Digital VHF technology marches forward at a steady pace. The Build 1 phase of the joint U.S. government/industry Controller Pilot Data Link Communications (CPDLC) program is scheduled to commence next month (September), employing VHF data link Mode 2 (VDL-2). American Airlines aircraft, equipped with Rockwell Collins radios compatible with VDL-2 and the aeronautical telecommunications network (ATN) protocol specification, are to enter flight trials in airspace controlled by the Miami air route traffic control center (ARTCC). American made the first revenue flight using VDL-2 in December 2001 in a new Boeing 757-200. Delta Air Lines plans to join American in the CPDLC trials, employing four Boeing 767-400s fitted with Teledyne Controls communications management units (CMUs) and Thales VHF digital radios.
Meanwhile, three industry teams recently submitted their proposals to the Federal Aviation Administration (FAA) to supply the ground segment of NEXCOM (Next generation air-to-ground VHF Communications), based on VHF data link Mode 3 (VDL-3). The NEXCOM program involves implementing digital VHF radios at 21 ARTCCs and three combined en-route radar approach facilities, supported by 1,513 remote communication air/ground facilities and backup emergency communication facilities. All are scheduled to be fully operational by September 2008. The FAA plans to select the supplier of the ground system in October.
Competitors for the NEXCOM ground segment are:
ITT with Northrop Grumman/Denro Systems, Northrop Grumman Systems and Information Technology, and Honeywell International;
Harris Corp. with Raytheon, Computer Sciences Corp., Lockheed Martin ATM, Rockwell Collins and Avidyne; and
General Dynamics, which declined to release the names of its team members.
The ground segment of NEXCOM calls for a radio interface unit (or router), integrated voice encoder, existing radio communication equipment, and telecommunication systems to accompany the about 37,000 programmable, multimode digital radios that ITT was contracted to provide, in July 2001. When the ITT radios are joined with the ground segment equipment, they will become VDL-3 capable. FAA also selected three companies on Feb. 20, 2002, to develop the airborne NEXCOM radios–Honeywell, Collins and Avidyne–completing the total hardware needs for the program.
NEXCOM’s allure is apparent. Over the past two decades, demands on VHF spectrum from air traffic services have grown by an average 4 percent annually. European authorities sought relief from the resulting signal congestion by subdividing the conventional 25-KHz VHF analog voice channel into three 8.33-KHz channels. FAA, however, believes NEXCOM/VDL-3, which can multiplex both digital voice and data communications on the same channel by using a time division multiple access (TDMA) algorithm, is a better solution. NEXCOM/VDL-3 would provide four channels to be employed at the radio user’s discretion, voice or data. Thus, some in industry foresee VDL-3 taking over VDL-2 for CPDLC.
NEXCOM/VDL-3 initially is to be used for voice communications, however. Digital voice operations are scheduled to begin in 2005 for use en route at high elevations.
But for now, the focus remains more on VDL-2, and both ARINC and SITA are converting their airborne communications addressing and reporting system (ACARS) ground stations to be VDL-2 capable. More than 20 years old, ACARS suffers from overuse.
ARINC has at least 50 ground stations equipped for VDL-2 in the United States and is installing nine stations in the Miami ARTCC (many in the Caribbean) for the CPDLC trials. SITA is focusing initially on upgrading its ACARS ground stations in Europe, "where [VHF communications] congestion is a major problem," according to Akhil Sharma, SITA’s manager of aircom service development. The company has converted 10 stations in Europe so far; it plans to make its more than 650 ACARS stations around the world VDL-2-capable by 2009.
ARINC’s VDL-2 transmitters are produced by Park Air Systems, a division of Northrop Grumman, while SITA transmitters are provided by Harris. Users, however, should find the two services comparable and the transfer from one service to the other seamless. At the Data Link Users Forum in San Francisco in late August, SITA and ARINC were to jointly announce their cooperation in streamlining the introduction of VDL-2, which, in part, means not duplicating test activities, according to Zibig Jasiukajc, SITA’s manager-avionics qualification and systems integration.
VHF in Mexico
Since October 2001, ARINC also has been upgrading its VHF air/ground domestic radio network to be digital. The conversion does not impact VHF voice operations (to pilots, it has been seamless), and airlines do not have to replace their radios. But the upgrade does make communications clearer, eliminating distortion and clicking sounds. And it positively impacts ARINC’s VHF operating costs by eliminating the need for expensive leased lines, which, in turn, has encouraged the company to consider expanding its voice service into Mexico. "We hope to open a test site there in several months," said Ron McGowan, ARINC’s voice services program manager in late August. He adds that the service in Mexico would require 12 ground stations. ARINC plans to complete the radio network upgrade in the United States by October.
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