GATM-izing Galaxy: New C-5 Avionics

By Charlotte Adams | February 1, 2004
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The U.S. Air Force plans to gut most of the analog electronics in its giant, 30-year-old C-5 Galaxy transports and install highly integrated, digital avionics. After that, there is a plan, still being matured, to install modern, commercially derived engines, full-authority digital engine controls (FADECs), updated fault monitoring and recording systems, and much else. With this avionics and propulsion overhaul, the service hopes the airplanes not only will hold their own in modernized, civil-controlled airspace, but exact a significantly lower outlay to operate and maintain.

Preserving the airplane's vast cargo capacity–roughly two C-17s' worth per C-5–is important. But the Galaxy is one of the most expensive aircraft to operate in the Air Force inventory. Their mission capability rate hovers at 60-odd percent, driven mainly by the aging powerplant. The two-part upgrade aims to lift the mission capability rate to better than 75 percent. Lockheed Martin, lead contractor for C-5 modernization, also claims the twin upgrades will reduce the Air Force's total ownership cost fleet-wide by 34 percent over the remaining life span.

The digital avionics to be installed in the C-5 Avionics Modernization Program (AMP) will enhance reliability only slightly but will lay the foundation for the major improvements that are expected in a follow-on Reliability Enhancement and Re-engining Program (RERP), says Dave Rycroft, chief engineer, strategic airlift, with Lockheed Martin Aeronautics. RERP has been funded as a development program. The Air Force plans to "RERP" two C-5Bs and one C-5A to verify the hoped-for performance and reliability boost. A production decision on the re-engining program is expected in FY2007.

If the service proceeds with the powerplant upgrade, the B models, used by the active forces, will be RERP'd first, a process that would not be completed until 2012. At that point, however, the average C-5A would be more than 40 years old–perhaps too old to justify a costly makeover. Air Force leaders would have to consider the changing C-5 role, ongoing C-5A "teardown" analyses, and (future) RERP field experience before making a decision on the C-5A. All of the upgraded aircraft will be designated C-5Ms.

On the other hand, new engines will be important to achieving air traffic management (ATM) compliance in areas where "you need to climb to a certain altitude within a certain time," says Col. Kevin Keck, C-5 development system manager at the Aeronautical Systems Center. The two sides of the modernization effort are connected, in that new engines will require new displays. But AMP's main purpose is to equip the aircraft to fly by the most direct routes, at the most advantageous altitudes–with the most efficient fuel usage and cargo loads–in civil airspace. AMP also provides an avionics architecture flexible enough to meet future communications, navigation, surveillance (CNS)/ATM requirements, which in the U.S. military, are filtered through the Global Air Traffic Management (GATM) program.

Key GATM avionics include:

  • Future Air Navigation System (FANS) data link,

  • Aeronautical operational communications (AOC) data link,

  • VHF com, 8.33-KHz spacing,

  • Multimode receiver (MMR) with protected ILS, VOR, microwave landing system (MLS) and marker beacon,

  • Dual, embedded inertial navigation system (INS)/GPS,

  • Identification, friend or foe (IFF)/Mode S transponder,

  • Traffic alert collision avoidance system II (TCAS II), Version 7, (added earlier),

  • Enhanced ground proximity warning system (EGPWS),

  • Backup air traffic control (ATC) data link printer, and

  • Versatile Integrated Avionics (VIA) system, with six primary "partitions" or applications, such as: flight management, com/nav/surveillance/identification (CNSI), com management, display services and all-weather flight control.

In addition, each C-5 will be fitted with an easier-to-fly glass cockpit. All told, in an AMP'd aircraft, 12,000 wires are removed and 4,000 are installed, a reliability improvement in itself, says Blair Marks, C-5 AMP program manager with Lockheed Martin Aeronautics.

New Capabilities

The new avionics systems will allow the aircraft to comply with reduced vertical separation minimum (RVSM) requirements as outlined by Advisory Circular (AC) -91-RVSM, says Rycroft. The airplane also will have an automatic dependent surveillance (ADS) 1A data link with a growth option for automatic dependent surveillance-broadcast (ADS-B). C-5 pilots will be able to fly AMP'd aircraft to required navigation performance (RNP) 4.0 en route with successive growth options of RNP 1.0 and 0.3 in the terminal area, Rycroft says. The aircraft also will have controller pilot data link communications (CPDLC) electronic messaging.

