Radio Communications in Aviation

Talking on the radio for the first time is intimidating for the new pilot. Understanding some basic rules, formats and conventions helps a lot and with a little experience under your belt radio communications become second nature. Here are some pointers meant for the beginner and the experienced GA pilot.

First, understand that the full, generic format of all initial calls. What does "initial contact" mean?. It's your first call to a controller or the first call to the next controller in flight following (or an IFR flight). Listening to an ATIS at a towered airport you will hear: "...upon initial contact advise you have Tango...".  So when you first contact either ground or tower, let them know you have "Tango".

Initial contact calls have the format:

1. Who are you
2. Who am I
3. Where am I
4. WaddaIwant

Ok, one at a time. Here is an example of an initial call:

1. This is who are you addressing. This ensures you are talking to the correct person. How many times have you said "ground, this is N12345" and been on the tower frequency! Because of the message format where you address who you think you are talking to, the mistake is corrected quickly and tower tells you to contact ground on another frequency. The pilot clearly announces to whom he thinks he is talking
2. The next phrase tells the controller who you are and often starts with the optional "This is...". So using our above example: "Santa Monica Tower, this is Cessna 12345". I like using the optional "this is" because it sets the controller's expectation as to what information follows.
3. Where am I tells the controller where you are located. If this initial call where to happen from the air, for example an initial call to establish flight following, you would state position and altitude. E.g., "I am over the SADDE intersection at five thousand, five hundred. This helps the controller identify you on a radar screen and is a sanity check for you because the controller will verify your position and your altitude in case you are not where you think you are or your Mode-C transponder is lying.
4. What do I want is really easy, but often has to include other information to get what you want. For example: "...I have information Tango and I would like a right shoreline departure".

Ok let's try the whole enchilada using this format:

"Santa Monica ground, this is Cessna 12345. I am at transient parking with information Tango and I would like a right shoreline departure."

Once the controller comes back with "Cessna 12345 this is Santa Monica ground, taxi to runway XX", you know that the connection is good: you asked for the ground controller (not the tower), the ground controller tells you who he is and he also told you which airplane he is addressing". This sounds kind of dumb, but it prevents errors when talking controllers. Never use your partial tail numbers in an initial contact! It's easy to imagine the confusion that might occur if there were also a Cessna 67345  in the area!

Often I get question from pilots of the form "the controller said ABC, what did he mean by this?" My standard answer is see if it is in the Pilot Controller glossary at http://www.faa.gov/air_traffic/publications/atpubs/PCG/. This document sets the concise understanding between the the pilot and the controller. I think of these phrases as handles on a larger, precise meaning. For example, when a controller says "Cessna 12345, you are cleared for the option", the phrase "cleared for the option" has a precise meaning given in the PCG. If the PCG does not show the meaning, ask a CFI or talk to someone at a FSDO or phone the tower supervisor. If nonstandard phrases are used by controllers, it may be they are making a mistake or you are dealing with local conventions. Of course, anytime you feel a communication is ambiguous while in flight, get it out in the open immediately with the phrase "unfamiliar with XYZ" where XYZ is whatever the controller told you to do. However, study up on phrases published in the PCG that you are likely to encounter so you do not have to use "unfamiliar" in reference to a well know phrase.. It's your responsibility to understand phrases that may be directed at you by a controller. My favorite example of a non-published phrase is when approaching a towered airport and ATC says "make a 3 mile right base". I have three definitions of this phrase from different controllers and it is not in the PCG. So, I respond with "unfamiliar with a 3 mile right base".
A pleasant "I am new to this area and I am unfamiliar with Highway 205" or "I am unfamiliar with a 3 mile right base" will strike a friendly tone and buy you a lot of help from a controller. Unfortunately "unfamiliar" is not part of the PCG, but is should be right next to "unable" which is in the glossary. Too often I have seen pilots new to an area not ask for help and knowing that a simple phrase like "unfamiliar" is ok to use would be a good thing. In any event, by informal convention, controllers know and respect this phrase.

For those of you whom English isn't your first tongue understand that the set of phrases you are going to hear is fairly limited and if you study these phrases and work to listen for them in flight you will eventually understand when you hear them exactly what is being directed your way. If you don't refer to the PCG and understand the format of aviation communications learning to communicate will take longer than necessary.

