What is SPD on Boeing 737? (Speed)

Speed, abbreviated as SPD, is a crucial factor in the aviation industry, governing the performance and safety of aircraft. On the Boeing 737, speed plays a vital role in various aspects of flight, including takeoff, climb, cruise, descent, and landing. In this article, we will explore the different types of speed measured on a Boeing 737 and their significance in ensuring a smooth and efficient flight.

Indicated Airspeed (IAS)

Indicated Airspeed (IAS) is the speed shown on the aircraft’s airspeed indicator, which measures the dynamic pressure of the air during flight. It represents the speed at which the aircraft is moving through the air mass. In the case of the Boeing 737, the indicated airspeed is crucial for both the pilots and the aircraft systems.

Pilots rely on indicated airspeed for various purposes, such as maintaining the recommended speeds for takeoff, climb, and landing. In the takeoff phase, they refer to the appropriate IAS to ensure a safe takeoff, considering factors such as aircraft weight, runway length, and environmental conditions. During climb, they adjust the aircraft’s speed based on the recommended climb speeds to optimize fuel efficiency and ascent rate.

On the other hand, aircraft systems use indicated airspeed to calculate values essential for flight operations. For instance, the autopilot system relies on IAS to maintain a specific speed and altitude as programmed by the pilots. Additionally, stall warning systems monitor the IAS to detect if the aircraft is approaching a stall condition, providing necessary alerts to the flight crew to prevent an aerodynamic stall.

True Airspeed (TAS)

True Airspeed (TAS) is the speed of the aircraft with respect to the mass of air it is moving through. Unlike indicated airspeed, true airspeed takes into account the impact of altitudes and temperature on the air density, providing a more accurate measurement of the aircraft’s actual performance.

The Boeing 737 relies on true airspeed for various calculations, including fuel consumption, range estimation, and maximum maneuvering speed. Fuel consumption is directly related to true airspeed since at higher speeds, the aircraft requires more power and subsequently burns more fuel. Range estimation relies on TAS to calculate the expected distance the aircraft can fly with a given amount of fuel.

Furthermore, the Boeing 737’s maximum maneuvering speed, also known as V.A, is based on true airspeed. V.A represents the maximum speed at which the aircraft can be subjected to full control inputs without exceeding the aircraft’s structural limits. By considering TAS, the aircraft’s true performance is accounted for, ensuring safe and controlled operations.

Groundspeed (GS)

Groundspeed (GS) refers to the speed of the aircraft relative to the ground, taking into account the speed of the aircraft through the air and the wind’s effect. It is essential for flight planning, navigation, and determining the time required to reach a destination.

Flight planning involves calculating the estimated time of arrival (ETA) at the destination, which relies on the groundspeed. By factoring in the wind’s direction and speed, pilots can determine the most fuel-efficient route and make adjustments to their flight plan accordingly. Additionally, groundspeed plays a crucial role in navigation, as it helps pilots identify visual landmarks and maintain an accurate position on their route.

It’s worth noting that groundspeed can differ from true airspeed in the presence of wind. If the aircraft is flying into a headwind, the groundspeed will be lower than the true airspeed, while flying with a tailwind will result in a higher groundspeed compared to the TAS.


Speed, encompassing indicated airspeed, true airspeed, and groundspeed, is a fundamental aspect of operating the Boeing 737. Indicated airspeed provides critical information to pilots and aircraft systems for maintaining safe and efficient flight operations. True airspeed allows for more accurate performance calculations and ensures the aircraft operates within its structural limits. Groundspeed enables pilots to plan routes effectively and estimate arrival times, taking into account the influence of wind on the aircraft’s movement. Together, these different measures of speed contribute to the safe and successful operation of the Boeing 737.

For more information on the Boeing 737 and its speed capabilities, you can visit Boeing’s official website.

For More: What is ANS on Boeing 737? (Alternate Navigation System)