Whether you fly an airliner or a jet fighter, the optimum word in safety is "avoidance." Avoid hitting the ground and avoid hitting other aircraft.
Today’s military aircraft operate in an environment that differs little from the one in which commercial aircraft fly. Not surprisingly, therefore, the U.S. military has mandated that all of its aircraft carrying troops, passengers or cargo, or used for refueling, join their commercial brethren by adopting the latest in accident avoidance avionics. These are the traffic alert and collision avoidance system (TCAS) and the ground proximity warning system (GPWS).
Ground prox has existed for some 30 years; TCAS made its debut more than 10 years ago. Both systems provide aural warnings and coordinated flight commands to military pilots in the event of an air- or ground-collision threat. Both also have evolved to enhanced performance, hence the letter "E" has been added to the acronyms.
The U.S. Department of Defense (DoD) has committed to install ETCAS and EGPWS (now commonly called TAWS, or terrain avoidance and warning system) in no fewer than 1,500 aircraft. More than 600 retrofitted aircraft have been fielded. Non-U.S. militaries plan for these systems’ installation, as well.
What no doubt accelerated these safety programs in the United States were two tragic accidents: one in Yugoslavia that took the life of U.S. Commerce Secretary Ron Brown in April 1996, and a critical, high-level C-130 mission accident near Jackson Hole, Wyo., on Aug. 17, 1996. DoD reacted by requiring the equippage of fourth generation TAWS and ETCAS by the end of 2005.
"The benefit of TAWS in the military is the same as for any commercial user, to avoid CFIT [controlled flight into terrain] situations," says Harvey Pekich, Honeywell’s business and military manager for EGPWS. Studies show a preponderance of military CFIT accidents occurring near terminal (air base) flight areas.
Avoiding Mil-Spec
The U.S. military has allowed the ETCAS and TAWS programs to migrate away from mil-standard procedures and toward commercial off-the-shelf (COTS) acquisition. According to Pekich, the U.S. Air Force discovered the need to centralize procurement contracts for the safety systems within the Indefinite Development, Indefinite Quantity (IDIQ) program managed by the service’s Electronic Systems Division. This program enables the service to order COTS on an "as needed" basis. The U.S. Navy and Army also utilize the IDIQ program to procure TAWS and TCAS.
According to Tony Codispodi, Honeywell’s manager of TCAS business development, the military traffic avoidance system marries the ARINC TCAS II and the military identification friend or foe (IFF) transponder with Mode S to provide aircrews with continuous TCAS and IFF simultaneously. The ETCAS display is night-vision goggle (NVG) compatible.
ETCAS for the military was designed to provide an extended surveillance range and to coordinate formation and rendezvous missions, in addition to standard TCAS operations. The FAA has granted ETCAS the frequency approvals necessary to ensure smooth integration into military operations and prevent frequency overlap with commercial operations.
Standard TCAS scans up to 20 nautical miles (nm) on each side and 15 nm aft of an aircraft. ETCAS will survey up to 40 nm, with an azimuth coverage (scanning around the forward, sides, and aft of the aircraft) of 360�. Also, standard TCAS will survey only to 8,700 feet (2,650 meters) above and below the aircraft, while ETCAS increases that limit to 12,700 feet (3,870 meters).
The additional accommodation for formation flying is unique in that it allows air traffic control to see only the lead aircraft. "Technically, this will allow as many military aircraft in a formation as necessary. This capability is not designed for use by high performance combat aircraft, [but] only transports and refueling aircraft," Codispoti says.
The formation and rendezvous enhancement is possible due to a capability on the flight deck to select or deselect a 4096 code, or Mode A transponder. For any specific military mission, by deselecting the code on all aircraft in the formation, except the lead, the ATC clutter will, thereby, be reduced to a single aircraft.
Within the next 18 months, the automatic dependent surveillance-broadcast (ADS-B) feature will be added to military ETCAS by enhancing the existing software. The demonstration will be conducted by Honeywell and will take place at the Aircraft Tankers Association meeting the first week in November. Air Force officers will be on location to observe the demo.
The Air Force and the Navy selected Honeywell as the ETCAS prime contractor for their transport aircraft fleet, with the exception of the C-5, which will be fitted with the L-3 (formerly Honeywell) TCAS 2000.
Beyond ADS-B, Honeywell is researching low-level tactical flights to "assist special operations aircraft involved in dynamic flight planning and rerouting," according to Catherine Griffin, the lead for the company’s commercial-to-government business development. "This technology started more than 10 years ago with the Air Force’s Quiet Night program," she adds.
Quiet Night technology consisted of early color displays of renderings showing distinctions in the terrain–a form of early digital mapping and flight management technology. The dynamic flight planning and rerouting in the system under development is created by combining the latest ETCAS and EGPWS technology, enabling low-level night insertion with full terrain-following features that can be changed "on the fly" by special operations pilots.
"Quiet Night is based on utilizing early forms of avoidance technology to avoid possible threats," says Griffin. Current research blends Quiet Night and the latest ETCAS and EGPWS technologies. The intent is to "optimize tactical mission planning techniques by creating an avionics system for low-level night insertion with full terrain following features," he adds.
