This summer I was traveling by airplane to see family and during the cruise, my son pulled out his bag of chips which he had brought from home. The packet had inflated like a balloon and my son thought it was hilarious and was afraid to open it. He asked why this had happened and I told him it was all to do with cabin pressurization.

Airplane cabins are pressurized to ensure every person on board has enough oxygen to breathe. As airplanes climb above 12,500 feet FAA regulations require everyone onboard an aircraft to be on oxygen or the cabin be pressurized. Pressurizing the cabin allows for greater passenger environmental comfort.

To ensure the cabin remains in a comfortable state for the passengers the aircraft pressurizes the cabin and carefully controls its atmosphere. To find out why and how this is done please read on… 

Why are Airplane Cabins Pressurized?

As a person climbs above 10,000 feet above sea level the pressure forcing oxygen molecules through the lining of their lungs and into their blood becomes insufficient and the number of oxygen molecules per given area is less. Without oxygen being constantly added to their blood they become Hypoxic (Blood Oxygen Starvation).

If left unchecked, hypoxia can lead to unconsciousness and death. There are two ways that persons traveling on an airplane can avoid hypoxia:

1. Supply each person with a constant oxygen supply
2. Pressurize the airplane cabin to a low altitude

As airplanes ascend to their cruising altitude, the pressure inside the airplane also decreases, unless it is a pressurized cabin. At sea level, the air pressure is around 100kPA/14psi. At around 35,000ft/10,000m the pressure is significantly less at around 26kPa/4psi:

For airplanes without pressurization systems, no supplemental oxygen is required when flying at or below 12,500 feet above sea level (ASL);

Above 12,500ft but up to 14000ft, the flight crew only are required to use supplemental oxygen if flying for over 30 minutes.

Above 14,000 all flight crew must be using supplemental oxygen. It must be available to passengers but they aren’t required to use it.

Above 15000ft, everybody must use supplemental oxygen at all times. 

With every commercial airliner typically flying over 30,000ft, without cabin pressurization everyone needs oxygen. Not only would this require large storage tanks, and be expensive to fill before each flight, but it would also be very uncomfortable for the passengers to wear a tethered mask for the entire flight.

Cabin pressurization changes that.

Why Not Just Fly Lower?

Airlines try to find the most fuel-efficient route for every flight. At altitudes of 35,000-40,000ft the air is thin enough to produce a minimal amount of drag, but dense enough to allow the engines to produce thrust. Below this, there is more drag, and above this, there isn’t enough oxygen for the engine to produce efficient thrust.

Because airplane engines are designed to be the most fuel-efficient at these higher altitudes the airline planners design their routings based on high altitudes. Flying lower means the engines work less efficiently and burn more fuel.

With fuel being the single biggest annual operating cost for an airline, every chance they get to reduce their fuel bill is taken. Flying at high altitudes accomplishes that.

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How are Airplane Cabins Pressurized? 

Cabins are pressurized via air from the engine. Turbofan engines take in air, pass it through a series of compression stages, mixes it with fuel, and ignites it for thrust. Some air is diverted after being compressed to be used for pressurizing and air conditioning the cabin. This is called Bleed Air. 

Compressed air is very hot, therefore, after being diverted, the bleed air is taken to a heat exchanger, and then to the refrigerating unit called an Air Cycle Machine for cooling. Moisture is removed from the air at the Water Separator before being introduced into the cabin. This is why your skin may feel dry on long-haul flights.

Diverting air from the engine reduces engine efficiency as not all of the air it compresses is used for combustion. Designing airplanes is all about compromise, and for this system, some fuel efficiency is sacrificed for bleed air pressurization in lieu of filling the plane with oxygen tanks. 

New airplane models like the Boeing 787 have incorporated electrically-driven compressors, eliminating the efficiency drop caused by bleed air pressurization from the engines. 

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How is Airplane Cabin Pressurization Controlled?

Cabin pressure is maintained by the Cabin Pressure Controller which controls a valve called the Outflow Valve. This valve allows air to escape the cabin at a controlled rate, controlling the amount of air pressure in the cabin. As the atmospheric pressure reduces, less air is allowed to outflow the cabin.

