Chapter 4 - Weather, Crosswind and Performance Takeoff and Landing, and Radio Aids to Navigation Flashcards
Roughly how many miles from the earth’s surface does the atmosphere extend?
350 miles
What layer of the atmosphere is the lowest, and most relevant to flying?
Troposphere
What elevations does the troposphere extend to?
20,000 ft above the north and south poles, 48,000 ft above the equator
How much does temperature decrease, typically, every 1,000 ft in the troposphere?
2 Degrees Celcius
Roughly how much does air pressure decrease for every 1,000 ft in atmosphere?
1 inch
What is the temperature lapse rate?
The rate that temperature and pressure changes as you move through the atmosphere
What causes wind?
Differences in pressure gradients in the atmosphere
What are lines of equal pressure called?
Isobars
How are pressure gradients exerted across isobars?
At right angles from high pressure to low pressur
The closer the isobars are space, the ____ the pressure differential
greater
What does a bigger pressure differential mean?
Stronger winds
Through what process is the majority of atmospheric circulation achieved?
Convection
Describe convection
As air heats up, it expands and becomes less dense and rises (and vice versa for cool air).
What is the corilois force?
A deflective force caused by the rotation of the earth. At scales that affect humans, it is imperceptible, but to large air masses and bodies of water it has a great affect
What does the amount of coriolis deflection depend on?
The latitude (greatest at the poles and diminishes to zero at the equator)
What directions are air in the northern and southern hemisphere deflected due to the coriolis effect?
To the right in the northern hemisphere, to the left in the southern hemisphere
What causes all of earth’s weather?
Uneven heating of the earth’s surface
What is the friction level?
The level below which air moves more slowly over the surface due to drag from the surface. Approx 2000 ft AGL
How does the friction level affect wind direction?
Wind below the friction level experiences surface drag, and thus is less affected by the coriolis force and so may take a slightly different direction than higher altitude winds
Which directions do resultant surface circulation tend to flow below the friction level?
Clockwise and outward around areas of high pressure, counterclockwise and inward around low pressure
Above the friction level, how do winds aloft tend to travel?
Parallel to the isobars, and clockwise around high pressure centers and counterclockwise around low pressure
Why do winds aloft tend to travel parallel to isobars?
Because coriolis and pressure gradient balance each other out
How does snow or frost form?
When water vapor sublimates into a solid
What is atmospheric stability?
The ability of an air mass to resist vertical motion
What characteristics do unstable air masses tend to have?
1) Cumuliform clouds
2) Showery precipitation
3) Rough air/turbulence
4) Good surface visibility
What characteristics do a stable air mass tend to have?
1) Stratiform clouds and fog
2) Continuous precipitation
3) Smooth air
4) Fair to poor visibility in haze and smoke
What are cumulus clouds?
Clouds formed when unstable air is forced aloft. Characterized by lumpy or billowy appearance
What are stratus clouds?
Clouds formed by the cooling of a stable layer of air, they have a uniform sheet-like appearance
What are the four families of stratus and cumulus clouds?
High clouds (16k to 45k ft), middle clouds (6.5k to 23k), low clouds (surface to 6.5k, including fog), and towering
What prefix and suffix describe a rain cloud?
nimbo or nimbus
Where is the greatest turbulence found?
In and around towering cumulonimbus clouds
What are the three conditions necessary to produce a thunderstorm?
Lifting force, high humidity, and unstable air
What are some examples of lifting forces that might contribute to a thunderstorm?
Lift from mountain ranges, convective heating from the earth’s surface, lifting from frontal activity, or convergence
What are the three stages of a thunderstorm?
Cumulus, Mature, Dissipating
Describe the Cumulus stage of thunderstorm formation
Not all cumulus clouds become thunderstorms, but all thunderstorms begin with a cumulus stage. Consists primarily of updrafts of air that may exceed 3000 ft per min, lifting water droplets which form into raindrops, eventually sinking in a downdraft when they fall
What signals the start of the “mature” stage of a thunderstorm?
The start of rain at the surface, where downdrafts may exceed 2,500 fpm
What causes strong gusty surface winds, a sharp temperature drop, and rapid rise in pressure around thunderstorms?
Downdrafting air hitting the surface and spreading out
What is a “gust front?”