For all pilots, the most important thing is to anticipate. That is, what is the controller likely to say next? This helps speed the learning process. Also, recognize that radio communications start with a pilot calling a controller or a controller calling a pilot. Both calls have a end to the dialog which is usually easy to understand in context. Once the dialog has ended this is when you need to open your ears to catch the next thing you hear on the radio. If it is a controller, the next thing spoken will be a tail number. If the tail number is not yours you can relax. If it is a pilot, then s/he should start with the name of the control facility (e.g. "SoCal approach", ....).

Something I cannot recommend enough for the beginner is purchasing a good active noise reduction (ANR) head set. Noise creates stress which leads to fatigue. The drone of a loud engine isn't conducive to learning. In addition, the ancillary stress of having to ask a controller "what did you say - repeat that" is a waste of time. It's penny wise and dollar foolish not to purchase an ANR headset. You do not need the most expensive, most will do. Ask around early in your training. Also, a good ANR set will have 2 microphones on the mike boom. One is used to analyze background noise and this data is used by a processor to subtract it out which means the controller hears you better. An ANR set will speed up learning and is worth the money.

Make sure you understand that some of phrases you have heard in the movies or on TV were used incorrectly. For example, do you really know the meaning of "roger"? It's in the PCG. It means: "I have received all of your last transmission". I cringe when a pilot is asked a question requiring a yes or no answer and his reply is "roger". "Cessna 12345 do plan to turn left at the freeway?" and the pilot answers "roger"...arghhhh! The pilot was asked for a yes or no answer (affirmative or negative) and instead responds with "I have received all of your last transmission". Pretty stupid reply don't you think. Read the PCG. Your life depends on it and mine does too.

More on Landings - deck angle of the tricycle rigged aircraft during landing

A problem I commonly see in landings is that a pilot pulls on the yoke often reaching a proper landing deck angle soon after the round out. Ok so far, but the next segment of the landing is where things go haywire: the pilot does not maintain this deck angle before the wheels touch and this is a mistake.

What is deck angle? I use it here as slang for the angle of the longitudinal axis of the aircraft from the landing surface, which usually means a runway surface.

To illustrate, assume that the XYZ make and model needs to be landed with a deck angle of 7.5 degrees. Right after the round out, the pilot flares to 7.5 degrees and then freezes - no more pulling on the yoke. What happens to the deck angle? Why? Answers: the deck angle decreases because the effectiveness of the elevator in maintaining pitch decays as the airspeed decays so the nose keeps dropping until a flat landing occurs - simple aerodynamics. In other words, to maintain proper deck angle, the pilot must keep pulling to increase elevator deflection to obtain a constant angle. Instead of a constant landing deck angle, this angle constantly decreases until the wheels touch. This means a poor transfer of weight from wing lift to wheels and it also means a lot more ground speed when the wheels touch. The former is hard on the airframe and the later   unncessarily increases tire wear.

Knowing deck angle in degrees is asking a lot out of most GA pilots and who wants to watch an AI during a landing - not me! There are indices that often work well in the cockpit. For example, for many trainers (not all!), proper deck angle can be acquired by flaring until the front end of the engine cowling is high, but no so high that the runway center line is covered by the cowling. For these aircraft, this means that the nose is really high, but the pilot can always see some center line markings off the very end of the cowling - not a lot, just some. It's my experience this is true for the following aircraft and perhaps more: The C152, PA28-161 & 181, C172(N,S), C182 (all models I have flown). 

Many pilots who do not maintain a proper deck angle are often uncomfortable with a proper landing because they feel the pitch is way to high and looking out at a lot of engine cowling frightens them. Remember - center line is always in sight. I suppose you could verify that you will not have a tail strike if you were to jack up the nose wheel to obtain this deck angle, step outside and verify that the tail is indeed a fair distance from a strike.

Some pilots feel uncomfortable because they feel they do not have the visual references needed for lateral control. This is normally not an issue as long as the center line is in sight over the engine cowling.

The proper amount of deck angle ensures you are reaching and holding the highest possible angle of attack into the touchdown without doing a tail strike. This is important because it tends to minimize runway length requirements for the landing and it is nice to the aircraft because you are milking as much lift out of a very slow aircraft for as long as you can which means nice gentle wheel contact at the lowest possible speed. The proper amount of deck angle is part of what leads to the "greased" landing. A greased landing is nothing more than a landing where the pilot has kept as much lift as possible on the wings until the moment of touch down leading to a smoother transfer of aircraft weight from the wings onto the mains.

Another common problem in landings is concrete legs during cross wind landings. I will save this topic for another time. Meantime, get out there and work on keeping proper deck angle while landing when there is no wind or the wind is down the runway. Be safe and be nice to your airplane - even if you are a renter.