Pressurization begins on the ground when full thrust is engaged. The Outflow Valve is automatically closed and bleed air pressurization begins. The cabin pressure initially increases.

As the plane ascends, the outflow valve slowly opens to a point where the amount of air escaping causes a decrease in pressure at a rate proportional to the rate at which the plane is climbing.

This initial increase and then gradual decrease in cabin pressure is provided so the passengers feel less of the transition from high pressure to low pressure. 

This is why you may need to clear your ear pressure during the climb and descent.

When the plane levels off at cruising altitude, the outflow valve begins to close up to a point where the cabin altitude levels off at the preset value, usually 8,000ft (2,400m). Planes with stronger composite materials used to build the main fuselage like the Airbus A350 or Boeing 787 can go as low as 5,000ft (1,500m). The outflow valve doesn’t fully close as the bleed air produced by the engines is more than is required to pressurize the cabin. 

If the outflow valve fully closed the engines would continue to fill the cabin with pressurized air until it burst like a balloon. Not a good scenario! To prevent that the airplane is fitted with multiple pressure relief valves to prevent both over and under-pressurization.

Why Not Just Pressurize the Cabin to Sea Level?

We all know that when an object descends deep into the ocean there becomes a point where the water pressure becomes so immense it will crush any object with air inside it. The opposite happens for an airplane.

As the airplane climbs, we see in the chart above that the air pressure drops to just a couple of kPa. If the air inside the cabin was pressurized to sea level for the flight, the difference between the pressure outside the airplane and inside the cabin would be around 74kPa (100kPA-26kPA) or around 10psi.

This does not sound like a lot of a difference but to the airplane designers who are designing the structure to ensure the air pressure difference does not crush the fuselage, it is huge. 74kPa or 10psi over the entire surface of a commercial airplane is a serious force.

By raising the cabin pressure to simulate its occupants being around 8,000ft (2,400m) for example would lower the pressure differential while also keeping passengers in a comfortable environment.
This creates an inside-to-outside pressure differential of around 50kPa (76kPa-26kPa) or around 7psi.

With composite fuselages able to withstand much higher pressure differentials designers are able to drop the cabin pressures down to 5-6,000ft to allow for even greater passenger comfort. If the airplane is cabin pressurized to 5,000ft (1,500m) the pressure difference would be only 60kPa (86kPA-26kPA) or around 8psi.

Designing an airplane to withstand 7-8psi is far easier than 10psi! If they could, they would!

It is for this reason that my son’s bag of chips inflated like a balloon. It was sealed to a pressure at sea level so when the cabin pressurization system set the cabin pressure to 8,000ft the pressure inside the bag was higher than the surrounding cabin pressure making the bag inflate. I told him to open them before the bag exploded!

Can Objects Get Sucked Out of an Airplane Like in Movies?

A sudden hole or opening in the airplane’s structure/skin will cause a rapid decompression. Air will rush from inside the cabin to outside of the aircraft as the air tries to equalize the pressure difference. The pressure will equalize within a matter of seconds and then the suction will stop.

Although the breeze from the big open hole as the airplane flies at 400knots will not!

Any object that is near the opening will be moved by the airflow. If the opening is large enough and any person is not strapped in with their seat belt they could be sucked out of the aircraft. This is one of the reasons why regulations advise you to always wear a seat belt when flying!

On February 24 1989, United 811, a Boeing 747 suffered an explosive rapid compression when a cargo door failed.

3 entire rows of seats were ripped from their mountings and exited the aircraft resulting in 9 fatalities. The pilots lost both starboard engines and suffered wing damage but were able to make a safe landing back in Honolulu 24 minutes later!

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I was asked by a friend the other day what the difference was between a Narrow-Body and a Wide-Body airplane. He had overheard two people talking but wasn’t quite sure what the difference was exactly.

Narrow-Body airplanes consist of a single passenger access aisle running front to rear of the airplane. There may be 2, 4, 5, or 6 seats across the airplane. A Wide-Body airplane has 2 aisles running front to rear. They may contain between 4 to 10 seats across the airplane depending on class.

When the Boeing 747 first took to the air in January of 1970 for Pan American World Airways, commercial aviation was forever changed. The world’s first “Jumbo Jet” was initially developed for Pan Am, who challenged Boeing to design an aircraft that was two and one-half times the size of the narrow-bodied Boeing 707, and at the same time lower the average seat cost by 30 percent.

