ASA has been committed to being a leader and innovator in aviation supplies and publications since 1947. We continually strive to bring the very best to our customers. The ASA philosophy is to surround ourselves with the best authors, software developers, product managers, and editors the world of aviation has to offer, and incorporate their experience and wisdom into the top quality products we provide. You can always count on ASA to be at the forefront of technology to bring you the best materials available.

Visit our Website at

Procedures and Airport Operations: Traffic Patterns

Today we’re featuring an excerpt from the Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25B).

At airports without an operating control tower, a segmented circle visual indicator system, if installed, is designed to provide traffic pattern information. Usually located in a position affording maximum visibility to pilots in the air and on the ground and providing a centralized location for other elements of the system, the segmented circle consists of the following components: wind direction indicators, landing direction indicators, landing strip indicators, and traffic pattern indicators.

Segmented circle

A tetrahedron is installed to indicate the direction of landings and takeoffs when conditions at the airport warrant its use. It may be located at the center of a segmented circle and may be lighted for night operations. The small end of the tetrahedron points in the direction of landing. Pilots are cautioned against using a tetrahedron for any purpose other than as an indicator of landing direction. At airports with control towers, the tetrahedron should only be referenced when the control tower is not in operation. Tower instructions supersede tetrahedron indications.

Landing strip indicators are installed in pairs and are used to show the alignment of landing strips. Traffic pattern indicators are arranged in pairs in conjunction with landing strip indicators and used to indicate the direction of turns when there is a variation from the normal left traffic pattern. (If there is no segmented circle installed at the airport, traffic pattern indicators may be installed on or near the end of the runway.)

At most airports and military air bases, traffic pattern altitudes for propeller-driven aircraft generally extend from 600 feet to as high as 1,500 feet above ground level (AGL). Pilots can obtain the traffic pattern altitude for an airport from the Chart Supplement U.S. Also, traffic pattern altitudes for military turbojet aircraft sometimes extend up to 2,500 feet AGL. Therefore, pilots of en route aircraft should be constantly on alert for other aircraft in traffic patterns and avoid these areas whenever possible. When operating at an airport, traffic pattern altitudes should be maintained unless otherwise required by the applicable distance from cloud criteria according to 14 CFR §91.155. Additional information on airport traffic pattern operations can be found in Chapter 4, “Air Traffic Control,” of the AIM. Pilots can find traffic pattern information and restrictions, such as noise abatement in the Chart Supplement U.S.

Example: Key to Traffic Pattern Operations—Single Runway

  1. Enter pattern in level flight, abeam the midpoint of the runway, at pattern altitude. (1,000′ AGL is recommended pattern altitude unless otherwise established.)
  2. Maintain pattern altitude until abeam approach end of the landing runway on downwind leg.
  3. Complete turn to final at least ¼ mile from the runway.
  4. After takeoff or go-around, continue straight ahead until beyond departure end of runway.
  5. If remaining in the traffic pattern, commence turn to crosswind leg beyond the departure end of the runway within 300 feet of pattern altitude.
  6. If departing the traffic pattern, continue straight out, or exit with a 45° turn (to the left when in a left-hand traffic pattern; to the right when in a right-hand traffic pattern) beyond the departure end of the runway, after reaching pattern altitude.

Traffic pattern operations—single runway.

Example: Key to Traffic Pattern Operations—Parallel Runways

  1. Enter pattern in level flight, abeam the midpoint of the runway, at pattern altitude. (1,000′ AGL is recommended pattern altitude unless otherwise established.)
  2. Maintain pattern altitude until abeam approach end of the landing runway on downwind leg.
  3. Complete turn to final at least ¼ mile from the runway.
  4. Do not overshoot final or continue on a track that penetrates the final approach of the parallel runway
  5. After takeoff or go-around, continue straight ahead until beyond departure end of runway.
  6. If remaining in the traffic pattern, commence turn to crosswind leg beyond the departure end of the runway within 300 feet of pattern altitude.
  7. If departing the traffic pattern, continue straight out, or exit with a 45° turn (to the left when in a left-hand traffic pattern; to the right when in a right-hand traffic pattern) beyond the departure end of the runway, after reaching pattern altitude.
  8. Do not continue on a track that penetrates the departure path of the parallel runway.

Traffic pattern operation—parallel runways.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Helicopters: Hovering

Today, we’ll introduce one of the aerodynamic fundamentals of helicopter flight, hovering, with an excerpt from the Helicopter Flying Handbook (FAA-H-8083-21A).

