The Honeywell/GEC HUD 2020 head-up display enhances the Gulfstream IV.

Peter Henley/SAVANNAH

THERE IS NO DOUBT that head-up displays (HUDs) for commercial aircraft have grown in importance during the past decade. The impetus behind their development is the potential for lower landing-minima in poor visibility, which the HUD achieves by enhancing the pilot's ability to control his aircraft precisely and to position it accurately right down to the flare. Indeed, Honeywell claims that its HUD 2020 provides guidance enabling the pilot to match the precision of a digital auto-pilot.

Because a HUD can provide situational-awareness and energy-management cues instantaneously, when the pilot would otherwise have to scan several instrument displays and integrate their information himself, Honeywell claims other important safety-enhancing capabilities for its 2020. For example, windshear-warning and recovery guidance can be displayed far more quickly than the time it takes for a pilot to become aware of the problem, and a so-called "black-hole" visual approach to a runway on a dark night can be flown by setting a glideslope and flying it through the HUD, thus eliminating inadvertent high or low deviations. The HUD 2020 development programme at Gulfstream, in Savannah, Georgia, is based on a logical, commercial, combining of three companies' expertise and experience.

GEC-Marconi Avionics, of the UK, based at Rochester, Kent, has produced some 10,000 HUD systems for fighter and transport aircraft, including the US Air Force McDonnell Douglas C-17 military transport, and it has responsibility for the overhead electro-optical unit, including the combiner.

Honeywell has produced the well-established SPZ series of flight-instrument and flight-control systems and, now, the Primus 1000 and 2000 systems, including flight-management systems (FMS) and engine-instrument and crew-alerting systems. It also has responsibility for HUD integration (with existing flight and navigation systems) and certification.

Gulfstream's role in the HUD development programme is described as being "much like that of a programme manager", since it wants to see customers being offered "the best HUD" for their aircraft. The 2020 is intended for use specifically in the GIV and GV, and Bob Morris, programme manager for HUDs, is confident that there is sufficient potential among Gulfstream operators alone to justify the development costs and to make the project economically viable.

Flight International visited Gulfstream at Savannah, Georgia, to fly the 2020, installed for development in a Gulfstream Honeywell GIV. Pre-flight briefings on the system and its technology, and on how to fly it, were conducted by Victor Jory, Honeywell's principal engineer for applications and engineering, and Jerry Norton, Honeywell's chief pilot for flight operations, respectively.

The GIV is a pleasant aircraft to fly, anyway, and the model I flew has the comforts of integrated auto-pilot and autothrottle, enabling a fully integrated HUD, flight director, auto-pilot and auto-throttle approach to be flown. To establish how easy the HUD is to use, however, a manually flown auto-throttle approach was tackled first, followed by a manually flown, manual-throttle, approach - both positioned by radar vectors in to a 2,000ft (600m) above-ground-level instrument pattern to an instrument-landing-system (ILS) localiser and 3° glide-path. The first approach intercepted the centre-line at about 15km (8nm), and the second at about 8km. Conditions were good for visual-flight rules, with light winds, broken cloud at 2,000ft, ground temperature 97°F and an altimeter QNH of 2996 (29.96 Mercury/1015mb).


The pre-flight flightdeck drills include one of a simple press-to-test systems-integrity check. Departure profiles are set using the flight-director controllers for runway direction, preselected altitude and V1 and Vr. A split V1/Vr was set merely to demonstrate the HUD's ability to show the pilot such details, although Savannah was clearly a "balanced field" for this take-off. At the point of brake release, the flightpath-vector-group symbols (see fig 1) overlie the outside view of the runway, and the speed-error tape appears as a long tail below the primary vector symbol (because the aircraft is stationary, whereas V1 and V2 are set as target speeds - seen by the computer as a "low-speed error").

As the aircraft accelerates, the tail shortens and the digital airspeed winds up. At Vr, demand information for the climb altitude is presented by the flight-director symbol (colloquially called the diamond) appearing above the horizon. Rotating the aircraft until the flight-path-vector group (less cumbersomely called the bore-sight) is superimposed on the diamond will give the correct climb altitude (see box). Following the cues is, in practice, easy and straightforward because the symbology and logic is user-friendly. Short familiarisation with "flying the bore-sight" quickly allows the pilot the spare capacity to scan the rest of the HUD information, such as altitude and heading (heading is a "non-confirmal" presentation - the heading scale is smaller than the world which the pilot sees beyond it. This was not found to be a significant drawback in use, however.

Although it may be possible eventually for the aircraft windscreen to be used for HUDs, the difficulties of doing so are likely to mean that the combiner is going to be around for a long time. It is not, however, unduly intrusive, although it is another thing for the unwary to bump into when getting into or out of the seat.

Correct eye position relative to the combiner is critical, but is easy to achieve by using the two reference balls for initial seat-positioning and then refining this position so that the HUD display can be seen comfortably without any blurring at the edges. Any significant moving of the head from this established position would, of course, impair clarity, but the best position can easily be re-acquired after deliberate movement - to conduct a cockpit scan, or to look at a chart, for example.

Wearing prescription spectacles does not pose any problems. Symbology brightness is controllable, to suit different pilots and conditions, and automatic brightening and dimming compensate for changing ambient-light conditions. Nevertheless, a marked change of circumstances (such as going from a dark terrain background to bright skies when going around from a low approach, for example) can cause a second or two's concern until the pilot's eyes adjust.