As the first twin-aisle passenger aircraft, commercial aviation now included aircraft described as narrow-bodied, with a single aisle from front to rear, and wide-body, with two aisles running the length of the aircraft.

Why Are There Narrow & Wide-body Aircraft?

Narrow-Body airplanes are primarily used to run shorter, more frequent routes moving fewer passengers but more often, up to multiple times each day. Wide-Body airplanes are designed primarily for long-haul flights on popular routes. Moving more people but less often, but over greater distances.

As the airline industry evolved during the 1950s jet age, the size of aircraft required by airlines changed. Initially, all passenger aircraft were narrow-bodied, as most flights were shorter than they are today. Four, five, and six across seating worked perfectly for domestic flights in the U.S. and Canada, as they rarely took more than three or four hours to complete.

As the airline industry grew, so did the demand for non-stop coast-to-coast flights of five to six hours. But it was the ability of the Boeing 707 and Douglas DC-8 to quickly cross the Atlantic Ocean that eventually led to the introduction of the Boeing 747, McDonnell Douglas DC-10, and Lockheed L-1011 widebody aircraft.

The larger aircraft offered more comfort and storage space in the cabin and were quicker for boarding and deplaning given that they now transported 300-400 passengers per flight, versus just 100-200 for narrow-bodied aircraft. The additional capacity also meant lower seat-mile costs and higher profits.

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What are the Advantages of Narrow-Body Airplanes?

Like every tool, it has the perfect job that it does very well. A narrow-body airplane is a perfect tool for certain routes. These routes are typically under 6 hours in duration with regular numbers of 100-300 passengers that can allow the airplane to fly at full capacity on each flight.

Here are Some of the Advantages of Narrow-Body Airplanes:

Smaller Size

Narrowbody aircraft can offer service to scores of small and medium-sized cities that have runways, terminals, aprons, and jetways designed for them. A small footprint allows narrow-body airplanes to operate to some of the world’s oldest airports.

The larger the airplane becomes, the airports that can handle airplanes of that size dramatically reduce which in turn limits the routes the aircraft can fly and thus the destinations the airline can offer to its customers.

Fewer Cabin Crew Required

FAA (Federal Aviation Administration) regulations call for a minimum of one flight attendant for every 50 seats (not passengers) on an aircraft. Obviously, single-aisle planes with fewer seats than widebodies require less staff for the operation of each flight.

With labor being the second biggest cost after fuel for airlines, the savings with the operation of narrowbody aircraft can be substantial.

Fewer Ground Personnel Required

Smaller aircraft require less servicing personnel and vehicles to work on the aircraft during passenger offloading and loading. Fewer baggage means fewer conveyors and baggage carts. Smaller fuel tanks mean a single fuel truck and driver. Fewer mouths mean only a single food delivery truck and waste hauling truck are required.

The bigger the airplane, the more ground personnel and vehicles are needed by the airport.

Shorter Turn Around Time

One of the biggest delays to airplane turnaround time is the time it takes to refuel. Smaller narrow-body aircraft require much lower fuel loads which take far less to deliver than large, wide-body airplanes.

If you would like to see just how long it takes to refuel some of the most popular narrow and wide-body airplanes check this article out:

How Long to Refuel an Airplane? – 15 Most Common Planes

Less baggage to come off and be loaded takes less time. Fewer seats mean shorter cleaning and inspection times by the cabin crew.

It isn’t unusual for narrowbody regional jets to arrive, deplane, board, and push off of the gate in around 40 minutes.

Basic Comfort Options

Passengers always want the cheapest fare possible. On shorter flights primarily operated by the narrow-body fleets passengers are willing to forego a little comfort for that cheaper deal. Narrower seats, less legroom, fewer bathrooms, and high-capacity seating configurations are all tolerable for a few hours.

When flying for long periods of time the necessity for comfort over price begins to play a bigger role in the passenger decision.