Hovering is the most challenging part of flying a helicopter. This is because a helicopter generates its own gusty air while in a hover, which acts against the fuselage and flight control surfaces. The end result is constant control inputs and corrections by the pilot to keep the helicopter where it is required to be. Despite the complexity of the task, the control inputs in a hover are simple. The cyclic is used to eliminate drift in the horizontal plane, controlling forward, backward, right and left movement or travel. The throttle, if not governor controlled, is used to control revolutions per minute (rpm). The collective is used to maintain altitude. The pedals are used to control nose direction or heading. It is the interaction of these controls that makes hovering difficult, since an adjustment in any one control requires an adjustment of the other two, creating a cycle of constant correction. During hovering flight, a helicopter maintains a constant position over a selected point, usually a few feet above the ground. The ability of the helicopter to hover comes from the both the lift component, which is the force developed by the main rotor(s) to overcome gravity and aircraft weight, and the thrust component, which acts horizontally to accelerate or decelerate the helicopter in the desired direction. Pilots direct the thrust of the rotor system by using the cyclic to change the tip-path plane as compared to the visible horizon to induce travel or compensate for the wind and hold a position. At a hover in a no-wind condition, all opposing forces (lift, thrust, drag, and weight) are in balance; they are equal and opposite. Therefore, lift and weight are equal, resulting in the helicopter remaining at a stationary hover.

To maintain a hover at a constant altitude, the lift must equal the weight of the helicopter. Thrust must equal any wind and tail rotor thrust to maintain position. The power must be sufficient to turn the rotors and overcome the various drags and frictions involved.

While hovering, the amount of main rotor thrust can be changed to maintain the desired hovering altitude. This is done by changing the angle of incidence (by moving the collective) of the rotor blades and hence the angle of attack (AOA) of the main rotor blades. Changing the AOA changes the drag on the rotor blades, and the power delivered by the engine must change as well to keep the rotor speed constant.

The weight that must be supported is the total weight of the helicopter and its occupants. If the amount of lift is greater than the actual weight, the helicopter accelerates upwards until the lift force equals the weight gain altitude; if thrust is less than weight, the helicopter accelerates downward. When operating near the ground, the effects of the proximity to the surface change this response.

The drag of a hovering helicopter is mainly induced drag incurred while the blades are producing lift. There is, however, some profile drag on the blades as they rotate through the air and a small amount of parasite drag from the non-lift-producing surfaces of the helicopter, such as the rotor hub, cowlings, and landing gear. Throughout the rest of this discussion, the term “drag” includes induced, profile and parasite drag.

An important consequence of producing thrust is torque. Remember Newton’s Third Law: for every action there is an equal and opposite reaction. Therefore, as the engine turns the main rotor system in a counterclockwise direction, the helicopter fuselage wants to turn clockwise. The amount of torque is directly related to the amount of engine power being used to turn the main rotor system. Remember, as power changes, torque changes.

To counteract this torque-induced turning tendency, an antitorque rotor or tail rotor is incorporated into most helicopter designs. A pilot can vary the amount of thrust produced by the tail rotor in relation to the amount of torque produced by the engine. As the engine supplies more power to the main rotor, the tail rotor must produce more thrust to overcome the increased torque effect. This control change is accomplished through the use of antitorque pedals.

A tail rotor is designed to produce thrust in a direction opposite torque. The thrust produced by the tail rotor is sufficient to move the helicopter laterally.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Aircraft Systems: Pressurized Aircraft

Aircraft are flown at high altitudes for two reasons. First, an aircraft flown at high altitude consumes less fuel for a given airspeed than it does for the same speed at a lower altitude because the aircraft is more efficient at a high altitude. Second, bad weather and turbulence may be avoided by flying in relatively smooth air above the storms. Many modern aircraft are being designed to operate at high altitudes, taking advantage of that environment. In order to fly at higher altitudes, the aircraft must be pressurized or suitable supplemental oxygen must be provided for each occupant. It is important for pilots who fly these aircraft to be familiar with the basic operating principles, which we’ll talk about today with an excerpt from the Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25B).

In a typical pressurization system, the cabin, flight compartment, and baggage compartments are incorporated into a sealed unit capable of containing air under a pressure higher than outside atmospheric pressure. On aircraft powered by turbine engines, bleed air from the engine compressor section is used to pressurize the cabin. Superchargers may be used on older model turbine-powered aircraft to pump air into the sealed fuselage. Piston-powered aircraft may use air supplied from each engine turbocharger through a sonic venturi (flow limiter). Air is released from the fuselage by a device called an outflow valve. By regulating the air exit, the outflow valve allows for a constant inflow of air to the pressurized area.

High performance airplane pressurization system.

A cabin pressurization system typically maintains a cabin pressure altitude of approximately 8,000 feet at the maximum designed cruising altitude of an aircraft. This prevents rapid changes of cabin altitude that may be uncomfortable or cause injury to passengers and crew. In addition, the pressurization system permits a reasonably fast exchange of air from the inside to the outside of the cabin. This is necessary to eliminate odors and to remove stale air.

Standard atmospheric pressure chart.

Pressurization of the aircraft cabin is necessary in order to protect occupants against hypoxia. Within a pressurized cabin, occupants can be transported comfortably and safely for long periods of time, particularly if the cabin altitude is maintained at 8,000 feet or below, where the use of oxygen equipment is not required. The flight crew in this type of aircraft must be aware of the danger of accidental loss of cabin pressure and be prepared to deal with such an emergency whenever it occurs.

