Pilot's Handbook of Aeronautical Knowledge
Chapter 11: Aircraft Performance
The performance or operational information section of the Aircraft Flight Manual/Pilot's Operating Handbook (AFM/ POH) contains the operating data pertaining to takeoff, climb, range, endurance, descent, and landing. The use of this data in flying operations is mandatory for safe and efficient operation.
Manufacturers' information and data is not standardized, and performance data may be presented on the basis of standard atmospheric conditions. Pressure and temperature have a major effect on aircraft performance, which pilots should take into account when predicting performance.
Pressure and Density Altitude
Pilots are mainly concerned with atmospheric pressure. Air a fluid substance that has mass, weight, and a force that is exerted equally in all directions. The effect of air on bodies within the air is called pressure. The pressure of the atmosphere varies with altitude and temperature. As air becomes less dense, it reduces power, thrust, and lift.
A standard temperature lapse rate observes the temperature decreasing at the rate of approximately 3.5 degrees F (2 degrees C) per thousand feet, up to 36,000 feet. Above this, the temperature is constant up to 80,000 feet.
A standard pressure lapse rate observes pressure decreasing at a rate of approximately 1" Hg per 1,000 feet of altitude gain, up to 10,000 feet. This often is referred to as International Standard Atmosphere (ISA) or ICAO Standard Atmosphere. [11-2]
Any temperature or pressure that differs from the standard lapse rates is considered nonstandard temperature and pressure.
All aircraft instruments are calibrated for the standard atmosphere. Thus, corrections must be applied to the instrumentation and predicted performance if actual operating conditions vary from the standard atmosphere.
The Standard Datum Plane (SDP) is a theoretical level at which atmospheric pressure is 29.92" Hg and the weight of air is 14.7 psi. SDP may be below, at, or above sea level as atmospheric pressure changes.
Pressure altitude is the height above the SDP. Pressure altitude is a basis for determining aircraft performance. It also is used for assigning flight levels to aircraft operating at above 18,000 feet (FL 180).
If the altimeter is set to 29.92", the indicated altitude is pressure altitude. Pressure altitude also can be determined by applying a correction factor to the reported altimeter setting, or by using a flight computer.
Density altitude is pressure altitude corrected for nonstandard temperature. Density altitude is the vertical distance above sea level in the standard atmosphere at which a given density is to be found.
As the density of the air increases (low density altitude), aircraft performance increases. As air density decreases (higher density altitude), aircraft performance decreases
High density altitude refers to thin air while low density altitude refers to dense air. An increase in the air density results in "lower" density altitude, not "higher" density altitude, even though the increased weight of the air has more (a higher amount) of pressure. "High density altitude" refers to a higher altitude with air that is less dense.
Density altitude is determined by first finding pressure altitude and then correcting this altitude for nonstandard temperature variations. A known density occurs for any one temperature and pressure altitude. Regardless of the actual altitude at which the aircraft is operating, it will perform as though it were operating at an altitude equal to the existing density altitude.
Air density is affected by changes in altitude, temperature, and humidity. Contributors to high density altitude are high elevations, low atmospheric pressures, high temperatures, and high humidity.
Density altitude can be computed with a flight computer or a tabular chart.
Air density is directly proportional to pressure. If the pressure is doubled, the density is doubled, and if the pressure is lowered, so is the density. (This statement is true only at a constant temperature.)
Increasing the temperature of a substance decreases its density. (This statement is true only at a constant pressure.)
In the atmosphere, both temperature and pressure decrease with altitude and have conflicting effects upon density. With less pressure, the air becomes less dense, while lower temperature will make the air more dense. However, the fairly rapid drop in pressure as altitude is increased usually has the dominant effect. Pilots can expect the density to decrease with altitude.
Air Pressure, Air Density, and Pressure Altitude
When thinking about air pressure, it's best to use a stack of blankets as a metaphor. Imagine 300 blankets, piled high in a column.
Now get under them. You'll feel squished.
The atmosphere is similar to a stack of blankets. Air is matter — it has molecules, and these molecules become compressed if there's a lot of air overhead, because that overhead air is pressing down.
The atmosphere's downward force is easy to measure with a mercury barometer (although these aren't widely used anymore). At sea level, we typically measure about 30 inches of mercury within a sealed tube. An open dish at the base of the tube also contains mercury, and the mercury in this dish is resisting the air that is pressing down on it.
