Eyes

Anatomically considered an extension of the brain, the eye is the biological camera for the human body. Focusing light energy and translating it into electrical energy then transmitting that data to the brain via the optic nerve is the complex process known more commonly as eye-sight.

Light first passes through the outer layer of the eyeball called the cornea. Working as a “lens cap” for the eyeball it also has refractive (bending) properties that help focus the light entering the eye. Next, light rays entering the eye are refracted by the lens and focused onto the retina. The retina is comparable to the film in a camera. Focus can be changed by ciliary muscles that surround the lens and with contraction or relaxation can change the shape of the lens which affects focus.

The colored membrane that determines eye color is the iris and the center portion of the iris is the pupil. By modulating the size of the pupil the eye can control how much light is allowed to enter and changes the depth of field. Allowing more light into the eye by increasing the size of the pupil, such as in low light situations, the depth of field is decreased. This means the nearest and farthest distances within which everything is in focus is shortened. This modulation is used primarily to make vision easier in high or low light situations.

Once allowed to enter the eye and focused, the light energy meets the retina, or the “film” of the eye. The retina contains cells that translate light energy into electrical energy. Using cone cells to sense bright lights and colors and rod cells for low light or night vision, this data is transmitted to the brain via the optic nerve. Rods are used primarily as peripheral vision and are considered to be 10,000 times more sensitive to light than the cones (which is the reason peripheral vision, or off-set viewing, is recommended for night time traffic scanning). Where the optic nerve is formed on the retina is devoid of cones and rods which results in a blind spot. Each eye compensates for the other eye’s blind spot.

There are several visual impairments that can either develop or be genetically inherited. Most common is myopia, or nearsightedness. This is caused by the focal point of the lens being in front of the retina. Conversely, presbyopia is a form of farsightedness caused by the stiffening of the lens makes accommodation (the ability to change the focal point) difficult.  This requires objects to be farther away from the eye to be in focus which could result in poor vision up close yet still yield good distant vision. Correction for this involves reading glasses which magnifies close up objects allowing them to be focused.

An additional impairment to visual acuity is called astigmatism, or an unequal and variable curvature of the lens and the cornea that prevents an equal focus at varying distances. This causes light rays to refract unequally through the lens creating varying levels of focus in either eye. This condition can be mediated or completely rectified with glasses, contact lenses or a vision correction procedure.

Along with refraction and focus irregularities, vision can be impaired by lens clarity. In some cases the lens can become opaque resulting in a cataract. Cataracts may form by age alone or extended exposure to ultra-violet rays absorbed while flying at high altitudes for long periods of time. In addition, less light may pass through the lens due to age-related yellowing which interferes with the depth of field. Prevention is the best method by wearing UV filtering sunglasses that block the full ultraviolet range. Once developed cataracts can be removed and replaced with surgery.

Finally, the eye can even be affected temporarily by factors that are known to affect the brain in the same manner. Hypoxia, fatigue, carbon monoxide, or toxins can severely impair the eyes ability to see clearly. Hypoxia increases time required for adaptation to night vision and can occur at altitudes as low as 5,000 feet. Carbon monoxide build up in the blood affects the pilot in the same way hypoxia does because carbon monoxide blocks the hemoglobin’s ability to attach to and carry oxygen. Fatigue can affect mental alertness and visual recognition, which could impair a pilot’s ability to scan, maintain focus, or even impair judgment. Toxins, such as alcohol, create a state of histotoxic hypoxia that can reduce visual acuity well past when the last drink was consumed.

These various components that work together, mostly unconsciously, allow us to operate visually in the cockpit and on a day-to-day basis. Maintaining a healthy lifestyle as well as taking precautions to protect and preserve your vision will ensure a long and safe career in the cockpit.

RVSM

REDUCED VERTICAL SEPARATION MINIMUMS (RVSM)

HOW TO HANG OUT IN CROWDED AIRSPACE

The flight levels these days are awfully crowded with corporate jet traffic, airliners, and now even the new very light jets. All this traffic means congestion and delays are more commonplace than anyone wishes them to be. One method used to reduce this congestion and inherent delays in some flight levels is called RVSM, or reduced vertical separation minimums.