The following terms will aid in understanding the operating principles of pressurization and air conditioning systems:

  • Aircraft altitude—the actual height above sea level at which the aircraft is flying
  • Ambient temperature—the temperature in the area immediately surrounding the aircraft
  • Ambient pressure—the pressure in the area immediately surrounding the aircraft
  • Cabin altitude—cabin pressure in terms of equivalent altitude above sea level
  • Differential pressure—the difference in pressure between the pressure acting on one side of a wall and the pressure acting on the other side of the wall. In aircraft air-conditioning and pressurizing systems, it is the difference between cabin pressure and atmospheric pressure.

The cabin pressure control system provides cabin pressure regulation, pressure relief, vacuum relief, and the means for selecting the desired cabin altitude in the isobaric and differential range. In addition, dumping of the cabin pressure is a function of the pressure control system. A cabin pressure regulator, an outflow valve, and a safety valve are used to accomplish these functions.

The cabin pressure regulator controls cabin pressure to a selected value in the isobaric range and limits cabin pressure to a preset differential value in the differential range. When an aircraft reaches the altitude at which the difference between the pressure inside and outside the cabin is equal to the highest differential pressure for which the fuselage structure is designed, a further increase in aircraft altitude will result in a corresponding increase in cabin altitude. Differential control is used to prevent the maximum differential pressure, for which the fuselage was designed, from being exceeded. This differential pressure is determined by the structural strength of the cabin and often by the relationship of the cabin size to the probable areas of rupture, such as window areas and doors.

The cabin air pressure safety valve is a combination pressure relief, vacuum relief, and dump valve. The pressure relief valve prevents cabin pressure from exceeding a predetermined differential pressure above ambient pressure. The vacuum relief prevents ambient pressure from exceeding cabin pressure by allowing external air to enter the cabin when ambient pressure exceeds cabin pressure. The flight deck control switch actuates the dump valve. When this switch is positioned to ram, a solenoid valve opens, causing the valve to dump cabin air into the atmosphere.

The degree of pressurization and the operating altitude of the aircraft are limited by several critical design factors. Primarily, the fuselage is designed to withstand a particular maximum cabin differential pressure.

Several instruments are used in conjunction with the pressurization controller. The cabin differential pressure gauge indicates the difference between inside and outside pressure. This gauge should be monitored to assure that the cabin does not exceed the maximum allowable differential pressure. A cabin altimeter is also provided as a check on the performance of the system. In some cases, these two instruments are combined into one. A third instrument indicates the cabin rate of climb or descent. A cabin rate-of-climb instrument and a cabin altimeter are illustrated in the figure below.

Cabin pressurization instruments. (Click to expand.)

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Procedures and Airport Operations: Short-Field Approach and Landing

Short-field approaches and landings require the use of procedures for approaches and landings at fields with a relatively short landing area or where an approach is made over obstacles that limit the available landing area.  Short-field operations require the pilot fly the airplane at one of its crucial performance capabilities while close to the ground in order to safely land within confined areas. This low-speed type of power-on approach is closely related to the performance of flight at minimum controllable airspeeds. Today’s post is an excerpt from the Airplane Flying Handbook (FAA-8083-3B).

Landing over an obstacle.

Landing on a short-field.

To land within a short-field or a confined area, the pilot must have precise, positive control of the rate of descent and airspeed to produce an approach that clears any obstacles, result in little or no floating during the round out, and permit the airplane to be stopped in the shortest possible distance.

The procedures for landing in a short-field or for landing approaches over obstacles as recommended in the AFM/ POH should be used. A stabilized approach is essential. These procedures generally involve the use of full flaps and the final approach started from an altitude of at least 500 feet higher than the touchdown area. A wider than normal pattern is normally used so that the airplane can be properly configured and trimmed. In the absence of the manufacturer’s recommended approach speed, a speed of not more than 1.3 VSO is used. For example, in an airplane that stalls at 60 knots with power off, and flaps and landing gear extended, an approach speed no higher than 78 knots is used. In gusty air, no more than one-half the gust factor is added. An excessive amount of airspeed could result in a touchdown too far from the runway threshold or an after landing roll that exceeds the available landing area. After the landing gear and full flaps have been extended, simultaneously adjust the power and the pitch attitude to establish and maintain the proper descent angle and airspeed. A coordinated combination of both pitch and power adjustments is required. When this is done properly, very little change in the airplane’s pitch attitude and power setting is necessary to make corrections in the angle of descent and airspeed.

Stabilized approach.

Unstabilized approach.

