An airline official once noted that "a major technological leap in weather radar is made about every 15 years." If so, now would appear to be the time that a major leap is taking place. Much improved processing power has opened the door to such innovations as automatic antenna tilting, data overlay, ground clutter removal and, overall, a more complete picture of storm activity up to 320 nautical miles (nm) in front of the aircraft.
Two manufacturers, Honeywell and Rockwell Collins, dominate the weather radar market in air transport. Another company, Telephonics, has manufactured many radars for the military market and now threatens to give Honeywell and Collins competition in the civil arena (see sidebar).
Both Honeywell and Collins are developing digital radar systems that, they claim, employ automatic antenna tilting to provide short-, medium- and long-range weather data with virtually no ground clutter. They do so, however, with quite different philosophies in weather radar design.
Honeywell Radar
Honeywell’s RDR-4B radar uses the company’s enhanced ground proximity warning system (EGPWS) to help control antenna tilt. Steve Hammack, Honeywell’s manager-technical marketing for radar, conjures a scenario to explain how this "AutoTilt" feature works.
"Let say you are flying north out of Denver," he begins. "You have mountains on the left and a flat plain on the right. Guided by the EGPWS worldwide terrain-elevation database, the radar [antenna] automatically adjusts to the contour of the terrain, eliminating ground clutter.
"We’ve divided the radar’s 180-degree scan into five segments, which look like slices in a pie," he adds. "The outer segments are each 45 degrees and the three, more critical segments in the center are each 30 degrees." During a sweep the antenna automatically makes tilt adjustments within each of the five segments, accounting for the various elevations of the terrain below. The RDR-4B also automatically adjusts for changes in the aircraft’s altitude.
Honeywell received Technical Standard Order (TSO) approval for its AutoTilt radar in April 2000 and gained Supplemental Type Certification (STC) for the system on a United Airlines Boeing 737 in June 2000. The first forward-fit AutoTilt radar was approved in a Singapore Airlines B777 in January 2002. Honeywell expected approval for a B757 installation for US Airways in April 2002. The radar’s approval in the A320 and A340 is expected in June and July, respectively.
The Phoenix-based manufacturer also is working on its next-generation radar, under development initially for American Airlines and also for the Airbus A380. It would incorporate uplinked weather information and use pulse compression to achieve greater range. For the A380, the radar would be integrated with EGPWS and a traffic alert collision avoidance system (TCAS) in a package called the Aircraft Environment Surveillance System.
Honeywell also plans to expand the windshear detection capability to provide enhanced turbulence detection in its RDR-4B and next-generation radar. "Windshear mode [on the radar] is only active when you are 2,300 feet above ground level [AGL] or below," says Hammack. "We want to use that capability at higher altitudes." With rainfall rates, radars normally "make approximations," he explains. "We want to use the windshear capability to make real calculations." Honeywell expects to have the enhanced turbulence detection software TSO’d in June 2002 and STC’d on its Convair 580 in July.
Further developments at Honeywell include the dual-redundant antenna drive, designed primarily for aircraft making long, transoceanic flights. With current, ARINC 708/708A radar designs, a single azimuth motor and single elevation motor are connected to two receiver/transmitters (R/Ts). If either motor fails, the radar goes down. Honeywell’s dual-redundant antenna drive includes two azimuth motors and two elevation motors.
For an airline that flies, say, 60,000 hours a year, the dual-redundant system can bring the number of in-flight losses of radar down from 19 annually to just 0.03, according to Hammack. TSO’d in August 2001, the system was designed to be a form, fit and function replacement; it requires no changes to the wiring, the R/Ts and the antenna mounting. A mod kit will be installed first in a Cathay Pacific aircraft via STC. The first forward fit delivery was scheduled for April for a Japan Air Lines B767.
Rockwell Collins
Rather than employing EGPWS-based automatic tilting, Rockwell Collins has developed its MultiScan radar for comprehensive weather detection. It plans to introduce a two-"beam" version of the radar in November 2002 (certified in a Boeing 747-400ER [extended range]) and a triple- beam version in 2004. The two-beam version will need only a software upgrade to become a triple-beam version.
Steve Paramore, radar marketing manager, explains how the triple-beam MultiScan radar works: "We take three scans. Each is held in computer memory, and we merge them into a single picture of all the weather ahead, and we use algorithms to eliminate the ground clutter."
"When the pilot selects ‘automatic,’ the radar [antenna] makes one sweep at one tilt angle and a second sweep at another tilt angle," he adds, explaining the multiple "beams." The Collins radar provides short-, medium- and long-range weather detection, as well as a top-to-bottom profile of a storm.
