Lesson 3 - Part 2
The Air Traffic Control 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 autopilot 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.
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 aren’t 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 “air pockets”. 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 you’re 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 don’t 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 25 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. Listen to my short narrative about wake turbulence.
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. Please email me with questions, comments or suggestions about the topics covered in Lesson 3.CLICK HERE TO CONTINUE TO LESSON 4