Previously the flight levels had a vertical separation of 2,000 feet between aircraft. By reducing this to 1,000 feet, the capacity of the domestic airspace in North America essentially doubled. Beginning at FL290 and extending up
to and including FL410, RVSM covers the entire domestic United States, Canada, Mexico, and throughout Europe and Asia.

By reducing the vertical separation to 1,000 feet, the capacity of the domestic airspace in North America is essentially doubled.

A few of the proponents that allowed RVSM to become a reality were technological advancements in traffic avoidance and barometric altimeters. Higher sensitivity in altimeters proved to be reliable enough to reduce the separation safely to 1,000 feet.

Specifically the advent and broad use of air data computers—the proliferation of traffic collision avoidance equipment and vast improvements in the technology that drives it. In the near future, advances in air traffic control will provide even better display and control of aircraft that will likely further reduce separation minimums, such as next generation technology ADS-B (automatic dependent surveillance broadcast).

Certain equipment requirements must be met prior to entering RVSM airspace, unless a specific waiver is granted. Two primary altimeters, autopilot, altitude hold with an altitude alerter, and a mode C transponder are required. Depending on aircraft certification, an installed and operable TCAS system may also be required. Along with aircraft equipment, aircrew training is also required for operation inside of RVSM airspace.

While operating in RVSM airspace, it is important to not overshoot assigned altitudes because of the reduced separation. When approaching a cleared flight level, vertical speed should be restrained between 500 to 1,000 feet per minute and not exceed 1,500 feet per minute.

At no time should the aircraft be allowed to deviate more than 150 feet from an assigned flight level without manual intervention. These feet per minute (fpm) tolerances and strict level-off requirements stem not only from separation standards but also help prevent undesired TCAS resolution advisories.

For the purpose of precision altitude keeping, the autopilot should be used to capture assigned altitudes and during level flight unless turbulence or aircraft re-trimming require otherwise.

Coupled with the technology and the training required, RVSM is a safe and effective way to reduce congestion and increase capacity for the valuable airways of the sky.

Holding

TEARDROP, PARALLEL, OR DIRECT

HOLDING-PATTERN ENTRIES USING AN FMS

of your primary instrument training is learning the ins and outs of holding. Often it can be a confusing and difficult skill to attain; however, once you get it, holding becomes second nature. One of the luxuries of advanced aircraft systems is the ability to program and define holding points pretty much anywhere you want, allowing the aircraft to navigate on autopilot to the hold, and then enter the hold.

Rarely are you given a holding instruction that doesn’t coincide with a depicted hold on either an arrival procedure or instrument approach. However, when you are given a non-standard or non-defined holding instruction, it’s just as easy to program and execute.

Modern airliners and even general aviation aircraft are commonly equipped with a flight management system or a global positioning system to simplify most navigation tasks. These systems incorporate a working database of instrument approaches, arrival and departure procedures, and en route navigation aids.

Included in this database are the published holds scattered throughout the national airspace system. This makes entering a published hold as easy as a few button presses. Defining a non-published hold is just as easy as entering the key components of the hold: inbound leg, defining fix, and leg distance or time. Once built, you can arm a hold hundreds of miles down your flight plan or you can fly direct to the fix and enter the hold immediately.

The most common use of this tool is during instrument approaches, or more correctly during the missed from an instrument approach. The database contains the entire procedure from initial to missed approach fix and, when coupled to an appropriate autopilot, the aircraft can be directed to complete the entire approach, missed approach, and enter the hold. It is, in fact, so smart that it will even tell you what type of entry to make when arriving at the holding fix.

It’s easy to let yourself become complacent with holding when you have such advanced avionics handling all the hard work. Be sure to practice holding the old-fashioned way for that rainy day when the ILS glideslope is unusable and you have to hold without the autopilot or a fancy FMS/GPS.

