked using a cyclic redundancy check which is verified at the destination. The high availability aspect of AFDX is implemented by redundant switches and parallel connection to those switches. Each network has one or more AFDX switches. A failure, either in hardware, protocol or software, will cause the network to become disabled. All messages are transmitted to both the networks. Each receiving end-system implements a policy of accepting the first valid copy of any message. By implementing this policy in the end-system the application software is relieved of any responsibility for dealing with the redundancy in the network.

AFDX has been implemented in the Airbus A380, military A400M as well as the Boeing 787 Dreamliner. In the A380, the AFDX backbone is connected to 23 major functions with about 120 subscribers. The advantages of using AFDX are that it reduces the weight considerably and provides simpler configuration management. The new A350XWB also will use this technology.

CONCLUSION

 ARINC, Department of Defence of various countries and other organizations are working continuously to publish new data communication standards for avionics applications in civil, defence and space sector. We have come a long way from the days of using simple electrical cables for data transmission which added considerably to the weight of the aircraft to the era of digital communication wherein data communication is taking place by means of buses whose specifications are being governed by various standards. The older standards are being modified according to the present needs.  Be it a MIL- STD or an ARINC standard, they all have the same aim of ensuring flexibility, reliability and interoperability so that these communication channels can be used with all types of systems in a fail proof manner to ensure proper functioning of the various systems and sub-systems thus enhancing factors like dependability and safety by many folds.

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AUTOMATIC DEPENDENT SURVEILLANCE-BROADCAST (ADS-B)

–       AN ULTIMATE CONCEPT IN MODERN NAVIGATION

(Published in AeSI newsletter in August 2010)

Automatic Dependent Surveillance-Broadcast (ADS-B) is a brand new technology that is redefining the paradigm of communication, navigation and surveillance in Air Traffic Management (ATM). ADS-B allows pilots and air traffic controllers to see and control aircrafts with much more precision over far greater percentage of Earth’s surface than it was possible earlier using Radars.  The technique has been developed as a part of the global CNS/ATM plan. The successful implementation of this new technology has resulted in many ground systems providing advanced platforms suitable for Air Traffic Management system based on the use of data link and satellite technology.

          

The main objective of air navigation service providers for implementing this new technology is to increase the level of safety and efficiency of the global aviation industry in a cost effective manner. 

The working principle of ADS-B is very simple. Contrary to radar which detects the presence of a target (aircraft) by sending a high power RF signal in space and then receiving the signal which has bounced back from the target, ADS-B uses Global Navigation Satellite System (GLONASS) technology and a simple broadcast communication link as its fundamental components. ADS-B uses an ordinary GLONASS (such as GPS) receiver to derive an aircraft’s precise position from the GLONASS constellation and then combines that information with any number of other information such as speed, heading, altitude, flight number etc. This information is then simultaneously broadcasted to other ADS-B equipped aircrafts, ADS-B ground stations as well as Air Traffic Control centers. The ADS-B data is broadcasted every half-a-second on 1090MHz digital data link.

An ADS-B system will consist of the following functional entities:-

• A transmitting subsystem which consists of message generation and transmission functions at the source, eg. aircraft
• A communication protocol, eg VDL mode 2 or 4, 1090 MHz ES  
• A receiving subsystem that includes message reception and report assembly functions at the receiving end eg. other aircraft, vehicles or ground station

There are many advantages when ADS-B is used.  ADS-B is relatively inexpensive technology than radar and costs only a fraction for the equivalent radar coverage. The ADS-B power requirements are also miniscule compared to radars thus enabling installation of ground stations in the most remote areas. In addition to this the ADS-B accuracy does not degrade with range, atmospheric conditions and target altitude. The information update interval does not depend on the rotational speed and reliability of the mechanical antennas like radar.

In case of conventional surveillance system, the ability of the ground station to detect a target depends on the altitude of the target, distance from the site and surrounding terrain. In case of ADS-B it is not so and with the use of this technology the coverage area of each ground station can increase by 250 nautical miles (450km) and it will also facilitate more efficient near the surface surveillance.

Some other major advantages of ADS-B are as follows:-

• Enhanced visual approaches
• Closely spaced parallel approaches
• Reduced spacing on final approach
• Reduced aircraft separations
• Enhanced operations in high altitude airspace for the incremental evolution of the     "free flight" concept
• Surface operations in lower visibility conditions
• Near visual meteorological conditions (VMC) capacities throughout the airspace in almost all weather conditions 
• Improved ATC services in non-radar airspace.

