This story first appeared in the July 2019 edition of Australian Aviation.
Flightdeck vision technology such as the head-up display (HUD) entered service on military aircraft as a means of simplifying pilot operations. The potential on civil aircraft soon became obvious and systems were developed for, and entered service on business jets and transport aircraft.
Continued development has seen HUDs fielded specifically for GA aircraft, while business jet and transport examples have become technically more capable. Further, the HUD technology-path has continued to receive inspiration from the military and now head-mounted displays (HMD) are being introduced.
A decision by the US Federal Aviation Administration regulations allow sensor imagery shown on HUDs to be used alone to land aircraft in low-visibility conditions has led to the development of such systems for business jets. This article discusses ongoing developments in HUDs and other vision systems for lighter civil aircraft, in particular turboprop transports, business jets, and GA aircraft.
Business jet head-up displays
A modern trend in HUDs is the combination of enhanced vision system (EVS) and synthetic vision system (SVS) capabilities in the display to deliver the combined vision system (CVS). The EVS receives information from infrared and visual-range sensors, while the SVS uses databases providing terrain, obstacle, navigation and airport/runway data.
The first operational CVS is the Dassault FalconEye, available on the large Falcon 8X, the super midsized 2000LXS/S and 900LX, and eventually on the large Falcon 6X business jet when it enters service in 2020. The FalconEye EVS comprises six nose-mounted sensors and the HUD, built by Elbit, has a field of view of 40 degrees horizontal x 30 degrees vertical, showing the EVS and SVS imagery separately.
According to Dassault, a pilot may adjust the split between the two, for example “(to) show more of the synthetic terrain for perspective from far distances, and more of the real world imagery when coming closer to the runway where detail is important”.
Collins Aerospace (then known as Rockwell Collins) launched another HUD-based CVS for the Bombardier Global 5500 and Global 6500 large business jets due to enter service at the end of 2019. In October, a Collins HUD-based CVS also became available on the Embraer Praetor 500 midsize and Praetor 600 super midsize business jets which are in the process of being certified. The EVS on both the Global and Praetor families comprises three nose-mounted sensors, however the HUD on the two families is different; Collins says the dimensions of the Praetor make it difficult to install a traditional HUD.
The HUD on the Global aircraft is the HGS-6000, with field of view 40 x 32 degrees, similar to the HUD (though without the CVS) used in the current Gulfstream business jet range and the Airbus A220. The HUD on the Preator is the HGS-3500, with a field of view 30 x 22 degrees.
The overall smaller size of the HGS-3500 system is due in part to “waveguide” image transmission rather than traditional overhead projection. It was specifically developed to fit into smaller aircraft such as the Praetor and also the midsize/super midsize Embraer Legacy business jets on which it is also used (without the CVS).
Developing a CVS is a manifold challenge. Collins explains that the positioning of the EVS sensors compared to the pilot’s eye has the potential to deliver a certain amount of parallax. In this context, the sensors’ nose-top location is advantageous – putting them close to the pilot’s line of sight. That positioning is preferable to the undernose location on a few earlier business jets despite the fact sensor coverage below the aircraft could be particularly useful close to the airport.
Further, there must be a correlation between the EVS sensor and the SVS database imagery and Dassault states that the FalconEye EVS and SVS imagery “perfectly match where they align”. In the Collins CVS, alignment is required throughout the HUD field of view which, in turn, demands more of the data processing software. It must also prevent the presentation of too much information and Collins says that as the EVS begins to detect objects, the software becomes aware and “filters them in”.
General aviation aircraft head-up displays
The CVS-displaying HUDs are the most capable on civil aircraft. In the GA world, the challenge is all about size of available space, capability of installed avionics and the amount of money an aircraft owner is prepared to spend.
While the outcome should be more modest operating specifications there are manufacturers in the sector seeking to produce systems that could provide the same information on screen and in a similar format to that of more capable HUDs.
