Lesson 3 of 5
The Aircraft and Its Environment
The Aircraft and Its Environment
Here we will focus on the airplane, how it flies, and the environment it operates in. Becoming more familiar with these subjects will answer questions and ease concerns which come up during flight.
"Dear Captain Chance, taking your course helped me so much. All four of my flights went very well. I'd never had turbulence before on flights, but I did on these, and I was able to stay calm. Take-off still makes me nervous, but I was able to remember that planes are built to fly and do their job well. I have another set of flights in a week, but I'm much less nervous now."
Commercial airline pilots go to great lengths to make your flight as smooth and motionless as possible, but you should know that these planes can really perform if needed. They have big powerful engines, sturdy efficient wings, and very responsive controls. Technically, these jets are not certified to be aerobatic, but they can really maneuver. We could even do loops and rolls, but I promise we won't!
Please don't be in denial about the plane. It is primarily designed as a flying machine, you should feel very safe on it.
Use deep breathing to calm yourself:
1. Push your stomach outward and slowly inhale through your nose.
2. Fill your lungs from the bottom up, and then pause.
3. Slowly exhale while whispering, "relaaaax".
Do this a few times and you'll be ready to continue.
Your Airplane is Not Going to Fall Apart
The FAA mandates that modern jet aircraft are designed and built with large safety margins. All aircraft and their equipment are built from FAA-approved designs and manufactured under FAA-approved systems.
Coming out of the factory the planes are thoroughly flight tested before certification by the FAA. Airliners can withstand many times the stresses and forces which can be imposed upon them in flight.
The wing of an aircraft is very strong. The wing is commonly built as one continuous unit extending through the fuselage. It is constructed with huge reinforced spars.
Unless one were to fly at speeds far greater than normal, there is no way the wing of an aircraft can produce enough lift to bend or break any of its structure. As long as you don't fly unusually fast, even very strong turbulence will not damage an aircraft, the wings just can't produce enough of a lifting force to bend anything.
Your Airplane is Not Going to Lose Control
Airplanes have a built-in stability, they will not tip over. This means that they will seek a natural state of straight and level flight. If you point the nose of the airplane up or down and let go of the controls, it will work its way back to level flight. This same leveling occurs when banking (turning) an airplane. That's why planes can fly "hands off", just like your car should track straight down the road. (Had an alignment lately?)
Your Plane is a Mechanical Marvel
Jet airliners are designed to be safe and reliable, they don't make money sitting on the ground. The plane's systems are built to last. If a plane is repair-prone the airline will find another plane to buy, Boeing and the other aircraft manufacturers know this.
Jet Engines are Simple and Reliable
Unlike the complexity of piston engines, jet engines just have a series of spinning fans. Air goes in the front, is compressed by fans, fuel is introduced and burned, and high pressure exhaust gases spin more fans to create thrust (Suck, Compress, Burn, and Blow).
There is no need for camshafts, timing belts, connecting rods, complicated valve trains, or ignition systems (except for igniters, used for starting). Once the fuel starts burning, it keeps burning. Just keep adding fuel and the jet engine keeps running, really very simple and dependable!
The main component of jet engine exhaust is water vapor. This is what creates the contrails that you see in the sky.
Back in the days of piston-powered prop airliners, an engine might fail on the average of once every 4000 hours of operation, this was considered fairly reliable. But when jet engines were introduced, the reliability increased TEN fold! Statistically, I would have to fly three careers, or about 75 years, before I would experience an engine failure.
And, in the extremely rare event of an engine failure, there is no phase of flight at which this should cause a significant problem. Every single flight is planned in such a way that if an engine was to fail, the plane must still have enough performance to fly safely. We are trained to handle engine failures in every phase of flight.
They Keep Going and Going...
When boarding a plane and reviewing the maintenance logs, I often note how nothing has broken on that plane for days or weeks. And when it does it is usually something like a loose arm-rest or a tray table in need of an adjustment. Jet airliners are well maintained.
The FAA mandates that every airline comply with a very strict and comprehensive maintenance schedule.
