Part the twoth
Earl Wiener, Ph.D., professor of management science and industrial engineering at the University of Miami, Florida, found that pilots whose aircraft are equipped with glass cockpits spend more "head down" time, particularly at low altitudes, as they interact with their flight management systems. These findings were also confirmed in a study (written by yours truly) published in the Transportation Research Record, a peer-reviewed journal of the National Research Council. That study concluded that pilots of automated cockpits, especially during high workload periods in terminal airspace, had a lower likelihood than pilots flying "steam gauges" of detecting aircraft on a collision course.
The increase of inside-the-cockpit duties (such as programming FMSes, running checklists and adjusting systems) has an additional negative effect on the see-and-avoid principle. The human eye is brought into focus by muscle movements, which change the shape of the eye lens. It takes time for the eyes to refocus from viewing objects inside the cockpit to those outside. This process is called "accommodation."
A young person will typically require about one second to accommodate to a stimulus; however, the speed and degree of accommodation decreases with age, which is a separate issue from the general degradation in visual acuity that often occurs with aging. Of further concern is the increased time required for accommodation as a pilot becomes fatigued.
The average person has a visual field of about 190 degrees, although field of vision varies from person to person and is generally greater for females than males. The field of vision begins to contract after age 35, and in males, this reduction accelerates markedly after 55 years of age.
A number of transient and psychological conditions such as vibration, fatigue, hypoxia or, more than likely, cockpit workload can cause the effective field of vision to contract even further. Experiments conducted at the NASA Ames Research Center indicated that a concurrent task could reduce pilot eye movements by up to 60 percent.
The small visual angle of an approaching aircraft may make it impossible for a pilot to detect the aircraft in time to take evasive action. Since thin wings on aircraft such as gliders are almost invisible when viewed from ahead or behind, such an aircraft must approach even closer before it presents a target of detectable size. In a special study conducted by MIT's Lincoln Lab for the NTSB's investigation of the 1986 Cerritos accident, the estimated probability of visual acquisition of a general aviation aircraft with one pilot looking out the cockpit is just under 20 percent at a range of just one mile.
Further limiting the ability of pilots to see and avoid is the design of flight deck windows. Most cockpits severely limit the pilot's field of view. Obstructions to vision can include window posts, instrument and annunciator panels, glareshields, sun visors, eyeglass rims, windscreen bug splatter, windscreen imperfections, wings and the pilot beside you. Obstructions will not only mask some of the view completely, but will result in certain areas of the outside world being visible to only one eye, making it less likely to be detected. The eye has a natural blind spot at the point where the optic nerve exits the eyeball. Under normal conditions of binocular vision, the blind spot is not a problem as the area of the visual field falling on the blind spot of one eye will still be visible to the other eye.
However, if the view from one eye is obstructed (such as by a window post), then objects in the blind spot of the remaining eye will be invisible. Bearing in mind that an aircraft on a collision course appears stationary in the visual field, the blind spot could potentially mask a conflicting aircraft. The blind spot covers a visual angle of about five degrees horizontal, which is roughly 18 meters (59 feet) at a distance of 200 meters (656 feet), or enough to obscure a Hawker. A second undesirable effect of a window post or similar obstruction is that it can draw the point of focus inward, resulting not only in blurred vision but distorted perception of size and distance.
When the size of a target becomes large enough, a pilot may see the target, if he is looking directly in that direction. Assuming a pilot has adequate visual acuity and adequate vision outside of the cockpit, there are still many reasons limiting his ability to see another aircraft on a collision course.
Detecting traffic can be difficult because aircraft usually appear against complex backgrounds of clouds or terrain. The human eye is very attuned to detecting borders between objects, but in the absence of contours, the visual system rapidly loses efficiency.