Dave Zittin's New Web Site

My business website has changed to www.learntoflypaloalto.com. Yes, it's long but what the heck. If you want to learn to fly airplanes, single or multi-engine or learn how to fly in clouds reference my new site.

I will likely keep this blog intact, but I may move future blogging to the website - TBD.

Have a great holiday break!
-Dave

Great day flying the Cirrus Prospective with Henry

Some time ago, I asked my good friend Henry, a fine wood worker if he would make a projector cabinet for me and I would give him a ride in a "modern" aircraft. I chose the Cirrus Prospective whose avionics and cockpit comfort I love.

Henry used to work for Consolidated Aircraft post WWII.

We decided to fly from his nearby airport in the Sierra Nevada foothills of California to Castle-Merced (KMER) airport which has a mongo runway and an interesting air musuem. It used to be a military base at which any kind of aircraft could land. It was a treat walking around the museum with Henry telling me the history of much of the aircraft and pointing out ones that he helped design.

We had a severe clear day - at least 100 miles of visibility until we descended into the central California gorp which was about 2000' feet deep.

To say he was very impressed with the Cirrus Prospective is an understatement. I guess he had no idea how far avionics and creature comforts had come since he was involved in aviation many years ago.

VOR Navigation Basics for Aviators

Let's admit it. VOR navigation isn't the most user friendly way of getting around, but once you understand a few basics and some recipes on how to use the darned system, it's really not that bad.

I am writing this blog post with the student pilot in mind, but hopefully the private pilot who never really understood VOR navigation will get something out of this posting.

There are two ways to work with VORs: the concept and the actual use. The concept is something you do with simulators or at home with pencil and paper. A very good and free simulator can be found here and I affectionately call it Tim's Airnav. Actual use of the system as I describe below means understand what you want to do, then follow the recipe for that item. If you are in the cockpit and working on the conceptual part, you are in the wrong place. You should be home at the kitchen table. The cockpit is a great place to make sure you can use the VORs, but not a place to understand how they work. The degree to which this is true is proportional to turbulence and how fast the weather is closing in.

There are three things you will normally do to navigate with VORs:

1. Intercept a radial and fly inbound (inbound means fly towards the VOR)
2. Intercept a radial and fly outbound (outbound means to fly away from the VOR)
3. Go direct from your current position to a VOR

Number 3 is really used once the radials mentioned in 1 and 2 are intercepted or it can be a "go direct to the Puddytat VORTEC" directive from your instructor or air traffic control).

Now, before I go any further, some concepts we must agree on or we will not get anywhere and I will be talking into the cone of confusion or perhaps addressing the zone of ambiguity.

A single VOR station is a group of antennas on the ground that fire at different times and emit radio signals during each transmit cycle. Your cockpit VOR receiver receives these signals and allows you to determine on which of 360 radials your aircraft is located. A radial is an electronic "line of position" (navigators say L O P). The radials are numbered 000 to 359. The 000 can also be referred to as the 360 degree radial. A technician turns a knob at the ground station and adjusts the ground track of the block of radials so that the 000 (360) radial is pointing at magnetic north for that particular spot on the earth. Remember that the angle of magnetic north from geographic north varies from point to point on the surface of the earth - that's why it's called "variation". Having radials reference magnetic points on the compass simplifies the life of the pilot because his references to direction are made via magnetic references (compass, magnetic flux detection, etc.) just as runway numbering simplifies our life because they are numbered by magnetic direction.

Next concept, the radial. Think of the VOR transmitter as a dot on the ground from which 360 lines emanate. These lines are called radials. Each line is numbered 000-359. Each line is a radial. Whoops, I repeat myself, but I did it intentionally. A radial always comes FROM (note the emphasis on "from") the VOR. For example, the 090 radial (magnetic direction is always expressed in 3 digits with leading zero(es) if necessary) radiates from the VOR and makes a ground track towards magnetic east. It doesn't matter if I jump on the 090 degree radial and I fly towards the VOR or I fly away from the VOR, I am still on the 090 radial. Let's say that I fly towards the VOR on the 090. In other words, I am flying magnetic west (towards 270). One mile away from the VOR I am still on the 090 and I am still flying west. A little later we are right on top of the VOR. At this point all the radials kind of come together - it's big mess and it's called the "Cone of Confusion". However, if I ignored the drunken CDI on my omnibearing selector (OBS) display, it will eventually settle down as I keep heading west and if all were executed just right, I have crossed the VOR, left the 090 degree radial and now I am flying outbound on the 270 degree radial heading away from the VOR and into the sunset.