Strong gusty winds caused by downdrafts during the mature stage of a thunderstorm. These can occur up to 15 miles away from any precipitation and cause extreme turbulence
During what stage do updrafts reach their maximum speed, and what speed is that up to?
During the mature stage, and speeds can exceed 6000 fpm
What shaped cloud identifies a thunderstorm in a mature stage?
Anvil shaped
During what stage is a thunderstorm producing its most dangerous flying conditions?
Mature stage
What characterizes the Dissipating Stage of a thunderstorm?
Strong downdrafts created by the falling rain, and the storm dying quickly unless it finds another sourfce of warm rising air (such as if it moves over a large, warm body of water)
What are the main types of thunderstorms?
Air mass, severe, supercell, embedded, squall
What is an “Air Mass” thunderstorm?
A non-severe storm that is not associated with frontal activity. Most late afternoon summer thunderstorms are Air Mass thunderstorms
What is a “Severe” thunderstorm?
Any storm that produces tornadoes, usually part of a larger weather system
What is a “Supercell” thunderstorm?
Storms that cover an area of 30 square km or more
What is an “Embedded” thunderstorm?
A storm hidden in an area of general cloud cover and light precipitation. These storms cannot be observed from the ground or air, they can only be detected with radar
What is a “Squall” thunderstorm?
A squall line is a narrow band of thunderstorms that often develop ahead of a cold front and represent the most intense hazards to aircraft in the form of heavy turbulence and icing
What are the main hazards that thunderstorms present?
Turbulence, icing, hail, lightning, low ceilings and visibility, and an adverse affect on altimiters
Where does the strongest turbulence in a thunderstorm occur?
Within the storm due to the shear between updrafts and downdrafts, but can also occur above or horizontally from a storm
What is the first rule for flying in turbulence?
Reduce airspeed to maneuvering speed
What is the second rule for flying in turbluence?
Maintain a level attitude and ride it out
How does icing occur?
Super-cooled water droplets that freeze when they make contact with the airplane, forming clear ice
How does hail form?
Super-cooled water droplets in a thunderstorm begin to freeze and additional water droplets freeze to it
Where can one encounter hail?
Within several miles of thunderstorm clouds
Does absence of hail at the surface mean absence of hail aloft?
No, because hail can melt before it hits the ground as rain
Are lightning strikes considered very dangerous?
Not necessarily, they can cause equipment issues or temporary pilot dissorientation but cause very few accidents. That said, they can cause permanent damage to the magnetic compass
What causes inaccurate altimeter readings around thunderstorms?
Rapid pressure changes
Should you ever try to fly under a thunderstorm?
No
Should you try to circumnavigate thunderstorms?
Not if more than half the area is reported involved with thunderstorms
How far should you stay away from thunderstorms reported as severe?
At least 20 miles
Why should you try to avoid flying under the anvil of a thunderstorm?
You might encounter hail
What type of lightning indicates a severe thunderstor?
Vivid and frequent
Should you ever fly near squall lines?
No, never. Squall lines produce the most severe conditions.
When in doubt with concerns to thunderstorms, what should you do?
Land and wait until it passes
What is essential for fog formation?
A low differential between the temperature and the dewpoint
How quickly can fog form?
Fog can cause conditions to go from VFR to <1 mile of visibility within minutes
What conditions are most conducive to the formation of radiation (and ground) fog?
Warm, moist air moving over low, flat land areas during clear, calm nights
What is advection fog?
Fog that forms when moist air moves over colder ground or water, and is most common along the coast
Where do you often find advection fog?
On the coasts, especially the US West Coast
How does Upslope Fog form?
When moist, stable air is cooled as it moves up sloping terrain
Where does upslope fog form in the US?
East of the rocky mountains, and less frequently east of the appalachian mountains
What types of fog are dependent upon the wind to exist?
Advenction fog and upslope fog
How does steam fog form?
In the winter when cold, dry air passes from land areas over comparatively warm ocean waters
What is steam fog also called?
Sea Smoke
What hazards are associated with steam fog?
Low-level turbulence and icing
What are some of the negative consequences of icing?
Increased weight, decreased thrust, decreased lift, increased drag, bad engine performance, and malfunctioning of flight instruments and flight surfaces
What conditions are necessary for structural icing?