So would painting all aircraft bright orange help pilots spot traffic? Not really. The color of an aircraft is less important than the aircraft's contrast, that is its difference in brightness with its background, and it's one of the major determinants of detectability. Contrast also involves reflectivity, background complexity and atmospheric visibility. A good example of contrast is the black letters on a white eye chart. With good lighting the letters can be easily observed in a doctor's office. However, out in the real world, identifying a target is much more difficult when an aircraft is viewed against the background of a city. A dark aircraft will be seen best against a light background, such as bright sky, while a light-colored aircraft will be most conspicuous against a dull background such as a forest. Contrast is further reduced when small particles of haze scatter light. Not only does haze scatter some light away from the observer, but it also scatters some light from the aircraft so that it appears to originate from the background, while light from the background is scattered into the eye's image of the aircraft.
In addition, glare can come directly from the light source or can take the form of veiling glare, reflected from crazing or dirt on the windscreen.
Furthermore, a pilot's age will affect his tolerance for glare. In general, older pilots will be more sensitive to glare.
TCAS was obviously motivated by the tragic accidents stemming from the limitations of the see-and-avoid concept. Those who have flown with TCAS know what a tremendous tool it can be. A common anecdotal observation by many colleagues is that without TCAS, they would miss the majority of traffic that would approach their aircraft at a close range. Human factors research noted by the Australian Transport Safety Bureau found that a traffic search in the absence of traffic information (i.e., no ATC alert, no TCAS TA) is less likely to be successful than a search where traffic information has been provided because knowing where to look greatly increases the chance of sighting the traffic. In fact, traffic alerts were found to increase search effectiveness by a factor of eight.
Providing additional evidence to the efficacy of TCAS-like advisories was the MIT Lincoln Laboratory study cited earlier. The same pilots in the study were given "TCAS-type" advisories as a second part of the research project. In this trial, 57 of the 66 encounters were acquired visually (as opposed to 36 out of 64 encounters without the TCAS-like advisory), with the median range of acquisition being 1.4 nm.
Has TCAS II been a successful factor in preventing collisions? Absolutely. In fact, TCAS II was cited as a factor in detecting and avoiding further loss of separation in 78 percent of reported NMACs in a recent 10-year period. Fifty-nine percent of the reported NMACs involved a resolution advisory from a TCAS II. However, like any warning system, it could not be designed to be absolutely effective in every situation. Fifteen percent of the business jets involved in NMACs were not equipped with TCAS II. In 8 percent of the ASRS reports, the "target aircraft" was not ordinarily equipped with an altitude encoding transponder. TCAS will not provide maximum protection from inflight collisions unless and until all aircraft are equipped with Mode C transponders or its equivalent.
Given the many limitations of the see-and-avoid concept, what must be done to ensure sufficient separation between high-performance and light, general aviation aircraft sharing the same airspace? Arguably, a multilayered protective system is needed in case one or two layers fail, and by design it should offset the fallibility of the see-and-avoid concept. This conclusion isn't my opinion, but rather stems from recommendations from respected organizations and authorities. The Australian Transport Safety Bureau's report stated, "Unalerted see-and-avoid has a limited place as a last resort means of traffic separation at low closing speeds, but is not sufficiently reliable to warrant a greater role in the air traffic system. Australia's Bureau of Air Safety Investigation considers that see-and-avoid is completely unsuitable as a primary traffic separation method for high-speed jet traffic."The separation of high-performance traffic from low-performance traffic has been previously suggested in the United States. In the aftermath of the MU-2/PA-32 accident near Greenwood, Ind., the NTSB suggested that "consideration should be given to establishing entry and departure corridors for high-performance airplanes that are separate from low-performance airplanes at uncontrolled airports."
Airspace separation would be just one layer in a multilayered remedy. "While visual scanning is necessary to prevent midair collisions, it is not sufficient," said the DOT's Morris, who continued, "Potential mitigation strategies include reliable altitude encoding transponders activated at all times in all aircraft, and affordable and reliable collision avoidance technologies in all general aviation aircraft, as the NTSB recommended in 1987."
In today's era of GPS precision, digital cockpits and synthetic vision, the fact that we still depend on the old, fallible "Mark VIII eyeball" to avoid midair collisions is confounding and dangerous. The rate of inflight collisions isn't likely to improve markedly until we get serious about implementing technological and procedural remedies to address this serious, continuing hazard.
And what Chuckles said.