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Airport elevation is the officially designated elevation of an airport above mean sea level. Airports are typically built at higher altitudes, but there are some airports that are located below sea level. For example, Amsterdam Schiphol is well-known for being below sea level, with an elevation of -11 ft or -3 m. The lowest elevation airport in the world is Bar Yehuda Airfield in Israel, which stands at -1,240 ft or -378 m.
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What You'll Learn
Airports below sea level
Yes, there are airports located below sea level. The lowest airport in the world is Bar Yehuda Airfield in Israel, which is 378 meters (1,240 feet) below mean sea level. Other airports below sea level include Furnace Creek Airport in Death Valley, California, which is 208 feet below sea level, and Amsterdam Schiphol Airport, which has an elevation of -11 feet or -3 meters. Atyrau Airport in Kazakhstan is also located below sea level, with an altitude of 72 feet below sea level, making it the lowest commercial airport on Earth.
Airports located at or below sea level face different challenges than those at higher altitudes. For example, they may experience problems with aircraft electronics and GPS connections because these systems are typically calibrated to work above sea level. On the other hand, landing and taking off at sea-level airports are generally less problematic because the air density is higher, reducing the need for long runways.
The elevation of an airport is essential for aviation safety and performance. Aircraft use sea level as the standard to measure atmospheric pressure and calibrate their altitude. When an aircraft lands at an airport, its altimeter should indicate the airport's elevation if correctly set to the local QNH value. However, pressure changes due to weather can affect barometric sensors, resulting in inaccurate readings.
Some airports near sea level may also be considered "effectively" below sea level due to their proximity to the coast. These airports can experience similar challenges to those truly below sea level, such as issues with electronics and GPS connections. Additionally, airports near bodies of water may be subject to more rapid weather changes and varying atmospheric pressure, further complicating aviation operations.
While there are challenges associated with airports below sea level, advancements in technology and aviation practices have made it possible to safely operate in these environments. However, it is essential to consider the unique characteristics of these locations to ensure accurate instrumentation, smooth flight operations, and the safety of passengers and crew.
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Negative density altitudes
Density altitude is the altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation. In simpler terms, the density altitude is the air density given as a height above mean sea level. The density altitude is an important factor in skydiving and aviation. In aviation, it is used to assess an aircraft's aerodynamic performance under certain weather conditions. An aircraft taking off from an airport at a high altitude, such as Quito Airport or Mexico City International Airport, is at a significant aerodynamic disadvantage. This is due to the effects of a density altitude that is higher than the actual physical altitude. An aircraft taking off from a high-altitude airport will accelerate more slowly and climb more slowly due to reduced power production. This may result in a decreased takeoff weight or the need to schedule takeoffs for cooler times of the day.
Density altitude is influenced by air temperature, atmospheric pressure, and humidity. An increase in temperature and a decrease in atmospheric pressure, as well as an increase in humidity to a lesser extent, will cause an increase in density altitude. In hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude. This can impact the performance of aircraft, including the lift generated by the aircraft's airfoils and the relationship between indicated airspeed (IAS) and true airspeed (TAS).
It is important to note that negative density altitudes can also impact aviation activities such as skydiving. Parachutists travelling to a drop zone with a different density altitude than they are accustomed to may face challenges. The higher susceptibility to hypoxia at high density altitudes, combined with an unexpected higher free-fall rate, can create dangerous situations. Parachutes at higher altitudes fly more aggressively, requiring greater pilot skill and posing challenges for high-performance landings. Therefore, negative density altitudes at airports or drop zones can have significant implications for aviation and skydiving activities.
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Altimeter readings
Altimeters are devices that tell you your vertical distance from either mean sea level (MSL) or above the ground (AGL). The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.
There are different types of altimeters, including pressure altimeters, radar altimeters, and GPS altimeters. Pressure altimeters work on the principle that for every 10 meters in altitude gained, the air pressure decreases by roughly 1 millibar. They contain a stack of sealed aneroid wafers with an internal pressure of 29.92" Hg. These wafers expand and contract based on the static pressure inside the casing of the altimeter.