Again, all radials have a name and they have an origin at at the VOR - they emanate "FROM" the ground based VOR transmitter.

Now the part that messes up the beginner and a lot of experienced folks, the notion of the "TO" and the "FROM" flag on the omnibearing selector display. If you turn the dial (omnibearing selector) and you center the CDI and there is a "FROM" indication then the value you read at the top of protractor is the radial on which you are positioned. If you center the CDI and a "TO" indication is shown in the TO/FROM window, then you are on the radial indicated on the bottom of the protractor. Confused? If so, don't feel alone. It's not so bad once you understand the reason for this and it revolves around the fact that humans aren't very good flying with reverse sensing. To illustrate, suppose you want to fly on the 090 degree radial towards our VORTAC and cross the ground station and keep on going into the sunset on the 270 degree radial. Let us fast forward into the future and say you have passed the VOR and you have 270 dialed on top of the OBS protractor scale. Let's go even a step further and you notice the CDI is exactly centered which means you are a great VOR navigator because your aircraft is located right on the 270 degree radial. Now let's suppose you parallel the 270, but drift southward. This would cause the CDI to drift to the right side of the display. It's telling you that the line you tuned in (270 degree) is on your right and you aren't on it anymore. You need to turn the aircraft a few degrees right to re-intercept the 270 degree radial. If the needle drifts to the left of the display while the aircraft parallels the 270 radial, you have drifted north and you must turn the aircraft to the left to re-intercept the 270 radial. Pretty neat. Desired radial on your left, needle on your left, turn left. And ditto for right except the radial is on your right, the needle is on your right and you must turn right. Get it? In both cases you turn into the needle to correct. How much turn? - hold on I will cover that later.

Once you understand this you will know what to do to keep on a radial when you are flying outbound from the ground station: dial in the radial number on the top of the OBS display, keep the needle in the center. If needle moves left, turn left a little; if the needle goes right, turn right a little. Now the catch which is conceptually troubling for most. The catch is that what happens if you are flying inbound towards the ground station on the 090 radial and you dialed in 090 on the top of the protractor? Well if the needle is centered, you are on the 090 radial and the TO/FROM flag will indicate "FROM". Now let's suppose that your aircraft drifts north. Which way does the needle go? Where do you want it to go? You want it to go to the left of center to tell you to turn the AC left to re-intercept the 090 radial. Does it? Answer: emphatic NO! Why? Because when you have a radial value dialed in and you are on that radial, 090 in this case, the system assumes that you are heading away from the ground based station so the deviation indicator shows that the line you desire is either right underneath you, to your right if you drifted north or to your left if you drifted south of the 090 radial. This introduces a very important concept: the VOR receiver in your aircraft knows nothing about the heading of your aircraft. It's is only telling you where you are in relation to a radial. If you are north of the 090 hanging by a sky hook and you spin the aircraft on its cable, the CDI will be to the right of center, assuming that you dialed in 090 on the OBS, regardless of where the aircraft is pointing at any moment as you pirouette in the sky. If you are on the 090 radial it will be centered as your aircraft makes its 360 rotation on the skyhook cable swivel. If you are to the south it's the same as north except the needle is to the left of center as you do your swivel trick.

In short, there is an implicit assumption that you are always going outbound on a given radial and that the CDI shows your deviation from the radial based on the assumed outbound direction of the aircraft. But we are NOT going outbound we are going inbound to the ground station on the 090! Well if you put 090 on the top of the OBS display you will have to be straight jacketed when you land because the needle will always be going the wrong direction relative to your deviation away from the 090 radial! For example, if the aircraft drifts north, while you are heading west, the needle moves to the right side! If you turn right to intercept - Ouch! If you keep your current position, but magically move the aircraft 180 degrees so you are going away from the VOR, then the needle is telling you the correct direction to turn to re-intercept the 090 radial. The fact that it goes the wrong way when you go inbound on the 090 with a "FROM" indication is called reverse sensing. The manufacturers of the receiver system said, hey we can help pilots with this problem (I made this up, but it works even if it's not true). If they are going inbound on the radial, we can let them dial in the reciprocal (radial + 180) which is 270 degrees (090 + 180) and give them proper sensing. Now things become ambiguous for the pilot if he gets a centered needle after dialing in 090 while on the 090 radial and he gets a centered needle if he dials in 270! Solution: put a TO/FROM flag on the display to tell the pilot whether or not he has the "real" radial or he has dialed in the reciprocal. Problem solved. So, if I am on the 090 radial and I am inbound to the VOR, I dial in 270, see a "TO" indication, and the sensing of the CDI needle is reversed so that if I am north of the 090, the CDI is to the left and so on.