Visible moisture and freezing temperatures
Why can structural icing sometimes occur as high as 2 degrees Celcius?
Because of aerodynamic cooling
What types of clouds do clear ice form in?
Cumulus Clouds
What type of clouds do rime ice form in?
Stratus clouds
What types of surfaces does ice tend to accumulate faster on?
Smaller surfaces like antennas, temperature probes, pitot tubes, etc
What is the danger of frost?
Uneven airflow over the airfoils resulting in reduced lift
What conditions cause frost?
When dewpoint and temperature of the collecting surface are below freezing
What is wind shear?
An abrupt, drastic change in wind direction or speed over a very short distance in the atmosphere
What conditions are low-level wind shear associated with?
Passing frontal systems, thunderstorms, and temperature inversions with strong upper level winds (greater than 25 kts)
What is a microburst?
A rapid change in wind speed and direction of up to 6000 fpm or 45 degrees associated with convective precipitation or from from thunderstorms
What is LLWAS?
Low-Leven Wind shear Alert System, for detecting microbursts
What are the minimum visibility requirements for VFR?
3 SM during the day, 5 SM at night
What is the minimum ceiling for VFR?
1,000 ft in controlled airspace
What might be in your logbook that would prevent you from flying VFR?
Conditions contrary to any limitations placed in the pilot’s logbook by an authorized instructor
What are winds aloft?
Winds above 2,000 ft AGL
What are surface winds?
Winds below 2,000 ft AGL
What is a crosswind condition?
Any time the wind is not aligned with the runway
What is the maximum demonstrated crosswind velocity in the C172?
15 Knots
Is the maximum demonstrated crosswind velocity in the C172 a structural limitation?
No; it’s the result of testing with an average pilot
What should you do if you notice a tailwind component when examining crosswind landing conditions?
Request another runway for landing
What are sideslips used for?
To keep the longitudinal axis and ground track the same during takeoffs and landings
What is a forward slip used for?
The steepen the glide path by increasing drag when flaps are inoperative
What will happen as you establish a slip?
The nose will tend to pitch down; you must apply back pressure on the elevator
What direction should slips be compared to the wind?
Into the wind
What happens to instruments during a slip?
The static vent and pitot tube will become unreliable, so airspeed will not be reliable
What is a sideslip?
An uncoordinated bank where ailerons and rudder are opposite in order to compensate for a crosswind at landing or after rotation
What is the difference between a forward slip and a sideslip with concerns to the flight path and longitudinal axis?
During a sideslip, the longitudinal axis is aligned with the flight path. During a forward slip, the longitudinal axis is not aligned with the flightpath
If flaps become inoperative, what can you do to increase your descent angle but maintain approach speed?
Perform a forward slip
During a power-off approach to landing, what can you not do?
Shallow the descent of the flight path
What is the most important variable affecting performance during a power-off approach
Wind
How do crosswind rotation and liftoff speeds compare to normal takeoffs?
They are the same
Which wheel do you try to touchdown first during a crosswind landing?
The upwind wheel so that the longitudinal axis remains aligned with the runway centerline
What are the primary factors most affected by the airplane’s performance?
Takeoff and landing distance, rate of climb, service ceiling, payload, speed, and fuel economy
Where can you find the data regarding airplane performance?
The POH
What are the primary factors affecting performance?
Airplane loading, atmospheric conditions, and runway environment
What does a CG located behind aft limits cause?
Decreased stability to a point that the airplane is dangerous to fly
What becomes more difficult as CF moves aft?
Stall recovery, sometimes to the point of not being able to recover
What does a CG ahead of the forward limit cause?
Increased stability, but may make it impossible to rotate for takeoff or flare to a proper landing attitude
What can being over the gross weight cause?
Structural problems
What is ISA and what is it used for?
International Standard Atmosphere; used for all aircraft to be compared and evaluated on
What is humidity?
The amount of water vapor contained in the atmosphere vs. the maximum amount of water vapor the air can support
What do high humidity conditions generally cause?
A decrease in performance
What atmospheric conditions would decrease an aircraft’s performance most?
High temperature, high relative humidity, and low pressure
What is density altitude an index to?
Aircraft performance
What does low density altitude do to aircraft performance?
Increases performance
What does high density altitude do to aircraft performance?
