Understanding the Various Types of Airspeed

It is easy to measure speed when on the ground. For these reasons, vehicles measure only one type of speed. The case is a little different in the air. Once an aircraft is airborne, factors such as air density and wind come into play. The measurement of speed has to account for these variations. This is where the four types of airspeed come into play. And they are vastly important. The different types of airspeed are one of the most valuable measurements in aviation.

The types of airspeed in aviation guide everything from takeoff to landing and every phase in between. As aspiring pilots, you need to know this concept by heart. Let's dive right in.

When pilots talk about types of airspeed, they are referencing one of the following four types:

Indicated Airspeed (IAS)
True Airspeed (TAS)
Ground Speed (GS)
Calibrated Airspeed (CAS)

As pilots, it is vital to understand how the 4 types of airspeed work, including what they measure, how the measurement is done, and how to use that information.

1. Indicated Airspeed (IAS)

The first in the list of types of airspeed is Indicated Airspeed (IAS), which is the measured speed of an airplane as it moves through the air. The cockpit airspeed indicator registers the IAS, and the pilot-static system collects the pressure readings.

So, what is indicated airspeed in aviation? When comparing two kinds of air pressure, the IAS shows how fast you are going. These are static pressure from one source and ram pressure from another. The difference between the two is the dynamic pressure, translating into a reading. Manufacturers often use the IAS to determine aircraft performance. Understanding what is indicated airspeed is essential because the IAS tests operational limits. These limits ensure the aircraft can withstand the stresses and loads during various flight conditions.

Another reason the IAS takes precedence among the 4 types of airspeed is that it usually remains relatively constant for a given flight phase, despite altitude changes. Indicated airspeed is also vital for achieving the correct speed for takeoff rotation and maintaining a stable approach and landing speed. All these reasons make it incumbent to know more about what is indicated airspeed.

2. True Airspeed (TAS)

The next entrant in the types of airspeed list is true airspeed. So, what is true airspeed? True airspeed is the speed of your aircraft relative to the air it is flying through. When you ascend, the TAS is higher than the indicated airspeed and decreases at higher altitudes. This is because fewer and fewer air molecules enter the pitot tube as you climb up. The indicated airspeed will always be lower than the TAS. In fact, for every thousand feet above sea level, your indicated speed will be less than the true airspeed.

A pilot can find the TAS using two methods. The first is to use a conventional electronic flight computer. The second is adding 2 percent to the CAS for each 1,000 feet of altitude. For instance, at 10,000 feet, you will fly 20% faster than your indicated speed.

While understanding what is true airspeed is essential, knowing why the TAS is vital is also crucial. When used with wind information, TAS can determine the required heading to maintain a desired ground track. As one of the different types of airspeed, true airspeed is also the primary speed used in flight planning, especially when estimating flight duration, fuel consumption, and range. Lastly, like indicated airspeed, true airspeed helps the pilot understand the aircraft's performance at various altitudes and air densities.

3. Ground Speed (GS)

The third item in our types of airspeed is ground speed. So, what is ground speed? Ground Speed is the movement of your airplane relative to the ground. In other words, it is true airspeed corrected for wind. For instance, with a true airspeed of 100 knots and a tailwind of 20 knots, your groundspeed will be 120.

A tailwind pushes the plane faster relative to the ground than to the air mass, so the ground speed is higher than the true airspeed.

Why is it important for aspiring pilots to discover what is ground speed? For starters, when ground speed measures the aircraft's speed relative to the Earth's surface, it leads the way for accurate navigation. Accurate navigation takes care of other areas like fuel management and flight planning, directly impacting how long it takes to reach the destination. As an essential item in the types of airspeed, ground speed is critical for ensuring safe landings, as it helps pilots calculate how long it will take to reach the airport and plan for descent and approach.

Ground speed plays a role in ensuring safe landings, as it helps pilots calculate how long it will take to reach the airport and plan for descent and approach. Lastly, ground speed is also used by air traffic controllers to evaluate when an aircraft will reach a certain point in its flight, which helps manage airspace and prevent conflicts.

4. Calibrated Airspeed (CAS)

The fourth item in the types of airspeed list is calibrated airspeed. It is indicated airspeed corrected for instrument and positional errors. At certain airspeeds and with specific flap settings, the installation and instrument errors may total several knots. This error is generally most significant at low airspeeds, with nose-high pitch attitudes. In fact, the indicated airspeed and calibrated airspeed are almost the same in higher airspeed ranges. Pilots can find the calibrated airspeed in the calibration chart of the aircraft manual.