With all of this maintenance and inspecting there is still more inspecting.
Before the first flight of the day, one of the pilots will do a thorough preflight inspection inside and out. And before flying each leg, the plane receives another walk around inspection by a pilot. On top of that, every day when an aircraft flies through an airline's maintenance base, a mechanic will meet the flight to do a quick checkup on the plane and examine its maintenance logs.
Most maintenance is performed at night during a plane's down time. When there is major maintenance or a scheduled inspection to be done, the plane is taken out of service.
As you can see, these planes are well attended to. Failure of a system or component is rare, and when they do fail, there are backup systems.
As an example, the plane I fly, a DC9 Super 80, has three separate electrical sources including an auxiliary power unit. The plane needs only one electrical source to power all systems. Even if all three sources failed, the airplane's batteries would power the essential systems long enough to land safely. And you know what? Without any electricity, the plane still has a window, wings and engines. It will still fly. It would be back to the basics, but something we could manage.
Later, see details about other aircraft systems (Fuel, Hydraulic, Pressurization, Fire Protection) on the Bonus Web Page.
The Basics of Flight
What makes a plane fly? Wings and speed through the air is all that is required to make a plane fly. The plane is just moving through the air - a fluid. The movement of a plane through the air is like swimming or surfing.
Like water, air is a fluid. Air is just thinner than water, but is still a significant mass. In fact, at this moment, you are experiencing about 15 psi (pounds per square inch) of pressure from our atmosphere. You don't notice it because it has always been there and presses on your body equally from all angles.
Speaking of how strong air can be; have you ever considered what holds your car up? It's not really the tires, it's air pressure - about 32 psi. That's a lot of weight for just some air to support! Think about it...
You may have a hard time believing that something as big as a jet can stay up in the air. What is holding it up there?
Have you ever stuck your hand out a car window at 30 mph, then again at 60 mph? Now multiply the force your hand feels at 60 mph times ten (Actually, the force increases with the square of velocity so it would be even greater, but I don't want to get too technical here.). That is the force your hand would feel flying at the speed of a jetliner! And if your hand was efficiently shaped like a wing, you could almost fly with just your two hands!
The faster you go, the thicker the air feels. To the plane it feels like a thick watery fluid capable of substantial support.
Whales are huge creatures. How can Shamu the Killer Whale fly through the air? To do this the whale swims to gain speed through the water. Using his tail fin he angles upward and his flippers create the necessary lift to fly up out of the water.
Jet airliners look massive, but for their size they are VERY lightweight. For the most part they are hollow and constructed primarily of aluminum. You have held an empty aluminum soda can, haven't you? It is very lightweight for its size.
You take big wings and get them going fast and it creates a tremendous lifting force. Big or small, all aircraft fly using the same principles. No magic, just physics.
The wing flaps are lowered during takeoff and landing. Wing flaps are used to create more lift so that planes can takeoff and land at slower speeds. The slower speed means the plane will require less runway length.
The wing has a curvature shape which creates lift. The greater the curvature the greater the lift, but with the greater curvature comes greater drag. During high speed cruise it is preferable to have a flat wing to reduce drag.
To satisfy both high and slow speed requirements for flight wing flaps are used. After landing the panels which pop up on top of the wing are called speed brakes.
Engines Create Thrust
Some people assume that a plane's engines are responsible for holding a plane up. The engines don't make lift, the engines simply provide the push to keep the plane moving forward so that the wings will create lift. Without the engine's "push", a plane will continue to fly by gliding slowly downward.
I'll let you in on a little secret, jetliners glide on every flight. Normally, about 100 miles from the destination airport, the pilots will throttle back to idle. The engines no longer provide the "push" they are nice and quiet, and this saves fuel. Near the runway the pilots will increase the throttles for any required maneuvering or speed changes.
So when you wonder what is holding the plane in the air, imagine that the air has turned into a thick fluid and the plane is simply swimming through it.
How Does an Airplane Turn?