Ok, now that we have established that let's talk about the 3 recipe items. Again, in order to execute one of the three recipes, you have to understand what you are trying to accomplish. For example, do you want to intercept a radial and go to the VOR station or do you want to intercept and fly away from the VOR station? With that in mind the recipes follows.

Here we go. I have assumed you have tuned and ID'ed the VOR by its Morse code. If you do not understand anything I have said above this point, just memorize the three recipes following.

Intercept a radial and fly in toward the ground station:

1. Dial in the desired radial on the bottom of the OBS protractor (a "TO" indication appears)
2. Note direction of needle: left or right of center
3. Decide on angle to use to intercept (45 degree intercepts are common, let's use it here)
4. Moving eyes from center of OBS protractor 45 degrees towards the CDI needle, note value
5. Turn your airplane to that value
6. Wait for needle to sweep towards center, as it does, turn towards value on top of OBS
7. You are now flying towards the ground station

Intercept a radial and fly in away from the ground station:

1. Dial in the desired radial on the TOP of the OBS protractor (a "FROM" indication appears)
2. Note direction of needle: left or right of center
3. Decide on angle to use to intercept (45 degree intercepts are common, let's use it here)
4. Moving eyes from center of OBS protractor 45 degrees towards the CDI needle, note value
5. Turn your airplane to that value
6. Wait for needle to sweep towards center, as it does, turn towards value on top of OBS
7. You are now flying away from the ground station

Intercept a radial and fly towards the ground station:

1. Turn dial, look for a "TO" indication
2. While the "TO" indication is present, center needle
3. Read value from top of OBS protractor
4. Turn aircraft to a magnet value equal to the value on top of the OBS protractor
5. Make appropriate corrections to keep the CDI needle in the center
6. You are on your way to the VOR

Memorize, memorize and memorize these 3 recipes, especially if you are a student pilot - works every time.

Here is an example for intercepting a radial and going inbound. You desire to intercept the 090 radial and go inbound. You are somewhere east'ish of the ground station. You dial 090 on the bottom of the OBS (that puts 270 on top - no math for you!). If you are north of the 090 radial the CDI will be towards the left of the display. Look at the top, it says 270. Count 4 big lines and a small line towards the needle across the protractor arc which yields 225. Turn your airplane to 225 degrees magnetic to obtain a 45 degree intercept. The needle will swing towards the center as you approach the line. As it does, turn your aircraft towards 270 degrees magnetic and keep the needle in the center.

The recipe is brainless: what do you want to do? Intercept and go outbound or inbound? Dial in the radial on the top or bottom of the display depending on whether you are going outbound or inbound respectively, obtain intercept value on the needle side of the display and turn to that direction to intercept then go inbound or outbound depending on what you wanted to do in the first place. The direct-to case is trivial: TO indication and needle in center then turn aircraft to value on top of the display and work to keep the needle centered as you cross the ground station.

You do have to have an idea roughly where you are located relative to the VOR for this to work. However, for practical purposes you will not be asked to, say, intercept the 090 radial and go inbound if you are west of the ground station. There are other tricks to fool a pilot that deal with zones of ambiguity and cones of confusion, understand why this is, but it's not likely you will encounter this on a check ride.

VOR Navigation Basics for Aviators

Let's admit it. VOR navigation isn't the most user friendly way of getting around, but once you understand a few basics and some recipes on how to use the darned thing, it's really not that bad.

I am writing this blog post with the student pilot in mind, but hopefully the private pilot who never really understood VOR navigation will get something out of this posting.

There are two ways to work with VORs: the concept and the actual use. The concept is something you do with simulators at home or pencil and paper. A great and free simulator can be found here and I affectionately call it Tim's Airnav. Actual use as I describe below means understand what you want to do, then follow the recipe for that item. If you are in the cockpit and working on the conceptual part, you are in the wrong place. You should be home at the kitchen table. The cockpit is a great place to make sure you can use the VORs, but not a place to understand how they work.

There are three things you will normally do to navigate with VORs:

1. Intercept a radial and fly inbound (inbound means fly towards the VOR)
2. Intercept a radial and fly outbound (outbound means to fly away from the VOR)
3. Go direct from your current position to a VOR

Number 3 is really used once the radials mentioned in 1 and 2 are intercepted or it can be a "go direct to the blah-blah VORTEC directive from your instructor or air traffic control).

