Pilots must constantly monitor climb rate. Expressed in feet per minute (FPM), it represents the speed at which an airplane ascends or descends. A positive climb rate indicates the airplane is ascending and gaining altitude. A negative climb rate indicates the airplane is descending and losing altitude. Below are several key factors that affect an airplane’s climb rate.
Flight Phase
While there are always exceptions, most airplanes have a slower climb rate immediately after taking off. The still-extended landing gear creates drag. At the same time, pilots often prioritize speed upon taking off. Only after achieving a target speed will pilots increase their angle of ascent.
Weight
One of the most influential factors in climb rate is aircraft weight. Heavy airplanes have a slower climb rate than lighter airplanes. Small single-engine airplanes, for instance, have an initial climb rate of roughly 300 to 1,000 FPM, whereas the jumbo-sized Airbus A380 has an initial climb rate of 1,500 FPM.
Thrust
An airplane’s thrust setting will affect its climb rate. The higher the thrust setting, the faster the airplane’s climb rate. With that said, airplanes can only climb when they have excess thrust. If an airplane’s thrust is less than its drag, it will descend. Regardless of size or engine type, airplanes must produce more thrust than their drag to achieve a positive climb rate.
Altitude
The altitude at which an airplane flies will affect its climb rate. Air is less dense at high altitudes, meaning the air molecules are spread farther apart. The less-dense air at high altitudes forces airplanes to work harder to generate lift. Furthermore, aircraft engines rely on air to generate thrust. At high altitudes, aircraft engines suck up less air, resulting in less thrust being produced. The bottom line is that airplanes generally have a slower climb rate at high altitudes.
Turbulence and Weather
Another factor that affects climb rate is turbulence and weather. Strong turbulence and wind shear, for example, can result in a slower climb rate. It will create drag that airplanes must overcome with thrust to climb. Rising air, in comparison, can actually improve an airplane’s climb rate. As the air rises, it will lift the airplane so that less thrust is needed.
In Conclusion
Climb rate is not just a number on the flight instruments. It reflects how well an airplane is performing in real time. Weight, thrust, altitude and weather all interact to shape how quickly an aircraft can gain altitude.