The C-5B models are now equipped with a flare-dispensing system, but only one C-5A version has countermeasures, says Keck. The Air Mobility Command recently identified self-protection as a high priority, but installation of such equipment is outside of the AMP baseline. The C-5 is a candidate aircraft for the Large Aircraft IR Countermeasures (LAIRCM) program, but no funding has yet been provided against that need.

Glass Cockpit

The most obvious part of the avionics upgrade is the new glass cockpit, with seven 6-by-8-inch color, flat-panel, multifunction display units (MFDUs) that integrate information from a large number of analog "steam gauges." Across the front panel are six displays–three for the pilot and three for the copilot. The flight engineer monitors the seventh display from a station in the rear cockpit.

The pilot's and copilot's secondary flight displays can present information on radio states, moving maps, weather radar, terrain, traffic–"any information you wish," says Joe Schwendeman, C-5 modernization program manager for Honeywell Defense and Space Electronics Systems, Lockheed's key avionics partner. Flight crewmen interact with the MFDUs via a cursor control device, although flight plan information is fed to the flight management system (FMS) through a traditional multifunction control and display unit (MCDU).

The crew can tailor the display presentations. Typically the center pair would show information such as cautions and warnings, engine data–such as turbine inlet temperature, speed, fuel flow–and built-in-test data.

A major benefit of the glass cockpit is increased situational awareness, says Keck. Crews like the ability to integrate a lot of the displays and overlay different views on a single display, he says. "You can toggle through your options easily," reducing workload.

The Heart of AMP

The heart of the avionics upgrade is Honeywell's Versatile Integrated Avionics architecture, which replaces nine or 10 black boxes in what previously was a highly federated architecture. (There are two VIAs, operating simultaneously, for redundancy. If the second VIA determines that the first is defective, the second takes over.) The VIA computer combines flight management, flight control, the management of the communications and navigation radios and the displays, com/nav/surveillance and identification processing, built-in-test monitoring, and mission integrity management, fault logging and bus control.

"The VIA architecture makes GATM compliance on a 30-year-old aircraft possible with a minimum number of LRUs [line replaceable units] because it has the maximum amount of flexibility," Schwendeman says. "The performance is all in the software and it can be changed–so you don't have to change the LRUs." Although weight savings wasn't the motivating factor for the choice, integrating the architecture saved 120 pounds (54.4 kg), Keck says.


The hardware risk of the VIA architecture is low. The hardware already has been certified on the Boeing 737-700 aircraft, the B717 and, as a retrofit, on FedEx Express' MD-10 fleet. VIA hardware also is used on the U.S. Navy's E-6 command and control aircraft and will be certified on KC-10 tankers. VIA repackages the Airplane Information Management System (AIMS) architecture originally certified on the B777.

Even in the software area, there is significant reuse. Honeywell's communications management function (CMF) software, which handles radio and data link operations, "is a direct port from a commercial application," Schwendeman says, referring to the Mark 2 com management module that Honeywell developed for the business/regional market. The FMS software, likewise, is based on Honeywell's commercial Pegasus technology and "the preponderance of software is identical" to that used in the KC-10 development program, Schwendeman says. Honeywell is bearing the cost for more than 95 percent of the applications code it is writing for VIA, which it is using on other programs.

Probably about 90 percent of the VIA software is based on prior Honeywell implementations and about 75 percent of the hardware is either directly off the shelf or derived from a commercial product, Schwendeman says. "The beauty of this acquisition is that there is very minimal hardware development cost paid for by the Air Force or Lockheed because we managed to make use of a maximum amount of our commercial product."

The AMP architecture specifies dual-redundant VIAs, plus a backup processor by BAE Systems. Each VIA includes two black boxes–the second known as the auxiliary interface unit–that operate as a single logical unit, a "virtual LRU." Not all of the software applications run on both boxes. The first box includes one processor, known as a core processing module (CPM), plus a currently unfilled growth slot, identified as CPM 2. (CPM 2 is slated to be added with the engine upgrade.) Each CPM is based on a commercial AMD 29050 processor. The second box contains another CPM, identified as CPM 3. Each 29050 has a throughput of 23 Vax MIPS (millions of instructions per second) and can be upgraded to about 40 Vax MIPS. The "backup integrating processor" by BAE is based on the company's design for the mission processor of the C-130J.

VIA Software

Key to VIA is Honeywell's time line concept, Schwendeman says. Honeywell's proprietary VIA operating system–backed up by hardware elements in the processing chips–ensures the separation of applications, or "partitions"–living on the same processor and the execution of each application's tasks in the processor at the correct time in the right place, as dictated by an overall schedule. That schedule determines the priority and frequency of each software task in the VIA system.