The short-field approach and landing is in reality an accuracy approach to a spot landing. The procedures previously outlined in the section on the stabilized approach concept are used. If it appears that the obstacle clearance is excessive and touchdown occurs well beyond the desired spot leaving insufficient room to stop, power is reduced while lowering the pitch attitude to steepen the descent path and increase the rate of descent. If it appears that the descent angle does not ensure safe clearance of obstacles, power is increased while simultaneously raising the pitch attitude to shallow the descent path and decrease the rate of descent. Care must be taken to avoid an excessively low airspeed. If the speed is allowed to become too slow, an increase in pitch and application of full power may only result in a further rate of descent. This occurs when the AOA is so great and creating so much drag that the maximum available power is insufficient to overcome it. This is generally referred to as operating in the region of reversed command or operating on the back side of the power curve. When there is doubt regarding the outcome of the approach, make a go around and try again or divert to a more suitable landing area.

Because the final approach over obstacles is made at a relatively steep approach angle and close to the airplane’s stalling speed, the initiation of the round out or flare must be judged accurately to avoid flying into the ground or stalling prematurely and sinking rapidly. A lack of floating during the flare with sufficient control to touch down properly is verification that the approach speed was correct.

Touchdown should occur at the minimum controllable airspeed with the airplane in approximately the pitch attitude that results in a power-off stall when the throttle is closed. Care must be exercised to avoid closing the throttle too rapidly, as closing the throttle may result in an immediate increase in the rate of descent and a hard landing.

Upon touchdown, the airplane is held in this positive pitch attitude as long as the elevators remain effective. This provides aerodynamic braking to assist in deceleration. Immediately upon touchdown and closing the throttle, appropriate braking is applied to minimize the after-landing roll. The airplane is normally stopped within the shortest possible distance consistent with safety and controllability. If the proper approach speed has been maintained, resulting in minimum float during the round out and the touchdown made at minimum control speed, minimum braking is required.

Common errors in the performance of short-field approaches and landings are:

  • Failure to allow enough room on final to set up the approach, necessitating an overly steep approach and high sink rate
  • Unstable approach
  • Undue delay in initiating glide path corrections
  • Too low an airspeed on final resulting in inability to flare properly and landing hard
  • Too high an airspeed resulting in floating on round out
  • Prematurely reducing power to idle on round out resulting in hard landing
  • Touchdown with excessive airspeed
  • Excessive and/or unnecessary braking after touchdown
  • Failure to maintain directional control
  • Failure to recognize and abort a poor approach that cannot be completed safely
[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Procedures and Airport Operations: Night Flight Approaches and Landings

The mechanical operation of an airplane at night is no different than operating the same airplane during the day. The pilot, however, is affected by various aspects of night operations and must take them into consideration during night flight operations. Some are actual physical limitations affecting all pilots while others, such as equipment requirements, procedures, and emergency situations, must also be considered. Today, we’re featuring an excerpt from the Airplane Flying Handbook (8083-3B) on flying approaches and landings at night.

When approaching the airport to enter the traffic pattern and land, it is important that the runway lights and other airport lighting be identified as early as possible. If the airport layout is unfamiliar, sighting of the runway may be difficult until very close-in due to the maze of lights observed in the area. Fly toward the rotating beacon until the lights outlining the runway are distinguishable. To fly a traffic pattern of proper size and direction, the runway threshold and runway-edge lights must be positively identified. Once the airport lights are seen, these lights should be kept in sight throughout the approach.

Use light patterns for orientation.

Distance may be deceptive at night due to limited lighting conditions. A lack of intervening references on the ground and the inability to compare the size and location of different ground objects cause this. This also applies to the estimation of altitude and speed. Consequently, more dependence must be placed on flight instruments, particularly the altimeter and the airspeed indicator. When entering the traffic pattern, always give yourself plenty of time to complete the before landing checklist. If the heading indicator contains a heading bug, setting it to the runway heading is an excellent reference for the pattern legs.

Maintain the recommended airspeeds and execute the approach and landing in the same manner as during the day. A low, shallow approach is definitely inappropriate during a night operation. The altimeter and VSI should be constantly cross-checked against the airplane’s position along the base leg and final approach. A visual approach slope indicator (VASI) is an indispensable aid in establishing and maintaining a proper glide path.


After turning onto the final approach and aligning the airplane midway between the two rows of runway-edge lights, note and correct for any wind drift. Throughout the final approach, use pitch and power to maintain a stabilized approach. Flaps are used the same as in a normal approach. Usually, halfway through the final approach, the landing light is turned on. Earlier use of the landing light may be necessary because of “Operation Lights ON” or for local traffic considerations. The landing light is sometimes ineffective since the light beam will usually not reach the ground from higher altitudes. The light may even be reflected back into the pilot’s eyes by any existing haze, smoke, or fog. This disadvantage is overshadowed by the safety considerations provided by using the “Operation Lights ON” procedure around other traffic.

The round out and touchdown is made in the same manner as in day landings. At night, the judgment of height, speed, and sink rate is impaired by the scarcity of observable objects in the landing area. An inexperienced pilot may have a tendency to round out too high until attaining familiarity with the proper height for the correct round out. To aid in determining the proper round out point, continue a constant approach descent until the landing lights reflect on the runway and tire marks on the runway can be seen clearly. At this point, the round out is started smoothly and the throttle gradually reduced to idle as the airplane is touching down. During landings without the use of landing lights, the round out may be started when the runway lights at the far end of the runway first appear to be rising higher than the nose of the airplane. This demands a smooth and very timely round out and requires that the pilot feel for the runway surface using power and pitch changes, as necessary, for the airplane to settle slowly to the runway. Blackout landings should always be included in night pilot training as an emergency procedure.

