Aging avionics and net-centric operations

Aging Avionics and Net .. Centric Operations

Ellis F. Hitt Strategic Systems Solutions

ABSTRACT

The transformation to net-centric operations necessitates evaluation of existing avionics capabilities, identification of deficiencies of these avionics for net-centric operations, and evaluation of alternative avionics that can provide the needed capabilities. The Global Information Grid (GIG) enables net-centric operations. The purpose of the GIG is to provide end users real-time or near-real-time access to multiple information sources ranging from airborne/satellite/ground sensors (video imagery and processed visual information/data) to databases. The end users in an aircraft view and interact with this information through the hUman system interface (HSI) or "smart" displays. The information is transmitted across a Gigabit Ethernet on-board the aircraft that interfaces with multiple channels of a software programmable radio that acts as a bub in the GIG network, or on-board sensors and processors. This paper presents the mandated capabilities, and the processes involved in determination of upgrades needed to achieve net·centric operations.

INTRODUCTION

Currently installed avionics are embedded in hardware and software architectures that started with the design of the aircraft and evolved as upgrades and new capabilities in terms of processor and display upgrades, sensors, and changes/ additions to payloads (passengers, cargo, weapons) carried by the aircraft were added. The majority of commercial aircraft use some form of the ARM 429 data bus while US military aircraft use the MIL-STD-1553 data bus. Due to address and capacity limitations, many military aircraft have anywhere from two to six dual redundant 1553 data buses as shown in Figure 1.

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IEEE A&E SYSTEMS MAGAZINE, DECEMBER 2005

During the life of the aircraft, the capabilities required to operate in the global airspace and perform the aircraft's mission have changed. As the aircraft aged, so did the avionics and the original suppliers may have gone out of business, or been acquired by another company that decided to discontinue support for the original avionics.

The owners/operators of existing aircraft must decide whether to invest in upgrading the aircraft's avionics to participate in net-centric operations, and continue operation in the global airspace, or pursue other alternatives such as being restricted in the types of missions that can be flown, and access to airspace. The operator could decide to acquire a new aircraft that has the avionics required for net-centric operations if the existing avionics upgrade needed is not affordable and the investment required cannot be recovered over the remaining life of the aircraft.

CAPABn.ITIES

Capabilities for US military aircraft are based on international, national, and commercial agreements and standards. Mandated capabilities are contained in the Joint Technical Architecture (JTA) [lJ. The avionics related mandates are in the section Weapon System Domain, Aviation Subdomain. The standards and guidelines were prepared by the Joint Aeronautical Commanders Group (JACG), Aviation Engineering Board (AEB), and Interoperability Sub-Board.

JTA AVIONICS FUNCTIONS

The following are the avionics functions specifically listed as having applicable standards:

• Communications

• Data Links

• NavigationlLanding Aids

• Identification Aids.

Each of these high level functions is broken down to sub-functions such as Global Positioning, which is further

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Fig. 1. Example of a Legacy MIL-STD·1553 Avionics Architecture

Fig. 2. Nodes in Net-Centric Operations

broken down into Global Air Traffic Management

Navigation. Mandated standards are called out for each level and sublevel of a function.

Other Sources of Required Capabilities In addition to those standards called out in the IT A, the

Federal Aviation Administration (FAA) and the Department of Defense (000) require conforming to documents such as the Master Navigation and Timing Plan [2]. This plan requires that the minimum performance standards for navigation equipment:

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. . . must conform with civil airspace required navigation performance (RNP) requirements.

prevent violation of civil air traffic clearances, and ensure safe separation of military and civil air traffic.

Table 1 summarizes many of the relevant capabilities required for net-centric operations.

The IT A navigation mandates and the requirements in the previous paragraph become the "yard stick" against which existing military navigation systems are measured to determine if they can provide the mandated capability. If the existing navigation system cannot provide the capability, the next step is to define alternatives that can provide the capability. These alternatives could include a modification to software, replacement of part of the system, or replacement of the complete system. The navigation system is impacted as new requirements are levied. For example. the decision was made that when the Joint Precision Approach and Landing System (JPALS) is installed in aircraft. the software will be embedded into the existing navigation computer. This necessitates an examination of the amount of memory required for the JP ALS software, the available memory in the navigation computer, and an assessment of the required processing on the overall data latency. Since the JPALS will provide output to the flight director and tie into the auto-land function, data latency on final approach cannot impact landing safety.