If we take this barometer to a location other than sea level, we'll see that the mercury in the measuring tube will fall, because the mercury in the dish is better able to resist the atmosphere's reduced downward force at higher elevations. The mercury in the dish rises, and the mercury in the measuring tube falls. If we drive up a mountain road, we'll see that (generally speaking) the atmosphere loses one inch of downward force for every 1,000 feet of elevation. As we climb, the mercury in the open dish continues to rise while the mercury in the measuring tube continues to fall.
So if we're looking at a barometer, we might say "Air pressure is 30 inches of mercury." We might even say "Current pressure is 30 inches." But we also could say "three hundred blankets" or "three thousand layers," because what we really care about are the measured layers of air molecules that are piled thousands of feet high.
People at or near sea level exist under about 3,000 layers of air molecules, most of the time. You can think of these as thin layers. In most of the earth's inhabited areas, each measurable layer of atmosphere — 0.01 inch of mercury — is about 10 vertical feet.
However, people who live at higher elevations, such as Denver, have adjusted to life under 2,500 layers of air molecules. Compared to a coastal atmosphere, the atmosphere in the Rocky Mountains is receiving less downward force, and this somewhat expanded air has fewer available oxygen molecules. That said, almost everyone adjusts to it.
Tibetans in the high Himalayas, above 14,000 feet, live under a mere 1,600 layers of air molecules. That's why visitors to camps at the base of Mount Everest feel a bit light-headed when they first arrive. There isn't as much air above them to press down on the air at the surface. Therefore, the air molecules aren't as squished together compared to a sea-level atmosphere, and this includes oxygen molecules. Up high, the result is "thin air."
Density vs. Pressure
Does the atmosphere at 14,000 feet have less oxygen than a sea-level atmosphere? Yes… and no. Because the air isn't being squished down to the same degree as at lower elevations, there aren't as many molecules roaming around in a block of air. The reduction in air pressure results in a reduction in air density. Without question, oxygen becomes scarce at higher elevations.
However, it would be inaccurate to say "The atmosphere has a reduced amount oxygen at higher elevations" — at least, if we are comparing oxygen to other atmospheric matter. About 99% of the tropopause is made up of nitrogen and oxygen. As air density reduces with increased elevation, these molecules become more disperse, which means that there is less oxygen available for organisms that require it. But since both the nitrogen and oxygen molecules become more disperse, it's incorrect to say that the relative amount of oxygen in the atmosphere decreases with altitude. Instead, all atmospheric matter becomes more scarce. (You may come across knowledge test questions on this, which is why it's worth noting.)
It's also important to note that air overhead pressing down on the air below — air pressure — is only one contributing factor when it comes to air density. Air presssure also is affected by changes in temperature, and air density is affected by altitude, temperature, and humidity. So while air pressure and air density are correlated, altitude is not the only variable that creates a specific density within a block of air. Two blocks of air at the same altitude, but with different temperature or humidity characteristics, will have different densities.
Where is the Standard Datum Plane (SDP)?
The Standard Datum Plane is always where the air pressure is 29.92 inches of mercury. Or, in our analogy, it's always buried under 2,992 layers of air molecules. On a standard day, this would place the SDP at sea level. Pressure variables in both time and location mean that the SDP typically is somewhere above or below sea level.
The Standard Datum Plane is a location in the horizontal pressure gradient. For example, if the air pressure at your location is 29.86, your location is buried under 2,986 layers of air, which is fewer than the 2,992 layers that rest on the SDP. Your location is above the SDP. By how much? If we drop one inch of mercury for every 1,000 feet of altitude, then we lose 10 feet for every 1/100th of an inch.
At the location of the SDP, the atmosphere has enough downward force to elevate 29.92 inches of mercury.
Thus, if the atmosphere you occupy has enough downward force to elevate 29.86 inches of mercury, your atmosphere is 60 feet above the SDP. Or "six ten-foot layers," since each .01 of mercury is about 10 feet tall (in the inhabited troposphere).
Therefore, the SDP is 60 feet below your location.
What's happening in the Flight Levels?
By regulation, every aircraft flying at or below 17,999 MSL must set its altimeter to a reporting station within 100 miles of its location. When this is done, the altimeter is continuously reset along the route of flight to account for variations in the horizontal pressure gradient. The altimeter thus measures the aircraft's true altitude — the height above sea level — and the aircraft, at constant indicated altitude, will fly a horizontal path above sea level. (Every station's elevation is redacted from the pressure reading so that all pressure values are reported as if the station were at sea level.)
