MIKE GERZANICS / PHOENIX, ARIZONA & ORANGE COUNTY, CALIFORNIA
Rather than replace aircraft, owners of ageing business jets can comply with new regulations by upgrading avionics. We test flew two leading systems
Ageing business jets present their owners with several challenges. While many of these aircraft clearly possess the range, speed and cabin comfort demanded by their operators, rising maintenance costs and an increasingly strict regulatory environment threaten their viability.
Consequently, airframes which retain significant intrinsic value are emerging as ideal candidates for avionics upgrades. Both Honeywell and Rockwell Collins have developed retrofits which draw on their respective Primus Epic and Pro Line 21 integrated avionics suites now being installed in the latest business jets.
While large-screen liquid-crystal displays (LCDs) are the most obvious enhancement over the legacy avionics these systems replace, they are only one of the benefits offered by upgrading. Reduced installed weight and operating cost, as well as increased reliability, are likely gains, although increased operational flexibility, safety and the ability to operate in the future communication, navigation, surveillance and air traffic management environment are perhaps the most significant improvements provided by these upgrades.
Flight International was able to fly both systems in the manufacturers' demonstrator aircraft, starting with a Bombardier Challenger 601 operated by Collins and equipped with the Pro Line 21 Continuum retrofit suite. The panel features four 200 x 250mm (8 x 10in) LCDs. An FMS-6000 flight management system (FMS) is installed, as well as three centre-pedestal control display units (CDUs). For navigation, two global positioning system (GPS) receivers replace inertial reference units (IRU), while triple AH-3000 solid-state attitude-heading reference systems provide for increased despatch reliability.
The existing engine instruments have been retained, as an upgrade to a full engine-indication and crew-alerting system was deemed too expensive. The upgraded avionics package shaves around 160kg (350lb) off the Challenger's gross weight, 65kg of the saving resulting from removal of the IRUs. Collins is offering the fully integrated Continuum for the Challenger 601, Dassault Falcon 20 and 50 and Raytheon Hawker 800.
The second aircraft, Honeywell's Cessna Citation V avionics testbed, is fitted with the Primus Epic CDS/R retrofit suite. This features three 200 x 250mm LCD displays, but Honeywell offers the option of two, three or four displays. The system's backbone consists of two IC-1080 integrated avionics computers. A pedestal-mounted CDU controls the single FMZ-2000 FMS and two GPS receivers, in the form of cards in the IC-1080 computer, provide positional information for the FMS.
As with the Challenger, the original engine instrumentation is retained. Installation of the Epic CDS/R reduces the Citation V's gross weight by 68kg. The retrofit suite interfaces with the aircraft's existing flight director and autopilot via cards in the IC-1080, whereas the Continuum requires updated equipment. The Epic CDS/R is available for the Citation V, Gulfstream II and III, as well as the Lockheed L-382 Hercules.
Both the Continuum and Epic suites feature nominal 200 x 250mm active-matrix LCDs. LCDs provide two direct benefits: reduced power requirements and increased reliability. Honeywell director of avionics retrofit programmes, John Glakas, says they offer a mean time between failures three times that of large-format cathode-ray tubes (CRTs). Additionally, LCDs do not suffer from image burn-in as do CRTs.
Viewable area on both displays is a little over 150mm in width and 200mm in height. Measured diagonally, the viewing area is around 280mm. Even in sunny conditions, and while wearing sunglasses, the brightness and contrast of each display type is sufficient for comfortable viewing. Resolution is quite good for all display modes tested, although some pixel segmentation is noticeable on curved and diagonal display elements. Cross-cockpit viewability for both display types was also good, easily allowing each pilot directly to reference the other's instruments.
Configuration options
Each LCD can be configured as either a primary flight display (PFD) or as a multifunction display (MFD). The number of displays installed and customer preference will determine how they are configured. A two-display system could be arranged with one PFD for the pilot, and a central MFD and conventional round-dial flight instruments for the co-pilot. The other two-display set-up would use them as PFDs for both pilot and co-pilot. A three-display system would add a central MFD to the dual PFD set-up. A four-display system gives each pilot an MFD and PFD.
Functionally interchangeable, an MFD can act as back-up for a failed PFD at its respective crew station. This does not obviate the need for suitable standby flight instruments, however. The Citation has conventional standby instruments, while the Challenger has a Goodyear ESIS-3000 electronic system. This single 75mm LCD takes up little panel space and shows basic attitude, heading, airspeed and altitude. It can also display VOR, instrument landing system and distance-measuring equipment navigation information.
A PFD replaces a host of conventional flight instruments. Its basic components are an attitude direction indicator (ADI), or artificial horizon, and a horizontal situation indicator (HSI), combined on one display. The ADI is displayed on top of the HSI as it would be in a conventional instrument layout. Airspeed is displayed to the left of the ADI, while altitude and vertical velocity is displayed to the right. HSI information can typically be displayed in a full compass rose or partial compass arc formats. Navigation bearing pointers and/or lateral deviation bars can be overlaid on the HSI portion of the PFD.
