The sight of a landing airplane is as majestic as it is complex and dangerous. In fact, the most critical and demanding phase of a flight is landing. Although automation (autopilot) has reduced the burden on most phases of a flight, landing the airplane is one phase that calls the pilot into full action. Taking this into consideration, how long does it take for a plane to descend?
Practically, the average minimum time required to land a plane is 10 minutes. However, due to a number of factors, it takes about 30 minutes for an airplane to descend from its cruising altitude to the runway. The descent of an airplane is guided by a thumb rule known as the Rule of three.
In a bid to better understand how long it takes for a plane to descend, we would look into the guidelines that dictate the descent rate of an airplane, paying emphasis on the rule of three. We would also touch on the preparations a pilot makes for descent and landing.
Table of Contents
How Fast Do Airplanes Descend from Cruising Altitude?
Airplanes weigh an average of 175 000 pounds. Despite the role of pressurization, the heavy weight of an airplane exposes its passengers to a lot of shock and impact pressure. Therefore, if a pilot decides to descend rapidly, he would cause a lot of discomfort to his passengers, not to mention the adverse effects of a rapid change in pressure on the eardrums.
A rapid descent by a pilot will see the airplane reduce its altitude at a rate of 3 000 feet-per-minute (fpm). Provided the pilot starts descending from a 30 000 ft altitude, it would take just 10 minutes for the plane to touch down. However, 3 000 fpm is an extreme rate and leaves the passengers exposed to enormous shock.
Therefore, to tackle the problem of shock exposure and rapid descent, pilots adopt a slow and steady descent.
First, the pilot often reduces the plane’s altitude to 10 000 ft, and then begins to descend steadily at a 300 fpm rate. At this rate, it would take the airplane a total of 30 minutes to descend. This whole process of descent is guided by a thumb rule known as the Rule of three.
The Rule of Three
The rule of three is a rule of thumb convention adopted by pilots to cushion the effects of landing on passengers as a result of varying pressures during descent. This rule states that a pilot must allow a travel space of 3 nautical miles for every 1 000 ft of descent.
Before this convention was adopted, most pilots flew in unpressurized cabins at a cruise speed of 87–104 knots. This meant that they covered 3 miles in 2 minutes, thus resulting in a decent rate of 500–660 fpm. This descent rate was however not desirable as it left passengers uncomfortable due to the rate of change of the pressure on their eardrums.
Therefore, the rule of three was adopted to make sure that a plane’s descent is comfortable enough for passengers at a slow and steady rate. Following this convention, the pilot begins to descend gradually on approaching the runway by allowing about 3 nautical miles for every 1 000 ft of descent.
Even though modern airliners could and sometimes will descend quicker, a 3:1 glideslope provides an efficient glide slope, and therefore will lead to decreased fuel costs.
The pilot maintains this gradual descent until he is 10 000 ft above the runway. At this point, the pilot then maintains a 300 fpm descent rate until he lands the airplane safely. From initiation to finish, it takes the pilot a total of about 30 minutes to land an airplane using this convention.
The rule-of-three landing convention is illustrated in the figure below.
How Pilots Prepare for Landing
Landing a plane is indeed one of the most crucial phases of flight. The process does not allow room for mistakes and demands the best from the pilot. As a result, a pilot must be sure to be at his very best before landing a plane.
Therefore, certain preparations must be put in place and flight protocols followed before a landing can be accomplished. Enumerated below is a step by step preparation approach for landing:
- Monitor speed and descent rate: Before landing, a pilot must first monitor the speed and descent rate of the plane. As a preparation protocol, he must also complete the pre-landing checklist, which involves extending the landing gear, leading-edge slats, and trailing edge flaps.
- Navigate: After making sure that the plane’s speed and descent rate is in order, the pilot must then navigate the airplane towards the airport following a standard terminal arrival procedure and an instrument approach procedure.
- Communicate: As soon as he sets the right course and begins to navigate towards the runway, starting with the air route traffic control center (ARTCC), the pilot must establish constant communication with the control tower, listen to the airport weather, and speak to approach control.
- Land: After all boxes are checked, the pilot will then follow through with the rule-of-three landing convention and land the plane safely.
How Pressurization Works When Descending
Pressurization is the reason we do not choke in airplanes during takeoff, in flight, and on landing. It is the process of permitting the flow of conditioned air in an aircraft cruising at a high altitude to create a conducive environment for passengers.
To maintain the air pressure in the cabin during flight, incoming air is preserved within the cabin by opening and closing an outflow valve which directs pressurized air from the engine into the cabin. As soon as the pilot begins to land the plane, the pressure sensors begin to take in more air to increase the air pressure in the cabin in order to equal the air pressure outside until the airplane reaches the ground. Once the airplane touches down, the outflow valve is left wide open and the airplane is unpressurized.
Summary
In conclusion, a pilot would need to be at his best during the landing phase of a flight as it is one of the most consequential stages of flying. Following the rule of three landing convention, it takes 30 minutes for a pilot to land an airplane safely at a 300 fpm descent rate.
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