Determining the speed of an airplane is not a straightforward matter, as pilots rely on various speeds depending on different factors and atmospheric conditions. In general, there are four distinct speeds used to measure different aspects of flight. Let’s establish two important facts before delving further: Firstly, the speed of an aircraft varies depending on the phase of flight it is in. Secondly, different types of aircraft have varying capabilities and can achieve different speeds.
How fast is an airplane in the air?
When an airplane is in the air, its speed is measured in knots, which is a unit of speed used in aviation. One knot is equivalent to 1 nautical mile per hour, and a nautical mile is approximately 1.15078 statute miles.
The primary type of airspeed used during flight is indicated airspeed. It is derived from the aircraft’s pitot-static system, which measures the dynamic pressure from the air entering the pitot tube and the static pressure from the surrounding air conditions. The indicated airspeed is calculated by determining the difference between these pressures.
However, indicated airspeed is not the most accurate metric for higher altitudes due to variations in temperature, atmospheric pressure, and other factors. Therefore, further conversions and corrections are required to obtain a more realistic and reliable airspeed at higher altitudes.
True airspeed is a measure that adjusts indicated airspeed to account for factors such as temperature and pressure at higher altitudes. As an aircraft climbs, the temperature tends to decrease and the air pressure decreases as well. By making these adjustments, true airspeed represents the actual speed at which the air is flowing over the aircraft’s wings at a specific altitude.
During the cruise phase, pilots rely on another speed parameter called Mach number. Mach number is the ratio of true airspeed to the speed of sound and is highly influenced by atmospheric conditions, particularly temperature. It provides a precise way to fine-tune the speed within a specific region. Air traffic controllers also use Mach number to maintain separation between aircraft at higher altitudes.
Some typical airspeeds
- Boeing 737 NG/MAX: Mach 0.78, about 450 knots true airspeed.
- Airbus A320 family: Mach 0.78, about 450 knots true airspeed.
- Boeing 787 Dreamliner: Mach 0.85, about 488 knots true airspeed.
- Airbus A350: Mach 0.85, about 488 knots true airspeed.
- Airbus A330: Mach 0.82, about 470 knots true airspeed.
- Boeing 757: Mach 0.80, about 461 knots true airspeed.
- Concorde: Mach 2.02, about 1,176 knots true airspeed.
What is an airplane’s average groundspeed?
Groundspeed is the speed at which an aircraft is moving relative to the Earth’s surface. It takes into account the effects of wind and altitude. Groundspeed is a straightforward measure that can be adjusted based on prevailing winds. For instance, if an A321 aircraft has a true airspeed of 460 knots (529 mph) while flying from New York to Los Angeles during a period of strong headwinds, the actual groundspeed will be lower. If the headwind component is 100 knots (115 mph), the aircraft’s groundspeed would be reduced to 360 knots (414 mph). This reduction in groundspeed would result in a longer travel time to reach the West Coast. However, the Mach number, which represents the ratio of true airspeed to the speed of sound, would remain unchanged as it is determined solely by the true airspeed.
An aircraft’s groundspeed is greatly influenced by the wind conditions it encounters during the flight. The specific groundspeed is not associated with individual aircraft types but can vary depending on the prevailing winds. As a general guideline, an aircraft’s groundspeed can range from 350 knots (in the presence of strong headwinds) to 550 knots (with strong tailwinds). However, there can be exceptions to this range. During winter, there are occasional reports of aircraft experiencing exceptionally strong tailwinds while flying eastbound over the Atlantic Ocean. These tailwinds can exceed 700 knots groundspeed or 805 mph. It’s important to note that although the groundspeed may be high, the aircraft is not actually flying faster than its normal speed. In fact, some flights may even slow down to conserve fuel given the favorable wind conditions. By taking advantage of these tailwinds, aircraft can achieve remarkably fast speeds.
On the other hand, aircraft flying westbound face the challenge of strong headwinds. To mitigate the impact of these headwinds, flight dispatchers often plan longer, more circuitous routes that avoid the strongest headwind areas. Despite covering a greater distance, the fuel savings achieved by avoiding the headwinds make these alternate routes more efficient than a more direct route directly into the headwinds.