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Popular Narrow-Bodied Aircraft

Bombardier CRJ 700

• 2-2 Seating Configuration
• 70-80 Seats
• Primarily used by major carriers to feed their hub operations

Airbus A220

• 2-3 Seating Configuration
• A220-100 = 133 Seats
• A220-300 = 160 Seats
• An All-Coach Configuration

Airbus A319/A320/A321

• 3-3 seating Configuration
• A319 = 129 Seats
• A320 = 186 Seats
• A321 = 236 Seats
• An All-Coach Configuration

Boeing 737-700/800/900

• 3-3 Seating Configuration
• 737-700 = 143 Seats
• 737-800 = 189 Seats
• 737-900 = 149 Seats
• An All-Coach Configuration

Boeing 757-200/300

• 3-3 Seating Configuration
• 757-200 = 200 Seats
• 757-300 = 289 Seats

In recent years, some airlines have begun flying narrow-bodied, long-range aircraft across the Atlantic Ocean to Europe. While these aircraft generally offer less overall comfort for passengers, this option can be quite attractive to carriers that don’t necessarily have the passenger feed to fill a large aircraft or do not have widebodies in their fleet.

I found this was a great passenger benefit when Westjet started doing seasonal non-stop flights from major Canadian airports direct to London, England with a Boeing 757. Having two young kids made the trip so much easier and with it being an overnight flight too, it really made making the trip back to the UK to see family so much easier.

This is also the scenario for the U.S. west coast to Hawaii market, which used to be served almost exclusively by wide-bodies. Today, Southwest Airlines, Alaska Airlines, and others operate five to six hour flights using narrowbody 737s and 757s to the Hawaiian islands.

Transatlantic examples of this include Delta Air Lines’ Boeing 757-200 which operates seasonally between Minneapolis/St. Paul International Airport and Reykjavik, Iceland, and JetBlue’s new service from JFK International Airport to London Heathrow, utilizing the new-age Airbus A321LR (long-range).

Delta’s decision to fly an aging, but right-sized aircraft to Iceland, and JetBlue’s marketing of fewer seats (just 114 in economy and 24 up front) with a less roomy single-aisle plane shows the creativity of airlines to have a fleet that matches their route structure.

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What are the Advantages of Wide-Body Airplanes?

Wide-body airplanes are the king of the long-haul routes or the seriously popular short-haul routes like New York to Los Angeles where a lot of passengers need moving every day.

The advantages of the narrow-body airplanes shown above are obvious once you read them, but again like any tool, the wide-body aircraft play their part in modern-day aviation.

Here are Some of the Advantages of Wide-Body Airplanes:

Passenger Numbers

Wide-body airplanes carry between 250 – 850 passengers depending on the airplane and seating configuration. When the airline orders an airplane with a specific routing in mind they do in-depth analysis to determine the best seating configuration to be the most profitable.

Popular short-haul routes like the NY to LA may have a high-density seating configuration due to the fact the passengers are only on the flight for a relatively short period of time compared to a Pan-Pacific long-haul route.

The size of the wide-body airplanes gives far more flexibility for the airlines to tailor the seating configuration to suit. Take the Boeing 747-400 above. The high-density configuration places only 24 seats in first class with the majority of the seats on both decks being economy seating. This would be typical for a highly traveled route like NY-LA.

Space & Comfort

With long-haul routes being the primary flights that wide-body airplanes undertake passenger comfort is high on the interior designer’s list. With the larger cabins mentioned above this allows the designers and airlines to create more ‘Classes’ or bigger classes depending on the routes the airplane flies.

Routes with regular wealthy or business travelers can adopt larger first and business classes while some airplanes like the Airbus A380 even have private rooms or suites for certain routes, and yes you know they are not cheap!

With bigger fuselages also comes wider aisles, wider seats, and more legroom. Crammed in for flights lasting up to 19 hours (Singapore to New York) would be a surefire way to have passengers select another airline.

By having room to walk up and down the aisles comfortably, and having larger and more vestibules to stand and stretch in allow passengers to tolerate the painfully long journeys of the long-haul routes.

In addition to more space to move around, designers spend a great deal of time on the seating ergonomics to ensure passengers can comfortably and safely sit for hours on end. Poorly designed seating can easily lead to leg cramps, blood clots, and pain which again will soo have passengers looking for alternative carriers.

To also help with bordem, most wide-body aircraft have sophisticated individual passenger entertainment systems that provide far more than the short-haul, narrow-body airplanes.