When flying level, the plane's lift is directed straight up. To turn, we bank (tilt) the plane by moving the wing's control flaps (ailerons). This redirects some of the wing's lift in the direction we wish to turn. Because of the centrifugal force of the turn, we don't feel any sensation of tilting. It is like a bicycle which leans into the direction of the turn.
The plane's built-in stability requires us to actually hold the plane in the bank to turn. You may worry that the plane will tip over in a turn, this cannot happen unless the pilot decides it's time for an air show and rolls the airplane over manually. Not a likely scenario!!!
To move (yaw) the plane side to side we use the rudder.
How Does an Airplane Climb or Descend?
To climb or descend we move the plane's tail "fins" (elevators) which cause the plane to nose up or down. To maintain the desired speed we either increase or decrease the throttle.
There is really no mystery about flying, we have wings to provide lift, engines to push us, and control fins to guide us. Look up at the sky, notice how the planes and birds fly. Think about how they fly. See how they swim through the air. Try to get more comfortable with the idea of flight.
The ATC System
Even though the sky is a big area, how do we keep planes away from each other?
That's where the Air Traffic Control system comes in. The controllers monitor radar screens in the tower and at ATC facilities to insure planes are properly separated. The controller is backed up by a computer which automatically squawks at the controller if separation is not maintained. The controller hates it when this happens because it means he has to fill out reports and answer to his supervisor.
The separation requirements are significant. At cruise altitude planes must be kept ten miles apart horizontally, and separated by at least 1,000 feet vertically. All planes flying eastbound fly odd numbered altitudes (31,000 feet, 33,000 feet, etc.) while westbound flights fly even altitudes (30,000 feet, 32,000 feet, etc.).
Another recent addition to our planes is an on-board collision avoidance computer. This system not only keeps us separated from other planes, but also warns us of terrain conflicts. The other "high tech" backup system is the good ol' windshield. It is the responsibility of at least one pilot to maintain a watch outside.
Next we will take a look at how weather affects flying.
Fog is a common occurrence and can be responsible for delays. There are regulations which prohibit takeoff if we don't have a certain amount of visibility. If we don't have the required visibility, normally about 600 feet, we wait until it improves.
Similarly, when a plane is approaching for a landing, the airport must report a minimum visibility before we can begin an approach. If the fog is really thick, most planes can be perform autopilot landings. The will fly the plane down to the runway, touch down, retard the throttles, track the centerline, and even apply the brakes. All the while, the pilots have their hands on the controls to back up the autopilot system, which has at least one other autopilot as a backup. The autopilot does a fairly smooth job of landing the plane, but of course, not as smooth as my landings!
If it is too foggy to land we enter a holding pattern to wait for the visibility to improve or head to a nearby airport. We always carry additional fuel and plan for landings at alternate airports whenever there is a chance for weather delays.
No matter how dreary it looks on the ground, it's always sunny above the clouds!
Flying through clouds can be fun. Horizontal shaped stratus clouds are smooth to fly through. Cumulus clouds are "puffy" shaped and often have updrafts. When flying through cumulus clouds you normally feel few bumps.
Another reason the airplane might experience a little turbulence while going through clouds is due to the changes in air density. Clouds are a little colder than the surrounding air, so the air density is slightly different.
Flying in snow is no big deal, but it can reduce visibility similar to fog. We are also limited to how much snow can be on the runway for takeoffs and landings. Sometimes flights are delayed while airports remove snow from runways. During snowy landings we use our anti-skid brakes, wing speed brakes, and reverse thrust. But if the runway is reported to be slippery, the airport will close the runway and we will land elsewhere.
When ice is present on an aircraft on the ground, we always call out the de-icing truck to spray special de-icing fluid onto the aircraft. Once airborne, all modern jet aircraft have anti-icing systems to protect the windshield, wings, tail, engines, and other surfaces from the accumulation of ice. These anti-icing systems may use electrical heaters or hot jet engine "bleed" air to keep the ice off.
There have been many technological advances to help us detect and avoid thunderstorms. We have both airborne and ground based radar as well as sophisticated satellite imagery to help us plan our course around bad weather. Recently, air traffic controllers have been supplied with improved weather radar which is helpful in directing aircraft away from storms.
