Friday, May 10, 2013

Opinion: Learning to Fly with Glass vs. 6-Pack?

INTRODUCTION AND CAVEATS

I confess up front that I find the arguments that the 6 pack is a better learning vehicle than glass to be questionable. I do not claim that one is better than the other because it depends on circumstances. For example, if you plan to rent and most of the rental fleet you plan to use consists of 6 packs or you own an aircraft that has a 6 pack and you have no intentions to switch to glass then you want to learn in a 6 pack. On the other hand, if you have access to a fleet of aircraft with both types, you may want to flip a coin if you are not sure or perhaps a rental-price differential will help with your decision. Generally glass cockpit aircraft rental rates are higher. If your future is flying to nearby airports or flying to local pattern, a 6 pack is a good choice. If your future is with the airlines, corporate flight, you appreciate modern technology, you plan to do a lot of IFR flight, etc. you may want to start with glass from day one. Personally I am biased, I lean towards going with glass.

BACKGOUND AND SOME HISTORY

There are ongoing arguments that deal with whether a beginner or the instrument pilot should do their training using a glass or a traditional 6 pack avionics set.

Glass is aviator's slang for a box with a liquid crystal display, often 2 displays, one that shows the flight instruments (PFD) and another that shows useful flight data, moving maps, engine parameters, etc. (MFD). The glass box has both a GPS and a VOR receiver. Most glass boxes display a horizontal situation indicator (HSI) and the pilot chooses which receiver drives the HSI.

Many glass installations are equipped with solid state devices that replace moving gyros and eliminate the need for a vacuum pump (One of Murphy's laws states that about 5 minutes after entering a cloud, the vacuum pump fails.)

A modern 6 pack has 6 circles cut out on the avionics panel, 2 rows, 3 columns, each cut out contains a flight instrument in the same relative position from aircraft to aircraft.

(A photo is coming here soon)

 In 1929 Jimmy Doolittle was the first to fly by using instruments without looking out the window. In 1937, the British Air Force standardized their fleet using most of the flight instruments we see today. The 6 pack has been with us several decades.

THE CURRENT STATE

The general aviation fleet is largely of the 6 pack variety, but glass cockpits are gaining in number because of retrofits to older aircraft and as standard equipment in many new production aircraft. Several companies offer retrofits which remove the classic 6 instruments and replace them with a single flat screen, Garmin and Aspen Aviation are examples of manufacturers who provide retrofit products.

THE DIFFERENCE BETWEEN THE TWO COCKPITS

Modern glass panels have fewer or no moving parts. The heading indicator and the attitude indicator operate from solid state devices which means no gyros. Data is displayed in liquid crystal rather than with mechanical "steam gauges". In the Garmin 1000 everything is solid state. There is no need for a vacuum pump on an aircraft with this unit providing the standby attitude indicator's gyro is electric. Since there are no gyros, there is no precession and no bearing surfaces to wear out which lead to inaccuracies and eventual failure.

A CASE FOR THE 6 PACK

  Some aviators are adamant that all initial training, especially at the pre-private and instrument rating level be conducted in a 6 pack. Their reasons vary. For the pre-private arguments that training should be in a 6 pack are generally of the nature that the glass presentation is too distracting and the student needs to learn to keep their eyes out the window. Glass somehow will cause a student to fixate on the glass components and keep their focus somewhere below the glare shield.

 The other argument, usually unspoken is: I learned how to fly with a 6 pack 30 years ago, so should you.

 I guess that is the best I can do for the pro-6 pack argument. Remember my confession about my bias?


A REBUTTAL TO THE CASE FOR THE 6 PACK

 Personally I find arguments regarding distractions caused by glass to be specious. As an instructor, I encounter this problem with students whether they are flying glass or a 6 pack. In both cases, the student needs a serious dose of what I call "the other function of the aviation chart" which is when I use the chart to cover the flight instruments. It is my observation that pilots of both cockpit types initially spend too much time looking at instruments. CFIs can catch this early by observing the pilot demonstrating latency errors leading to pilot induced oscillations (PIO) or jerky bank rates, excessive push and pull on the yoke and more. The beginner needs help to become aware of the substantial latency, especially with the instruments in the 6 pack.