"Pressure altitude" is the altitude that appears on a barometric altimeter when the pressure is set to 29.92 inches of mercury. This is done above 17,999 MSL, starting at Flight Level 180 — and "The Levels" replace MSL because, when an altimeter is set to 29.92 and disregards reported pressures from ground stations, the aircraft no longer is flying a horizontal path above sea level, but instead a determined value above the Standard Datum Plane. This permits high-speed, high-altitude aircraft in the Flight Levels adequate vertical separation, while freeing each from the task of continuously resetting altimeters to ground stations.
Because of this, aircraft in the Flight Levels don't fly a perfect horizontal path. The true altitude drifts up and down, since the indicated altitude is tracking the pressure gradient, following a determined value above where 29.92 inches of mercury registers directly below.
Can I use my altimeter to find the Standard Datum Plane?
If you try to use the altimeter as an instrument to locate the SDP, you will become frustrated, because if you enter a pressure value in the Kollsman window that is heavier than your current air pressure, your altimeter will rise, not fall. Why? Because the altimeter is not used to interrogate the vertical pressure gradient.
Think of "High to low, look out below." If you depart from a location where the pressure is 30.22" Hg, and you do not correct your altimeter along your route of flight, then your airplane will not maintain a consistent horizontal path above sea level as you maintain a consistent indicated altitude. Instead, the aircraft will follow the horizontal pressure gradient, rising and falling as necessary to track where 4,000 feet MSL is measured when the air pressure is 30.22" Hg.
If your aircraft enters an air mass where the pressure is 28.82" Hg, that represents a 0.4-inch reduction in mercury, compared to the pressure at your point of departure. Because your altimeter is seeking heavier air — 30.22" — and the air mass you have entered has relatively lighter pressure, then your altimeter, when kept at a consistent indicated 4,000 MSL, will guide the pilot to fly lower in order to locate the 30.22" Hg requested in the Kollsman window.
If you realize that you haven't reset your altimeter and, after tuning in a local ASOS, set your altimeter to the correct 28.82" Hg:
- You will provide the instrument with a lower pressure;
- The indicated 4,000 MSL will become 3,600 MSL (it goes down, not up);
- You will realize that you had been flying 400 feet closer to terrain than you previously thought;
- And you will climb in order to return to your cruising altitude of 4,000 feet.
The altimeter does not interrogate the vertical pressure gradient — it's not used to ask "show me at what altitude 29.92 inches of mercury can be found," even though it's tempting to try to use the device in this manner.
Instead, the altimeter consumes the air pressure it's asked to consume. The instrument, in motion, tracks the horizontal pressure gradient. It can only present the aircraft's height above sea level when it's continuously reset during a cross-country flight.
Thus, when the Kollsman window set to a higher pressure (30.20") than the actual pressure (28.82") at a new location, and the pilot has maintained a consistent indicated altitude en route, the airplane will track the horizontal pressure gradient to a lower altitude, where 30.20" can be found. "High to low, look out below."
(And this may be the hardest single concept to explain in the pilot curriculum.)
Humidity
Humidity can be an important factor in aircraft performance. A small amount of water vapor suspended in the atmosphere may be negligible under certain conditions, but the air is never completely dry.
Relative humidity refers to the amount of water vapor contained in the atmosphere and is expressed as a percentage of the maximum amount of water vapor the air can hold. Warm air can hold more water vapor, while colder air can hold less.
Water vapor is lighter than air. As the water content of the air increases, the air becomes less dense, causing an increase in density altitude, which reduces performance. Air is at its lightest and least dense when it contains the maximum amount of water vapor.
Humidity alone is usually not considered an essential factor in calculating density altitude and aircraft performance, but it does contribute. There is no rule-of-thumb or chart used to compute the effects of humidity on density altitude, but pilots should expect a decrease in overall performance in high humidity conditions.
Performance
Performance describes an aircraft's useful abilities. This can include takeoff, landing, rate of climb, payload capacity, altitudes, airspeeds, range, maneuverability, stability, fuel burn, and any other metrics deemed useful. All result from the combination of aircraft and powerplant.
When an aircraft is in straight and level flight, the condition of equilibrium must prevail.
Thrust is a force or pressure exerted on an object, and is measured in pounds or Newtons.