 One major application of ADS-B is going to be collection of weather data. Presently the cockpit crew gets the weather data from the on board weather radar system and on some occasions from the Air Traffic Control. The ADS-B is developed in such a manner that it acquires weather related information from the satellites and ground based meteorological stations. So it may be possible in future to eliminate the need of an on board weather radar system thus enabling the reduction of the aircraft payload. 

        ADS-B is still in a developmental stage. Like every other technology it has its own advantages and disadvantages. But with proper usage of this upcoming technology Air Traffic Management can be much more effective and the global airspace can become a much safer and secure place to fly in. 

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Evolution of Cockpits- An avionics perspective

(Published in quarterly journal of Honeywell, Bangalore)

Abstract: In this paper, evolution of cockpits has been discussed from avionics point of view. The paper talks about cockpits in the days, when aircrafts were just an experiment to the present day state of the art airliners. The paper discusses about the use of various technologies in cockpit instrumentation through different eras of aeroplanes, the involvement of ergonomics (Human Factors )in the design of cockpits and the entry of electronics into the flight deck facilitating reduction in pilot workload, better human machine interface and more work friendly environment

Keywords- Semi-Glass cockpit, Glass cockpit, Reversionary mechanism, Flight deck, ECAM, EICAS. 

Cockpit is the area at the front of the aircraft from where the flight crew controls the aircraft. Cockpit is also referred to as flight deck by some. Cockpit is the workstation of the flight crew. It contains all the flight instruments and controls which enables the flight crew to fly the aircraft.

The term cockpit was first used in the year 1914. In an aircraft, cockpit is the most flight and mission critical area. If anything goes wrong in the cockpit, the safety and security of the whole aircraft can get compromised. Thus one can see that every aircraft manufacturer is spending lots and lots of money in designing a more comfortable and easily comprehendible working environment inside the cockpit. Their main aim is to present the flight crew with a workspace wherein they can work for long hours without getting fatigued.

The plane flown by Wright brothers didn’t have a cockpit at all. But as aero planes started evolving from a mere experiment to a mode of transportation and later a war machine, cockpits started becoming a significant part of the aircraft. The first aircraft with an enclosed cockpit was The Grand built by Igor Sikorsky in 1913. The early passenger and fighter aircrafts had open cockpits. Aircrafts with enclosed cockpits became prevalent in the middle of 1920s. By 1950 open cockpit concept had become extinct.

     The very primitive cockpits had very few flight instruments and controls. The bi-plane of World War-I had a control yoke for controlling the pitch and roll and a pair of rudder pedals. The flight instruments in the cockpits of that era were very basic such as the engine rpm meter, the fuel indicator, heading indicator, artificial horizon etc. All these instruments were mechanical in nature. 

In 1937 the Royal Air Force introduced the Basic-T configuration of instrument layout in the cockpit. The basic-T configuration consists of four basic flight instruments namely the Attitude Director Indicator (ADI), airspeed indicator, pressure altimeter and the heading indicator. Apart from these instruments the other instruments placed on the instrument panel were the Vertical Speed Indicator (VSI) and the turn and bank indicator along with some gauges which indicated engine parameters and associated information such as engine rpm, oil temperature, fuel quantity etc.

After the introduction of the basic-T configuration and addition of engine instruments, cockpits became an environment full of gauges and dials. Cockpits of that era looked like this:

One can very well understand the complex environment in which the flight crew had to work. All the gauges and meters looked almost alike and all the information was presented to the flight crew at the same time. This resulted in availability of more information at a time than the flight crew could properly assimilate. As a result the probability of the flight crew overlooking some information which requires their immediate attention was very high. In order to avoid this, the flight crew had to be very attentive and alert at all times. Thus the job used to be very stressful and demanding. 

   With advancement in electronics and associated technologies in late 1970s came the advent of semi-glass cockpit concept. This type of cockpit uses CRT display technology and electro-mechanical gauges for indicating various flight parameters on the flight deck. At the onset, this concept was used only in military aircrafts. The peculiarity of the aviation industry is such that whenever a new concept evolves, it is first used in the military aircrafts. If the concept delivers well with the defense sector then only it is introduced in the less demanding civilian sector, the reason being that when it comes to civil aviation, safety gets more importance than technological advancements.

              Till late 1970s commercial aircrafts had cockpit with electro-mechanical gauges. The reason was that the concept of using CRT displays in the cockpits was relatively new and neither the aircraft manufacturers nor the civilian operators were ready to take it. 

In 1982 Boeing launched 757, the first commercial airliner to be equipped with a semi-glass cockpit.