During radar vectoring for approaches to Savannah, two conflicting traffic warnings, were given by the radar controller and both aircraft provoked, convincing traffic-alert and collision-avoidance system (TCAS) warnings on the HUD. These warnings consist of "bucket"-shaped overlays on the display, indicating to the pilot the airspace to avoid - examples can clearly be seen on the photograph (P31), which shows a typical pilot's view on visual approach.

The two HUD approaches flown to Savannah were conducted using an ILS with a 3° glide-slope. Norton orchestrated the proceedings from the right-hand seat, coping with communications and setting up the navigation aids, while I enjoyed flying the GIV, using the HUD. Auto-throttle was used for the first positioning and approach, while the second was by manual throttle, to see how easily the HUD's cues for acceleration changes, could be met by the aircraft and its Rolls-Royce Tay engines.

The GIV is a clean aircraft, with plenty of power, and small power changes, with a little anticipation, make speed control easy. The GIV also suffers little pitch change with configuration alterations, so there is no difficulty with "flying the bore-sight", as gear and flaps (both of which proved commendably quiet in operation) were selected.

Heading-demand cues for crosswind, intercept and capture of the localiser were all exactly as one would expect from any flight director, as was glide-slope capture.


Several things happen to the HUD format during the approach. The conformal lateral-deviation display (a patented, exclusive, feature of this HUD) appears, giving the pilot powerful centre-line orientation cues, as well as showing glide-slope-deviation dots. Radar altitude (RAD ALT) and decision height (DH) appear (see box, also shown in fig 2). An airport symbol embraces the runway at 1,200ft RAD ALT, the function of which is really as a "target marker".

A runway symbol then imposes itself within the airport box at 350ft RAD ALT; the airport and runway symbols appear together for 50ft of descent, and then the airport image disappears, leaving the runway extremities clearly and closely defined for short trials and the flare. The letters "DH", are presented at the preselected RAD ALT DH and the flare demand, appears at 50ft. The last one is, perhaps, the least easy to follow and some practice is essential before having the confidence to rely upon it.

With this minor exception, I found that the HUD approach to be easily flown to accurate standards, with the HUD delivering the aircraft with consistent accuracy to the same place along the runway, the precise touchdown being dictated only by the pilot's threshold - speed accuracy and how quickly he closes the throttle in the flare. A low go-around can be flown by pressing a control-wheel button, which clears the combiner of approach symbology and presents climb and departure information. Although waypoints cannot be shown on the HUD, a profile to achieve an altitude and target point (in nautical miles) can be programmed.

Significant crosswinds encountered during an approach would be shown by the aircraft reference symbol being displaced to the into-wind side of the centreline. The pilot would, of course, have to "kick off" drift before touchdown. Because of the good weather, I could not see first-hand how the HUD presentation would cope with significant angles of drift close to the flare, but, presumably, the image would be a little lopsided.

So, the Honeywell HUD appears to work well and to be acceptably easy to fly in benign weather. The question is, when modern flight directors, FMS and autopilots can make ILS-equipped aircraft extremely safe and capable, and, with global-positioning systems (GPS) and satellite landing systems looming large to bring even greater capability in the foreseeable future, who is going to want a HUD, and why?

Honeywell and Gulfstream emphasise the safety aspects of their HUD in the areas of greater precision to visual and instrument approaches (day and night), and enhanced warning of collision risk and windshear - but are these assets alone going to be enough to persuade many Gulfstream IV and V customers to part with about $500,000 extra (the predicted unit cost) to have a HUD? Clearly they would not on these parameters alone, but the more compelling appeal of a HUD is that it can reduce approach minima.


If it could be certificated to Category III minima, it would justify its cost to those operators who habitually fly in conditions where such capability makes a difference to the number of flights which they could complete, rather than having to cancel because of weather. This could have particular appeal to corporate operators, whose aircraft are management tools and to whom the ability, for example, to deliver board members to vital business meetings almost regardless of weather, could be crucial. Gulfstream's Morris cites the numerous HUDs already in service in Alaska and other north-western territories susceptible to persistent mist and fog, which, he says, are completing more services in adverse weather, at a fraction of the cost of using an aircraft equipped and certificated to ILS Cat III.

Morris' ambition for the 2020 is "Cat III capability with Cat I ground equipment". Fulfilling that ambition will take a little time, but it is on its way, he says. Development is under way of an enhanced-vision system - more positive acquisition of the runway in poor conditions through on-board infra-red systems - able to detect runway lighting. The HUD is already integrated with the Gulfstream GPS for "landing-point enhancement" (helping to pinpoint the touchdown point), and the prospect of an eventual integration of satellite-landing system (SLS) and the HUD - giving instrument-approach capability to airfields without any instrument-landing equipment - is a real possibility.

Once again, Morris says, a HUD 2020-equipped, SLS-capable, aircraft could be flown to lower minima than those of the same aircraft without a HUD. This is where the operator really gets value for money - virtually any suitable airport destination, regardless of its ground-approach equipment, becomes within his ambit.

Meanwhile, development and certification proceed, with US Federal Aviation Rules certification hoped to be gained later this year followed soon after, by European approval. Current interest in the programme has resulted in 12 orders to date and no fewer than 40 demonstration flights to Gulfstream customers in one recent week.

Were the ultimate success of the project to depend upon the enthusiasm of Morris and his team, it would doubtless be a runaway winner.

Source: Flight International