Power is a measurement of the rate of performing work or transferring energy, and is measured in horsepower (hp) or kilowatts (kw).
Mechanical energy can be kinetic or potential. Kinetic energy (KE) comes from speed, while potential energy (PE) is stored.
A climb can be achieved by applying excess horsepower. A climb also can be achieved by an exchange of energy, if the pilot converts the kinetic energy of airspeed (KE) to a gain in altitude (PE). As the altitude increases, airspeed is reduced.
Angle of Climb (AOC) is a comparison of altitude gained relative to distance traveled, i.e. the inclination (angle) of the flight path. Maximum AOC is used to clear obstacles, represented by the performance speed Vx. If excess thrust is available, the greater force can result in a steeper climb.
Rate of Climb (ROC) is a comparison of altitude gained relative to the time needed to reach that altitude, represented by the performance speed Vy, and resulting a maximum gain in altitude over a given period of time. Maximum ROC occurs at an airspeed and AOA combination that produces the maximum excess power.
Climb performance is directly dependent upon the ability to produce either excess thrust or excess power.
A change in weight changes the drag and the power required, affecting both the climb angle and the climb rate. An increase in weight also reduces the maximum ROC.
An increase in altitude also increases the power required and decreases the power available. Therefore, the climb performance of an aircraft diminishes with altitude.
The service ceiling is the altitude at which the aircraft is unable to climb at a rate greater than 100 feet per minute (fpm). At the absolute ceiling, there is no excess of power and only one speed allows steady, level flight. Consequently, the absolute ceiling of an aircraft produces zero ROC.
Power loading is expressed in pounds per horsepower and is obtained by dividing the total weight of the aircraft by the rated horsepower of the engine..
Wing loading is obtained by dividing the total weight of an airplane in pounds by the wing area. Wing loading determines the airplane's landing speed.
Endurance involves consideration of flying time, rather than distance traveled. Range is the ability of an aircraft to convert fuel energy into flying distance.
Maximum endurance requires a flight condition with minimum fuel flow.
Maximum specific range requires a flight condition with a maximum of speed per fuel flow.
Maximum endurance occurs at the point of minimum power required, since this requires the lowest fuel flow to keep the airplane in steady, level flight. Maximum range condition occurs where the ratio of speed to power required is greatest. The maximum range condition is obtained at maximum lift/ drag ratio (L/D max).
Long-range aircraft have a fuel weight that is a considerable part of the gross weight. Cruise control procedures employ scheduled airspeed and power changes to maintain optimum range conditions.
A flight conducted in a propeller-driven aircraft at high altitude has a greater true airspeed (TAS), and the power required is proportionately greater than when conducted at sea level because of the higher TAS. The drag of the aircraft at altitude is the same as the drag at sea level.
An aircraft equipped with a reciprocating engine experiences very little, if any, variation of specific range up to its absolute altitude.
Region of Reversed Command
The aerodynamic properties of an aircraft determine the power requirements at various conditions of flight. Powerplant capabilities determine the power available at various conditions of flight.
The power required to achieve equilibrium in constant-altitude flight at various airspeeds is depicted on a power required curve.
At low airspeeds, the power setting required for steady, level flight is high.
In the region of normal command, a higher airspeed requires a higher power setting and a lower airspeed requires a lower power setting to hold altitude. Most flight is conducted in this region.
In the region of reversed command while holding a constant altitude, a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting to hold altitude. This exists for flight speeds below the speed for maximum endurance, i.e. the lowest point on the power curve. This is often referred to as "flight behind the power curve" or "the backside of the curve." [11-14]
If an unacceptably high sink rate should develop on the backside of the power curve, it may be possible for the pilot to reduce or stop the descent by applying power. If additional power is not available, the airplane may stall or be incapable of flaring for landing. The only recourse is to lower the pitch attitude in order to increase airspeed, which inevitably results in a loss of altitude. If sufficient altitude does not exist, impact is possible.
Takeoff and Landing Performance
Takeoff
The most critical conditions of takeoff performance are the result of some combination of high gross weight, altitude, temperature, and unfavorable wind. An accurate prediction of takeoff distance can be determined from the performance data of the AFM/POH.
An airplane on the runway moving at 80 knots has four times the energy it has traveling at 40 knots. Thus, an airplane requires four times as much distance to stop as required at half the speed.
