Synthetic and enhanced vision systems reduce pilot workload and improve situational awareness.
By Shannon Forrest
President, Turbine Mentor
ATP/CFII. Challenger 604/605,Gulfstream IV, MU2B
An approach in instrument meteorological conditions (IMC) is a difficult task for a pilot to perform flawlessly. The most critical phase of the maneuver is when the pilot transitions from instrument to visual flight in the brief period just before landing.
If either the ceiling or visibility are low – or worse yet, both – the pilot only has a few seconds to acquire the landing environment and shift from looking inside to looking out. The decision point is a function of the type of instrument approach being flown, and the terminology to describe that position in space changes accordingly.
However, once that point is reached, there’s only 2 options: continue to a landing or execute a go-around. FAR 91.175 prescribes what the pilot must see to continue an approach in IMC to touchdown.
According to the rules for a Category I instrument approach, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot – the approach light system, the threshold, the threshold markings, the threshold lights, the runway end identifier lights, the visual approach slope indicator, the touchdown zone or touchdown zone markings, the touchdown zone lights, the runway or runway markings, (or) the runway lights.
Except for the approach light system, all the references are on or immediately adjacent to the runway environment. For that reason, there’s a caveat when it comes to using the approach lights to continue to a landing.
The regulation states that the pilot may not descend below 100 ft above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.
Reviewing approach procedures
When conducting an approach briefing in a 2-pilot crew, or reviewing the approach procedure in a single-pilot operation, it’s not uncommon to reference the type of approach light system installed. For example, “The inbound course is 234, altitude 1500 ft until the final approach fix, then down to a DA of 200 ft. ALSF-2 approach light system, with a PAPI on the right.”
Briefing the approach light system configuration can become a habit rather than a means of denoting valuable information. How many pilots can state the specific differences between an ALSF-1, ALSF-2, SSALR, MALSR, MALSF, or ODALS?
When you hear the word ALSF-2, if you immediately think “247 steady burning lights with 49 green threshold lights, 9 rows of red side row bar lamps, 144 high intensity steady burning white lights, and 15 flashers spaced at 100-ft intervals starting at the threshold and projecting outward to 2400 ft from the runway and flashing sequentially 2 times a second,” you’re likely in the minority.
The ALSF1/2 design is the premier system. However, unless you’re flying into a larger airport that has the capability for lower minimum Cat II/III approaches, you’re unlikely to see it. Instead, you’ll see a scaled down system. For instance, the ILS Rwy 6 to TEB (Teterboro NJ) uses an MALSR (a combination of steady burning lights and flashers).
Further, the way the descend-below-100-ft rule is written can cause some to believe that red side bars and terminating bars coexist on a single approach light system and appear on every system. Red bars are only installed on ALSF1 and ALSF2 systems.
An ALSF-2 has side bars, whereas an ALSF-1 (less common in the US) has wing-shaped terminating bars. Neither system has both. All systems do have sequenced flashing lights. The slang term for this is the rabbit, and pilots believe it is named after the stuffed rabbit used to lure racing greyhounds around a racetrack. The rabbit is what pilots are likely to fixate on during the final stage of the approach.
Once the sequenced flashing lights come into view, there’s a propensity for target fixation and continuation bias. The tendency is to continue an approach that results in a landing rather than executing a go-around, despite not having one of the landing cues in sight at the proper time.
Even more interesting is the phenomenon on inattention blindness, or the fact that pilots don’t see what they don’t expect to see.
In the late 1970s and early 1980s, a team of NASA researchers conducted a series of studies on information display technologies.
One of them involved the use of heads-up displays (HUDs) and how this technology could benefit pilots while conducting instrument approaches. Although the HUD was initially developed for military purposes, the civilian application seems obvious – a pilot could see relevant flight parameters like air speed, altitude, and track displayed in his field of vision while remaining “heads up” or focused out the front windshield.
A HUD could now reduce visual errors (including myopia) that occur during the transition from instrument to visual flight. In one of the experiments, seasoned airline pilots flying a Boeing 727 simulator were assigned to conduct a series of approaches in low visibility conditions.
After repeated approaches, the pilots became well versed using the HUD. Once the experimental subjects had conducted multiple successful trials, researcher Richard Haines added a variable unbeknownst to the pilots: just after breaking out of the clouds, an aircraft taxied out onto the runway right in front of the landing aircraft.
Although the pilots had 7 seconds to respond to the threat and execute a go-around, a few of the pilots landed right on top of the aircraft guilty of the runway incursion. The pilots were incredulous – in their minds the runway incursion didn’t happen.
