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Tuesday, February 1, 2005

Agusta Westland’s EH101

The EH101 is among a unique breed of helicopters that can be equipped specifically for the search and rescue mission. We look at the latest version of this medium-lift aircraft, destined for service in Denmark and Portugal.

David Jensen

Search and rescue (SAR) crewmen are a special breed. So are their aircraft.

Consider, for example, the U.S. Coast Guard crewmen who won the 2004 Rotor & Wing magazine Heroism Award. Over frigid Atlantic waters some 150 miles off North Carolina's coast, they rescued six sailors from a wrecked tanker. Choking from noxious fumes while their helicopter hovered over 3.2 million gallons of ethanol spewing from the ship, the crewmen, wearing night vision goggles, hoisted the sailors to safety in the dead of a February night.

And consider the Canadian Forces crewmen who, on a nine-hour mission, in 70-knot December winds and icing conditions, flew their helicopter to a Norwegian bulk carrier off Newfoundland's coast to transport a sailor who had sustained life-threatening injuries requiring hospital treatment.

Few individuals are prepared for such missions, and the number of helicopter types for SAR is equally finite. Dedicated SAR craft usually are medium-lift helicopters--large enough to bear emergency equipment, hoists, medical gear and rescue crewmen, as well as two pilots. They must be equipped to fly in darkness and all weather conditions, and to communicate with various entities in the air and on the ground. Among the three or four helicopters that fit this bill is the AgustaWestland EH101.

Of the 146 EH101s sold, 41 were ordered for the SAR mission. AgustaWestland has delivered 95 EH101s to date. Fifteen of the SAR variants belong to the Canadian Forces, which received the triple-engine helicopters in 2000 after they were self-deployed to Canada from AgustaWestland's Vergiate, Italy, plant, at least a 6,500-nautical mile (nm) flight.

The company's newest SAR customers are closer to home. The Portuguese Air Force (PAF) ordered 12 EH101s for search and rescue, as well as to help protect fishery and natural resources within Portugal's economic exclusion zone. The PAF accepted its first two aircraft in December 2004. And deliveries of the 14 EH101s ordered by the Royal Danish Air Force (RDAF) for SAR, troop transport and utility roles will commence in early 2005. The PAF and RDAF helicopters, which are comparable but have several distinct features, will be the most advanced SAR EH101s built so far.

AgustaWestland will enter comparable variants of the aircraft in a Japanese competition for SAR helicopters. Japan already has purchased 14 EH101s, three of which will be used to support missions in the Antarctic region and the remaining 11 for airborne countermeasures/amphibious missions. In addition, AgustaWestland has joined with Lockheed Martin (serving as the prime contractor) and Bell Helicopter Textron to enter the US101, a variant of the EH101, as a candidate for the U.S. Coast Guard's Deep Water program, as well as for the U.S. Marine Corps' VXX program for VIP/presidential transport. The US101 also is to be a contender in the U.S. Air Force's personnel recovery vehicle program, for which a request for proposals is expected this year.

All new EH101s come equipped with "glass" cockpits and fully integrated avionics suites designed to make missions such as search and rescue as easy for air crewmen as possible.

Color Displays

The Danish and Portuguese militaries will be the first to receive EH101s equipped with flat panel, active matrix liquid crystal displays (AMLCDs). Replacing the cathode ray tubes in the earlier variants, the six 6.3-by-6.3-inch color displays line up across the EH101 cockpit panel like paintings in a gallery. The two outside screens, which commonly serve as primary flight displays (PFDs), are slightly elevated to ensure optimum viewing by the crewmen.

Display maker Smiths Aerospace designates the EH101's electronic flight information system (EFIS) as the SDS 4010 and the individual screens as IDU (integrated display unit) 660s. Smiths also furnishes the integrated standby units for the new EH101s. For eight of the RDAF aircraft the company provides two 6.3-by-6.3-inch tactical displays for the operator's console in the starboard rear compartment, as well as other systems mentioned later.

