Military ATM: Meeting Civil Standards

As the civil air traffic management (ATM) infrastructure evolves to accommodate rapid traffic growth, military managers are rushing to meet changing coms, nav and surveillance (CNS)/ATM requirements. Otherwise, they risk penalties–from inefficient routings to denial of airspace.

Compliance involves Mode S-capable transponders, 8.33-KHz VHF radio channel spacing, and avionics for required navigation performance/area navigation (RNP/RNAV), reduced vertical separation minimum (RVSM) and automatic dependent surveillance (ADS).

"Modernization is important for the safety and economy of operation," says Paul Hogg, system chief engineer with the F-16 Systems Group of the Aeronautical Systems Center (ASC). As the airspace gets more crowded, "CNS/ATM initiatives attempt to better control the air traffic so our aircraft may fly safely, be efficiently handled at cluster points, and fly the most direct routes."

The Air Force and Navy began modernizing transport, tanker, VIP and utility aircraft first. Fighters, bombers and special mission aircraft were added to the list more recently, largely because of European mandates for VHF channel spacing and Mode S.

U.S./European talks have aimed at "equivalence," the use of equipment that is functionally equal, if not the same, as what is mandated. Eurocontrol welcomes this approach but insists on the deadlines.

The USAF and Navy both are well on the way to achieving 8.33-KHz spacing and are making good faith efforts to achieve Mode S. Soon-to-be retired aircraft, as well as trainers, which won’t fly in European airspace, will be exceptions.

Information Challenge

The Air Force’s Global Air Traffic Management (GATM) program helps acquire CNS/ATM gear for various aircraft.

Cargo carriers and tankers have been leading the pack since they’re more closely associated with the commercial carriers, says Lt. Col. Mike Harrington, GATM program chief. The program office assists Air Force units with their integration efforts. It also helps Air Mobility Command and Air Combat Command (ACC) determine the civil communications, navigation and surveillance capabilities that need to be integrated on their aircraft.

Harrington’s shop provides services to aircraft acquisition sustainment groups. This includes understanding regional, national and international standards in airspace requirements. "We extract the relevant data from each document source and collate it as concisely as possible into what we call performance matrices," he explains. The office has cataloged 34 of them, including 8.33-KHz spacing, Mode S, automatic dependent surveillance-broadcast (ADS-B), satcom and traffic alert collision avoidance (TCAS) systems. The matrices are tailored to different operational requirements for various airspaces.

Air Force units choose their own vendors or have them provided to varying degrees through Harrington’s office.

Harrington’s office also develops indefinite delivery/indefinite quantity contracts with commercial vendors to acquire commercial off-the-shelf (COTS) systems. "We also, in a sense, advertise to our primary customers–our Air Force acquisitions program groups–what we have … by system, by component."

Once a system has been integrated, the GATM office, as an independent organization, provides a functional, technical assessment of each capability. Experts analyze test data, "based on the requirements that we’d assisted each aircraft acquisitions group to develop," Harrington says.

Not surprisingly, there have been "little speed bumps and roadblocks," he says. But, for the most part, the unit has "done fairly well with the integration of capabilities," he asserts, especially with the larger aircraft. "We’ve done four assessments since 2003 for the KC-135."

The team also is finalizing a formal functional performance assessment of the first of potentially four planned upgrades to the E-3 command and control aircraft.

Eurocontrol

Two GATM contract engineers are working with Eurocontrol to define the testing and minimum operating performance standards for Mode S enhanced surveillance. "We’re often directly involved in influencing the development of those standards," Harrington says.

Unfortunately, however, the original timelines, especially for Mode S, were so near-term that the Air Force was unable to meet them. Now the schedule for Mode S has been stretched out to March 31, 2009.

The GATM office is working with Eurocontrol. "I don’t believe they will ever say, `we are going to deny your aircraft access to the airspace,’" Harrington says. But the agency has indicated that there potentially could be some delays or reroutings away from preferred routes and altitudes, "depending on the timing of a particular aircraft’s arrival into that airspace."

This is not expected to be overly burdensome. "Any time you experience in-flight changes, you’re just going to have to deal with them," he says. Of course this is not the ideal situation, as it can decrease military efficiency and effectiveness, he adds. "By putting the correct capabilities on the aircraft, we hope to avoid introducing additional `on-the-fly’ changes made to the mission plan." Harrington is excited by prospects for ADS-B. If FAA mandates ADS-B for the military and civil worlds as early as 2014, "that would be of huge importance to the U.S military," he says. The cost of integrating it into the ground and air infrastructure would be "very, very insignificant [compared with] the huge long-term gain out beyond 2030."

Tactical Aircraft

Fighter aircraft are affected, too. "Modernization is important for access to civil airspace worldwide," says USAF Col. Michael Holmes, chief of the Systems Support division in Air Combat Command’s Requirements Directorate. "Access is essential to mission accomplishment without ATC [air traffic control] delays. We foresee the ATC environment getting busier and busier."

The process has been a challenge, however. On the 8.33-KHz VHF radio initiative, Holmes recalls, "the Europeans initially stated that military aircraft need not comply if they primarily flew as operational air traffic and were equipped with UHF radios." F-15s were not previously equipped with VHF radios.

