HUD technology improves safety and enables more efficient flight ops.
By Shannon Forrest
President, Turbine Mentor
ATP/CFII. Challenger 604/605, Gulfstream IV, MU2B
The FalconEye HUD design complements the advanced flight deck of the Falcon 8x. It allows pilots to descend to lower minimums in IMC.
Pilots fight a constant battle between “need to have” and “nice to have” when it comes to cockpit furnishings. Since the decision is often made by the aircraft owner, who controls the budget, discretionary funds are used towards aft cabin upgrades or amenities. After all, owners rarely see (or understand) what goes on up front, so they assume everything goes off without a hitch every time. The presumption is that pilots have what they need to perform their job in the flight deck.
On the other hand, most pilots tend to be “gadget-oriented” and would prefer to have the latest and greatest technological marvel if it reduces workload, makes the job easier or more efficient, or enhances safety. The safety argument is an easy one to make, and in some cases is made by a regulatory authority like FAA or EASA.
In this situation it’s not a matter of whether an owner wants to install a certain piece of equipment. Rather, it’s mandated based on the type of operation being conducted. An early example of this was the requirement for a Mode C transponder when operating within 30 nm of US Class B airspace. This regulation was enacted decades ago and has since morphed into the ADS-B rule as the technology improved over the years. Other examples include ground proximity warning systems (GPWS) and traffic collision avoidance systems (TCAS).
Jet era standard technology
In the nascent days of jet aviation, these systems weren’t in use nor considered essential. Later, accident analysis determined that controlled flight into terrain (CFIT), mid-air collisions, and close calls represented significant threats to pilot and passenger safety.
The remedy was to mandate GPWS (or EGPWS) and TCAS for specific aircraft types and/or types of operations. Older aircraft either had to be retrofitted or stop flying. Today, many aircraft manufacturers recognize the safety value of these systems and are choosing to install them in their aircraft – either as standard or optional features – despite not having to do so under current regulations.
Operational efficiency can be quantified objectively or subjectively. If fuel can be found at a significantly cheaper price twenty minutes from the intended destination, the quandary is deciding whether the financial savings is more valuable than the lost time. Tabulating the cost of fuel is an objective mathematical exercise. The value of time is subjective, and the answer depends on who’s asked.
Global positioning system (GPS) is an operational efficiency which has become so common that it’s taken for granted. It’s entirely possible to operate an aircraft under instrument flight rules (IFR) without GPS. Traditional instrument landing system (ILS) approaches are still prevalent, and a pilot can transit the airspace using V or J Airways and proceeding direct to VORs (or even to NDBs in some places). Doing so would be horribly inefficient, but nonetheless possible.
An enhanced benefit of combining a HUD with synthetic vision is the ability to see terrain that would otherwise be invisible at night. This helps when conducting go-arounds or missed approaches.
A deeper dive into the GPS argument wouldn’t be complete without discussing wide area augmentation systems (WAAS). In addition to delivering better lateral precision, WAAS lowers instrument approach minimums. The WAAS-based localizer performance with vertical guidance (LPV) approach can provide minimums like that of an ILS, but brings with it notable advantages. WAAS approaches don’t need the ground-based infrastructure of an ILS, which equates to lower cost of installation and virtually no maintenance.
Another operational advantage of LPV over ILS is less signal interference, which may be a problem when one aircraft is conducting an ILS approach on autopilot while another departs from the same runway. The fuselage of the departing aircraft can momentarily disrupt the ILS signal, causing a “wobble” or “burble” for the arriving aircraft.
The autopilot of the arriving aircraft attempts to follow the wandering localizer or glideslope signal. In doing so, it exhibits oscillations in roll or pitch. This errant glideslope behavior can trigger a GPWS alert if it occurs with terrain on or in proximity to the final approach course. The scenario is that the disrupted glideslope signal causes the autopilot to pitch down, which the GPWS interprets as proximity to the terrain.
This is illustrated by looking at the ILS approach to Rwy 33 at BVT (Burlington VT), where a hill sits close to the airport, directly in line with the final approach course. Using the LPV approach in lieu of the ILS to Rwy 33 would allow minimums of 250 ft AGL with the added security of an uninterrupted signal, and perhaps even an unnecessary go-around.