VIA hosts some 1.75 million lines of applications source code. This includes partitions written by Honeywell, Lockheed Aeronautics and Lockheed Systems Integration-Owego, but executed under Honeywell's operating system.

C-5 AMP includes four software iterations, each successive block of which adds features, functions and fixes to the base code. Initial work focused on the basic ability to aviate, navigate and communicate, says Marks.

The first chunk, block 1.1, focused on the digital flight control system, basic displays and basic airworthiness. Based on feedback from flight tests, changes were made and folded into the next software build. The second block, 1.2, contained a more refined autopilot, as well as FMS flight planning and lateral guidance, and all the flight control functions except vertical navigation (VNAV) and autoland.

The last two blocks, 2.1 and 2.2, focus more on the communications and navigation systems. Block 2.1 adds Category IIIa autoland, EGPWS, TCAS, weather radar and other functions. It contains full flight control functions, full CMF functions, and all FMS functions, except vertical guidance and performance calculations.

The final software increment adds VNAV, performance calculations, military radios, military flight planning and MLS. And it completes the functionality of all the major software applications. After the final software build has been flight-tested and a "block 2.2.1" has been created, there will be a four-week functional qualification test.


As of January, all of the applications software had been written, and the first two blocks had been flight-tested. Flight testing of the third block had begun and was expected to conclude by February of 2004. The final software block was in Lockheed's laboratory and was expected to enter flight test in March or April of 2004.

After flight test, the software will go into verification testing against the system specification requirements. Operational test and evaluation (OT&E) is to begin at the end of 2004 and culminate early in 2005.

"The risk is in software integration, and the risk is principally schedule-driven," Keck says. The first aircraft modifications will begin this summer, and AMP'd C-5s are to start reaching the field in January 2005. By that time, the Air Force expects to have completed verification activity, but OT&E still will be going on.

"We accept that kind of schedule risk, "Keck says, "and we believe that, with the verification activity being conducted this summer, the concurrency with our initial installs is manageable." While there's a "distinct likelihood" that fielded software will need to be tweaked, the phasing and sequencing of the installs was designed with that in mind.

In a project this big, integrating blocks of application code by multiple companies, and using algorithms and code developed on other programs, glitches are expected. The iterative software development process was designed to successively identify and correct these problems and feed in changes as the program proceeds. In Block 2.1 flight tests, for example, issues had to be addressed with the flight management and flight control functions. At press time, Honeywell had delivered a fix for the flight management problem, which was being readied for flight test.

Modernized Support for C -5

A key part of the U.S. Air Force's planned C-5 Reliability Enhancement and Re-engining Program (RERP) is to replace the airplanes' malfunction detection, analysis and recording system (MADARS). MADARS records and detects information such as built-in-test (BIT) failures and structural and engine exceedances.

The new embedded diagnostics system (EDS), a combination of hardware and software, is intended to "optimize [aircraft] availability and mean time to repair," says Lt. Col. Darrel Watsek, RERP program manager. "EDS not only records data but allows the continuous monitoring of aircraft systems,with readily available troubleshooting and diagnostics."

EDS interfaces with the propulsion, environmental, secondary power, mechanical, flight control, selected cockpit instrumentation, diagnostics, radar, communications and navigation systems. It is to record engine trend information, structural exceedances and flight data, among other things.

A subset of EDS will be hosted on Honeywell's Versatile Integrated Avionics (VIA) computer, the C-5's electronic brain. BIT data, evaluated largely at the subsystem level, is transferred to the VIA, which makes "high-level fault declarations."

Part of EDS, the auxiliary maintenance computer (AMC) will further processs fault data to pinpoint the cause of detected failures, Watsek explains. Developed by Demo Systems, the AMC is a relatively off-the-shelf computer, running the Windows operating system. The box is intended for ground-based maintenance, allowing technicians to see what faults have occurred during a flight, says Dave Rycroft, chief engineer, strategic airlift with Lockheed Martin Aeronautics. AMC acts as a "server" in relationship to "clients," such as VIA or other devices, Watsek says. It may, for example, be "requested" to route data for reports to printers or data links. The AMC also will host and manage a fault history database.

The U.S. Air Force's Air Mobility Command, meanwhile, is looking at data linking logistics trend information to the ground as an option for all of its mobility aircraft under the Mobility 2000 (M2K) concept. The C-5 will have the necessary pieces in place to make this possible, if the Air Force decides to do so.

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