In this era of large commercial passenger jets, small airplanes are a delight to a large number of airplane enthusiasts. Be it a single-engine sleek trainer, an acrobatic bi-plane with colorful full-body paint, or even a classic fighter from the world war era restored to its original pristine condition. These small planes carry a sense of adventure to those who fly them and source of wonder to those who watch them. Piloting a small single-engine airplane brings back the romance of flying. It is a hobby and a joy for many and especially to those who spend hours taking care of their beloved machines and enjoy flying them as high as it would take them. Are these airplanes safe and you may wonder how high these planes can fly?
A small single-engine propeller airplane like the popular Cessna 172 can fly up to 15,000 feet. Since these airplanes mostly unpressurized airplanes, they cruise mostly cruise below 10,000 feet. A small business jet can fly up to 45,000 feet and cruises at 41,000 feet. A popular business jet, Gulfstream G650, is certified for a ceiling up to 51,000 feet.
In this article, we are going to look closer at why small airplanes fly at the altitudes they do, and what limitations there are!
Let’s start!
Table of Contents
Why do planes have to fly so high?
As the airplane takes off the runway, the pilot’s first job is essentially to get as high as and as quickly as possible. This is to avoid any land-based obstruction like tall buildings, electric towers, mountains, and most of all low flying birds. Another important reason to gain altitude quickly is to have enough height to navigate the plane to turn back to the runway for a safe landing, in case of an emergency.
Various types of airplanes have different maximum design ceilings and cruising altitudes. There are distinct advantages of flying at high altitudes but the reason is different for each type of aircraft. These smaller types of airplanes rarely fly above 10,000 feet. These airplanes have unpressurized cabins, meaning that pilots would need oxygen to fly much higher.
Business Jets
A business jet can fly at a height of up to 45,000 feet, though most cruise at 41, 000 feet. This is generally higher than even the large commercial jets which are designed to fly at 35,000 to 38,000 feet. Airlines prefer to fly at that altitude as it is the most efficient altitude to fly, which is above weather variations, and because of the maximum pressure differential, their fuselage can withstand. These airplanes are designed to have an internal cabin pressure equal to the altitude of 8,000 feet.
The small business jets are designed to fly higher for many reasons. It is more efficient to fly at a higher altitude where the air drag is less and the jet engines are more efficient. As the airplane flies higher, the surrounding air gets thinner and less dense, a jet airplane flies more efficiently and can fly faster because of less resistance from the air.
At this altitude there no weather issue nor there is any commercial jet traffic so they can chart a more direct course to their destination.
A private business jet pilot has a larger range of altitude available to him, so he can choose the optimum cruising altitude depending on the distance of the journey, to reach his destination as fast as possible, as speed, not the economy is the primary goal.
What are the limitations of flying at high altitudes?
Reduced air density and lift
As an aircraft climb higher, reduced air density results in increased human, engine, and aerodynamic problems. Above 10,000 feet to 14,000 feet, air density is too low to support human breathing.
The FAA requires supplemental oxygen to be available in the airplane at 12,000 feet for pilots, 14,000 feet for passengers. All business jets are pressurized to provide safe and comfortable travel to both pilots and passengers.
Planes are designed to fly up to up to a specific ceiling but If the plane tries to exceed this limit then its wings will not be able to create sufficient lift to maintain that altitude. When the plane gets too high, there is not sufficient oxygen to fuel the engines.
The air is less dense at this altitude, so the engine can pull in a lesser amount of air as it goes higher and at some altitude, the engine can no longer deliver enough power to climb.
At this point, the maximum speed and at stall speed become very close. This is called the ‘coffin corner’. Either of the two speeds is to be avoided. It is not safe to be flying at the maximum design altitude. At any point above this, the airplane will become uncontrollable and literally fall out of the sky.
All planes that are designed to fly above 15,000 feet should have a pressurized cabin. The fuselage of each airplane is designed to fly up to a specific height. Pressurization of the cabin for high-altitude flying exerts internal tensile stress on the fuselage. It is the strength of the fuselage that determines whether the airplane can tolerate such pressures. Flying an airplane above its designed celling may result in structural failure and is always avoided by the pilot.
Regulations
Apart from the technical issues, there are international and national regulations that limit the altitude of a particular type of airplane up to a particular altitude. These international rules adopted by the International Civil Aviation Organization (ICAO) have classified airspace into various classes for safety and operational reasons. Each country has adopted these classes with some modifications. The classes are fundamentally defined in terms of flight rules and interactions between aircraft and air traffic control (ATC).
The airspace above 18,000 feet is Class ‘A’ airspace and the airplanes which use this airspace have to be flown with Instrument Flight Rules (IFR). All such airplanes in this airspace should be equipped with IFR instrumentation and the pilot should be IR rated.
There are limits on altitude depending on the design of the airplane. It may be different based on engine type such as naturally aspirated engines, turboprops, turbofan, turbojet, and engines with afterburner. The airplane must be structurally sound to be able to withstand high winds at high altitudes. The airplane should also be equipped to be able to fly in extremely low temperatures as there is a significant decrease in temperature at higher altitudes.
There is also an altitude limitation depending on its type of aircraft, whether it is ultra-light, general aviation, commuter, or commercial airplane.
How high can military jets fly?
Modern fighter jet aircraft can fly at over 50,000 feet and some other combat aircraft such as stealth bombers even higher. The actual limits are classified for each model.
In most cases, a pressure suit with oxygen supply is provided to the pilot so that he can breathe normally and airplane cabin remains unpressurized. Some high-altitude military planes are designed for surveillance and spying purposes. The famous U-2 spy aircraft, which was first brought into service in the 1950s can cruise at up to 90,000 feet.
What about unpowered gliders? How high can they go?
Gliders are do not have an engine and rely solely on air currents to increase their altitudes once they are in free flight. Gliders climb in hot air currents rising to higher altitudes up to the base of large cloud formations which can be anything from 3,000 to 6,000 feet.
In 2018 two Argentinian pilots flew up to 76,100 feet in a glider. That is the highest altitude ever reached by humans aboard an unpowered fixed-wing aircraft.
Have manned balloons flights gone higher?
Beginning with the 18th century, ballooning has continually achieved higher altitudes. Normally when balloons fly over populated areas, they legally have to be flying above 1,000 feet in the air. Because of the harsh conditions at higher altitudes, hot air balloons normally do not surpass 3,000 feet. The highest altitude man has flown in a hot air balloon is 68,986 feet, which was achieved by an Indian who flew over Mumbai, India in November 2005.
The record for helium balloons is even more impressive. Helium balloons are filled with lighter than air helium gas so they rise in the air. As a helium balloon increases their altitude, the outer pressure decreases which expands the helium making it even less dense and lighter which makes the balloon go higher and higher. The current altitude record for a helium balloon was set by the American, Malcolm Ross, who flew to over 113,000 feet.
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