Linked by an ARINC 429 bus system, the stand-alone displays can be reconfigured by the flight crew, and data can be transferred from one IDU to another. Each of the six ruggedized, night vision goggle-compatible, cockpit IDUs are "smart" displays. They contain their own commercial off-the-shelf (COTS) open GL (graphics language) graphics engine, COTS applications processor, and COTS video processor with dual video inputs. COTS was used to make the system more affordable and to get the best technology. The IDUs also include an input/output (I/O) processor. They receive ARINC 453 data and decode it for the applications processor and then for anti-aliased raster graphic generation.

EH101 crewmen can reconfigure the displays by using the multifunction keys surrounding each IDU on a bezel. The keys allow them to select map ranges and navigation sources, display mission video data, adjust datums and transfer sensor sources. The display modes--PFD, nav display, power systems display and fuel, etc.--can be summoned or swapped on the six IDUs through the display mode selector, a small black box located in the helicopter's center console. Much of the data--fuel quantity, pressures, torque readings, etc.--for the power system display derive from the full authority digital electronic control (FADEC) systems accompanying the EH101's three Rolls-Royce Turbomeca RTM-322 turboshaft en0gines.

The display interchangeability is allowed within predefined limits to ensure that essential flight data is always provided to the crew. Also, when displays are interchanged, the IDUs are to be viewed in pairs. For example, crewmen would interchange displays on the panel's two outside IDUs, which serve as a PFD and nav display, and would swap displays between the two center IDUs, which commonly present power formats and mission data.

The IDUs handle flight plan data and output from digital map generators that-- with a database sourced by customers according to national arrangements--can produce color map imagery. EH101 operators would input the map data, for example, via PCMCIA (personal computer memory) format cards, depending on the equipment specified, in a data input system.

The Smiths IDUs allow room for growth, with card slots available for, say, voice control or tactical processing. Drawing 140 watts, each 28-volt DC display has its own Eldec power supply, designed to Smiths requirements, and cooling fan.

Smiths developed the display formats in partnership with AgustaWestland. The display software was written in C++ to Level C of the DO-178B standard. Level A monitoring software is installed within the IDUs, ensuring that the data shown on the displays is consistent with the sensor data used to create the images.

Standby Displays

Smiths also produces the EH101's integrated standby instrument system (ISIS), comprising two 3-by-3-inch, 3-ATI liquid crystal displays. The LCDs are positioned to the extreme left and right of the cockpit panel. One is a smart display, while the other is a repeater unit, to save weight and cost. Replacing up to three analog instruments, ISIS provides the color display of attitude, altitude, airspeed and slip-skid.

For the Danish EH101s, Smiths also designed a video management system, which principally enables sensor video to be distributed to all the IDUs. It also provides a non-tactical data link function, enabling text messages and images to be sent and received via satcom.

Central to the EH101's integrated avionics suite are the duplex aircraft systems management computers (ASMCs). Italy's Galileo Avionica provides the ASMC's hardware and basic operating system, though all of the application flight software is specified, written and qualified within AgustaWestland. One computer serves as the master, while the other one remains in "hot standby" mode. Though not responsible for flight critical functions, the ASMCs do provide an interface for equipment and subsystem management, flight management functions, flight performance predictions and engine data.

The AFCS

What probably contributes most to making the SAR helicopter pilot's job easier in the EH101 is the digital automatic flight control system (AFCS), which includes both autopilot functions and automatic stabilization. The AFCS is linked to the flight management system (FMS), which provides area navigation and automatic search patterns, and prompts the helicopter's fully automated transition to and from a hover.

With the AFCS, the EH101 automatically maintains a steady hover, which is crucial when a hoist lowers a crewman (usually a swimmer) for a rescue. The AFCS controls height through a radar altimeter input and velocity through an input from the aircraft's Marconi Selnia Doppler velocity sensor.

