Category: AOPA

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.

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.

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

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.

TRAFFIC COLLISION AND AVOIDANCE SYSTEM

ANOTHER SET OF EYES IN THE SKY

ONE OF MANY systems you will find concurrently on turbojet aircraft is the Traffic Collision and Avoidance System, or TCAS. Following years of improvements and technological advances, TCAS provides basic and advanced aircraft avoidance through monitoring and interpreting of Mode C and Mode S transponders.

TCAS systems today can provide not only traffic information to supplement visual avoidance, but it can also provide escape guidance from the intruder aircraft. Early TCAS systems merely provided the azimuth of the intruder as well as its relative altitude. Now with the TA/RA mode equipped and enabled, you will receive a resolution advisory for the most expeditious way of escaping a collision.

Using escape path and trend information from each aircraft, the TCAS system determines whether a climb or descent is more appropriate for each respective aircraft. It then displays and aurally warns the crew by verbal and visual resolution advisories.

The TCAS systems of two equipped aircraft will even communicate to coordinate the escape. If one aircraft issues a descent advisory to the crew, the opposite crew will receive a climb advisory. The systems will continue to calculate the paths of the two aircraft to determine whether the current resolution is sufficient, or requires a higher rate of climb or descent. It will then issue a second advisory to either increase or decrease, or even maintain, a recommended vertical speed.

The FARs provide language involving a deviation of an ATC clearance in the event of a resolution advisory. The crew is to advise ATC as soon as practicable after such an incident. It is important to remember that nothing relieves the crew from being vigilant to see and avoid traffic; however, TCAS helps to identify and maintain visual contact with aircraft in high-traffic environments.