It was only after the videotape was played back that the pilots realized they were looking without seeing, and never “saw” the runway incursion – the very definition of inattentional blindness. Psychologists Christopher Chabris and Daniel Simons, winners of the 2004 Nobel Prize for psychology, point out that although the HUD helps pilots perform the task they are trying to accomplish, it doesn’t help them see what they are not expecting to see, and it might even impair their ability to notice important events in the world around them.
The conundrum when it comes to landing in instrument conditions is how to make the invisible more visible. According to the Flight Safety Foundation (FSF), providing more accurate information to the pilot during the critical stages or complex approaches enhances safety in several ways. The pilot can better manage surrounding environments, the traffic, and the terrain, which may present a threat.
The added information decreases the threat level to the pilot, enhancing his or her ability to handle any event that may occur. Especially in bad weather or fog, a high level of stress, and difficult or special approaches, the extra information on eyes-out technologies could also increase a pilot’s ability to perform.
A 1970 study by FAA measured the heartrate of general aviation (GA) pilots conducting instrument approaches to minimums. One of the conclusions was that the period between IMC and visual conditions imposes a speed or pacing stress on the pilot.
In the case of an ILS, as the pilot nears the approach minimums, the amplitude of needle movement increases, taxing a pilot’s reactive, intellectual, and cognitive processes. As expected, a pilot’s heartrate increases as the aircraft gets closer to the runway without having it in sight.
Recent technological advances in enhanced and synthetic vision technology have made great strides in improving safety. Enhanced vision (EV) uses sensors (typically infrared) and cameras mounted externally to generate live video of the operating environment outside the aircraft.
Information can be displayed on a multifunction display (MFD) or a HUD, and there’s a subtle difference between the 2. If EV is employed on a HUD it’s called enhanced flight vision system (EFVS), and can result in lower landing minimums, including removal of the admonition of seeing the red side or terminating bars.
The Collins EVS-3000 camera has 3 detectors that combine data into a single image. Subtle temperature differences detected and processed by the sensors allow a pilot to see through low visibility conditions like haze or smoke.
One recent concern was that runways illuminated with LEDs, which produce a very low heat signature, would not be detectable by older EFVSs, but upgrades in sensor sensitivity has rendered that concern moot.
A synthetic vision system (SVS) uses GPS data, aircraft databases, and 3D mapping to generate an artificial image.
Data can come from various sources, and each manufacturer of SVS has a proprietary methodology for incorporating the imagery. SVS has been in development since 2004, and was tested on a Gulfstream aircraft over the course of 59 test flights in a 2-month period.
As published by NASA, results indicated that pilot situational awareness (SA) improved by 150% when using SVS. Gulfstream was the first business jet manufacturer to receive approval for SVS (2008). In 2016 Gulfstream was granted permission to retrofit GIV-SP PlaneDeck-equipped aircraft with SVS.
Synthetic Vision is now standard on the G650/650ER and an option on the G550, G450, and G280. Garmin offers SVS on its G1000 and G3000 avionics suites. The Garmin SVS combines with TCAS/TIS/TAS to display targets in 3D, which assists pilots in collision mitigation. The Pathways option simplifies enroute navigation by generating an intuitive flight track to follow.
A combined vision system (CVS) is a hybrid composed of EFVS and SVS. It consists of real time thermal imagery with weather independent 3D database image generation. The Collins CVS can achieve reduced decision heights with full-view dynamic object detection, obstacle, and runway data across the display, and improved visibility in degraded weather conditions.
The Collins EVS-3600 uses short-wave infrared, long-wave infrared, and a visible camera projected onto the HUD. Collins advertises that the installation decreases operating costs by minimizing go arounds (and perhaps diversions as well).
Bombardier uses a single-view CVS in the Global 5500 and Global 6500. Conclusion If budget is not an issue, a CVS represents the greatest enhancement in safety and operational efficiency. If flight departments are faced with having to decide on one SVS or EFVS, typical mission profile is an important consideration.
Terrain, average weather conditions typically encountered, the volume of traffic, and the type of approach available (along with the associated approach minimums), are all important factors that can sway a purchase decision.
One slight advantage that SVS has over EFVS is that it constantly “pushes” information to the pilot. It’s more intuitive than interpreting a thermal-based EFVS image. It also tends to be more user friendly to the younger generation of pilots raised on video games and constant access to information technology.
As a result, operators are reporting reduced training costs when dealing with aircraft equipped with SVS. To be fair, both systems have the potential to increase SA. But they can also be a crutch that leads to a misplaced sense of security and a precursor to bad decision-making. Mother nature always wins despite a pilot’s best attempt to circumvent it. Sometimes, the go-around and the diversion are the best options.