The AFCS controls 4 axis: pitch, roll, yaw and collective, i.e., vertical motion created by a collective change in pitch angle of the main rotor blades. It reduces crew workload by automatically driving the electromechanical series and parallel actuators that, in turn, drive the rotor system hydraulics to accommodate the various modes of flight, as defined in the AFCS software.

The Smiths system is a dual-duplex AFCS, with two flight control computers, each with four dissimilar processors--two made by Motorola and two by Intel--to increase integrity. Smiths employed dissimilar processors and software code from multiple sources to make certain defects cannot make their way through the system without being detected by the built-in test functions.

To make the system fault-tolerant, the two flight control computers compare incoming data. Should a "miscomparison" occur, either the actuator drive system is transferred or the drive disengaged. The system will attempt to "vote out" the failed input, though where only dual inputs exist, the crew must make an arbitration.

The AFCS is partitioned into line replaceable units (LRUs), and an embedded operational flight program commands their interface, control and actuator drives. The LRUs include a pilot control unit (PCU), flight control computers, hover trim controller, and a dynamic sensor that supplements the available sensor data in the yaw axis to provide sensor redundancy. Each LRU also incorporates modules such as a central processing unit, power supply, conditioning units and I/O.

The software providing AFCS implementation is partitioned within the hardware architecture and segregated into higher- and lower-integrity software tasks. The AFCS, too, has monitoring software for safety.

To further enhance safety, Smiths took care with the AFCS human interface, which is through the PCU located in the center console. For example, the company created dedicated knobs to display the selected targets for hover height, radar height and airspeed. Each knob was designed to provide different tactile feedback, which can be detected even when the pilot wears gloves. Switches light up to indicate the appropriate action a pilot should take, and displays are color-coded: amber to provide a warning and green to confirm correct operation.

Nav/Com and Radar

For navigation the Danish and Portuguese EH101s are equipped with VOR/ILS, tactical air navigation (TACAN), and automatic direction finder (ADF). It has an embedded GPS/inertial (EGI) nav system, as well. The Danish aircraft is equipped with a VHF/UHF homing system and single-channel Inmarsat-based satellite communications (Aero-M satcom). These aircraft also are equipped with an emergency locator transmitter and underwater locator beacon in the unfortunate event of an emergency landing or ditching. Because of its large fuselage (more than 64 feet [19.5 meters] long) the EH101 can accommodate the numerous antennas associated with the SAR mission.

For its SAR and combat SAR missions, the PAF and RDAF aircraft also are equipped with a Chelton Group direction finder/personal locator system. It is based on an electronically steered antenna and includes decoding of the maritime VHF global maritime distress and safety system (GMDSS) and COSPAS/SARSAT emergency transmissions. For combat SAR missions, the direction finder can be used in conjunction with the personal locator system (PLS), developed by Chelton in cooperation with Cubic Corp. Working with the direction finder, the PLS enables voice communication with military-type personnel location beacons while providing range and bearing data to the beacon.

EH101 crewmen maintain contact through the cockpit/cabin communications system, with control panels in the cockpit and various locations in the cabin. It includes a wireless system, with headsets that don't require plug-ins, for the often-scrambling cabin crew. The EH101's cabin volume is large enough to accommodate a patient treatment area, including stowage and electrical supplies for medical equipment. There is space for an operator console that allows a cabin crewman to control the aircraft's radar and forward-looking infrared (FLIR) system, as well as maintain all necessary radio contact. And space is available for survivors and other equipment required for a multimission SAR helicopter.

The Danish EH101s are fitted with the Telephonics RDR-1600 search and weather avoidance radar, which includes five operation modes. With a 60-degree scan angle and 28-degree per second scan rate, the radar can detect beacons and surface targets, perform ground mapping, observe weather and give weather alerts. For precision landings--say, on an offshore oil platform--the radar contains a narrow-pulse mode, allowing a minimum detection range of 450 feet (137 meters). The radar display is presented on any of the IDUs, where the FMS navigation waypoints can be overlaid. The Portuguese EH101s are equipped with a belly-mounted radar that provides 360-degree surveillance capability.