Extensive movie, TV show, and music libraries, games, external cameras, real-time airplane data and moving map technologies, and even full wifi is now starting to creep into most airlines.

When paying high prices for a long-haul ticket even passengers situated in economy wish to have comfort and exceptional service – All of which airlines try their hardest to provide, especially on wide-body airplanes.

Crew Rest Bunks

With the wide-bodies dominating the long-haul routes thought has to be provided for the crew. Working nonstop for 19 hours is neither safe of acceptable and to overcome that most wide-body aircraft have crew bunks hidden away to allow crews to rotate and get some rest – especially flight crews.

Unbeknown to most passengers is a set of crew bunks tucked away in the front of the airplane. Either located above or sometimes below the first-class cabin can be either a pair or more crew bunks.

By allowing crews to rest it maintains the highest levels of safety and service and these bunks can only be fitted into the large wide-body airplanes.

Popular Wide-Body Aircraft

Boeing 787

• 3-3-3 Seating
• 330 Passengers in Coach, or
• Typically 242 Passengers in Multiple Classes

Boeing 767

• 2-3-2 Seating
• 375 Passengers in Coach, or
• Typically 218 Passengers in Multiple Classes
• No longer in production

Airbus A330

• 2-4-2 Seating
• 406 Passengers in Coach, or
• Typically 270 Passengers in Multiple Classes
  

Boeing 777

• 3-4-3 seating
• 414 Passengers in Coach, or
• Typically 314 Passengers in Multiple Classes

Airbus A350

• 3-3-3 Seating
• 440 Passengers in Coach, or
• Typically 300-350 Passengers in Multiple Classes

Airbus A380

• 3-4-3 Main Deck Seating
• 2-4-2 Upper Deck Seating
• 853 Passengers in Coach, or
• Typically 3644 Passengers in Multiple Classes
• (The A380 is no longer in production.)

Why Do Airlines Need Wide-Body & Narrow-Body Airplanes?

Large airlines that cater to both the short-haul and long-haul markets need aircraft that can fly both as efficiently as possible. They require both wide-body and narrow-body airplanes. Short-haul airlines can focus on narrow-body airplanes which are cheaper to buy, maintain and run.

As each decade passes aircraft have become more fuel efficient, giving them the capability to fly longer distances than their predecessors. Routes like Singapore-New York, Perth-London, and Melbourne-Dallas/Fort Worth were simply unimaginable just a decade ago.

Today, larger derivatives of popular narrow and wide-bodied aircraft are flying longer routes than ever before. Most of these new models, such as the 787-10, 737-MAX9, Airbus A330-900NEO (new engine option), and the Airbus 321XLR (extra long range) are flying internationally, but as the industry continues to evolve, we’ll see both single-aisle, mostly for shorter routes, and twin-aisle aircraft, mostly for longer routes, being ordered by airlines worldwide.

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It has become the norm for aircraft manufacturers to design planes with engines below their wings. This is especially true with large passenger planes and is commonly seen on Boeing and Airbus planes. Is this engine placement just conventional or are there specific reasons for this? 

Airplanes with large, heavy engines are mounted under the wing to keep the main weight of the engines below the airplane’s center of gravity. This helps with control stability and when thrust is applied by the pilots, underwing-mounted engines will help pitch the aircraft nose up during takeoffs & climbs.

When designing a new airplane designers have to spend large amounts of time when considering engine placement on the aircraft. To find the most efficient position to place the engines, engineers have to consider many aspects, among them being:

• Position of the Center of Gravity of the Airplane 
• Ground Clearance 
• Landing Gear Length
• Accessibility 
• Sound Damping 
• Wing Bending Relief
• Flutter Damping

If you wish to gain more knowledge in how these things are pondered by the design engineers when deciding on mounting location then please read on…

How Does the Engine Placement Affect an Airplane’s Center of Gravity?

On most airplanes, the Center of Gravity (CG) is located just in front of the Center of Lift (CL) of the plane. The center of lift is where all the lift forces produced by the wings act on the plane. This is usually mid-wing and along the fuselage of the plane. Mounting engines under the wing keeps the CG forward.

The CG is designed in front of the CL so that in case the plane gets into a stall, the plane will naturally tend to assume a nose-down position and restore airflow over the wings and help recover from the stalled condition.