F-15 installations are now nearly complete, but the radios require modifications to add control features. ACC began considering this function for F-16s after Eurocontrol announced plans to tighten the requirement for military aircraft. The command also has requested funds to upgrade F-16s to 8.33-KHz spacing.

The USAF is equipping fighters for Mode S elementary surveillance, as well. Block 50 F-16s have been equipped with Mode S-capable identification-friend or foe (IFF) hardware and will be fully capable in FY08, with the addition of software. Installation of hardware on the Block 40 F-16s is slated to begin in late FY08. The F-15s should begin receiving Mode S-capable IFF transponders this year.

RVSM is a challenge, too. "Air Force Flight Test Center studies identified potential problems meeting the altimeter accuracy requirements of RVSM while carrying external stores," Holmes notes. In order for such aircraft to meet the accuracy standards, software source error corrections would have to be applied for each configuration operating in RVSM airspace. ACC considered developing a couple of corrections for "standard configurations," Holmes says. But impacts from the lack of RVSM equipment on the F-15s and F-16s "are not great enough to justify the expense."

RNP isn’t easy either. Fighters don’t carry the sophisticated flight management systems (FMS) and autopilots necessary to comply, Holmes says. ACC is reviewing its capabilities and future access requirements to determine what RNP level to equip the fleet to. However, neither Eurocontrol nor FAA has established a mandatory equipage date.

One of the attractions of RNP/RNAV is that it depends on performance rather than specific equipment. Holmes says: "We are examining both current capabilities and future airspace access requirements to determine the needed level of RNP/RNAV for legacy fighters. We have planned for the future implementation of ADS-B by requiring new Mode S IFF transponders to have a growth capability for ADS-B 1090 Extended Squitter."

For the F-16, ACC has focused on FM interference (FMI) and BRNAV/RNP-5. The F-16 Block 40/42/50/52 upgrade for selective availability anti-spoofing module/embedded GPS inertial system (SAASM/EGI), Hogg says, will make it easier to implement the navigation portions of the CNS/ATM that require GPS.

While Hogg acknowledges that Eurocontrol is the prime driver for U.S. military avionics upgrades, he anticipates FAA imperatives, too. "It is understood that eventually many of the CNS/ATM initiatives will also be required in U.S. airspace."

Navy Upgrades

Chris Hoover, the Navy’s CNS/ATM team lead at PMA 209, Air Combat Electronics, says the Naval Air Systems Command’s (NAVAIR’s) program focuses on 8.33-KHz channel spacing, Mode S, RNP/RNAV, and RVSM.

Hoover calls FMI "not really a capability but an improvement on a deficiency," dealing with ILS systems and FMI for radios’ coms control. "We’ve taken care of FMI for ILS systems for most of the platforms, and new radios being procured have FMI."

The goal for RNP/RNAV, he continues, was to "minimize surgery and downtime to the aircraft and go for RNP 0.3 with containment alerting, which encapsulates all the other RNP requirements, as well."

The P-3 and E2-C Hawkeye 2000–the only tactical naval aircraft without 8.33-KHz channel spacing–are being brought up to CNS/ATM standards. Beginning in FY07, P-3s will be upgraded for RNP/RNAV, channel spacing and Mode S. Because the P-3, C-2 and E-2C do not fly above FL290, they do not require RVSM capability.

As to Eurocontrol’s requirement for both elementary and enhanced Mode S (depending on aircraft performance requirements and platform characteristics), Hoover says, "Most NAVAIR platforms require enhanced surveillance, save for helicopters and fighters which can get by with elementary."

Now that the date for elementary and enhanced has shifted to March 2009, Hoover believes enough type/model series will be modified by then to "allow us to accommodate our missions in those airspaces that require Mode S."

The Navy also plans to leverage military avionics as much as possible to meet civil requirements. "We’re not putting two transponders or different navigation systems into the aircraft to accommodate civil and military requirements. We’re ensuring our solutions meet both civil and military capability requirements today and meet or support cost- and schedule-effective growth to civil and military requirements of the foreseeable future."

The F/A-18, for example, already has a combined interrogator/transponder that is being upgraded for Mode S. The Navy is integrating Mode S in the current block upgrade E/Fs.

"We surveyed all our avionics across the Navy to see if what was out there was upgradeable to meet the new civil inter-operability requirements," Hoover says. "Where they were able to grow … we’ve done so, such as [with] the embedded GPS/INS (EGIs) for RNP/RNAV."

Analog transponders like the APX-100s also are being replaced with existing APX-118s. "So we’re not developing anything new," says Hoover. The Navy is leveraging existing avionics and upgrading where necessary.

Upgrades to the EA6-B Prowler electronic countermeasures platform for Mode S should commence in late FY06/early FY07, Hoover says. The aircraft already has 8.33-KHz spacing.

The Navy is doing a good job in meeting civil interoperability requirements, says Hoover. "Our GPS solutions aren’t just going to meet RNP/RNAV in the civil requirements; they’re going to support our future military GPS requirements for NavWar and Joint Precision Approach and Landing System (JPALS)." The Navy’s Mode S architectures also will support not only civil requirements but future military IFF or surveillance requirements, he says.