As can be seen in the picture, this cockpit has electronic displays (CRT) as well as electro-mechanical gauges for indicating flight information. The electronic displays are called EFIS 40/50 system. EFIS stands for Electronic Flight Instrument System and the 40/50 are the dimensions of the outboard and centrally located screens respectively in inches. 40 denote the screen size to be 4 inches and 50 denotes 5 inches. The outboard screens in front of the Captain and the First Officer display the Attitude Director Indicator (ADI) and the Horizontal Situation Indicator (HSI). Since these are electronic displays thus these two units are know as Electronic Attitude Director Indicator (EADI) and Electronic Horizontal Situation Indicator (EHSI). The centrally located screens indicate parameters related to the engine and aircraft performance. They are the first instruments in the genre of integrated avionics. In addition, each pilot also has a Control and Display Unit (CDU) located on the central panel. The CDU helps the pilots in selecting flight plan, initializing navigational aids and control other instruments. The semi glass cockpit layout made the flight deck much more compact and tidier than the older cockpits. Now the information available to the flight crew was much better organized and easy to read and comprehend as a result reducing the crew workload and making the work environment less demanding.

          The latest concept in cockpit instrumentation is the glass cockpit. This concept was introduced in the market by Airbus Industries in its narrow bodied airliner A-320 in the year 1988. After A-320 all modern airliners followed suit with implementation of glass cockpit. Even older aircrafts like Boeing 747s were upgraded to glass cockpits in their later variants. Glass cockpit concept uses fully electronic displays (CRT or LCD) for cockpit instrumentation. This facilitates high level of automation, system integration, better user interface and most importantly lesser work load for the flight crew. A glass cockpit consists of 6-8 electronic displays which display all the flight information.

Glass cockpit concept consists of the following displays:-

•      Primary Flight Display (PFD)
•      Multi Function Display (MFD)
•      Electronic Centralized Aircraft Monitoring (ECAM) display or EICAS (Engine      Instruments and Crew Alerting System) in case of Boeing aircraft
•      Multi-purpose Control and Display Unit (MCDU)

The PFD is located outwardly in front of both the pilot seats. The PFD shows all the primary flight information such as airspeed, altitude, artificial horizon etc. The MFD is located inwardly in front of the pilot seats. MFD can be used for displaying any information ranging from the flight plan, traffic information, engine parameters or even the primary flight information. The ECAM or EICAS displays are used for indicating the engine and other aircraft related parameters and are located centrally on the cockpit instrument panel. The MCDU helps the flight crew in setting up various navigation, communication and guidance systems while on ground as well as in flight. One can say that the MCDU is sort of a mediator between the flight crew and the aircraft systems.

All the displays generated on the screen are software controlled. This enables interoperability of the display console i.e. a display console can be used as a PFD, MFD or ECAM display depending on the pin configuration by which it has been connected. This is a major boon from the maintenance point of view. For redundancy, glass cockpit employs a reversionary mechanism i.e. if a display console fails, the content of that display console can be displayed on another display console (except PFD). In glass cockpits the information presented to the pilots are managed by Display Management Computer (DMC). Thus the pilots are presented with information which are most relevant to that phase of flight or which require their immediate attention.

Cockpit is an interface between the flight crew and the aircraft yet the process adopted for designing cockpits is not standardized and varies from manufacturer to manufacturer. While flying, pilots perform many tasks simultaneously such as monitoring the various flight parameters, communicating with the Air Traffic Control and most importantly flying the aircraft safely. Thus designing of cockpit is very crucial. 

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Integrated Modular Avionics for Regional Jet Platforms– Beginning of a new era in Aviation

(Published in AeSI newsletter in March 2013)

Aviation has come a long way from the days of Wright brothers. Aviation today has evolved into an interdisciplinary field making use of advancements in the fields of mechanical, electronics, electrical and software engineering. Aviation over the years has also become more accessible to the masses.  Today, almost all major towns and cities on this planet are connected by air and people are opting for air travel more than ever before. This has given rise to a new vertical in aviation called Regional aviation and new genre of aircraft called Regional Transport Aircraft (RTA). RTAs are usually medium sized, single aisle aircraft designed for short duration flights.

In this article, we have discussed about a modern avionics architecture called Integrated Modular Avionics (IMA) and how its application in RTA can be beneficial to the aircraft operators. Integrated Modular Avionics (IMA) is a term used to describe a distributed real-time computer network aboard an aircraft. This network consists of a number of computing modules capable of supporting numerous applications of different  criticality levels.