Roundout when tire marks are visible.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Ground Reference Maneuvers: Rectangular Course

A pilot must develop the proper coordination, timing, and attention to accurately and safely maneuver the airplane with regard to the required attitudes and ground references. Ground reference maneuvers are the principle flight maneuvers that combine the four fundamentals (straight-and-level, turns, climbs, and descents) into a set of integrated skills that the pilot uses in their everyday flight activity. A pilot must develop the skills necessary to accurately control, through the effect and use of the flight controls, the flightpath of the airplane in relationship to the ground. From every takeoff to every landing, a pilot exercises these skills in controlling the airplane.

Today, we’re featuring an excerpt from the Airplane Flying Handbook (FAA-H-8083-3B) on a principle ground reference maneuver known as the rectangular course.

The rectangular course is a training maneuver in which the airplane maintains an equal distance from all sides of the selected rectangular references. The maneuver is accomplished to replicate the airport traffic pattern that an airplane typically maneuvers while landing. While performing the rectangular course maneuver, the pilot should maintain a constant altitude, airspeed, and distance from the ground references. The maneuver assists the pilot in practicing the following:

  • Maintaining a specific relationship between the airplane and the ground.
  • Dividing attention between the flightpath, groundbased references, manipulating the flight controls, and scanning for outside hazards and instrument indications.
  • Adjusting the bank angle during turns to correct for groundspeed changes in order to maintain constant radius turns.
  • Rolling out from a turn with the required wind correction angle to compensate for any drift cause by the wind.
  • Establishing and correcting the wind correction angle in order to maintain the track over the ground.
  • Preparing the pilot for the airport traffic pattern and subsequent landing pattern practice.

First, a square, rectangular field, or an area with suitable ground references on all four sides, as previously mentioned should be selected consistent with safe practices. The airplane should be flown parallel to and at an equal distance between one-half to three-fourths of a mile away from the field boundaries or selected ground references. The flightpath should be positioned outside the field boundaries or selected ground references so that the references may be easily observed from either pilot seat. It is not practicable to fly directly above the field boundaries or selected ground references. The pilot should avoid flying close to the references, as this will require the pilot to turn using very steep bank angles, thereby increasing aerodynamic load factor and the airplane’s stall speed, especially in the downwind to crosswind turn.

The entry into the maneuver should be accomplished downwind. This places the wind on the tail of the airplane and results in an increased groundspeed. There should be no wind correction angle if the wind is directly on the tail of the airplane; however, a real-world situation results in some drift correction. The turn from the downwind leg onto the base leg is entered with a relatively steep bank angle. The pilot should roll the airplane into a steep bank with rapid, but not excessive, coordinated aileron and rudder pressures. As the airplane turns onto the following base leg, the tailwind lessens and becomes a crosswind; the bank angle is reduced gradually with coordinated aileron and rudder pressures. The pilot should be prepared for the lateral drift and compensate by turning more than 90° angling toward the inside of the rectangular course.

The next leg is where the airplane turns from a base leg position to the upwind leg. Ideally, the wind is directly on the nose of the airplane resulting in a direct headwind and decreased groundspeed; however, a real-world situation results in some drift correction. The pilot should roll the airplane into a medium banked turn with coordinated aileron and rudder pressures. As the airplane turns onto the upwind leg, the crosswind lessens and becomes a headwind, and the bank angle is gradually reduced with coordinated aileron and rudder pressures. Because the pilot was angled into the wind on the base leg, the turn to the upwind leg is less than 90°.

The next leg is where the airplane turns from an upwind leg position to the crosswind leg. The pilot should slowly roll the airplane into a shallow-banked turn, as the developing crosswind drifts the airplane into the inside of the rectangular course with coordinated aileron and rudder pressures. As the airplane turns onto the crosswind leg, the headwind lessens and becomes a crosswind. As the turn nears completion, the bank angle is reduced with coordinated aileron and rudder pressures. To compensate for the crosswind, the pilot must angle into the wind, toward the outside of the rectangular course, which requires the turn to be less than 90°.

The final turn is back to the downwind leg, which requires a medium-banked angle and a turn greater than 90°. The groundspeed will be increasing as the turn progresses and the bank should be held and then rolled out in a rapid, but not excessive, manner using coordinated aileron and rudder pressures.