Also key to the MultiScan radar are the storage and merging of scan data to provide steady and consistent weather imagery and anti-clutter algorithms, for which Collins has four patents pending. With these algorithms, the center of the radar beam, which has the greatest energy for weather detection, can be lowered without concern for ground clutter. Lowering the beam provides a better long-range, over-the-horizon view of weather. If the beam is not lowered, the radar might overshoot a storm that is some 300 nm ahead and thus low on the horizon. Paramore admits that this feature may require some "rethinking" among pilots, as most air transport crewmen adjust their radars to ranges no greater than 160 nm.
A patent also is pending for Collins’ SmartScan feature, which provides rapid (faster than the usual four to eight seconds) weather updates when the aircraft is in a turn. The MultiScan radar also will employ "adaptive radar threshold techniques" (ARTT), which automatically adjust the radar scans when the aircraft enters a climb or descent during cruise.
Both Collins and Honeywell believe that clear air turbulence (CAT) is an elusive problem. "Sixty percent of clear air turbulence is not clear air turbulence; it’s the top of a storm," says Paramore. Likewise, Hammack believes, Honeywell’s enhanced turbulence detection of moisture in relatively dry areas could spot much of what crewmen believe is CAT. He adds that the airlines will have to determine the cost/benefit of true CAT detection, using either forward looking infrared (FLIR) or light detection and ranging (LIDAR) technologies, which can be costly solutions.
"We’ve looked at LIDAR and passive infrared," says Hammack. Paramore says Collins is conducting research in FLIR for clear air turbulence detection.
However, Paramore believes several features being developed for the Collins radar can eliminate much of the turbulence problem. One is "storm top prediction," which is being developed for the MultiScan radar system and uses Doppler to detect the rate of a thunderstorm’s growth or decay. "Storms can grow at a rate of 6,000 feet per minute," says Paramore. Using storm modeling, this feature predicts the location of a storm’s top and the turbulence bow wave above the storm within 40 nm of the aircraft. For its modeling database, he adds, Collins is collecting data of regional storm patterns.
To prevent an aircraft from inadvertently penetrating a storm top, Collins also is developing an "OverFlight Protection" feature. OverFlight Protection stores digital data from prior scans and compares it with the latest sweep information. It displays the stored data for any storm cell top that is within 5,000 feet of the aircraft. Collins’ radar will include "Enhanced" OverFlight Protection, providing the third, significant down tilt.
Paramore emphasizes that OverFlight Protection and Enhanced OverFlight Protection represent Collins’ "first line of defense against precipitation-based turbulence. We also will be adding Enhanced Turbulence as a sensor of last resort for turbulence avoidance."
Air transport carriers may encounter a bump or two while flying en route. But new technologies in weather radar appear set to smooth out the ride.
Telephonics: New Product, New Market
Watch Farmingdale, N.Y.-based Telephonics, the weather radar manufacturer that so far has focused on the military and paramilitary markets. Within two years, according to Joseph Battaglia, Telephonics’ president, the company hopes to enter the civil market with "a radar in the $20,000 range," either through product development or through an acquisition.
Current Telephonics radars cost considerably more than $20,000 because they must be ruggedized and protected against shock and corrosion for military use. For example, its radar has been selected for the U.S. Navy’s LAMPS III upgrade program, which places it in the punishing environment of helicopter anti-submarine warfare.
Some 80 percent of Telephonics’ radar business is with military customers, says Battaglia. The company has delivered about 8,500 units worldwide. These are Telephonics’ RDR-1400, which does not interface with "glass" cockpits; RDR-1600, which does interface with glass cockpits; and RDR-1500, which is like the 1400 model but also includes a search-and-rescue function.
Telephonics is about to introduce its RDR-1700, which is an "outgrowth" of the RDR-1500, says Battaglia. "It has an open architecture to interface with other systems," he adds. The RDR-1700 is being tested and prepared for TSO approval.
Companies
Aircraft Engineering & Installation www.aeisinc.com
ARNAV Systems www.arnav.com
AVCOM Avionics & Instruments www.avcom-avionics.com
Ballard Technology www.ballard.tech.com
Gables Engineering www.gableseng.com
IFR Systems www.ifrsys.com
Inertial Airline Services www.inertial.com
Meteorologics www.meteorologics.com
Pentar Avionics www.pentar.com
Rockwell Collins www.rockwellcollins.com
Satellink Technologies www.satellinktech.com
Teledyne Controls www.teledyne-controls.com
Telephonics Corp. www.telephonics.com
Universal Weather & Aviation www.univ-wea.com