Such a manufacturer is MyGoFlight. The company’s HUD has a field of view of 8 x 4 degrees with potential for fit on a wide range of GA aircraft beyond the Cirrus SR22 on which it has flown so far. Development has been much simplified by the fact that it is “non conformal”, unlike the CVS HUDs and traditional civil HUDs. This means that the display symbology does not precisely match the view of the world seen through the display. Pilots who have flown the Cirrus fitted with the MyGoFlight system have not taken long to adjust.
The MyGoFlight HUD also differs from traditional models in that the on-screen symbology is not monochrome, in green, but in two colours: green and magenta. Green has traditionally been considered the symbology colour with capacity to maintain enough of a contrast against a background that ranges between ground, sky, sea, and sun. Now MyGoFlight says magenta is also “viewable in all lighting conditions”, and the FAA had no issue with that when it awarded certification to the HUD.
While most symbology remains in green magenta is “used to create attention to data the pilot needs to focus on, alerts, and transitions”. It is used, for example, for the flight director cue, making it stand out from the (green) flight path marker (the pilot required to keep the flight director cue within the flight path marker to follow the flight path).
Another GA HUD is the Epic Eagle from Epic Optix first developed for the Garmin G1000 suite. In addition to the avionics system, this HUD can also receive data from an electronic flight bag or portable electronic device. HUD characteristics include on-screen information in ‘full’ colour with a high level of brightness.
The Epic Eagle is self-contained, portable, and said to be capable of a fit on the glareshield of most GA aircraft. For these reasons it has not required certification. Textron is marketing it for use on Cessna and Beechcraft aircraft and will be offering it as original equipment on new single-engined types.
While these HUDs give GA class aircraft a basic HUD capability, activity in the turboprop transports and business jets markets is intended to take display capability to the next stage with head mounted displays (HMD) – part of the pilot’s gear rather than mounted in the cockpit. From HUD to HMD the field of view increases to 360 degrees – wherever the pilot is looking.
Two commercial HMDs have been revealed: the Thales TopMax and the Universal Avionics (UA) SkyLens.
The latter was initially an Elbit product but became part of the UA range after the company’s acquisition by Elbit. The early pattern for the HMD has become apparent – both include a glass monocle-type display on which information is projected.
In both instances the manufacturers have sought display capability at least comparable to that attained in HUDs, including EVS, SVS and CVS. UA says that SkyLens has “full HUD functionality and capability”.
One challenge of an HMD is ensuring the integrated headgear is not too heavy. TopMax weighs less than 500g, SkyLens about 600g. UA says that SkyLens is made of lightweight materials, but that it is robust.
TopMax was first out of the blocks and is scheduled to enter service in 2020 with business jets and transports. SkyLens, which is set to be certified soon, has already been ordered for use on ATR 72-600 turboprop transports being delivered this year to UK-based airline Aurigny.
ATR offers SkyLens as an option on new ATR 72/42-600s, part of a UA/Elbit product suite known as Clearvision which includes the EVS, with six nose-mounted sensors, SVS and CVS.
At this stage Aurigny has only selected the EVS which will, however, allow landing in the fog that regularly affects the airline’s base on the island of Guernsey in the English Channel. Indeed it is said that had the Clearvision EVS been available on Aurigny’s current, earlier generation ATR 72s, it could have prevented half the disrupted landings at Guernsey over a period of a year.
The airline is set to receive its first ATR 72-600 in August, with two more to follow. They will replace the three earlier ATR 72s.
In October last year it was announced that the UA InSight display system was to be integrated into SkyLens.
InSight has received supplemental type certification for the Cessna Citation VII midsize business jet and could be introduced on others. The integration means aircraft flight management system (FMS) information will become available on the SkyLens display.
The pilot would be able to perform FMS commands including programing and updating the flight path and the runway selected. Most innovatively, he (she) would be able to perform these commands partly through eyesight alone. The equipment uses a sensor in the system which tracks eye movement.