Safety Equipment

Included in the navigation packages for the RDAF is a laser obstacle avoidance system produced by Marconi Selenia, a Finmecannica company in Italy. The system's eye-safe laser scans the area in front of the helicopter within a field of view that is 40 degrees horizontal by 30 degrees vertical.

With a 164-foot (50-meter) minimum range and 6,560-foot (2,000-meter) maximum range, the laser will create an "echo" from an obstacle that the system detects "through an analog process, comprising optical-electrical conversion, signal pre-amplification and threshold comparison," according Marconi Selenia literature.

A special software algorithm analyzes the detected echo and classifies it as either a vertical obstacle (tree, pole or pylon) or an extended obstacle (bridge, building or hill), or as the helicopter pilot's worst nightmare, a difficult-to-see wire. The current EH101 implementation uses a simple display panel to show the crew the relative bearing and time to go to the most significant obstacle threat; however, this can be expanded in the future to provide a video image of the detected scene. The company claims its obstacle avoidance system--which has Mil-Std-1553B electrical interface and uses a +28 volt DC, 300-watt power supply--provides 99.5 percent obstacle detection probability.

For terrain avoidance, the Danish EH101 also comes equipped with Honeywell's Mk 22 enhanced ground proximity warning system (EGPWS). The system uses a terrain elevation and obstacle database to output a display on a dedicated EGPWS screen on the instrument panel. Aural alerts warn crewmen of terrain/obstacle hazards. To further enhance safety, the EH101 is equipped with a traffic alert collision avoidance system (TCAS), identification friend or foe (IFF) and both voice and flight data recorders.

Both PAF and RDAF helicopters are equipped with health and usage monitoring systems (HUMS) to monitor engine and transmission use and conditions. And both aircraft are fitted with basic ice protection systems. The Danes, often operating above 54 degrees latitude, also have full rotor ice protection, thanks to an ice and snow detection systems (ISDS) made by Penny & Giles. The ISDS is an optical-based system that measures liquid water content.

Both the PAF and RDAF EH101s are fitted with nose-mounted FLIRs. In October 2002, AgustaWestland awarded FLIR Systems Inc. a contract valued at more than $10 million to supply 20 of its Star SAFIRE II thermal imaging systems for the two militaries. Deliveries began in February 2003 and were scheduled to be completed in early 2005.

The Royal Danish Air Force "takes a bit of pride" in the fact that they were the launch user of the initial Star SAFIRE design, according to Roelof Van der Spuy, FLIR Systems' director of original equipment manufacturer (OEM) airborne sales. The earlier design was installed on Denmark's S-61 and Lynx helicopters about 10 years ago.

The RDAF and PAF thermal imaging systems have a dual-control capability. The operator of the console in the starboard rear compartment can monitor various sensor displays, including one for the FLIR. However, the FLIR master switch is in the cockpit's center console, allowing the flight crew to take over the sensor's control if necessary or beneficial. "Often the pilots have a better peripheral view and can better steer the [FLIR] turret to the target. After directing the system [using a `coolie-hat'-shaped knob], they can hand over control to the operator in back," explains Van der Spuy, describing one purpose for the dual control.

The Star SAFIRE II's range can vary, depending on conditions. However, under ideal conditions [relatively calm seas], it should help spot a person's warm body bobbing in cold water at about 8,200 feet (2,500 meters), says Van der Spuy.

Specifications show the FLIR detector's resolution to be 320 by 240 pixels. But, according to Neil Bertram, FLIR Systems' director of program engineering, with micro scanning--in which a pixel is displaced (or "dithered") up and across to fill gaps--the pixel count is effectively quadrupled and resolution is doubled, to 640 by 480 pixels.

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