So, why is the CAS important among the different types of airspeed? The CAS provides a more accurate representation of the aircraft's air speed than the indicated airspeed. Additionally, calibrated airspeed is used in performance charts and calculations for various performance parameters. Lastly, when true airspeed is based on calibrated airspeed, it leads to more accurate flight planning, including fuel burn calculations and estimated arrival time (ETA).

Other Types of Airspeed

We looked at the 4 types of airspeed and answered questions like what is indicated airspeed, what is true airspeed, what is ground speed, and what is calibrated airspeed. Pilots need to have a thorough understanding of two more types of airspeed.

Equivalent Airspeed (EAS): This airspeed is calibrated speed and corrected for air compressibility.
Mach Number (M): The Mach Number is the ratio of the true airspeed to the local speed of sound. Pilots can see the Mach number on the Machmeter. M varies depending on atmospheric conditions, air temperature, and density.

Why are Airspeeds Important?

The types of airspeed we discussed today are crucial for pilots to be familiar with. Each of these airspeeds impacts an aircraft's performance, fuel efficiency, and ability to navigate safely and securely.

Flight performance and safety: The different types of airspeed in aviation, notably indicated airspeed, are critical parameters for pilots to maintain a safe flight.
Navigation and flight planning: Airspeeds, such as true airspeed, are essential for accurate navigation and flight planning. Pilots employ true airspeed, along with wind speed and direction, to assess the required heading to maintain a desired ground track.
Fuel efficiency: Pilots will learn more about fuel efficiency when they study how airspeeds change with altitude and other factors, such as wind and temperature.
Aerodynamics: All the types of airspeed are crucial for understanding how aircraft wings generate lift.

Common Misconceptions About Airspeed

The types of airspeed are undoubtedly crucial for pilots to be aware of. That being said, airspeeds are not devoid of misconstrual. When learning to fly, there is a mountain of information to conquer. To make learning easier, complex airspeed concepts are often simplified. While this is not a bad thing, some misconceptions get attached.

1. Airspeed and Stalling

The myth about airspeed and stalling is that if an aircraft goes fast, it cannot stall. The reality is much different. Stalling is determined by the angle of attack, which is the angle between an aircraft's wings and the oncoming air. If the angle of attack becomes too high, a plane can stall at any of the different types of airspeed.

2. Indicated Airspeed (IAS) vs. True Airspeed (TAS)

The myth surrounding these types of airspeed is that the IAS is the same as TAS at all altitudes. The reality is that the IAS is calibrated for specific atmospheric conditions at sea level. The TAS is the actual speed of the aircraft. As altitude increases, the air becomes less dense, and TAS will be higher than IAS.

3. Airspeed and Ground Speed

The misconception here is that airspeed and ground speed are the same. This is far from the whole truth. In reality, airspeed is the aircraft's speed relative to the airmass. Ground speed, on the other hand, is the aircraft's speed relative to the ground.

4. Airspeed and Ground Effect

The misconception is that the ground effect is essentially the "cushion of air" created when aircraft wings press down. However, this is not true. The ground effect occurs when the aircraft's proximity to the ground reduces wingtip vortices, leading to a reduction in induced drag and a potential increase in lift.

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Conclusion

Understanding the types of airspeed is fundamental for anyone who aspires to get into the aviation field, whether a student pilot or an experienced professional. Each airspeed, Indicated Airspeed (IAS), Calibrated Airspeed (CAS), True Airspeed (TAS), and Groundspeed (GS), serves a unique purpose and plays a vital role in enabling pilots to make safe and informed flight decisions.

Among the different types of airspeed, indicated airspeed is what pilots rely on most during flight. It is vital for aircraft control, especially in scenarios such as landing and takeoff. On the other hand, calibrated airspeed refines that reading, while true airspeed helps pilots and flight dispatchers with accurate flight planning. The final link in this cycle is the ground speed, which allows pilots to assess how fast an aircraft moves over the ground.

As pilots, it is vital to understand how these airspeeds relate to each other and how they are affected by altitude, temperature, and wind. Knowing this phenomenon can refine your situational awareness and decision-making skills. Of course, reading airspeed is more than just reading the instrument; it is about understanding how your aircraft reacts when in contact with the broader environment. Whether you fly a small jet or a commercial airliner, knowing the distinction between aircraft types can be the differentiator in ensuring safety.

As you get better at reading the types of airspeed, it will be a good idea to update yourself on the other areas of pilot training, such as understanding the six basic aircraft instruments. These instruments provide fundamental data for a pilot to control and navigate an aircraft safely. With more pilot jobs opening up, keeping your knowledge current is always a good idea. That is how you will differentiate yourself from the competition.

The Pilot’s Guide to the Types of Airspeed