  I have heard some say that an analog presentation is better than a digital or ribbon presentation for items like airspeed and vertical speed indications, it is somehow more human. To me, this is a religious issue. I cannot fathom why someone who is brought up reading digital time from a cell phone would be uncomfortable with digital airspeed. I can fully understand why someone who has been looking at analog gauges and 3-handed watches for decades finds it difficult to read a digital value or read a ribbon, but this means your ability to catch on depends on your own past experiences, not an "inhuman" characteristic. Also, the load of instrument interpretation is fatiguing. For example, as a pilot who learned to fly instrument on a standard VOR omnibearing selector and then switch to an HSI. The HSI is clearly a winner because it overlays heading with course and reduces a part of the interpretation load by a noticeable factor. Not only does the HSI closer to representing reality, it also reduces the amount of scan work needed by the pilot. There is nothing better than having instruments that are as close as possible to representing reality. Some argue that the 6 pack does, but this takes a lot of brain work by the pilot especially understanding position and the scan real estate is much larger than the small rectangle displaying airspeed, course and heading data, altitude, vertical speed, etc., on a PFD.

Another argument against the glass cockpit: the complexity and pretty colors are too distracting and the pre-private will fixate on the nooks and crannies of the device, being awed by pretty colors, knobs, pages, etc. and will not become a proper stick and rudder pilot. Again, this argument is pretty weak because it is up to the instructor to emphasize which features of the glass panel are relevant to the VFR student and keep the focus on those items. When the proper focus is set and enforced by the instructor, the glass panel is arguably easier because data the pilot needs to reference are in close proximity rather than spread out, sometimes over long distances in older cockpits that have undergone mystical retrofits. For example, VHF radios are often scattered over the panel (common retrofit condition on older aircraft) causing the pilot to sometimes have to lean to reach a considerable distance to tune radios or other equipment. Having all critical instruments displayed on a LCD in a few square inches of real estate is a good thing.

  Advocate for the 6 pack claim that you need to learn from that first and then learn how to use glass. I find this to be a weak argument. As an instrument instructor, I have found that in teaching for the instrument rating that the student who starts with glass has very little problem going back to a 6 pack. It does take a few hours with an instructor, but it is apparent to me that knowledge acquired from a glass panel with and HSI, etc. can easily be transferred to learning how to fly the analog gauges of a 6 pack. On the other hand, my experience has been that those who learned in a 6 pack have a much more difficult time of transitioning to a glass panel. It takes longer and leads to a lot more cussing than going the other direction. A lot of this is to do with using the various knobs and buttons. To successfully learn how to use either system, you need to a lot of repetition in the learning process. The glass system seems more complicated and in some ways it is, but remember that the comm radio, the nav radio, a CDI selector, an altimeter setting function, etc. are all in one box instead of scattered over several places on the avionics panel. A higher density of knobs and buttons exist, but not necessarily more, it's just a lot of stuff is in closer proximity. Then, add to this flight plan storage, and a host of other things one can add to an MFD (weather, airport data, etc.). No question it is a lot, but so is carrying a green AFD, the one in your pack on the back seat, and suffering through the experience of not having near real time weather at your finger tips when making long cross country flights.

Both panel types take a lot of time to learn and to use competently. If you think that you will eventually be using glass, why wait? Start early in your lessons where new things tend to stick with you.

Personally, I have heard no good reason to not use glass, but it does boil down to what is you intend to do with your learning experience after you get your ticket. IMHO, pilots who advocate against glass really do not present a strong argument. Analog gauges are not human and require a deep understanding of what it is that is producing the data that drives each gauge, how to interpret each item and how to take data from several instruments that are far removed from reality and process these between your ears to help acquire situation awareness. Much of this load is replaced by an HSI and a moving map. I am sure that the aviators of the 1930s claimed you needed to learn using low frequency radio ranging (A-N ranging) to really understand how to navigate before you used VOR when the VOR system came out in the 1940s. I am sure that many aviators lament the passing of the NDB/ADF combination, but personally I would rather take the non-precision GPS approach if available and it is getting hard to find airports without GPS approaches.

I guess if you went way back, pilots would tell you if you could not follow railroads you couldn't call yourself a pilot. I have seen the same phenomenon in blue water boating when the GPS came out and navigators using sextants would ask me what would happen if I dropped my GPS receiver in the water. My stock answer was what if you dropped your sextant into the water? I have a dry, spare GPS receiver, did you bring a spare sextant? That was when hand held GPS receivers were not cheap. Today they are a dime a dozen so to speak. There was an important advantage to using the GPS over the sextant - time. In seconds I could do what a skilled star shooter took a few hours to accomplish and I could do it even when it was cloudy and anytime time of the day. Yes, sextants are fun to learn to use for most of us, but not necessarily the best tool given today's technology.