To keep the CG towards the front of the aircraft, mounting the engines around the center of lift, ie the wings, is the best design case.

Placing engines at the tail position shifts the position of the CG backward from the center of lift, giving it a nose-up attitude in case of a stall. This is especially the case with larger, heavy engines that power today’s modern airliners.

Not only would the weight of the engines themselves dramatically shift the CG rearwards but also the weight of the structure needed to support them. It is for this reason alone that designers of commercial airliners do not mount engines at the rear of large commercial airplanes.

On smaller commuter jets and private/corporate airplanes, the weight of the engines themselves is considerably less allowing for much less supporting structure weight. To help offset this design it necessitates redesigning the plane to make the portion of the fuselage in front of the wings longer than the back portion. This restores the position of the CG in front of the center of lift.

Engine Weight Examples:

Airbus A350 Engine = Rolls Royce XWB-84 = 16,045lbs/7,277Kg each
MD-80 Engine = Rolls Royce BR-715 = 4,595lbs/2,085Kg each

This type of design can be seen in the older MD-80. This rearward CG makes it harder to control the pitch of a plane as it makes the elevator less effective hence why rear-mounted engines are now generally confined to small jet designs.

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How Do Engines Above the Wing Affect Center of Gravity? 

When engines are mounted below the wing, they are usually below the center of gravity. This means that when full thrust is applied by the pilots, the plane will naturally pitch upwards by rotating around the center of gravity. This is usually the intended attitude when the pilot applies maximum thrust, for example during takeoffs or climbs. 

Placing the engines above the wing usually has the opposite effect. The engines are above the CG and therefore produce a pitch-down rotational force when thrust is applied.

In addition to the rotational force created by the thrust is also the static stability of the airplane. When engines are mounted above the center of gravity it places a heavy mass up high making the aircraft ‘Top Heavy’

Like a ship, when most of the weight is below its center of gravity it increases stability, when placed above the center of gravity it makes the vessel or in this case, the airplane want to move away from its point of balance and rollover.

When the engines are mounted below the wing and the center of gravity they act like a pendulum and increase the static stability of the airplane.

For Example:

The Boeing 777 uses General Electric GE90 engines. Each engine weighs 18,260lbs. Placing over 36,000lbs above the aircraft’s CG dramatically alters the aircraft’s stability requiring bigger elevators and ailerons to manage the momentum and dynamic forces created by the top heavy engines.

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How Does Aircraft Engine Placement Affect Accessibility? 

With engines mounted under a wing, it allows easy access for maintenance engineers to take quick looks at potential problems during turnarounds. Most commercial airline engines can be completely accessed by step ladders making quick inspections and diagnosis possible without affecting the schedule.

Another major bonus to having engines under the wing is it allows for easy inspection by pilots while completing the pre-flight walk-around. Pilots are able to see in both the front and rear of the engine whereas, engines mounted high on the rear of the fuselage or on top of the wing make it difficult to complete a full visual inspection.

Engines on top of the wings need specialized equipment such as access gantries/platforms or personnel lifts to allow engineers to inspect and maintain them. Working with engines mounted above the wing could also be dangerous since simple mistakes such as dropping equipment like wrenches can damage the wing skin leading to lengthy and costly repairs. 

How Does Aircraft Engine Placement Affect Wing Flutter?

Wing flutter is the flapping of the wing caused by vibrations. As the plane lifts into the air the weight of the fuselage pulls down on the inboard sections of the wings, while the lift is pulling up on the wing tips. As the airplane flies through certain airspeeds or encounters with turbulence allow harmonic vibrations to develop.

When mounting the engines under the wing it helps to control how much the wing bends upwards due to the engine’s weight but also helps to dampen the vibrations within the wing similar to how a piano hammer stops a string from vibrating and making noise.

With engines mounted above the wing, the dampening effect would be far less leading to wing designs that would require extensive engineering to control and dampen the vibrations leading to wing flutter.

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To some people, the thought of an engine failure on an airplane is terrifying enough to never allow them to travel by air. We have all seen videos from passengers of aircraft when a jet engine has malfunctioned or a propellor has stopped turning while in flight. The question is though can a plane still fly on one good engine?