Swept Wing

THE SWEPT WING

A STANDARD FOR TRANSPORT CATEGORY AIRCRAFT

MOST OF THE training aircraft you will fly use the rectangular or semi-tapered wing design. They provide stable and safe platforms for flying slow or even gliding when needed. One of the most prolific and utilized designs in Transport category aircraft, however, is the swept wing.

Since the birth of aviation, the goal has always been to go faster, farther, and higher. The swept-wing design helped push those goals beyond what was thought to be the limit. The entire design of a swept wing is a trick. The goal is to trick the airplane into believing it is flying slower than it actually is. It accomplishes this by allowing relative wind to strike the airfoil at an angle. This “tricks” the wing into believing it is flying at a speed slower than the actual true airspeed. Thus, the overall drag created is lower, allowing higher and faster flight.

The premise of the whole trick has everything to do with compressibility. The upper, curved portion of the wing acts like half of a venturi; the still-undisturbed air above the wing is the other half. This accelerates the relative wind over the wing. As an airfoil travels through the air at subsonic speeds, the air flowing over the wing might actually exceed the speed of sound, or Mach 1.0. This creates a shock wave over the wing that is drastically detrimental to performance, destroying lift and dramatically increasing drag. The speed at which these shock waves become apparent and critical is known as critical Mach. By tricking the wing into believing it is flying more slowly, the wing operates farther away from this critical point at higher speeds.

Using a thin, low-cambered wing increases the critical Mach number, allowing higher-speed flight. The downside here is low-airspeed flight. A swept, thin, low-cambered wing might be great for high-speed flight, but how about during takeoff and landing? To counteract these pitfalls, the leading and trailing edges are equipped with high-lift devices. Leading- and trailing-edge flaps increase the aircraft’s overall ability to produce lift by increasing wing area and reenergizing the local airflow. Combine the high-speed benefits of the swept wing with the low-speed generosity of Fowler flaps and leading-edge slats, and you have the efficient and proven design installed on almost every Transport category aircraft.

Runway Incursion Prevention

RUNWAY INCURSION PREVENTION

COMING TO AN AIRPORT NEAR YOU

THE INTERNATIONAL CIVIL Aviation Organization defines a runway incursion as “any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle, or person on the protected area of a surface designated for the landing and takeoff of aircraft.” The FAA has worked hard to implement new procedures and technologies to help reduce and prevent runway incursions.

One such procedure was the implementation of a change of phraseology from “position and hold” to “line up and wait.” Some new technology that may still be unfamiliar is becoming more prominent around the United States.

Airport surface detection equipment, Model X, or ASDE-X, is ground-based traffic monitoring that provides ATC with location information for taxiing aircraft. ASDE-X is a fusion of information from surface movement radar, multilateration sensors, ADS-B sensors, and aircraft and vehicle transponders. This provides the controller with position and identification information of each aircraft on the ground. It can be invaluable in low-visibility situations or at night. The system can also produce aural and visual warnings of possible collisions.

What does this mean for the pilot? Airports that incorporate the ASDE-X system will request you to operate your Mode C transponder while on all runways and taxiways. Look in the Airport/Facility Directory to find if your destination utilizes ASDE-X.

Runway status lights, or RWSL, is a system comprised of sensors and lights that can show the pilot if a runway is occupied or otherwise unsafe.

Combined with ASDE-X technology, it can detect when aircraft or vehicles are occupying, crossing, departing, or landing on a runway. It provides status of the runway by use of runway entrance lights, takeoff hold lights, and runway intersection lights. These lights are in the pavement and show a line of red lights either across the entrance to the runway or alongside the centerline for takeoff hold lights. When the lights are illuminated pilots are advised not to enter or cross the runway or take off when given a “line up and wait” clearance.

Both technologies will increase safety as well as efficiency and capacity at U.S. airports. We pilots must ensure constant vigilance and situational awareness to help prevent runway incursions.