The same is true in the cockpit. For example, using a G1000 I can immediately size up my cross and head wind components while on an instrument approach - just look at two wind vectors in the liquid crystal. I can recognize and correct approach errors much more rapidly than if I only had a CDI (near real time ground tracking data). The tools of the modern cockpit save time in assessing the external environment and this promotes a higher level of safety.

Most modern glass estimates the ETE to your next waypoint and the fuel expected to be consumed between your current point and the next waypoint and your destination. This can be calculated in one's head or by bringing along an E6B which has now fallen under your seat and is out of reach. Two of the most useful things that glass brings to the pilot is instantaneous ground track and ETE as mentioned earlier. When doing an approach with a 6 pack, at best I could sometimes get distance data to the next way point (DME or radial crossings). Distance, however, is marginally useful. I find time to the next way point a more human measure, how many more minutes do I have to do my next few things before I have to do a step down? Given distance only, I would have to estimate ground speed and then do a calculation to convert that to time. Anyone who does an approach with a 30 kt tail wind vs. a 30 kt head wind appreciates what I am getting at when I say that ETEs are much more useful than knowing indicated airspeed, guestimating ground speed, etc. Having an instantaneous track readout is wonderful because it clues the pilot to early deviations from a desired ground track, often before they show up in the deviation bar of the HSI.

A NOTE TO HELP THE INSTRUMENT STUDENT DECIDE

A general note first: Many instructors tell you need learn your IFR skills while hand flying, that is, not using any automation. I do not agree with this approach because it takes time to develop the finger skills to operate this kind of equipment just as it does for operating a modern glass panel with a flight management system. The only way you will become proficient with this equipment is to start using it from day one in your training.

Am I advocating that we never learn to hand fly? Heck no because stick and rudder is a must-have skill to possess if you want to fly safely. However, as an instrument pilot if you can hand fly an aircraft for at least an hour demonstrating good stick and rudder flight and you can do a hold and two approaches with no outside references while flying partial panel, what more do you want? No question, it is important to become a good stick and rudder pilot. Too much effort is placed on hand flying in the instrument environment even when a student is learning in an automated cockpit (glass + autopilot) producing pilots who are poor at using the automation. Many CFIs believe you need to hand fly and then at the very end of your instruction, learn to use automation. I respectfully disagree.

If you have an autopilot integral to the glass box (G1000 with a GFC700 autopilot) or even when it is not integral but nonetheless is a well integrated system (e.g., Avidyne/G430 with an S-TEC55 found in many older Cirrus aircraft) it will likely set an example for a learning instrument pilot on how to fly by instrument because of the smooth control, standard rate turns, etc.

Automation is your friend. Today automation is exceptionally reliable, but this does not mean 100% reliable (what man made apparatus is?). A modern autopilot will generally fly the airplane better than most pilots especially when the automation is obtaining digital input from reliable (no gyro) devices.

Yes, there is overhead in learning to use automation. There is also overhead in fully understanding the limitation of the automation. However, the return on investment in workload reduction and improved situational awareness pays back big time (IMHO).

If you start you instrument lessons in a glass cockpit and you have not had any glass experience, it will be difficult because you have to learn basic operations of the glass functions. For the pilot that did start with glass there are a lot of new things to learn that deal with IFR flight. Whether or not you have experience with the glass, it is best to undertake your lessons at a facility with a reasonable simulator incorporating the same equipment you plan to use in the aircraft. Also, consider purchasing a trainer-simulator that will run on your home PC/Mac so you can play and understand the features of the glass box you will be using. I like to think of trainers as a way to make sure I really understand what is going on - head work if you will rather than than use proficiency which will come with an training device or the real thing in the cockpit. Also, download either the user's manual or pilot's guide, preferably both and read it in while playing with your trainer-simulator at home.

If you are using a modern airplane with good automation, I would be wary of learning to first fly instrument by hand only leaving the automation part until later in the lessons. My approach has been to start with full automation and once the student becomes proficient, start breaking things so that they have to cope with a bad ADHRS, ADC, etc. or an autopilot that has gone south. Furthermore they must be able to operate under a heavy workload for at least an hour with these failure modes, demonstrating they can hand fly, keep on top of the workload and perform whatever approaches are available to them given the type of failure. And they have to demonstrate good stick and rudder technique at the same time using good trim and appropriate control input to keep the aircraft coordinated and flying at assigned altitude and heading or course.