Head-up vision technology
The compact design of the Garmin GHD 2100 means it can be installed in smaller jets. Symbology mirrors that of the primary and multifunction flight displays.
The perfect cockpit technology would decrease workload, increase efficiency, and enhance safety. Although perfection may not be attainable, the head-up display (HUD) makes a nice attempt at all 3. HUDs have been around for a long time, and there’s a plethora of literature and articles that describe what they are and how they work. In a nutshell, the HUD takes information normally displayed on the flight instruments and projects it directly in the focal view of the pilot (called the combiner), eliminating the need for a pilot to look elsewhere.
Early generation HUDs merely provided the essential parameters like airspeed, altitude, and course. Newer generation HUD’s, however, incorporate outside forward-looking infrared cameras and sensors, which, when combined with internal terrain databases and GPS, can provide a synthetic view of the environment.
It sees what a human eye can’t. There’s a lot of hype surrounding what the HUD can do, but the question one might be asking is, “What is a HUD supposed to do?” In commercial aviation, the primary function of the HUD is to allow landings in inclement weather that would have otherwise resulted in a missed approach. Aircraft manufacturers understand the inherent advantages of operating with a HUD. As a result, many of them are offering HUDs as standard equipment. The Embraer Praetor super mid-sized jet can combine the HUD with Embraer’s enhanced vision system (E2VS), enhanced video system, and a synthetic vision guidance system (SVGS) for the ultimate in safety and efficiency.
According to Collins Aerospace, its HUDs guide the way day or night, letting pilots fly consistent approaches regardless of conditions. With fewer go-arounds, diversions, and cancellations because of low visibility, operators save fuel and keep operations on schedule.
The Collins HGS-6000 is a full-sized HUD that can depict flight parameters, TCAS resolution flightpath guidance (providing an escape maneuver from a traffic conflict), tail strike avoidance pitch information, and low visibility rollout guidance. The HGS-6000 can be installed as a single or dual system, and can be combined with the manufacturer’s EVS-3600 to deliver synthetic vision. A compact version of the HUD is offered for smaller flight decks with less headroom.
The Garmin GHD 2100 HUD, designed for light to super mid-sized business aircraft, consists of a small self-contained projection unit that sends info to a high-resolution glass combiner. Garmin uses flightpath marker graphics to show where the aircraft is going in relation to where it should be going, which enhances situational awareness and allows for early corrective action should a problem develop.
A declutter function removes unnecessary symbology close to the ground, which intensifies pilot attention during a critical phase of flight. Garmin’s proprietary SurfaceWatch technology outlines graphically the runway selected by the pilot on the HUD, which prevents confusion when approaching an airport with closely spaced parallel runways or divergent runways that begin in
HUD technology is especially important for operators conducting Cat I and II ILS approaches. In 2017, FAA Order 8400.13D allowed a visibility reduction at runways with a Cat I ILS or LPV if the approach is flown using a flight director or autopilot with an approach coupler or HUD. The most common visibility reduction is from 2400 to 1800 RVR with the use of the HUD, but approaches can vary based on OPSPECs or letters of authorization (LoAs) granted by FAA.
Information relevant to the approach will be shown in the notes section of the approach chart. For example, The ILS Rwy 16C into SEA (Intl, Seattle WA) indicates that the RVR required for a Cat I approach is 2400. However, that can be reduced to 1800 if the HUD is used to the decision altitude (DA). In addition, the notes for a Cat II ILS require 1200 RVR, which can be lowered to 1000 if the HUD is used to touchdown and an LoA authorizes it.
By design and default, a HUD reduces pilot workload. Industry pundits project that the HUD market will be capitalized at $2.18 billion this year. Although the advantage of having a HUD is not immediately obvious on every flight, it’s obvious on flights that really matter. It’s better to have it and not need it than needing it and not have it. It’s a worthy aftermarket retrofit. No one buys a jet that will fly for hours on end only to divert at the destination because the ceiling is 100 ft lower than forecast.