Table 1. Required Capabilities by Aircraft type

Table 1. Required Capabilities by Aircraft Type

The international decision to change the surveillancel identification friend or foe (IFF) (see the JT A WS.AV.2.4.I(a)) [I] function to gain addresses for more than 4,096 aircraft, and implement Mode S Elementary Surveillance (ELS), and Enhanced Surveillance (EHS) illustrates the impact of a mandate, on what was a stand-alone function, to the data flow involved in network centric operations. Existing IFF systems provide the aircraft identification and barometric pressure altitude when the transponder is interrogated. EHS requires the current aircraft state vector data from the navigation system, and hence connection to the data source, as well as multiple software changes on existing aircraft to ensure that the required information (current aircraft state with minimal data latency). in the correct format, is in the transponder when it is interrogated. An evaluation of the existing IFF systems reveals they must be replaced since they are not connected to the required data source nor can the existing systems be reprogrammed to respond to the Mode S interrogations. These interrogations may come from not only ground surveillance radars, but also from interrogators carried on other aircraft. As shown in Figure 2, aircraft are nodes in the net-centric operation of the surveillance function.

CAPABILITIES EV ALVA TION

Once the mandated capabilities have been collected, a capabilities evaluation must be performed on the existing installed avionics 'to determine if the mandates can be satisfied "as-is," jf a modification to the existing systems will provide


the mandated capability, or whether a major modification replacing one or more deficient systems is required.

The systems and architecture in Figure 1 will be used as an example of capabilities evaluation for net-centric operation. Evaluation of the architecture's capability to present high bandwidth information to the aircrew reveals that the present display architecture provides crew members limited selection of video imagery and processed visual information/data. The monochrome monitors have no processing capability with their input coming from either the display electronics or the ASQ-151 video distribution unit. The resolution of these monitors is less than that available on most laptop computer displays. If an XGA display (1024 horizontal and 768 vertical pixels) were to replace the existing monitor, a maximum visual resolution of 538 TV lines is available. If the input signal is band-limited to 20 MHz, the visual resolution drops down to 377 TV lines and it will not be possible for the crew member to view all of the detail present in the format. If the signal is band-limited further, the visual resolution on a single display will be even lower. The bandwidth of all devices in the video signal path must be considered in evaluation of existing capability and determination of the required capability. Further examination of the video path in Figure 1 required to provide the needed net-centric capability reveals other updates are needed. If the system were to be retrofitted with "smart displays" such as a tablet computer, or laptop, a standard digital video interface (DVI) should be used, which indicates the need to convert the existing sensors output to provide DVI that could be routed over a high bandwidth fiber optic LAN to a crew member that selects that source through the human system interface.

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Fig. 3. Example of Life-Cycle Cost Analysis

IDENTIFICATION AND EVALUATION OF ALTERNATIVES

Continuing with the Mode S example, information must be collected on alternatives that may be capable of meeting the mandates and also affordable . This requires information from potential suppliers on the physical size, weight, power, environmental system requirements, predicted failure rates, failure modes, fault tolerant design features, as well as production capability, development and acquisition costs, and logistics support scenarios.

CONSTRAINTS

The potential suppliers must be provided information on the present aircraft mechanical, electrical, and environmental system interfaces, and any other constraints that may impact installation and operation costs. These constraints may include existing wiring, data bus addresses used and available, and the memory and throughput available on computers that will play a role in formatting and routing information to the transponder. Electrical power required versus electrical power available may be a constraint since the connection to a power bus must consider the criticality of the identification function and the different electrical bus's capacity and aircraft electrical power system load management.

SYSTEMS ENGINEERING TASKS

The first task is to ascertain whether the functional system can provide the mandated performance capability. Performance of the alternatives needs to be evaluated to ensure that the system or component can provide the mandated capability. Performance assessment tools to be used depend on

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the function being evaluated. For example, the navigation system performance in terms of meeting the RNP can be determined through modeling and simulation to ascertain the navigation accuracy (95% of the flight time or any part of any single flight) for typical missions in the areas of the world where the RNP has been determined. Since the navigation system' s state vector is output through the transponder when interrogated, performance is quite important since the reported position needs to closely match the actual position. If it does not, the air traffic control system may not have high confidence in the actual aircraft track. Performance evaluation for identification is binary, i.e" the alternative meets the waveform, timing, etc., or it doesn't. If the alternative can

provide the required performance, the next step is to determine the cost of acquiring and installing an alternative.