For the maneuver to be executed properly, the pilot must visually utilize the ground-based, nose, and wingtip references to properly position the airplane in attitude and in orientation to the rectangular course. Each turn, in order to maintain a constant ground-based radius, requires the bank angle to be adjusted to compensate for the changing groundspeed—the higher the groundspeed, the steeper the bank. If the groundspeed is initially higher and then decreases throughout the turn, the bank angle should progressively decrease throughout the turn. The converse is also true, if the groundspeed is initially slower and then increases throughout the turn, the bank angle should progressively increase throughout the turn until rollout is started. Also, the rate for rolling in and out of the turn should be adjusted to prevent drifting in or out of the course. When the wind is from a direction that could drift the airplane into the course, the banking roll rate should be slow. When the wind is from a direction that could drift the airplane to the outside of the course, the banking roll rate should be quick.

The following are the most common errors made while performing rectangular courses:

  • Failure to adequately clear the area above, below, and on either side of the airplane for safety hazards, initially and throughout the maneuver.
  • Failure to establish a constant, level altitude prior to entering the maneuver.
  • Failure to maintain altitude during the maneuver.
  • Failure to properly assess wind direction.
  • Failure to establish the appropriate wind correction angle.
  • Failure to apply coordinated aileron and rudder pressure, resulting in slips and skids.
  • Failure to manipulate the flight controls in a smooth and continuous manner.
  • Failure to properly divide attention between controlling the airplane and maintaining proper orientation with the ground references.
  • Failure to execute turns with accurate timing.
[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Weather: Fronts

Today, we’re featuring an excerpt from Bob Gardner’s The Complete Private Pilot.

A weather front exists where air masses with different properties meet. The terms “warm” and “cold” are relative: 30°F air is warmer than 10°F air, but that “warm” air doesn’t call for bathing suits. Cold air is more dense than warm air, so where two dissimilar masses meet, the cold air stays near the surface. Figure 1 shows a cold front: cold air advancing from west to east and displacing warm air. Because the cold air is dense and relatively heavy, it moves rapidly across the surface, pushing the warm air up. Notice that in both cases the warm air is forced aloft and the cold air stays at the surface. When air is lifted, stuff happens. Just how bad that “stuff” might be is determined by the moisture content of the warm air and where that moisture is coming from.

Figure 1. Cross-section of a typical cold front

Friction slows the cold air movement at the surface, so that the front is quite vertical in cross-section and the band of frontal weather is narrow. Cold fronts can move as fast as 30 knots. Your awareness of this rapid movement, together with facts you already know about temperature and dew point will allow you to make the following generalizations about cold front weather.

Visibility: Good behind the front. Warm air and pollutants rise rapidly because warm air is less dense than cold air.
Flight conditions: Bumpy as thermal currents rise.

Precipitation: Showery in the frontal area as the warm air is forced aloft and its moisture condenses. The ability of the air to hold moisture decreases as the air cools, and as the moisture contained in each column of rising air condenses into water droplets, showers result.

Cloud type: Cumulus, due to air being raised rapidly to the condensation level. Cumulus clouds are a sign of unstable air; the rising air columns are warmer than the surrounding air and continue to rise under their own power.

Icing possibility: Clear ice. Cumulus clouds develop large water droplets which freeze into clear sheets of ice when they strike an airplane.

A warm front exists when a warm air mass overtakes a slow-moving cold air mass; the lighter warm air cannot displace the heavier cold air, and the warm air is forced to rise as it moves forward (Figure 2). This slow upward movement combined with the slow forward movement characteristic of warm fronts allows the warm air to cool slowly. As it reaches the condensation level, stratiform clouds develop. While cold frontal conditions exist over a very short distance, warm fronts slope upward for many miles, and warm frontal weather may be extensive.

Figure 2. Cross-section of a typical warm front

You may encounter warm front clouds 50 to 100 miles from where the front is depicted on the surface analysis chart. The following are the characteristics of warm frontal weather:

Visibility: Poor; pollutants trapped by warm air aloft. Air warmed at the surface can only rise until it reaches air at its own temperature.

Flight conditions: Smooth, no thermal activity.

Precipitation: Drizzle or continuous rain as moist air is slowly raised to the condensation level.

Cloud type: Stratus or layered, the result of slow cooling.

Icing possibility: Rime ice; small water droplets freeze instantly upon contact with an airplane and form a rough, milky coating.

Occasionally, a fast-moving cold front will overtake a warm front (Figure 3) and lift the warm air away from the surface. This is called an occlusion, and occluded frontal weather contains the worst features of both warm and cold fronts: turbulent flying conditions, showers and/or continuous precipitation, poor visibility in precipitation, and broad geographic extent of frontal weather conditions.

Figure 3. Occluded fronts

Air masses can maintain their warm/cold identity and yet not exert any displacement force. When this happens, the front becomes stationary, and the associated weather covers a large geographic area. In your planning, what you see is probably what you will get during the flight.

When you look at a weather map which shows frontal positions, cold fronts will be marked in blue, warm fronts in red, occluded fronts will be purple, and stationary fronts will alternate red and blue. You can identify fronts on black-and-white charts because the cold front symbols look like icicles and warm front symbols appear as blisters (Figure 4). Visualize the lifting process, and you will be on your way to being your own weather forecaster.