I found the PFDs on both flights easy to use, allowing precise hand flying of the aircraft. Flight director commands are displayed on both PFDs via a V-type command bar. Flight director guidance in both pitch and roll is followed by aligning the ADI's aircraft symbol with the V bar. I found both V-bar displays easy to follow. While both manufacturers offer the option of a two-bar flight director command display, I did not evaluate them during my flights.
Neither aircraft has an autothrottle, which means airspeed has to be closely monitored. In general, I find it easier to maintain a constant airspeed on dial-type airspeed indicators as opposed to tape-type displays used on both the PFDs. Each PFD had an airspeed trend vector - a bar on the airspeed display graphically showing what the speed would be in 10s, given current acceleration. This eases the task of maintaining a constant airspeed. One safety-enhancing feature on both airspeed displays, in addition to Vmo/Vmo references, were markers to show a low-speed condition. The Continuum's air data computer displays references at 1.3Vs (stall speed) and Vs. The Epic's computer indicates 1.1Vs for aircraft equipped with an angle-of-attack sensor, or a manually input speed (V2, Vclean, or Vref), depending on flight phase.
The HSI portion of a PFD, as well as providing basic navigation information, can also be used to display traffic alert and collision avoidance system (TCAS), terrain awareness warning system (TAWS) and weather radar information. Standard TCAS target symbology on the HSI portion of both Collins and Honeywell PFDs is logical and easy to interpret.
If conflicting traffic triggers a resolution advisory, both systems will provide guidance to avoid a collision. In addition to audible "climb" or "descend" commands, pitch path guidance is shown on the ADI portion of the PFD. In the Collins system, pitch guidance is displayed on the vertical speed scale, showing the pilot a target vertical velocity to maintain. In the Honeywell system, a "fly to box" is shown on the ADI, the pilot placing the aircraft symbol in the box to avoid a collision. Pitch attitude "do-not-fly" zones are also displayed on the ADI. Of the two pitch guidance displays, Honeywell's "fly-to-box" is more intuitive and easier to follow.
Safety problem
Controlled flight into terrain is a continuing problem area for aviation safety. Both suites have a TAWS in the form of Honeywell's enhanced ground proximity warning system (EGPWS). TAWS is a predictive system which uses aircraft position and a terrain elevation database to alert the pilot to impending ground impact. In both suites, terrain information relative to aircraft altitude can be displayed on the HSI portion of the PDF or on the MFD, greatly enhancing situational awareness. While the weather radar may also be displayed on the HSI, both EGPWS and radar cannot be shown at the same time. Even if the radar display is selected, "pull up" commands will be issued if the EGPWS detects a terrain conflict.
The primary purpose of the MFD in both systems is to provide a large format display for navigation information. They are each capable of displaying FMS-generated waypoints in either a map or plan mode. The map mode places the aircraft at the bottom of the display, in a God's-eye view, with range scale varying from 9-1,110km (5-600nm) for the Continuum and 9-1,850km for the Epic. The display is oriented with aircraft heading up and the active flight plan depicted. Ground-based navigation aids as well as airports along the route of flight can also be shown. In the Continuum, this same information can be displayed on the HSI portion of the PFD. The plan mode displays flight route in a north-up format, allowing the pilot to review the flight plan with ease.
In general, both displays are equally useful, with one exception. While not a function of the display itself, the Continuum's FMS software makes changing a flight plan much easier. The Continuum displays both the current and proposed route on the MFD, allowing the pilot to assess it easily, before executing. Epic's FMS software does not show the proposed flight plan until it has been executed.
In map mode, TCAS, EGPWS and weather radar information can also be seen on the MFD. While the map display takes up the majority of the MFD's screen, a good portion of the display is available for other functions. Both systems offer electronic checklists: the Continuum's above the map display, and the Epic's below. While these are useful, the major benefit of a large-format MFD is the flexibility it gives for future growth. With appropriate databases, both systems can display en route charts and terminal approach plates, a huge step towards the paperless cockpit. Moving maps and airport diagrams are also a near-term prospect. The MFDs may also be used for datalink functions. It is this growth potential that makes these retrofit systems so viable.
The Continuum and Epic retrofit avionics suites both feature LCDs of impressive size and clarity. Brightness levels are more than adequate for even sun-lit conditions. Both PFDs are logically arranged, with critical flight information easily interpreted. The MFD map displays are also logically presented and easy to use.
Selection of one suite over the other for retrofit on to a business jet will probably hinge on regulatory agency approval for the modification, rather than any operational characteristic of the system. While eminently suited for operations in today's airspace system, both suites lay the foundation for compliance with future regulatory requirements and continued operations in the 21st century.
Source: Flight International