Lightning is rarely dangerous to aircraft. I know it sounds frightening, but if an aircraft is hit by lightning (my plane was once hit), it almost never causes harm to the aircraft. I have seen the effects of lightning strikes on a few aircraft, and all it amounts to is a small pitted area in the metal about the size of a dime. Aircraft are designed in such a way that every metallic part is wired together to allow the flow of electricity to exit through "static discharge" wicks located on the wings and tail.
When flying at night in clouds near thunderstorms you may see flashes of lightning that appear to be nearby. Flashes of lightning from over 50 miles away can be visually transmitted through clouds making it seem like the lightning is close. If you see these flashes, remember that this is an illusion, and you are likely a safe distance from storms.
Windshear is a by-product of thunderstorms, it is the sudden change in direction and velocity of the wind. Years ago, there were a number of incidents involving windshear. Since then, a great deal of study into windshear detection and avoidance has been made. To provide for the early detection of windshear a new type of Doppler radar has been installed in aircraft and at airports around the country. Also, a rigorous training program for pilots has been implemented. This new training includes simulated encounters with windshear and teaches pilots how to achieve maximum performance from the aircraft to escape safely. With the new technology and training, the problems of windshear can be avoided.
Strong turbulence is normally associated with the heavy rain of severe thunderstorms. Radar uses raindrops to reflect its beams. Radar screens display precipitation, not clouds. Standard industry policy is to give thunderstorms a wide berth of at least 20 miles. If a thunderstorm is near the airport, takeoffs and landings are postponed until the thunderstorm dissipates or moves away. Typically thunderstorms travel over the ground from 15 to 35 mph. Often, if you wait 30 minutes the storm will move off and it will be safe to resume operations.
A common wintertime turbulence called "mountain wave" is produced when the jet stream is at a lower altitude. Like water flowing in a river with small eddies, wind flowing over obstacles such as mountains cause turbulence. Mountain wave turbulence is typically found just east of the Rocky Mountains during strong jet stream activity. Weather forecasters are experienced at predicting this type of turbulence because it is easy to track the location of the jet stream. Often we change cruising altitudes to minimize its annoying affects.
Turbulence can also be caused by shifting wind currents in the sky. When you transition from one wind current to another, such as crossing a weather front, the air can get stirred up. Planes flying through these transition areas can experience some turbulence. Again, it may be annoying, but not a problem.
One of the more common types of daytime turbulence is called "convective turbulence". As the sun warms the ground hot air rises and makes the air bumpy. You may see evidence of this by small, puffy shaped clouds.
This type of turbulence is normally felt at the lower altitudes during takeoff and landing on hot sunny afternoons. It poses no danger and is rarely classified as anything but light or mild turbulence. Birds such as hawks and eagles use this rising energy of hot air to soar above fields allowing them to effortlessly search for prey.
There are many sources of information about turbulence available to pilots. We get information from the weather service, our company dispatch, ATC, other aircraft, and our own observation of the sky and cloud formations.
"Thank you so much for the online course. It helped me a lot. I'm TERRIBLY afraid of flying (or I should say I WAS..) and I have a trip planned in a week - I'm sure I'll do much better with his information! My biggest fear is turbulence. This course helped me understand turbulence - which was the main problem - I didn't understand it. Thanks again!"
People often misunderstand turbulence. When encountering turbulence, nervous passengers may feel that the plane is falling out of the sky. It is natural to only feel the "down" bumps, but for every "down" bump there is an "up" bump. The "downs" are just more noticeable.
What do the pilots do during turbulence?
Normally the autopilot is engaged during cruise and it does a great job of controlling the plane during turbulence. Only the strongest turbulence will be too much for the autopilot, and that is very rare.
If the autopilot is off the pilot will gently guide the airplane. The plane already has built in stability, so the pilot isn't really "fighting" to keep the plane in control. The plane knows how to fly naturally, there is no need to struggle with the controls.
Whenever turbulence might threaten the safety or comfort of passengers moving about the cabin we turn on the Seat Belt Sign and make a PA to remind passengers to fasten their seat belts. We might also give information about the possible duration and reason for the turbulence.