The point at which the sensor detects that the pilot is looking is shown with a cursor. If that point is a tagged object in the SVS database, a menu appears from which a selection can be made. This is done by looking at an item, which is then highlighted, and pressing a button on the control column. Further selections may be made as required until the command is put into effect.
One advantage of HMDs over HUDs is that they can be retrofitted to in-service aircraft relatively easily and TopMax is being marketed as capable of retrofit on any aircraft type. The traditional HUD, meanwhile, is much more difficult to retrofit.
The lower end of the SkyLens market could be an aircraft such as the twin turboprop Beechcraft King Air (the current version of which has a passenger capacity comparable to a light business jet, six–seven persons).
At the larger end of the civil aviation market, UA and services company Aersale are pursuing FAA supplemental type certification for Clearvision (including SkyLens) on the Airbus A320.
Enhanced flight vision systems
Another technological advancement is the enhanced flight vision system (EFVS), a promulgation in which sensor imagery presented on a heads-up or other display with flight guidance and other symbology clearly visible to the pilot in his normal position with the line of vision forward along the flight path. Further, the sensor imagery always conforms to the HUD, unaided view.
Use of the EFVS has been allowed by the FAA since December 2016 to land instrument approach aircraft in low visibility. The critical point in the landing comes when the pilot must make a decision to begin an immediate missed approach or continue. The decision is based on he/she having seen the visual references, including aids, long enough for assessment of aircraft position and motion relative to the desired flight path. The critical point is called the Decision Altitude (DA) if measurement is made with reference to mean sea level, or Decision Height (DH) if it is made with reference to elevation at the runway threshold (beginning of the runway).
The critical point, now a critical altitude, could also be that altitude below which the pilot may not descend until he has made a decision on beginning an immediate missed approach or continuing the landing. It is called the Minimum Descent Altitude (MDA), with reference to mean sea level.
Use of the EFVS to approach the runway had been allowed prior to December 2016. The EFVS imagery was usable alone on straight-in approaches to descend below DA/DH or MDA to 100ft (30m) above what is known as the touchdown zone elevation (TDZE), the highest elevation in the first 3,000ft (910m) of the runway. EFVS imagery together with unaided vision was used to descend below 100ft (30m) above the TDZE. The new regulation allows EFVS imagery to be used alone to descend below DA/DH to touchdown and rollout. Visibility must be 1,000ft (300m) runway visual range or greater.
The first aircraft certified to use an EFVS to land is the Gulfstream. Its flight testing included different approaches flown under actual low-visibility conditions by Gulfstream and FAA test pilots. The Gulfstream G280 super midsize and G450, G550, G650, G500ER large business jets are currently certified to use their EFVS’s to 100ft (30m) above the TDZE, but have completed flight testing to allow use of the EFVS’s to land and are soon to be certified. The large-category G600 will be certified when it receives its type certification.
At Bombardier the Global 5500/6500 are being flight tested to allow use of the Collins CVS’s EFVS capability to land, as part of the flight test program of the aircraft. At Dassault the Falcon 8X is to be fitted with dual HUDs which will allow use of the FalconEye CVS’s EFVS to land. Certification
is expected in 2020.
The aircraft is currently certified by the European Aviation Safety Agency (EASA) and the FAA to use FalconEye to descend to 100ft (30m).
These aircraft could eventually be joined by those employing the SkyLens HMD. The display fits the definition of that required for an EFVS, while the system overall was developed to meet the requirements allowing the use of an EFVS to land aircraft. (The Clearvision A320 program mentioned earlier includes EFVS capability.)
With the CVS, HMD and EFVS, business jets and lighter transports are pioneering vision technologies that could eventually be introduced on other aircraft types. As the safety benefits of these technologies are demonstrated, and as they mature and their costs drop, their attraction will only increase.
VIDEO: A look at the FalconEye system from the Dassault Falcon YouTube channel.
This story first appeared in the July 2019 edition of Australian Aviation. To read more stories like this, subscribe here.