Radar altimeters are highly effective at low altitudes, using frequencies from under the belly of the aircraft to bounce off the surface of the ground to measure height in AGL. They are used in low-visibility approaches and auto-land functions and are found on almost every commercial plane.
GPS altimeters have become more accurate as technology has advanced, but they can still be off by 500 to 1,000 feet, and up to 400 feet in hiking and climbing contexts.
In most flights, the goal is to set your altimeter to read out your aircraft's height above Mean Sea Level (MSL). However, altimeters can never show a negative altitude. Even in airports below sea level, such as Schiphol Airport in Amsterdam, the official aerodrome elevation is given a positive value. For example, Schiphol Airport's elevation is listed as -11 ft or -3 m, but this is not a negative altitude reading.
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Air pressure and temperature
Air pressure is the weight of all the air above us. It is measured in Pascals, named after Blaise Pascal. One pascal equals 0.01 millibars. Meteorologists have used millibars to measure air pressure since 1929. The standard pressure at sea level is 1013.25 millibars.
As elevation increases, the number of molecules in the atmosphere decreases, and so the density of air is lower, which means there is a decrease in air pressure. This is why air pressure at high altitudes is lower than at sea level. The decrease in pressure with height makes it challenging to compare the air pressure at ground level from one location to another, especially when the elevations of each site differ.
Air pressure can be increased or decreased in two ways. Firstly, by adding or removing molecules from a fixed volume. For example, when you inflate a balloon, the molecules inside are packed more closely together, increasing the density of the air and, therefore, the air pressure. The second way to change air pressure is by adding or removing heat. When you heat a balloon, the air pressure inside increases. Air pressure depends on the temperature of the air and the density of the air molecules. Atmospheric scientists use equations to describe how pressure, temperature, density, and volume are related to each other. They call these equations the Ideal Gas Law.
Airports can have negative elevations, meaning they are below sea level. For example, Bar Yehuda Airfield in Israel is at an elevation of -378 meters or -1240 feet. Amsterdam Schiphol Airport is also below sea level, with an elevation of -3 meters or -11 feet.
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Airport elevation and runway design
The design of airport runways is heavily influenced by a set of standards established by aviation authorities, such as the Federal Aviation Administration (FAA) in the United States. These standards ensure safe and efficient operations for various aircraft types. The length of a runway is critical for the takeoff and landing of aircraft and is determined by factors including aircraft type, airport elevation, weather conditions, sea level, and geographical and environmental considerations. Longer runways are essential for larger aircraft, higher temperatures, and higher altitudes, as they require more space to reach takeoff velocity and to slow down upon landing.
The average length of a runway at major commercial airports is between 8,000 and 13,000 feet, accommodating large commercial jets. In contrast, runways on aircraft carriers are much shorter, typically around 1,000 to 1,200 feet, designed for military jets that use catapult systems for takeoff and arresting wires for landing. Private jets generally require shorter runways of 5,000 to 6,000 feet, while small planes can operate with a minimum runway length of 2,000 to 3,000 feet.
In addition to length, runway design also encompasses width, separations between runways and taxiways, safety areas, shoulder width, jet blast pads, and object-free areas. Lighting and signs are crucial components of runway design, guiding pilots during takeoff and landing. Visual indicators, such as markings and lights, point pilots toward essential areas like terminals, parking, fuel, gates, and transitory aircraft areas.
Master planning combines airside and landside principles and designs, including airport layout, approach, and clear zone plans. Architects and planners must also consider noise contours to forecast and address future noise issues. Overall, the design of airport runways requires a comprehensive understanding of aircraft characteristics, safety standards, and operational requirements to ensure efficient and secure aviation operations.
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Frequently asked questions
Yes, airports can have negative elevation. Airports near the sea are often at or below sea level. For example, Amsterdam Schiphol Airport is famous for being below sea level, with an elevation of -11 ft or -3 m. The lowest elevation airport in the world is Bar Yehuda Airfield in Israel, which is -1,240 ft or -378 m below sea level.
Airport elevation is the officially designated height of an airport above mean sea level. It is measured from the highest point of an airport's usable runways.
Airport elevation is important for aircraft performance. Airports at higher elevations may have thinner air, which can impact how an aircraft performs during takeoff and landing.