Most of the glass failures will likely have to be experienced with the use of a ATD, especially when damage can result to opening circuit breakers in an aircraft and the manufacturer of the glass or the aircraft prohibit the use of breakers to simulate failures in the cockpit. Some failure can be simulated with Post-it paper while in flight, but some of these failures do not invoke various side effects, for example an inibility to display track up on an MFD when the ADHRS fails or flying an approach with a heading indicator not working on the HSI. You need to experience these failures on a simulator so that you can recognize them right away and understand how your scan will change.

SUMMARY

 Know your automation and how to use the knobs on your glass box like a concert pianist who has memorized a concerto. Later, learn how to fly with various components broken, including the autopilot. The instrument pilot must recognize each type of failure and what response is needed. It is imperative that the pilot always be in front of the automation by noting what is the next thing the automation going to do and making sure it does the next thing correctly. You still must stay on top of the gauges and monitor the automation. Even with this workload, it is much less fatiguing than hand flying, managing comms, dialing in nav frequencies, ID'ing localizers (instrument pilot), etc. all at once.

Remember that modern equipment, if used correctly is a wonderful workload reducer because it is not as fatiguing as hand flying and it gives the pilot more energy to use towards the safety of the flight. Another part of the safety aspect is due to the integration and display of information on the flight plan, aircraft systems and external parameters such as airport information, frequencies, weather and wind conditions.




Friday, April 15, 2011

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 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 or what is often referred to as initial contact. 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 were made in flight it would also include 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 aircraft's Mode-C transponder or altimeter is lying.
  4. What do I want is 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 are communicating with the ground controller (not someone else). This sounds kind of dumb, but it prevents errors when talking to 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! If a controller recites an incorrect tail number, now is the time to make corrections.

Often I get question from pilots of the form "the controller said ABC, what did he mean by this?" My answer is see if it is in the Pilot Controller glossary at http://www.faa.gov/air_traffic/publications/ and click on the link "Pilot/Controller Glossary". The PCG creates a 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 a phrase used by a controller, ask a CFI for advice 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. 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 phrase the controller used or whatever the controller told you to do. Study up on phrases published in the PCG that you are likely to encounter so you do not have to use "unfamiliar" any more than necessary, especially to a common phrase. 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" to get expectations out in the open.

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 help from the 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 end up blundering their way into sharp retorts from the tower. Knowing "unfamiliar" and using it politely will save you a lot of grief. 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 limited and if you study these phrases in the PCG and work to listen for them in flight you will eventually understand when you hear them. If you refer to the PCG frequently and understand the format of aviation communications learning to communicate will not be as difficult.

For all pilots, it is important to anticipate. That is, what is the controller likely to say next? This helps speed the learning process. Anticipation promotes safety. Recognize that radio communications start with a pilot calling a controller or a controller calling a pilot. 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 a pilot initiates a communication, then s/he should start with the name of the control facility (e.g. "SoCal approach", ....). Even a controller initiation starts with a tail number that is not yours, it is good to pay especially when it is a traffic alert to another aircraft of the form: "You have traffic at your 11 o'clock, 4 miles, 4 thousand 500 feet, a Cessna heading west bound) and you happen to be in a Cessna at 4500' and heading west bound because the odds are high that the controller is pointing you out to another pilot. Often the next call is to alert you to the previously called traffic. Ditto in pattern work when the controller tells another aircraft they are behind you in pattern, etc.

I recommend beginners purchase 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 external sounds 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.


Monday, January 31, 2011

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.

Wednesday, December 15, 2010

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

Saturday, November 20, 2010

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

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 learn something too.

As with many aspects of aviation there are two ways to work with any system: the concept and the actual use. The concept is something you do during simulating 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 procedures you frequently encounter with VOR navigation:
  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. Fly direct from your current position to a VOR
Before we proceed there are some concepts we must agree on or I will be writing into the cone of confusion or perhaps addressing the zone of ambiguity. :-)

A single VOR station is composed of a group of antennas on the ground that fire at different times, in a prescribed order, emit a group of radio signals during each cycle. Your cockpit VOR receiver receives these signals and enables you to determine on which of 360 radials your aircraft is located. A radial is an electronic "line of position" (navigator's acronym: LOP). A line of position is a line on the ground on which you are located. If it is a radial than you can state you are on a line that starts at a position on the earth (the VOR station) and tracks the surface of the earth on a magnetic direction which is the value of the radial. 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 rotates all 360 radials so that the 000 (360) radial points at magnetic north for that particular spot on the earth. Remember that the angle of magnetic north from geographic north varies from place to place 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 cockpit references to direction are made via magnetic references (usually a magnetic compass, magnetic flux detection, etc.).

