Flying Seasons

The Eyes Have It

August 1, 2007

Your best midair-collision-avoidance tool

Pilots who install traffic advisory systems (TASs) often are surprised to find that they are unable to visually locate target airplanes pointed out by these electronic traffic detectors until the airplanes are too close for comfort. Fortunately, with the traffic icons displayed you can safely maneuver away from traffic.

This became patently obvious in Palm Springs, California, last fall. I was flying the 2005 AOPA sweepstakes Rockwell Commander with a Ryan International 9900BX TAS (now Avidyne TAS 600). My wife and I took off for home on Sunday morning as aviation-satiated AOPA Expo attendees launched into ceiling and visibility unlimited (CAVU) weather. The TAS showed us the location of other airplanes on the Chelton electronic flight information system and multifunction display (MFD). The scary part was that, despite CAVU weather conditions and the azimuth, distance, and climbing or descending icons pointing to each target, we never established visual contact with another airplane that day. We were shocked at how hard it was to see other airplanes — and we knew where to look.

Being involved in a midair collision is extremely unlikely, but informed and prepared pilots can increase the odds in their favor.

Vision limitations

The human eye is a less-than-stellar collision-avoidance tool. Human eyes best detect movement in the peripheral vision, and the central vision is best at identifying details such as whether the moving object is an airplane. The amount of area detailed by the central vision is tiny. A typical field of vision is equivalent to the area covered by a 25-cent piece at a distance of 4 and a half feet. Peripheral vision's ability to discern movement is compromised when the contrast between the moving target and the background decreases. We're less able to see other airplanes when the sky is overcast or when haze lessens visibility.

Each human eye also has a blind spot where the optic nerve exits to the back of the retina. This spot is 10 to 16 degrees to the left of the optical axis (directly ahead) of the left eye, and vice versa for the right eye. This can be demonstrated by drawing two small dime-size marks 4 and a half inches apart on a sheet of paper. Cover your left eye with your left hand while focusing on the left mark. Then use your right hand to move the piece of paper closer to and farther away from your right eye until the right mark disappears. You've just located the blind spot of your right eye. By mixing the optical signals from the left and right eyes, the brain compensates for these blind spots, but if the optical signals from one eye are blocked by an object, such as a windshield center post or a door frame or some other obstruction, a target in the remaining eye's blind spot isn't detectable.

The third vision limitation is what's called empty-field myopia. Empty-field myopia simply means that unless the pilot is actively focusing on an object in the distance, the eye will go to its default mode of focusing on a spot that's only 4 to 7 feet away. This means that pilots must actively focus on different objects — just gazing out into the ether isn't an effective collision-avoidance practice (see " Scanning for Traffic," October 2004 Pilot).

Pilots need to develop effective scan techniques. An AOPA Air Safety Foundation DVD titled Collision Avoidance calls a proper scan, "a sequence of intense observations." A continuous vision sweep across the sky's expanse is not effective.

FAA Advisory Circular 90-48C, titled "Pilots' Role in Collision Avoidance," suggests that scans should consist of a series of small eye movements of no more than 10 degrees with no less time than one second per movement. Remember to scan the air behind, below, and above your airplane. Some pilots use a left-aft-to-front-to-right-aft scan; others spend most of their time scanning the sky in front of the airplane and adding an occasional scan aft. Few pilots realize that studies have shown that it can take up to 12 seconds from the moment a possible midair collision threat is first detected until evasive action is taken.

Statistics on midair collisions

"The pilot of the Cessna had an approximate 21-second opportunity to acquire the Piper had he been scanning down and to his right, while cruising at 2,600 feet. The pilot of the Piper had a 21-second opportunity to acquire the Cessna, if he had been scanning forward and to his left while climbing out from 725 feet to 975 feet and turning from a course of 190 to 250 degrees.... The airplanes were not in a position for the respective pilots to see each other during the two and a half minutes that preceded the accident." — Portion of an NTSB report of a midair accident between a Cessna 150 and a Piper PA-28

According to a study of 79 civil aircraft midair collisions that occurred between 1994 and 1999 presented by Narinder Taneja and Douglas A. Wiegmann of the University of Illinois at Urbana-Champaign, 93 percent of midair collisions took place during day-VFR conditions. Thirty-eight percent took place in the vicinity of the airport during either the takeoff or the approach-to-landing phase of flight; 27 percent during cruise flight; and 17 percent during maneuvering flight. This report also says that 85 percent of midair-collision accidents cite inadequate lookout by one pilot as a cause. Given what we've learned about the average pilot's ability to visually detect other aircraft, are there any other factors that lessen the effectiveness of our first line of defense against MACs?

Eye-tracking studies show that pilots don't spend enough time with their heads up, looking outside for other aircraft. It's recommended that pilots discipline themselves to spend 75 percent of their time looking outside the airplane for traffic. With the widespread advent of large-screen multifunction displays, pilots may think they can depend on TAS technology to protect them from MACs. The 1987 FAA-mandated installation of traffic alert and collision avoidance systems in air-carrier aircraft has greatly reduced the number of air-carrier-to-small-airplane MACs, but even this sophisticated equipment is no guarantee against a MAC, as evidenced by the September 2006 midair in Brazil between a three-week-old Boeing 737-800 and a new Embraer Legacy 600 on a delivery flight to the United States.

Only 5 percent of all MACs are head-on crashes; 82 percent of them take place when one airplane overtakes another on a converging course, and most of these take place within 5 miles of an nontowered airport. Unfortunately, window placement and size are often limiting factors when scanning to the aft, above, and below the average GA airplane.