Figure 4. Surface analysis chart symbols

In flight, when you fly through a front you will notice a change in outside air temperature and wind direction; you will change heading to the right in order to stay on course.

Occluded fronts show both icicles and blisters on the same side of the front in the direction of movement, and stationary fronts show the symbols on opposite sides of the frontal line, indicating opposing forces.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Aircraft Systems: Fuel Injection Systems

Today we’re featuring an excerpt from The Pilot’s Manual: Ground School (PM-2C).

Many sophisticated engines have fuel directly metered into the induction manifold and then into the cylinders without using a carburetor. This is known as fuel injection.

A venturi system is still used to create the pressure differential. This is coupled to a fuel control unit (FCU), from which metered fuel is piped to the fuel manifold unit (fuel distributor). From here, a separate fuel line carries fuel to the discharge nozzle in each cylinder head, or into the inlet port prior to the inlet valve. The mixture control in the fuel injection system controls the idle cut-off.

With fuel injection, each individual cylinder is provided with a correct mixture by its own separate fuel line. (This is unlike the carburetor system, which supplies the same fuel/air mixture to all cylinders. This requires a slightly richer-than-ideal mixture to ensure that the leanest-running cylinder does not run too lean.)

The advantages of fuel injection include:

  • freedom from fuel ice (no suitable place for it to form);
  • more uniform delivery of the fuel/air mixture to each cylinder;
  • improved control of fuel/air ratio;
  • fewer maintenance problems;
  • instant acceleration of the engine after idling with no tendency for it to stall; and
  • increased engine efficiency.

Starting an already hot engine that has a fuel injection system may be difficult because of vapor locking in the fuel lines. Electric boost pumps that pressurize the fuel lines can help alleviate this problem. Having very fine fuel lines, fuel injection engines are more susceptible to any contamination in the fuel such as dirt or water. Correct fuel management is imperative! Know the fuel system of your particular airplane. Surplus fuel provided by a fuel injection system will pass through a return line which may be routed to only one of the fuel tanks. If the pilot does not remain aware of where the surplus fuel is being returned to, it may result in uneven fuel loading in the tanks or fuel being vented overboard (thus reducing flight fuel available).

Typical fuel injection system.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

Aircraft Systems: Propeller Principles

The propeller, the unit which must absorb the power output of the engine, has passed through many stages of development. Today we’ll feature an excerpt introducing the general concepts of a propeller from our recently released book Aircraft Systems for Pilots.

Propeller Principles
The aircraft propeller consists of two or more blades and a central hub to which the blades are attached. Each blade of an aircraft propeller is essentially a rotating wing. As a result of their construction, the propeller blades produce forces that create thrust to pull or push the airplane through the air.

The power needed to rotate the propeller blades is furnished by the engine. The propeller is mounted on a shaft. which may be an extension of the crankshaft on low-horsepower engines; on high-horsepower engines, it is mounted on a propeller shaft which is geared to the engine crankshaft. In either case. the engine rotates the airfoils of the blades through the air at high speeds, and the propeller transforms the rotary motion (power) of the engine into thrust.

The engine supplies brake horsepower through a rotating shaft. and the propeller converts it into thrust horsepower. In this conversion, some power is wasted. For maximum efficiency, the propeller must be designed to keep this waste as small as possible. Since the efficiency of any machine is the ratio of the useful power output to the power input, propeller efficiency is the ratio of thrust horsepower to brake horsepower. The usual symbol for propeller efficiency is the Greek letter η (eta). Propeller efficiency varies from 50% to 87%, depending on how much the propeller “slips.”

THP = BHP × Propeller Efficiency

Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch (see figure 1). Geometric pitch is the distance a propeller should advance in one revolution; effective pitch is the distance it actually advances. Thus, geometric or theoretical pitch is based on no slippage, but actual, or effective pitch, recognizes propeller slippage in the air.

Figure 1. Effective and geometric pitch.

The typical propeller blade can be described as a twisted airfoil of irregular planform. Two views of a propeller blade are shown in figure 2. For purposes of analysis, a blade can be divided into segments, which are located by station numbers in inches from the center of the blade hub. The cross sections of each 6-in. blade segment are shown as airfoils in the right-hand side of figure 2. Also identified in figure 2 are the blade shank and the blade butt. The blade shank is the thick, rounded portion of the propeller blade near the hub, which is designed to give strength to the blade. The blade butt, also called the blade base or root, is the end of the blade that fits in the propeller hub. The blade tip is that part of the propeller blade farthest from the hub, generally defined as the last 6 in. of the blade.

Figure 2. Propeller blade design.

A cross section of a typical propeller blade is shown in figure 3. This section or blade element is an airfoil comparable to a cross section of an aircraft wing. The blade back is the cambered or curved side of the blade, similar to the upper surface of an aircraft wing. The blade face is the flat side of the propeller blade (“facing” the pilot, if the propeller is up front in the tractor position). The chord line is an imaginary line drawn through the blade from the leading edge to the trailing edge. The leading edge is the thick edge of the blade that meets the air as the propeller rotates.