Next concept, the radial. Think of a 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 intentionally. A radial starts at a VOR transmission station and radiates FROM (note the emphasis on "from") the station. For example, the 090 radial (magnetic direction is expressed in 3 digits with a leading zero or leading zeroes) radiates from the VOR and creates an electronic 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 - direction of flight is irrelevant. Let's fly towards the VOR on the 090. This means the aircraft is tracking magnetic west (track=270 deg. magnetic). One mile away from the VOR the aircraft is still on the 090 and still tracking 270 deg. magnetic. A moment later the airplane crosses the VOR. At the crossing all radials come together - it's big mess and it's called the "Cone of Confusion". However, if I ignore the drunken CDI on my omnibearing selector (OBS) display, it will eventually settle down as I keep heading west and if all goes well, I cross the VOR, leaving the 090 degree radial behind and now I am flying outbound on the 270 degree radial heading away from the VOR and into the sunset. Remember radials start at the VOR and radiate out form there. A specified radial does not cross the VOR station. In this case we track inbound on the 090 radial, cross the station and are then tracking the 270 degree radial.

Summary, all radials have a number and 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 OBS display. If you turn the OBS dial and you center the CDI with a "FROM" indication then the value you read at the top of protractor is the radial on which your aircraft is 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 at flying with reverse sensing. Keep reading for more on this topic.

To illustrate the reverse sensing concept, suppose you desire to fly the 090 degree radial towards the VOR, cross the ground station and keep going into the sunset on the 270 degree radial. Suppose you have passed the VOR, you have 270 dialed on top of the OBS protractor scale, the CDI is perfectly centered and the OBS displays a "from" indication. This means you are on the 270 radial. Suppose the aircraft drifts southward. This would cause the CDI to drift to the right side of the display. It's telling you that the radial you have tuned in (270 deg.) 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 deg. 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. If you are flying parallel to the desired radial and the needle is on the left, you need to turn left to intercept the radial. For a CDI on the right the radial is on your right and you must turn right to intercept. In both cases you turn into, or "towards" the needle to intercept the radial.

When flying outbound from a VOR station: dial in the radial you desire to track on the top of the OBS display, keep the needle in the center (you will have a "from" indication). If needle moves left, turn left a little; if the needle goes right, turn right a little.

The conceptually troubling part for many pilots is that what happens when  flying inbound towards the ground station, for example flying in on the 090 radial and you incorrectly dialed in 090 on the top of the protractor? 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: NO! Why? Because when you have a radial value dialed in and you are on that radial, the system assumes that you are heading away from the ground based station. In this case you have dialed 090 and have a "from" indication. 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 with 090 dialed into the OBS and you spin the aircraft on its cable, the CDI will not change (right of center in this case) regardless of where the aircraft is pointing at any moment as you spin on the sky hook. If you are on the 090 radial it will be centered as your aircraft makes its 360 rotation on the sky hook. 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.

So, 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 going inbound to the ground station on the 090! If you put 090 on the top of the OBS display and intend to fly the 090 inbound 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: If the aircraft drifts north, on your westward heading the needle moves to the right side! If you turn right to intercept - ouch, you are flying away from the line! 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 090 dialed in and a "FROM" indication is called reverse sensing. The manufacturers of the receiver system said we can help pilots with this problem (I made this up, but it works even if it's not true). If flying inbound on a radial, we can have them dial in the reciprocal (radial + 180) which is 270 degrees (090 + 180) and correct sensing will occur. So imagine what would happen without a TO/FROM flag: if the aircraft is on the 090 radial, the needle would center when either of 090 or 270 is dialed into the selector, but one would give you reverse sensing! Solution: put a TO/FROM flag on the display to tell the pilot if the aircraft is on "real" radial (emanating FROM the VOR) or he has dialed in the the "virtual" radial, or the reciprocal (270 is the reciprocal of the 090 radial). Problem solved. So, if I am on the 090 radial and I am inbound to the VOR and I dial in 270, I see a "TO" indication, and the sensing of the CDI needle is now correct so that if I am north of the 090, the CDI is to the left and so on. You are still on the 090 radial as you go inbound, but now you have correct, not reverse sensing.