Any runway surface that is not hard and smooth increases the ground roll during takeoff. Runways can be concrete, asphalt, gravel, dirt, or grass.
The amount of power that is applied to the brakes without skidding the tires is referred to as braking effectiveness. Water on the runway can reduce braking effectiveness.
The gradient or slope of the runway is the amount of change in runway height over the length of the runway. The gradient is expressed as a percentage, such as a 3 percent gradient. This means that for every 100 feet of runway length, the runway height changes by 3 feet. A positive gradient indicates the runway height increases, and a negative gradient indicates the runway decreases in height. Up-sloping and down-sloping runways affect takeoff performance.
Dynamic hydroplaning is a condition in which the aircraft tires ride on a thin sheet of water rather than on the runway's surface. The minimum hydroplaning speed (in knots) is determined by multiplying the square root of the main gear tire pressure in psi by nine. (If the tire pressure is 36 psi, the square root is 6, and thus the hydroplaning speed is 54 knots.) Once hydroplaning starts, it can continue well below the minimum initial hydroplaning speed.
The lift-off speed is a fixed percentage of the stall speed or minimum control speed for the aircraft in the takeoff configuration. It can be anywhere from 1.05% to 1.25% the stall speed or minimum control speed.
Any item that alters the takeoff speed or acceleration rate during the takeoff roll affects the takeoff distance. Increased gross weight creates a higher lift-off speed, because there is a greater mass to accelerate and an in increase in drag and ground friction. For example, a 21% increase in takeoff weight requires a 10% increase in lift-off speed to support the greater weight.
The effect of a headwind is to allow the aircraft to reach the lift-off speed at a lower groundspeed, while the effect of a tailwind is to require the aircraft to achieve a greater groundspeed to attain the lift-off speed. The effect of wind on landing distance is identical to its effect on takeoff distance.
An increase in density altitude can produce a greater takeoff speed, as well as decreased thrust and reduced net accelerating force.
Proper accounting of pressure altitude and temperature is mandatory for accurate prediction of takeoff roll distance.
If an aircraft of given weight and configuration is operated at a pressure altitude above standard sea level, the aircraft requires the same dynamic pressure to become airborne at the takeoff lift coefficient. Thus, the aircraft at altitude takes off at the same indicated airspeed (IAS) as at sea level, but because of the reduced air density, the TAS is greater.
An increase in altitude above standard sea level brings an immediate decrease in power output for the unsupercharged reciprocating engine.
Landing
The most critical conditions of landing performance are combinations of high gross weight, high density altitude, and unfavorable wind.
The landing speed is some fixed percentage of the stall speed or minimum control speed for the aircraft in the landing configuration. Runway slope and condition are additional factors.
Minimum landing distance is obtained with extensive use of the brakes for maximum deceleration. An ordinary landing roll may allow use of aerodynamic drag to minimize wear on the tires and brakes. Aerodynamic drag is applicable only for deceleration to 60 or 70 percent of the touchdown speed.
Wind alters the groundspeed at which the aircraft touches down.
An increase in density altitude increases the landing speed. An aircraft at altitude lands at the same IAS as at sea level but, because of the reduced density, the TAS is greater. Deceleration is the same as with the landing at sea level, but the TAS will affect the landing distance.
The approximate increase in landing distance with altitude is approximately three and one-half percent for each 1,000 feet. At 5,000 feet, the minimum landing distance is 16 percent greater than the minimum landing distance at sea level.
A ten percent excess landing speed causes at least a 21 percent increase in landing distance. A tail wind of ten knots also increases the landing distance by about 21 percent.
Performance Speeds
- True airspeed (TAS): The speed of the aircraft in relation to the air mass in which it is flying.
- Indicated airspeed (IAS): The speed of the aircraft as observed on the ASI. It is the airspeed without correction for indicator, position (or installation), or compressibility errors.
- Calibrated airspeed (CAS): The ASI reading corrected for position (or installation) and instrument errors. (CAS is equal to TAS at sea level in standard atmosphere.) The color coding for various design speeds marked on ASIs may be IAS or CAS.
- Equivalent airspeed (EAS): The ASI reading corrected for position (or installation), for instrument error, and for adiabatic compressible flow for the particular altitude. (EAS is equal to CAS at sea level in standard atmosphere.)
- VS0: The calibrated power-off stalling speed or the minimum steady flight speed at which the aircraft is controllable in the landing configuration.