Decrease performance
How does high density altitude affect cruise performance?
Generally increased due to decreased friction and higher true airspeeds
How can you find the pressure altitude of the airplane?
Set altimeter to 2992 and check the altitude displayed on the instrument
How much should you increase takeoff and obstacle clearing distances when using a grass runway?
Increase by 15%
How should you adjust for wind when figuring out takeoff and obstacle clearing distances?
Reduce by 10% for every 9 knots of headwind
How much should you increase landing and obstacle clearing distances when using a grass runway?
Increase by 45%
How should you adjust for wind when figuring out landing and obstacle clearing distances?
Decrease by 10% for every 9 knots of headwind
What are the atmospheric conditions that affect density altitude?
Temperature and pressure
Generally speaking, what runway conditions do performance charts assume?
Paved, level, smooth, and dry
How is runway gradient expressed?
As a percentage; 2% = 2 ft down/up per 100 ft forward
How is a short field takeoff defined?
As a takeoff made when the takeoff surface is hard, of sufficient length for the airplane performance expected, and obstacles are present at the departure end of the runway
What is the goal of a short field takeoff?
To accelerate as quickly as possible on the hard surface and then climb at a steep angle to clear any obstructions
What is the recommended rotation speed for a short field takeoff at max weight in the C172R?
51 KIAS
What is the best angle of climb airspeed in the C172R with 10 degrees flaps and max weight?
56 KIAS
What is a short field landing?
A landing made when the runway surface is hard, of sufficient length for the airplane performance expected, and obstacles are present at the arrival end of the runway
What is LDMAX?
The speed beyond which it is impossible to make a short field landing
What is LDMAX of a C172R with full flaps at max weight?
61 KIAS
What is the typical power setting for a short field landing?
1300 rpm
What is ground effect?
When the aircraft is within a wingspan of the ground, wingtip vortices are reduced, which reduce the drag on the aircraft
What is the most important element of a short field landing?
To maintain a stabilized final approach at the correct airspeed
How can brake effectiveness be increased during a short field landing?
By retracting the flaps
What is the main objective when taking off from a soft field runway?
To transfer the weight from the wheels to the wings as quickly as possible and liftoff at the slowest possible speed
How can you reduce stress on the nosewheel when taxiing on a soft taxiway?
Keep elevator backpressure
What will happen during a soft field takeoff if you try to climb before the plane leaves ground effect?
There will be a rapid increase in drag and you’ll settle back onto the runway
How is a soft field landing defined?
A landing made on a runway with tall grass, soft sod surfaces, snow covered, or rough dirt runways without obstacles at the approach end of the runway and the runway length is greater than the POH lists for total landing distance under current conditions
What is a VOR Radial?
A course FROM a VOR station
What must you set in order to track a course TO a VOR station?
The reciprocal of the VOR Radial
What must the OBS always be
Set to match your desired direction of flight!
What does VOR stand for?
Very high frequency Omnidirectional Range
What are the three basic types of VOR systems?
VOR, VOR/DME, and VORTAC
What is VOR DME?
VOR with Distance Measuring Equipment
What is a VORTAC?
A VOR where military tactical air navigation (TACAN) is equipped, and they always have DME
What frequency ranges do VORs operate in?
108 to 117.95 Hz
What type of limitations do VHF signals hold?
Line of sight limitations
For most VORs, what is the useable range?
40 to 50 nm at an altitude of 1000 feet AGL, which increases with altitude
What is always the first step when using any navaid?
Identify the station via its morse code identifier
What does the VOR Indicator consist of?
An OBS (omni bearing selector), CDI (course deviation indicator), and a to/from indicator or flag
What is a VOR Signal Test?
A test available at certain airports to ensure your VOR is working properly. If you tune the VOT signal and turn the OBS to 360, the CDI needle should center with a FROM flag. If you tune to 180, the CDI needle should center with a TO flag
What would a needle indication moving left on your VOR indicate?
A wind from the left
What is the minimum number of GPS receivers needed to yield a three dimensional position?
4
What is Dihedral with regards to stability?
The canting of the wings that provides lateral stability
What helps counteract the forward CG of aircraft?
The stabilizer of the plane is attached at a negative angle of incidence, resulting in a negative angle of attack during flight and forcing the tail down/nose up.