We normally ask ATC for ride reports ahead and request to change to a smoother altitude if available. Turbulence can be a somewhat common experience, so pilots view it as routine. We strive to give our passengers the smoothest ride possible. If we flew for a cargo airline such as Fed Ex turbulence would be of little concern because packages arenít bothered by bumps!
Car vs. Airplane Turbulence
Have you ever driven fast over a bump in the road which caused you to come up off of your seat? It feels fairly violent and the jolt would certainly spill any drinks you were holding. How large of a bump does it take to do this? Not very large.
It is very rare to experience strong enough jolts while flying to spill drinks. Even if you do experience strong jolts the plane is not falling hundreds or thousands of feet, it only hit a bump a couple of feet high. Altimeters in the cockpit would barely register such a bump. When you feel turbulence, it's not that big of deal so try not to let your imagination get out of hand.
The next time you are driving on a bumpy road picture yourself as a passenger on a plane experiencing turbulence. Now take a look at the road. How big are the bumps that create the rough ride? The air is usually very smooth, but sometimes small ripples can make it feel like "bad" turbulence! It doesn't take much to feel like the plane is bouncing around, but in reality the plane remains very stable. You get a rougher ride in a car, but for some reason don't worry about that.
Contrary to news reports planes don't "plummet" when they encounter turbulence. There are no such things as ďair pocketsĒ. You can think of flying like being in a boat on a lake. Sometimes the water is smooth and sometimes it gets stirred up from the wind or currents. Riding on a choppy lake may be bumpy and you might encounter a wave big enough to jolt the boat. Riding the down side of a wave may give you the feeling youíre dropping, but there are no holes (pockets) in the water where the boat (or plane) is going to fall into.
Air pockets are a myth, because planes donít just fall out of the sky, there is always air for support. Have you ever been unable to breathe because you were walking along and found yourself in an air pocket???
In over 30 years of flying I have never felt that I have been in turbulence bad enough to jeopardize aircraft structure or control. For the most part turbulence is merely an annoyance. As far as I know, no airliners in modern history have crashed solely due to turbulence while in cruise. Turbulence won't break the plane.
Unfortunately, some unrestrained flight attendants and passengers have been injured during unexpected turbulence encounters. So do like the pilots do - always keep your seat belt fastened while seated.
Wake turbulence is turbulence generated behind aircraft in flight. Like a boat that leaves a wake behind it on the water, wake turbulence is formed behind aircraft in flight. The wake behind an aircraft lasts for a couple of minutes and tends to slowly sink below the aircrafts flight path.
All pilots are taught to be aware of wake turbulence. A wake encounter is not necessarily hazardous. When crossing the wake of an aircraft you may experience one or more quick jolts or you may experience some wing rocking. Government and industry groups are making concerted efforts to minimize or eliminate the hazards of wake turbulence.
How do we avoid wake turbulence? We establish a safe interval behind other aircraft. Air traffic controllers provide at least a 2 to 3 minute time separation behind aircraft landing or departing. Also, we remain at or above the flight path of the preceding aircraft and we fly slightly upwind.
Wake encounters are very rare because wake turbulence affects such a small area and exists for only a brief period of time, but we always strive to avoid it to provide you with a safe and smooth flight.
Lesson 3 Summary
You have learned that planes are well designed and built strong. They are thoroughly tested, inspected and maintained. They have built in stability to fly smoothly and safely. You have seen how simple flight is, just keep your speed and you will have lift and control. Our atmosphere is very capable of supporting jet aircraft.
You now know that there are many procedures and backups in the ATC systems to provide safe aircraft separation. And you have seen that modern advances in weather information technologies make avoiding bad weather a breeze.
You have learned the cause of turbulence. While it may be annoying, it is somewhat common to experience some turbulence on a typical flight. You must understand that turbulence will not harm the aircraft. Before the flight you can ask the pilots about any expected turbulence.
With this lesson you should feel more comfortable about flight.
End of Lesson 3
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