Airplanes with two or more engines are designed to fly with one engine failed. Depending on when the engine fails during the flight pilots may return to their departure airport, divert to a nearby airport, or continue to their destination. Depending on the malfunction an engine may be restarted.

It is possible for twin-engined aircraft to operate perfectly well with one engine, both landing and taking off without difficulty. A loss of an engine during flight is a major event but it is easily dealt with by the pilots who are trained to deal with this scenario on a regular basis.

Regardless of the severity of the incident, pilots are taught to abide by basic aviation rules. Depending on the engine’s status, pilots know how to respond when an engine fails, so an engine outage should very rarely be considered a serious issue. 

To find out just how aircraft can fly with only one engine remaining please read on…

How Do Pilots Deal With Engine Failures?

Pilots are trained to deal with engine failures on a regular basis at all stages of flight. A single pilot will run a mental checklist to secure or restart a failed engine, whereas a multi-pilot crew will run through a checklist to secure the engine, trim the aircraft and assess all options available.

The second part to this question all depends on the type of airplane the pilot/s is flying.

Single Engine Airplanes:

If the engine fails on an airplane with only that engine the pilot has two options:

1. Try restarting the engine if altitude permits and the source of the failure is possibly known
2. Make an emergency landing

Unfortunately, the pilot only has these two choices and sometimes an emergency landing is the only option, and even then the area upon which they must try and land the aircraft could be very unfavorable. This is why many single-engine airplanes are shown crashing in videos after an engine failure.

If the engine fails while at cruise with lots of altitude, the pilot may be able to restart or glide to a suitable landing site whether that be a runway, open field, or even a highway.

Losing the engine in a single-engine airplane is never a good situation.

Twin-Engine Airplanes:

Airplanes with two engines stand a much better chance of being able to stay airborne and allow the pilot/s to assess the severity of the situation and return to land or continue the flight.

When a pilot loses an engine in a twin-engined aircraft they will be able to adjust the flight controls to offset all the thrust coming now from just one side of the airplane. Depending on when the engine failure occurs will dictate what the pilots do and the options available to them. (More on this later).

Tri or Quad-Engine Airplanes:

Just like the pilots of a twin-engine aircraft, the pilots of tri & quad-engine airplanes have far more options and the likelihood of them reaching their original destination are far greater due to the fact they have more engines available.

However, issues arise when pilots of these aircraft begin to lose a second or third engine as this dramatically reduces the performance of the aircraft and may mean the pilots should have begun an emergency landing or are now required to.

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What Happens if Pilots Lose an Engine on Takeoff, Cruise, or Landing?

No matter how many engines an airplane has lost, the working engines alter the balance of how the aircraft flies. The pilot/s must react using control inputs to maintain the aircraft in a safe configuration, be that during a takeoff roll or airborne, any further issues are dealt with after.

To deal with engine failures, the airplane manufacturer creates a step-by-step checklist on how to deal with an engine failure depending on when it happens, how to try and restart it, or how to secure it and trim the aircraft to fly as efficiently as possible.

When pilots are new to the aircraft type the emergency procedures take up the majority of the training time and again, when pilots come back for their annual or bi-annual proficiency checks. The use of Computer-based simulators are the training tool of choice and is why most major airlines will have their own simulator training facility to ensure their pilots can be exposed to the worst possible case scenarios while in the safety of a simulator.

Practice makes perfect and that is why I am personally a big fan of simulator training!

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What Happens if an Engine Fails During Takeoff?

During the preflight readiness of the aircraft, the pilot/s will asses the weight of the aircraft with fuel, cargo, and passengers, atmospheric conditions, and runway length to calculate a speed at which a takeoff can be safely rejected. This is known as the Takeoff Decision Speed (V1).

Should an engine failure occur before the aircraft reaches the V1 speed the pilot/s will reject the takeoff by reducing power to all engines and placing them into reverse thrust to help decelerate, then apply the air and wheels brakes at their maximum capacity.

It is important for the aircraft to stop before the end of the runway!

In the event that velocity V1 is exceeded, the pilot who is not manipulating the flight controls will announce “V1” to the flying pilot. When the speed is over V1, the flying pilot will know they must continue and take off, regardless of what happens to the engines otherwise, they could possibly run out of runway! 