Existing aircraft present the problem of getting the Mode S transponder connected to the existing antennas (top and bottom) which shOUld work since the Mode S system operates on the same frequencies as the existing IFF system. Perhaps the existing wire harness between the existing transponder and antennas will be usable and perhaps it will need replacing due to age or connector differences. It is certain that wiring changes will be needed to connect the Mode S Mode 5 transponder to the data source; i.e" a data bus connected through some routing to the navigation computer. Ideally, the data bus that the navigation computer is connected to as a remote terminal in a MIL-STD-1553 equipped aircraft would have a spare remote terminal address and connector, but that is seldom the case. Many of the existing IFF transponders (APX-64, APX-72. APX-IOO, and APX-IOl) and interrogators are not connected to an aircraft data bus.

Routing the required data to the transponder requires that each aircraft type's software and wiring be examined to detennine which data buses have a spare address in the

IEEE A&E SYSTEMS MAGAZlNE, DECEMBER 2005

MIL-STD-1553 equipped aircraft, and the data bus the navigation computer is connected to. If only a single aircraft type were involved, there would be no problem in switching transponders between aircraft tail numbers as long as the correct tail number was loaded when the transponder was removed from one aircraft and installed in another (assuming the connectors contained the same signal on each pin in each aircraft). Unfortunately, it is much more complicated when the fleet of aircraft is different types. If interchangeability is required to minimize transponder failure impact on aircraft availability, then all transponders should have a conunon set of connectors, and mapping of signals to pins, as well as common software to route the correctly formatted messages to the memory locations in the transponder that are read by the transmitter when an interrogation occurs.

Once the physical wiring has been designed, tested, and installed, other changes to existing systems and software will be needed to complete the routing of the required information. The bus controller software (perhaps for more than one bus) must be updated to route the transponder messages from the navigation computer through the appropriate set of buses and computers to the transponder while minimizing data latency.

Implementation of Mode S Mode 5 identification and its use in network centric operations impacts many systems and functions including communication and naVigation. If the navigation computer had enough memory for the PALS software, the engineers now have to revisit the memory and throughput available to determine if changes to the navigation computer are required to format the messages to be sent to the transponder.

If the navigation computer has sufficient memory and throughput to format the messages required by the transponder, the software engineering team responsible for the navigation computer has to develop the software documentation needed to initiate the design of the additional software. The DoD AIMS program office, working with other government agencies, specified the format of specific information such as Latitude and Longitude that will be transmitted from the transponder when it is interrogated with a Mode 5 code. For example. longitude is to be 19bits, two's complement with the MSB equal t o -180°. One problem is that one military aircraft had longitude encoded as 23 bits with units of semicircles while another had it encoded as 18 bits. ARINC 429 has longitude encoded as 20 bits BNR. The software engineering team will have to write code for the different navigation computers to translate the data from its current format to the required format if it is not in the correct format.

Assuming the software modifications and upgrades needed to get the information to the transponder have been determined, the analysts need to determine how much money will be required to implement these changes, as well as how long it will take to develop, verify, and validate the changes prior to putting the new capability into operation.

The human system interface with the Mode S Mode 5 capable system also needs to be developed and tested. There are various alternatives including dedicated control panels that


are derived from the legacy Mode C Mode 4 system that is being replaced, to implementation through the "smart display."

ECONOMIC VIABILITY

After all of the data is collected to permit evaluation of the alternatives' performance, development and acquisition, and operation and maintenance costs, one of two possible analysis approaches should be used to determine the alternative's economic viability. The traditional approach is to compare each alternative to the existing system in terms of total ownership cost. .The second approach is to determine the differential cost between alternatives, but not compare them to

the existing system baseline. This second method is easier to do, but it does not necessarily provide useful information on the total life cycle system cost savings, payback period, or return on investment. Decision makers need the information from the analysis comparing alternatives to a baseline in order to select the best alternative for funding and implementation.