- VS1: The calibrated power-off stalling speed or the minimum steady flight speed at which the aircraft is controllable in a specified configuration.
- VY: The speed at which the aircraft obtains the maximum increase in altitude per unit of time. This best ROC speed normally decreases slightly with altitude.
- VX: The speed at which the aircraft obtains the highest altitude in a given horizontal distance. This best AOC speed normally increases slightly with altitude.
- VLE: The maximum speed at which the aircraft can be safely flown with the landing gear extended. This is a problem involving stability and controllability.
- VLO: The maximum speed at which the landing gear can be safely extended or retracted. This is a problem involving the air loads imposed on the operating mechanism during extension or retraction of the gear.
- VFE: The highest speed permissible with the wing flaps in a prescribed extended position. This is because of the air loads imposed on the structure of the flaps.
- VA: The calibrated design maneuvering airspeed. This is the maximum speed at which the limit load can be imposed (either by gusts or full deflection of the control surfaces) without causing structural damage. Operating at or below maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time.
- VN0: The maximum speed for normal operation or the maximum structural cruising speed. This is the speed at which exceeding the limit load factor may cause permanent deformation of the aircraft structure.
- VNE: The speed that should never be exceeded. If flight is attempted above this speed, structural damage or structural failure may result.
Performance Charts
Performance charts are found in the AFM/POH, as provided by the manufacturer. They allow a pilot to predict the takeoff, climb, cruise, and landing performance of an aircraft. Data from the charts will not be accurate if the aircraft is not in good working order or when operating under adverse conditions.
Charts are not standardized and may appear in a variety of formats. Pilots should be familiar with the conventions of performance charts in the AFM/POH of their airplanes.
See the Pilot's Handbook of Aeronautical Knowledge for examples of various performance charts.
The Crosswind Component Graph
Each airplane has an upper limit to the amount of direct crosswind in which it can land. The crosswind component graph is used to determine if your airplane will be able to safely operate in observed or forecast wind conditions when the wind is not aligned with the runway at your destination.
Crosswind component graphs have two variables:
- The angle between wind direction and runway
- Wind velocity (in knots)
While the graph is fairly simple, it's easy to forget how it should be used to determine headwind and crosswind component values, since it's a series of numbers repeated along four metrics. (Fortunately, the graph included in the test booklet includes a sample problem.)
Think of the crosswind/headwind diagram as a depiction of the airplane coming in for a landing, with the '0' as the touchdown zone.
What is the angle between the wind and the runway? This the final approach course.
What is the wind velocity? Stop your approach here, on the airspeed arc. Look directly out your left and right windows at the horizontal and vertical metrics. You are looking at the crosswind and headwind components.
The most common reason why test-takers will select an incorrect answer is because they don't compute the initial variable correctly and select the wrong differential between the runway heading and the crosswind angle. Always double-check that you are using the correct angle. Often, the test will offer correct answers for wrong crosswind angles.
Note: As a rule of thumb, most airplanes have a maximum crosswind capability equal to 0.2 of VS0. Therefore, an airplane with a VS0 of 40 knots would have a maximum crosswind component of 8 knots.
Commercial Pilot & Flight Instructor Test Questions
What effect does high density altitude, as compared to low density altitude, have on propeller efficiency? Efficiency is reduced because the propeller exerts less force at high density altitudes than at low density altitudes.
As density altitude increases, which will occur if a constant indicated airspeed is maintained in a no-wind condition? True airspeed increases; groundspeed increases.
— An increase in density altitude will indicate that the air has become less dense.
Which statement is true regarding takeoff performance with high density altitude conditions? The acceleration rate is slower because the engine and propeller efficiency is reduced.
If atmospheric pressure and temperature remain the same, how would an increase in humidity affect takeoff performance? Longer takeoff distance; the air is less dense.
— Water vapor is less dense than dry air.
What effect does an uphill runway slope have upon takeoff performance? Increases takeoff distance.
In a propeller-driven aircraft, maximum range occurs at maximum lift/drag ratio.
— "Maximum endurance" occurs at minimum power required.
What can a pilot expect when landing at an airport in the mountains? Higher true airspeed and longer landing distance.
What can a pilot expect when landing at an airport located at a much higher elevation? Higher true airspeed and longer landing distance.
GIVEN:
Pressure altitude 12,000 ft
True air temperature +50 °F
From the conditions given, the approximate density altitude is 14,130 feet.