Integrated Modular Avionics (IMA) is a newly adopted approach towards commercial and regional aircraft avionics architecture. Intent of IMA is to facilitate general purpose computers, called platforms. A platform does not perform any avionics functions itself but provides communication, computing and memory resources to the avionics software. In other words the avionics systems have software centric design and their features and capabilities do not rely upon hardware characteristics.

The platform has a generic processor hosting several system functionalities. The core software inside the platform (Operating System) provides the partioning of the functions that allows hosting of software belonging to different criticality level on the same hardware. The platforms are common digital modules with standard input/output interfaces. Data communication takes place via networks like AFDX (Avionics Full Duplex Switched Ethernet). All the data from sensors and other equipment are translated from/to the standard data network. The network is configured to route the information anywhere within the architecture, which facilitates easier system integration.

Each avionics computer has a standardized open system interface, called an Application Programmable Interface (API). Using ofAPIs like ARINC-653enables third party vendors to develop application for a given platform. This enhances competitiveness of both avionics platform and application suppliers in the market.

         

Partitioning is one of the significant features of IMA architecture that ensures fault containment and independence among applications sitting on the same hardware. IMA incorporates two types of partitioning namely Spatial partitioning and Temporal partitioning. Spatial partitioning (space based partitioning) ensures that an application is not able to intervene in the operation of other application hosted on the same hardware. Temporal partitioning (time based partitioning) ensures that each application on a given hardware uses the shared resources like (processor capability, input/output services) only to the extent demarcated for it. 

As stated earlier, a regional transport aircraft is designed for short duration flights. This means that a regional transport aircraft has to undergo more number of take-offs and landings in a day compared to an aircraft meant for long haul flights. It is also prudent to say that a regional transport aircraft carries more passengers in its lifetime than a long haul airliner. Also, these aircrafts need to be capable of undergoing pre-flight check in very short span of time so that they can be despatched for the next flight at the earliest. This can be ensured largely through easy and speedy checks and maintenance. IMA can contribute in a big way towards achieving this.

IMA facilitates use of general purpose computers that can host different applications. This means that an operator does not need to maintain an inventory of function specific hardware. In case of hardware failure, maintenance personnel can just replace the faulty hardware with another one and load the appropriate software on it. This flexibility can reduce the diversion rate of flights due to lack of maintenance facilities at certain airports. Even if a system fails due to software malfunction, it can just be re-booted in order to reset it. These features of IMA architecture can provide a lot of operational flexibility and save lot of money for the aircraft operators. It can also decrease the down time of an aircraft by significant amount. The figure below depicts the reduced maintenance cost of Airbus A-380 when compared with similar airplanes, due to use of IMA. 

Another way in which IMA can be advantageous to regional transport aircraft is weight reduction. IMA uses network based communication protocols like Arinc-664 (Avionics Full Duplexer Switched Ethernet) and centralised distribution systems like Data Concentrator Units for data transfer and interfacing of different avionics systems. This eliminates the need for kilometres of interconnecting wires inside the aircraft. Additionally, the hardware composition of IMA is totally different from conventional federated architecture. In IMA, the Line Replaceable Units (LRUs) are replaced by computing cards called Line Replaceable Modules (LRMs). Contrary to federated architecture, where a wire bundle runs in and out of every LRU, the LRMs fit into a box called the Integrated Avionics Cage (IAC). The IAC acts like the mother board of a personal computer facilitating interfacing of the avionics systems with the rest of the architecture, thus further reducing weight.

Integrated Modular Avionics (IMA),as described in ARINC 653, distributes functional modules into a robust configuration interconnected with a “virtual backplane” data communications network. Each avionics module’s function is defined in software compliant with theAPEX Application Program Interface. The Avionics Full Duplex Ethernet (AFDX)replaces the point-to-point connections used in earlier federated systems with“virtual links”. This network creates a command and data path between avionics modules with the software and network defining the active virtual links over an integrated physical network. In the event of failures, the software and network can perform complex reconfigurations very quickly, to ensure robustness.

Of late, the aerospace industry has been open to adopting better avionics architectures to take advantage of advances in computer engineering. The IMA concept helps to have fewer quantities of maintenance spares stored for each fleet at different places. During an aircraft’s service period, cost of modification, parts obsolescence mitigation and functional upgrades are very significant expenditures on the part of an airline Application of IMA can completely turn the tables around as far as these factors are concerned, thus bringing a significant change in the business and operational dynamics of Regional Transport Aircraft operators.

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Disclaimer: The contents of this page have been taken from technical papers authored/co-authored by me and published in different journals. In the course of making those papers, I have taken information from internet attributing appropriate sources. The sole intent of putting the content matter here is academic and no copy right infringement is intended.