For each alternative that can provide the mandated capability, estimates must be developed to determine the investment required by Fiscal Year until the system installation is completed in all aircraft that will receive the system. The investment includes both Research Development Test and Evaluation (RDTE) and Procurement funds. The cost elements are similar for both fund types and include:

• Group A kit (aircraft wiring modification and installation adapters)

• Group B (equipment to be installed)

• Software

• Integration and assembly

• Systems engineering and program management

• Systems test and qualification

• Training

• Data

• Technical/Change Orders

• Peculiar support equipment

• Spares

• Installation

• SimulatorfTrainer Updates/Replacement

• WarrantylInterim Contractor Support

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• Depot Support Equipment/Software.

In order to determine the Operating and Maintenance (O&M) costs for the baseline system, as well as the alternatives, it is necessary to arrive at a viable forecast of operating hours by year for the next 25 years. This is a function of the flying hours for the fleet of aircraft transformed into flying hours per aircraft for a fleet that is changing in terms of total quantities, multiplied by the number of aircraft in the fleet. The next step is to determine the ground operating time for the system in terms of hours per aircraft per year. This ground operating time is added to the flying time to determine the total operating time each year. From this information, and histOrical maintenance and supply transactions, the O&M cost for the baseline can be computed and forecast into future years.

During the installation time period, the O&M costs of the old system and the replacement system must be determined. This requires determining the number of old systems remaining in service and the total number of new systems in service each year.

It also requires determining how many maintenance actions and failures will occur each year for both the old system and the replacement system. The sum of these costs is allocated to the alternative for use in comparison to the baseline (even though the baseline (existing system) cannot provide the capability.

The yearly software and support equipment costs must be estimated for the baseline and alternative. If they are the same for the baseline and the alternative, the same value is added each year to the maintenance costs due to failures. If the software and support equipment costs are different, the value for the baseline is added to the baseline maintenance costs and the value for the alternative is added to the alternative's maintenance cost.

The final O&M cost element is the cost of the fuel for the baseline and alternative. This cost is a fUnction of the aircraft's fuel costs per pound of weight of the aircraft. Fuel consumption (gallons per flying hour), fuel cost ($ per gaUon), fuel density (lbs/gal), and average weight for the average sortie duration all contribute to the cost of fuel per pound of system weight. If the baseline and alternative have the same weight, the costs are the same for each. If the alternative weighs half the baseline cost, the fuel costs will be half that of the baseline each year.

The economic analysis for each alternative computes not ' only the yearly cost, but also the cumulative life-cycle cost (LeC) of the baseline and the alternative. The difference

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between the alternative and baseline's Lee is the net savings or additional cost (negative savings). The point that the savings balance the total LCC of the alternative is referred to as breakeven. The number of years from the start of the program to that time is the number of years to breakeven, which is 14 years for the linear trend as shown in Figure 3. This illustrates that historical data can be useful in forecasting future costs for different baselines. The traditional approach of using only the prior years costs indicate that breakeven would not occur in 25 years.

Return on investment (ROI) is determined by applying the Office of Management and Budget discount factors [3] to the cumulative investment and cumulative differential between the costs of the baseline and the alternative. The ROI is the discounted cumulative differential divided by the discounted cumulative investment.

CONCLUSIONS

The avionics installed in most aircraft that are older than three years are not net-centric capable. Many commercial and military aircraft will require modifications to upgrade to some degree of net-centric capability. The owners/operators of these aircraft must determine whether to invest in modifications to these existing aircraft, or acquire funding for new aircraft that would be net-centric capable. This paper presented a system engineering approach that begins with an avionics capability evaluation and concludes with a comparison of the total life-cycle costs of alternatives. The cash flow required to acquire, operate, and sustain these is used for comparison with the existing system's costs to determine the payback period, savings, and return on investment for alternatives that can provide the required capability.

REFERENCES

[I] Joint Technical Architecture, Volume 1,

Version 6.0,3 October 2003, Department of Defense.

[212000 CJCS Master Positioning, Navigation, and Timing Plan, CJCSI 6130.01 B,

15 June 2000, Joint Staff, Washington, DC.

[3] OMB CircuJar\A-94, Appendix C,

http://wwwl.whitehouse.govIWHlEOP/OMBIHTMUcircu!ars/

a0941a094.htrnl. A


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Aging avionics and net-centric operations