Meanwhile, at Rockwell Collins, Bob Gabel, the company’s director of marketing for integrated applications-government systems, says that while Collins does not produce ETCAS, it does provide systems integration for the military, including that of ETCAS and TAWS with weather warning systems.
Rockwell Collins’ focus is on the overall Global Air Traffic Management (GATM) requirements now being implemented by the military. The TCAS 2000 will be part of GATM for the C-5. GATM programs on Air Force C-17s and KC-135s will be achieved by integrating the Honeywell ETCAS and TAWS. The C-130 program is also a priority target for GATM upgrades.
The Military View
Within the Air Force, the Air Mobility Command (AMC) directs not only the safety surveillance systems upgrade, but the much broader Global Air Traffic Management program, which includes such technologies as Ground and Traffic Collision Avoidance, Global Navigation Satellite System (GNSS), ADS-B and improved displays called human computer interfaces (HCIs).
AMC has dictated strict, implementation time limits to include 2003 for the enhanced TCAS and 2005 for the fourth generation GPWS. Earlier versions of GPWS are on nearly every passenger/cargo aircraft in the fleet. The same is true of Navy aircraft in the same category. COTS products supporting the safety systems upgrade and the GATM program are listed in the Global Air Traffic Office (GATO) catalogue produced by the Air Force’s Electronic Systems Division. Contract management is through the IDIQ program.
"We’re continually in contact with our sister services, in particular the Navy, interfacing on available GATM technology," says Don Hartman, the Air Force Laboratory’s chief of electronic sensors. He says AMC’s relationship with the supplier community also is strong. "After all, the commercial avionics suppliers drive this technology."
Looking into the future, Hartman claims, "We’re looking to be digitally capable in all areas. The end result is to tighten up navigational accuracy across the entire fleet."
The Air Force also is interested in predictive windshear technology. Honeywell recently received an FAA Technical Standard Order (TSO) for a predictive wind-shear system (RDR-4B).
Navy Schedule
The U.S. Navy mandated installation of ETCAS and EGPWS just over a year ago. The service’s mandate is for three levels of aircraft, by priority: new and remanufactured aircraft, then passenger and troop carrying aircraft, and finally all other aircraft. The safety systems’ fleet-wide installation is "scheduled to be completed in 2004," says Ann Newsome, Naval Air Systems Command’s (NAVAIR’s) deputy program manager for flight safety systems.
The EGPWS and ETCAS retrofit programs are being worked concurrently to ease strain on the fleet. It takes one month to complete both retrofits on an aircraft. The only modification to the current EGPWS is to enable aircraft carrier landings without the system issuing a false warning. Also, a mission switch has been installed to desensitize EGPWS dampening nuisance warnings. The safety systems are all Honeywell based, while the displays are Rockwell Collins products.
The Air Force and Navy haven’t forgotten their fighter fleets; both have programs that will rely upon digital, 3-D database systems. BAE Systems produces the Air Force system, TERPROM (for terrain navigation and ground proximity), which actually has been installed on some F-16s and is being studied for use on bombers and other high performance aircraft.
"We are also looking at TERPROM for the C-17 and C-130 fleet," says Hartman. "Those aircraft are ‘fly anywhere, land anywhere’ aircraft and demand an upgraded database map system."
The Navy companion program, TAMMAC (tactical aircraft moving map capability), is a Honeywell product, not yet funded. TAMMAC generates a 3-D digital map and is a replacement for moving map displays on older fighters in the Navy inventory. The program has been accepted as the baseline digital map system for the F-18 E/F. Installation is scheduled to begin before the end of the year on Lot 23 (the batch number) and retrofitted to Lots 21 and 22 of the Super Hornet.
The tactically viable TAWS system would also be added to other platforms, including the AV-8B Harrier and legacy helicopters. Bill Wescoe, NAVAIR’s deputy program manager for EGPWS, says, "Those installations could progress in the next couple of years. We’ve identified aircraft with nine of the 12 worst safety records for the retrofit program…[I]n all, PAMMAC could be installed on no less than 3,500 naval aircraft."
TAWS is being installed in the new C-17 and C-130J (see Avionics Magazine, July 2000) programs. The retrofit program includes: KC-135/KC-10 refueling, C-141/C-5 heavy lift transports, C-130 medium lift transport, E-4 airborne command post, C-2 Navy COD and VP/UP-3, C-9 medical evacuation, C-40 replacement 737 for the C-9, several general aviation personal transports, and all VIP passenger transports. Offshore programs include: Danish C-130, British Nimrod, Dutch G-IV, Spanish CASA CN-295 medium transport, CASA/IPTN CN 235, and Alitalia/Lockheed Martin C-27J.
The Air Force’s TAWS retrofit programs (along with their potential numbers) include: C-130 (550), C-141 (90), C-17 (70), KC-10 (60) and KC-135 (600). The Navy’s TAWS retrofit installation will total 140 aircraft, including the C-2, C-130 and VP/UP-3.
Two future international programs also are looking at ETCAS, including the UK’s Future Large Aircraft (FLA) and Airbus’ A400M. ETCAS can be upgraded to meet virtually all future military communications and navigation requirements.