Now, before I go any further, some concepts we must agree on or we will not get anywhere.

A VOR station is a group of antennas on the ground that emit a radio signal. Your cockpit VOR receiver receives these signals and allows you to determine on which of 360 radials your aircraft is located. A radial is an electronic "line of position" (navigators say L O P). The radial are numbered 000 to 359. The 000 can also be referred to as the 360 degree radial. A technician turns a knob at the ground station and adjusts the radials so that the 000 (360) is pointing at magnetic north for that particular area. Remember that the angle of magnetic north from geographic north varies from point to point on the surface of the earth - that's why it's called "variance". Accounting for variation is important because you will follow this line with the combination of your magnetic compas and a needle on the omnibearing selector display called a course deviation indicator (CDI). A given VOR ground transmitter then reflects directions you see on your magnetic compass. More on this later.

Next concept, the radial. Think of the VOR transmitter as a dot on the ground from which 360 lines emanate. Each line is numbered 000-359. Each line is a radial. Whoops, I repeat myself, but I did it intentionally. A radial always comes FROM (note the emphasis on "from") the VOR. For example, the 090 radial (magnetic direction is always expressed in 3 digits with leading zero(es) if necessary) radiates from the VOR and makes a ground track towards magnetic east. It doesn't matter if I jump on the 090 degree radial and I fly towards the VOR or I fly away from the VOR, I am still on the 090 radial. Let's say that I fly towards the VOR on the 090. Inother words, I am flying magnetic west (towards 270). One mile away from the VOR I am still on the 090 and I am still flying west. A little later we are right on top of the VOR. At this point all the radials kind of come together - it's big mess and it's called the "Cone of Confusion". However, if I ignored the drunken CDI on my OBS display, it will eventually setting down as I keep heading west and if all were executed just right, I have crossed the VOR, left the 090 degree radial and now I am on the 270 degree radial heading away from the VOR and into the sunset.

I used a lot of words above to illustrate what I said earlier - all radials have a name and they have a start at the VOR - they emanate "FROM" the ground based VOR transmitter.

Now the part that messes up the beginner and a lot of experienced folks, the notion of the "TO" and the "FROM" flag on the omnibearing selector display. If you turn the dial (omnibearing selector) and you center the CDI and there is a "FROM" indication then the value you read at the top of protractor is the radial on which you are positioned. If you center the CDI and a "TO" indication is shown in the TO/FROM window, then you are on the radial indicated on the bottom of the protractor. Confused? If so, don't feel alone. It's not so bad once you understand the reason for this and it revolves around the fact that humans aren't good with flying using reverse sensing. To illustrate, suppose you want to fly on the 090 degree radial towards our VORTAC and cross the ground station and keep on going into the sunset on the 270 degree radial. Let forward into the future and say you have passed the VOR and you have 270 dialed into the your magnetic compas

Ok, now that we have established that let's talk about the 3 recipe items. Again, in order to execute one of the three recipes, you have to understand what you are trying to accomplish. For example, do you want to intercept a radial and go to the VOR station or do you want to intercept and fly away from the VOR station? With that in mind the recipes follows.

Aircraft Meteorological Data Reports

For the eyes of aviators only, others enter here at your own risk :-) ....AMDAR (Aircraft Meteorological Data Reports) is really neat. Some airlines participate in putting a small data gathering device on their aircraft. As the aircraft ascends/descends, a broadcast wind direction, gusts, temperature and more (http://amdar.noaa.gov/FAQ.html gives detail) is sent to a data gathering agency. One of the more important factors transmitted is moisture content. Currently, around 140,000 samples are collected/day. This means wx folks and aviators have access to almost real time radiosonde-like sounding data. One example using this data can be found at http://rucsoundings.noaa.gov/. "RUC" stands for rapid update cycle. If you are not familiar with the display format, take the Texas A & M tutorial (link on bottom of rucsoundings page). The format is a log-p skew-t graph, something that weather experts have been using for years. However, the Java version of this graph allows you to get dew points, temperatures, wind velocity and direction, etc. in the atmosphere over the airport you selected and up to about FL400. You can also lift a hypothetical air parcel to see if it is stable or results in bad things. It's easy to find freezing levels, saturation altitudes (where clouds are liable to form, etc.). Nice stuff for aviators. Even if you only use it in a basic way.