In this case, they take off and climb to assess their situation.

At any speed over V1, modern airplanes are certified to take off and climb with one engine inoperative and because of this pilots will establish a steady climb, adjust the flight controls to ensure the airplane flies in the correct aerodynamic configuration, and will advise air traffic control of their situation who will standby to provide any needed assistance.

It is common that large, commercial airliners have higher permitted takeoff weights compared to their allowable landing weight. This is due to the fact that they have usually burned off the majority of their fuel before landing at their destination. Most airliners’ landing gear cannot absorb the impact of the aircraft with full fuel tanks.

In this scenario, pilots must either dump fuel or divert to an airport by which time they have burned enough fuel to be under their maximum landing weight. Each incident requires collaboration and careful consideration to ensure the passengers, aircraft, and persons on the ground remain safe at all times.

What Happens if an Engine Fails During Cruise Flight?

If an engine fails in cruise and no damage has occurred pilots may elect to try and restart it. If it fails to restart pilots will secure the engine and plan for a diversion to an airport that is within the airplane’s certified ETOPS (Extended Range Twin-Engine Operations Performance Standard).

Just like an emergency, the decision as to what the pilots do afterward depends on the initial occurrence. If the engine flamed out for no reason, the pilots may elect to conduct a restart if all the indications look OK.

If the engine started to lose oil pressure, the pilots may elect to shut the engine down to prevent damage from being caused.

If the engine had a catastrophic malfunction and created damage to the cowls, wing, or fuselage the pilots may have to make a rapid descent and land at the nearest airport to which the airplane can safely land.

No matter the situation, the pilots are trained regularly to deal with the worst-case scenarios – To many people that would seem like losing an engine when over the middle of the ocean.

To assist pilots that face this situation the airplanes are certified to a set ETOPS standard. ETOPS refers to the length of time that a two-engined aircraft can fly without one of its engines.

When on a long flight far from suitable airports aircraft without an ETOPS certification must follow the blue line above. This makes them stay within an hour’s flight time from their emergency alternate airports during cruise.

With new aircraft and engine technology, airframes are certified to fly longer distances away from alternate airports making their routes shorter and faster. Most modern commercial airliners are certified with ETOPS:

There are many well-known aircraft out there with ETOPS ratings.

For example:

• The Boeing 737 has ETOPS-180 (180 minutes of single-engine endurance)
• The Boeing 787 Dreamliner has ETOPS-330
• The Airbus A350-900 has even more extended endurance ratings of 370 minutes.

On a single engine, Airbus claims the A350 can travel 4,630 kilometers in over six hours, an impressive distance for a single engine. Nevertheless, losing an engine has consequences. A loss of 50% of an aircraft’s power will affect its altitude, resulting in the aircraft having to revert to an intermediate altitude for the remainder of the flight which causes the remaining engine to be less efficient and burn more fuel.

With aircraft now being certified under ETOPS to fly further on a single engine, you will find most manufacturers are now focusing on aircraft with only two engines. The Boeing 787, 777 and Airbus A350 are great examples of this.

Airplane engines are a huge expense to buy and maintain and the fewer an aircraft designer can use the more popular the airframe becomes to airline fleet purchasers. With the Boeing 747 and Airbus A380 beginning to come towards the end of their life, it will be interesting to see if any manufacturer designs another 4 engine commercial airplane.

What Happens if an Engine Fails During Landing?

If an engine failure occurs during landing the pilot’s main priority is to maintain a safe flight configuration of the airplane. If the airplane has just started the descent pilots will secure the failed engine. If on short final they will leave the engine until landed.

Trimming is, of course, crucial. During low altitudes, even the slightest mistake can cause the aircraft to deviate out of control. This is why it is crucial to adjust the remaining engine’s power in accordance with the required speed.

Overpowered engines may cause the airplane to veer abruptly, or underpowered engines may cause it to stall (uncontrolled loss of altitude). Before every landing, possible engine failure scenarios are discussed in detail well before to ensure each pilot knows what action to undertake should an engine failure occur.

If an engine has failed during the cruise part of the flight the pilots will use the appropriate emergency checklist pilots check what needs to be done and how the aircraft needs to be configured for the emergency landing of the aircraft.

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