So much for the conceptual topics, let's jump to cockpit pragmatics. There are 3 recipes you need to know. To select which one of the 3 recipes you need to accomplish your task, you first need to define the task to be accomplished. 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?

The following assumes you have tuned in and ID'ed the VOR by its Morse code. The following precludes the use of calculating reciprocal courses - cockpit math should be avoided at all costs:

Recipe 1. Intercept a radial and fly in towards the ground station, assume the 210 deg. radial:
  1. Dial in 210 on the bottom of the OBS protractor (a "TO" indication appears)
  2. Note direction of needle relative to center: Left or right of center?
  3. Decide on angle to intercept the radial (45 deg. intercepts are common)
  4. View the top center of the OBS and scan 45 degrees in the direction of the needle and note value
  5. Turn airplane to a heading of that value to fly a 45 degree intercept towards the desired radial
  6. As the need sweeps towards center turn to a heading equal to the value on top of OBS
  7. As you maintain this heading and a centered needle, you are flying towards the ground station on the 210 deg. radial
Recipe 2. Intercept a radial and fly in away from the ground station, assume the 210 deg. radial:
  1. Dial in 210 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 (assume 45 deg. intercept again)
  4. Moving view from top center of OBS protractor 45 degrees in the direction of the needle  and note value
  5. Turn airplane to a heading of that value to fly a 45 degree intercept towards the desired radial
  6. Wait for needle to sweep towards center, as it does, turn towards value on top of OBS
  7. As you maintain this heading and a centered needle, you are flying away from the ground station on the 210 deg. radial
Recipe 3. Fly direct to the ground station from your present position:
  1. Turn dial, look for a "TO" indication
  2. While maintaining a "TO" indication, center needle
  3. Read value from top of OBS protractor
  4. Turn aircraft to a heading 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
  7. When the TO/FROM flag and the CDI move erratically you are on the VOR
Memorize these 3 recipes, especially if you are a student pilot - works every time. Again, nothing conceptual here just recipes.

Beginner warning: if you have a strong wind blowing the aircraft away from the line as you do your intercept, it may take a long time to make the intercept. Too shallow of an intercept can lead to the same problem. Trying increasing the intercept angle, but avoid using more than a 60 degree intercept.

An example: 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). 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 (10 deg.) and a small line (5 deg.) 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. You are on your way to the VOR, tracking the 090 radial.

Ask yourself what it is I want to do and then select one of the recipes.

  1. Intercept a radial and go inbound? Recipe 1: Dial in the radial at the bottom of the display, obtain an intercept value on the needle side of the display and turn to that direction to intercept then turn onto the radial using the direction at the top of the OBS. Keep the CDI in the center.
  2. Intercept a radial and go outbound? Recipe 2: Dial in the radial at the top of the display, obtain an intercept value on the needle side of the display and turn to that direction to intercept then turn onto the radial using the direction at the top of the OBS. Keep the needle in the center.
  3. Fly direct to the VOR from your current position: turn dial to obtain a "from" indication then center needle. Turn aircraft to the heading shown at the top of the OBS and keep the CDI in the center.

You do have to have an idea roughly where you are located relative to the VOR for this to work. However, for practical purposes on a private check ride 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 aspects of VOR use that can cause problems for the novice, notably the cone of confusion and the zone of ambiguity. Be aware of these, but on the typical private check you will most likely get the simple intercept, fly to/from or fly direct to a VOR. As you pass over a VOR, you must fall back on the magnetic compass to maintain a constant course as the CDI and TO/FROM flag flip around erratically. Once you get a strong "from" indication you can turn to the assigned radial or stay on the reciprocal, whatever is appropriate.

If you cross a VOR and are assigned a radial that is not the reciprocal of the inbound radial, you will usually overshoot the new radial as you pass through the cone of confusion. Once you get a strong "from" indication, execute the following: turn, time, twist in that order. Turn means turn the aircraft to the same magnetic direction of the radial, time means set/reset a timer if appropriate for your navigation and twist means turn the OBS dial to the new radial. The CDI will not likely be centered because you overshot the VOR in order to get a strong "from" indication. If this happens use recipe 2 to intercept the desire radial.

Beginner warning: The CDI indicates angular error. Adjacent radials are very close to each other when you are close to the VOR ground station. Use small intercepts when crossing a VOR and intercepting the new radial.

Wednesday, September 8, 2010

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.