Figure 3. Cross section of a propeller blade.

Blade angle, usually measured in degrees, is the angle between the chord line of the blade and the plane of rotation (figure 4). The chord of the propeller blade is determined in about the same manner as the chord of an airfoil. In fact, a propeller blade can be considered as being made up of an infinite number of thin blade elements, each of which is a miniature airfoil section whose chord is the width of the propeller blade at that section. Because most propellers have a flat blade face, pitch is easily measured by finding the angle between a line drawn along the face of the propeller blade and a line scribed by the plane of rotation. Pitch is not the same as blade angle, but, because pitch is largely determined by blade angle, the two terms are often used interchangeably. An increase or decrease in one is usually associated with an increase or decrease in the other.

Figure 4. Propeller efficiency varies with airspeed while constant speed propellers maintain high efficiency over a wide range of airspeeds.

Forces Acting On The Propeller
A rotating propeller is acted upon by centrifugal, twisting, and bending forces. The principal forces acting on a rotating propeller are illustrated in figure 5.

Figure 5. Forces acting on a rotating propeller.

Centrifugal force (A of figure 5) is a physical force that tends to throw the rotating propeller blades away from the hub. Torque bending force (B of figure 5), in the form of air resistance, tends to bend the propeller blades opposite to the direction of rotation. Thrust bending force (C of figure 5) is the thrust load that tends to bend propeller blades forward as the aircraft is pulled through the air. Aerodynamic twisting force (D of figure 5) creates a rotational force (twisting moment) about the center of pressure, causing the blade to tend to pitch to a lower blade angle (streamline).

At high angles of attack this twisting moment is reduced as the center of lift moves forward. At very high blade angles of attack, the blades may exhibit a weak tendency to pitch toward a greater blade angle.

Centrifugal twisting force also twists the blade to flat pitch (unless the blade is counterweighted so its center of mass is behind the center of rotation). This is a strong force at normal propeller speeds. Imagine a string tied to your finger and to a small weight (see figure 6). If the weight is spinning about your finger, the weight will align itself directly in line with the point on your finger where it is tied (reference the plane scribed by the spinning weight). This same force causes the center of mass of the propeller to align itself with the center of rotation on the spin-plane, causing a strong pitch tendency toward minimum blade pitch angle.

Figure 6. Propeller forces.

A propeller must be capable of withstanding severe stresses, which are greater near the hub, caused by centrifugal force and thrust. The stresses increase in proportion to the RPM. The blade face is also subjected to tension from the centrifugal force and additional tension from the bending. For these reasons, nicks or scratches on the blade may cause very serious consequences.

A propeller must also be rigid enough to prevent fluttering, a type of vibration in which the ends of the blade twist back and forth at high frequency around an axis perpendicular to the engine crankshaft. Fluttering is accompanied by a distinctive noise often mistaken for exhaust noise. The constant vibration tends to weaken the blade and eventually causes failure.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |

IFR: Precision Instrument Runway Markings

Today, we’re sharing an excerpt from The Pilot’s Manual Volume Three: Instrument Flying. This post is a follow-up to last month’s IFR: The Instrument Landing System (ILS).

To assist pilots transitioning to a visual landing at the conclusion of a precision instrument approach, precision instrument runways have specific markings.

A displaced threshold on an instrument runway is indicated by arrows in the middle of the runway leading to the displaced threshold mark. The runway edge lights to the displaced threshold appear red to an airplane on approach, and to an airplane taxiing to the displaced threshold from the absolute end of the runway. They appear white when taxiing back from the displaced threshold toward the absolute end of the runway. The green runway end lights seen on approach to a runway with a displaced threshold are found off the edge of the runway.

The runway surface with arrows to the displaced threshold is available for taxiing, takeoff and landing roll-out, but not for landing. The initial part of this runway is a non-touchdown area. If chevrons rather than arrows are used to mark the displaced threshold, then the surface is not available for any use, other than aborted takeoff from the other direction.

Displaced threshold markings with preceding blast pad or stopway.

Displaced threshold markings with preceding blast pad or stopway.

A precision instrument runway will contain a designation, centerline, threshold, aiming point, touchdown zone, and side strips as seen in the figure below. Runway threshold strips can be configured in two ways. Four solid strips on either side of the centerline or configured as such that the number of strips correlates to the width of the runway (see table). The runway aiming point markers are large rectangular marks on each side of the runway centerline usually placed 1,000 feet after the threshold and serve as a visual aiming point for the pilot. Touchdown zone markers identify the touchdown zone for landing operations, providing coded distance information in 500 foot intervals and shown as either one, two, or three vertical stripes on either side of the centerline.

Runway width based on number of runway threshold strips.

Runway width based on number of runway threshold strips.

Markings on a precision instrument runway.

Markings on a precision instrument runway.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]
Subscribe to this Feed |
You may want to put some text here



Get this Wordpress newsletter widget
for newsletter software