According to ASF's Collision Avoidance, almost all MACs take place below 3,000 feet agl, with fully one-third of these taking place below 500 feet agl. So be especially vigilant during the takeoff and landing phases of flight.

Mechanical solutions

Since vision — even with its limitations — is our number-one tool for preventing MACs, it's important to do everything possible to best utilize this tool. The following steps are important to remember:

  • Clean the windows. If cleaning does not seem to make much difference, it's time to install a new windshield and side windows. Time takes a toll on windshields and side windows — they become clouded or crazed because of extended exposure to sunlight, or they may have been scratched because of negligence or mishandling. Few things are more impressive and uplifting than the first look out a new windshield, especially when the old one is in poor shape.
  • If it's offered, choose a one-piece windshield option. One-piece windshields are thicker than two-piece windshields. This permits the removal of the vision-blocking center strip.
  • Take proper care of the windshield and windows. There are a number of good cleaning products on the market, but the real key to preventing damage to the surprisingly soft surface of aircraft windows is to use the proper cloths. The best cloths are made of microfiber. These are available almost everywhere. All visible dust or dirt should be flushed with a liberal dose of water before using your favorite cleaning product.
  • Keep your transponder and altitude encoder in good condition and ask for flight following on all flights.

Although flight following isn't an absolute guarantee that air traffic control (ATC) will always be able to provide traffic advisory services, it is a helpful tool when it's available.

  • Install a strobe-light system and one of the supplemental-type-certificate-approved pulse-light systems. Pulse-light systems consist of a small pilot-controlled module that pulses the landing and taxi lights on and off during flight. Pulsing the lights highlights the airplane movement and has been proven to greatly improve the eye's ability to detect a moving airplane.

Installation of a Mode S transponder with traffic information service (TIS) capabilities, when interfaced with an MFD, will provide a graphical display of the location of other transponder-equipped aircraft. TIS is currently available in the vicinity of 107 large airports; however, newer-style radars being installed to upgrade approach and departure radar systems around the United States are not equipped with TIS capabilities, so Mode S transponders as traffic avoidance tools seem to have a limited future.

The wide acceptance of MFDs and the reduction of the costs of active TAS such as the Avidyne TAS 600, which retails for about $10,000 installed, and the L-3 Communications SkyWatch system — at around $18,000 installed — mean that more and more pilots will have the help of electronic traffic-spotter technology as they ply the skies. These boxes are amazing but even the best systems have blind spots, and are able to see only aircraft with functioning transponders. They are not a substitute for well-honed see-and-avoid procedures.

Operations tools

Whenever flying at 3,000 feet agl or higher, follow the hemispherical-cruising-altitude rule. VFR traffic flying a magnetic course between zero and 179 degrees should fly at odd-number thousands of feet plus 500 feet (for example, 3,500, 5,500, and 7,500 feet), and pilots flying on magnetic courses between 180 and 359 degrees should fly at even-number thousands of feet plus 500 (4,500, 6,500, 8,500 feet).

Make it a practice to fly standard traffic patterns. This increases predictability, which makes it much easier to locate other traffic. A standard traffic pattern utilizes left turns. Airports with right traffic will have that noted in the airport data box (for example, RP 14 denotes a right pattern for Runway 14) below the altitude, runway length, and frequency data line on sectional charts, or in the traffic pattern indicators adjacent to the segmented circle.

Although it's not required, safety-savvy pilots also standardize their pattern entries by flying a 45-degree entry to downwind at pattern altitude to merge with existing traffic in the pattern. This entry gives the best view of the entire traffic pattern and airport environment. Again, this practice increases predictability. Slow down and get down to pattern altitude early. This lengthens the amount of time available to locate and identify traffic and increases the odds of making a good landing.

Tuning in and listening to the automatic terminal information service, automated weather observation system, or automated surface observation system for wind direction and speed and runway-use information should begin at least 10 to 15 miles from the destination airport.

Use your radio to announce your position and your intentions. Make brief informative radio calls. Take a minute or two to determine where you are before your first call to the tower, or to the common traffic advisory frequency. The first call should give your position, altitude, and plans. For instance, "Freebish Airport traffic, Skylane 23A, 10 miles east, 3,500 feet, planning left traffic for landing Runway 19." Calls also should be made at regular intervals, such as when entering the 45-degree leg, when entering the downwind, and making the turns to base and final legs of the pattern.

When flying practice IFR approaches in VFR conditions, monitor the destination airport frequency. Make position reports based on miles to, and direction from, the airport rather than by referring to airway or approach fixes. Most VFR pilots have no idea what direction any of the IFR approach initial or intermediate fixes are.

More help

Give your passengers a short course in effective scanning techniques, and familiarize them with the clock location system ATC uses when providing traffic alerts.

These steps will aid flyers in avoiding MACs:

  • Practice cockpit resource management. A well-organized cockpit, and a well-researched and organized flight plan, lessens the amount of time spent head down inside the airplane.
  • Establish sterile cockpit procedures during the takeoff, approach-to-landing, and landing phases of flight. Because of the requirement to balance the increased workload and the need to keep an effective traffic scan during these phases of flight, even the slightest distraction is dangerous.
  • Turn on position, strobe, landing, and taxi lights in the vicinity of airports.
  • Take extra care near airports, use standard procedures, broadcast your plans, and take good care of your eyes, GA's best midair-collision-avoidance tool.

E-mail the author at steve.ells@aopa.org.