Printed headline: U.S. Military Works on ADS-B Compliance
The operator of the world’s largest aircraft fleet will only partially comply with the FAA’s Jan. 1, 2020, mandate that all aircraft flying in U.S.-controlled airspace signal their position to the ground using automatic dependent surveillance-broadcast (ADS-B) “Out” avionics.
Roughly one-fifth of military aircraft operated by the U.S. Defense Department will be ADS-B-equipped by the compliance date, according to numbers released this summer by the U.S. Air Force, the lead service overseeing implementation.
The Air Force disclosed that 2,936 manned aircraft will be fitted with the necessary avionics as of the deadline. That number represents 21.5% of the 13,596 aircraft operated by the Air Force, Army, Navy, Marine Corps and Special Operations Command, according to Aviation Week’s Fleet Discovery Military.
The leading category of military aircraft that will be ADS-B-equipped are helicopters (1,129); followed by air mobility and transport aircraft (923); command-and-control/intelligence, surveillance and reconnaissance aircraft (259) and trainers (625), the Air Force says.
Since it published the final regulation for ADS-B Out performance requirements in May 2010, the FAA has acknowledged that some accommodations will be necessary for national defense missions. Last year, the FAA and the Pentagon signed an agreement that established “a broad framework of follow-on actions and milestones” the military services will follow to equip their fleets for ADS-B.
In the fiscal 2019 National Defense Authorization Act, Congress prevented the Transportation Department from enforcing the ADS-B requirement for fighters, bombers and special mission aircraft until the FAA and Pentagon reach agreement on how such types “will be reasonably accommodated” in the national airspace system.
To interact with the FAA’s nationwide network of ADS-B ground stations, aircraft flying above 18,000 ft. mean sea level in U.S.-controlled airspace require DO-260B standard Version 2 ADS-B Out systems, including the Mode S 1090-MHz Extended Squitter transponder and GPS Wide Area Augmentation System-capable position sensor.
The equipment set broadcasts the aircraft’s GPS-derived position, identity, vector, altitude and velocity once per second to air traffic controllers—the function called ADS-B Out.
“It’s a topic we’ve been spending a lot of time on lately,” says Marc Ayala, Collins Aerospace director of Air Force sales and business development. “The Defense Department seems to have recognized the problem going back several years but has struggled to get the funding associated with actually making the changes necessary.
“That’s been further hampered by the standard federal acquisition regulations,” he says. “We can’t go out and establish an STC [supplemental type certificate] for a military aircraft the way we could for a Challenger business jet or a Boeing 737.”
Modifying a military aircraft for ADS-B Out functionality depends on whether the aircraft is required to have an identification friend or foe (IFF) transponder and if the IFF is the primary transponder, says Ayala.
For most Air Force aircraft, the IFF is the Raytheon APX-119, which is provisioned for Mode S ADS-B Out functionality. Army and Navy aircraft are fitted with the BAE Systems APX-123 Common Transponder, an IFF system that also supports ADS-B Out broadcasts.
Military IFF transponders come with an “inhibit switch” that allows pilots to turn off ADS-B or other signals if necessary during a mission.
Commercial derivative aircraft can use civil-certified transponders to meet the ADS-B requirement, but they present a challenge for avionics suppliers, says Ayala.
“The interesting dilemma that this presents for us and other commercial providers is that the military services generally include a requirement that they want to be able to inhibit each of the different modes that the transponder is transmitting for security reasons,” says Ayala. “Our transponders don’t generally come with that capability, but for these specific applications we have some options that we offer to allow that to happen.”
The 923 air mobility and transport aircraft that will be equipped for ADS-B by January include C-5 Galaxy, C-17 Globemaster III, C-130J Super Hercules, KC-10 Extender and C-21 transports as part of ongoing updates, the Air Force says.
Collins Aerospace is participating in upgrade programs for the KC-10 and the KC-135 Stratotanker refueling aircraft. In August, L3Harris Technologies tapped the manufacturer to provide avionics for the nearly $500 million C-130H Avionics Modernization Program Increment 2 (AMP 2) program.
Collins initially installed its Flight2 integrated avionics system on the KC-135 as part of the Global Air Traffic Management program in 2000 and reports accomplishing several updates and refreshes since then. The tanker now is undergoing a Block 45 upgrade that installs a large-format engine instrument display in place of analog gauges, along with a new digital autopilot.
While ADS-B Out was not part of the original Block 45 program, the Air Force expected to start installing the capability on its fleet of 417 KC-135s in September. The service has taken over the modification line at its Oklahoma City Air Logistics Center and is performing the remainder of the installations with Air Force personnel.
Collins says it will integrate ADS-B with the Flight2 system on the KC-135 using the aircraft’s IFF transponder to broadcast position.
“Our system will interface with the various components—the GPS position source and some of the aircraft state data that gets fed into the [IFF transponder], basically the ‘electronic handshake’ for that box to work properly within the system,” explains Ayala.
In September, engineering contractor iAccess Technologies said it had nearly completed delivering ADS-B Out kits for 176 Air National Guard and Air Force Reserve C-130H Hercules turboprops under an AMP 1 contract awarded in 2017. The AMP 1 contract required that iAccess design, fabricate, integrate, install and test ADS-B Out and Enhanced Surveillance (EHS) functions on five Lockheed C-130H variants to meet civil airspace mandates. EHS is a variant of Mode S transponder protocol that enables a ground station to extract downlink aircraft parameters (DAP), a tracking function that can serve as a backup if GPS data is lost.
Main components of the kits iAccess is supplying include an upgraded Raytheon APX-119 IFF transponder, CMC Electronics GPS sensor and Mitchell GPS antenna for the ADS-B Out requirement. Shadin Avionics produces the EHS Bus Converter, which integrates with the aircraft’s navigation processor to provide DAPs, and an Altitude Management System for crew entry of parameters.
Trial kit installations were completed on four variants at Little Rock AFB, Arkansas. Flight tests required participation by multiple government agencies and were completed on budget and schedule, according to iAccess, which is based in Santa Ana, California, with a design center in Warner Robins, Georgia.
Installations will be performed at Air National Guard and Air Force Reserve locations in several states.
Collins will supply its Flight2 system on the same Air National Guard and Air Force Reserve C-130Hs under the follow-on AMP 2 program—a glass cockpit upgrade that will support ADS-B Out functionality. Work on that program will be centered at the L3Harris facility in Waco, Texas, and is expected to run through September 2029.