Identifying VORs

As we said, VOR's identify via a 3-character tag that's sent in Morse code, but unlike NDB's that promise voice identification and don't deliver, VOR's do indeed have the voice ID. The one near my house sounds like this: "Montour VOR....dahdah....dahdah....didahdahdah", with those code characters translating to MMJ, the identifier for Montour. And also like NDB's, they vary in power depending on the coverage area intended. VOR's that define high-altitude Jet airways, as you might expect, are higher in power than those that only serve the immediate area around an airport.

Some selected VOR's have an added "bonus": weather information for pilots known as Transcribed Weather Broadcasts. TWEB's are recorded weather information played continuously on the VOR frequency. They are primarily geared toward the private pilot, and include things like present conditions, forecasts for airports and certain routes, any pilot reports of significant weather, and so on.

Since this is, after all, the VHF radio band we're talking about, VOR's are pretty much limited to the line-of-sight reception we've already discussed. But every once in a while, the band may "open up" to sporadic-E propagation or other exciting but temporary propagation phenomena. Many ham radio operators have gotten spectacular DX on the two-meter (144 MHz.) amateur band when conditions are right. There are many books on VHF propagation and I won't go into detail about it here. But if DXing VOR's is your "thing", I suggest taking your aviation band radio, along with a good directional antenna, on a hilltop expedition. Find a nice high elevation and tune your aviation band radio through 108.0 to 117.95 MHz. Listen for the Morse identifier since the voice ID may be very watery and unintelligible. Good luck!

Intersections

VOR's have three-letter identifiers such as LGA (New York LaGuardia Airport) and OBK (Overbrook, near Chicago O'Hare). However, if you monitor the aeronautical bands long enough, you'll come across some 5-letter identifiers too. They actually resemble quasi-English words, like GUUBA and MAYZE. What the heck are these things?

They are not navigation aids like our trusty VORs or even NDBs. They're intersections, more-or-less imaginary points in the airspace system that the FAA has defined by using at least two navaid components. What do I mean by components? You can define an intersection by using a VOR and its paired DME. Or, it could be defined by two VOR's. The important thing is that it's a point that the Feds have created, usually for a very good navigation-related reason. Actually, thinking three-dimensionally, an intersection is more like a vertical line straight up through the sky. As an example, you could be at GOOFY intersection westbound at 5,000 feet while another aircraft reports over GOOFY at 12,000 feet, heading northbound.

Let's look at the most common way that the FAA defines an intersection. You may remember from geometry class that the radius of a circle intersects that circle at a point. Think of the radius as being any one of the 360 spokes or "radials" from a VOR facility. For the sake of this example let's take radial 278. Now think of a particular fixed DME reading, say 54 nautical miles. If you connected all the points together that were 54 nm. from the VOR/DME, you'd have a circle. The radius (278) intersects the circle (54 nm.) at one--and only one--point. If that VOR/DME was SEA (Seattle, Washington), you've just defined the intersection known in the air traffic control system as ARRIE intersection, or simply ARRIE.

There are some intersections, especially across water routes, that are not defined by any navaids. They are, however, defined by Latitude and Longitude. For instance, in the North Atlantic, intersection KOHOE is located at 42 degrees 25.3 minutes North, 61 degrees 39.2 minutes West (that's roughly 400 nautical miles east of Nantucket island). Aircraft with GPS equipment may use this intersection to navigate with.

For that matter, if using GPS you can simply load each intersection's Lat/Long in and use it for navigation. When an intersection is part of a route of flight, you may hear it referred to as a waypoint.

You'll hear these intersections referred to frequently during instrument approaches. By the way, if you have a PC, consider getting one of the flight simulation packages where you can experience first-hand how a VOR works, and how well you can "navigate" with it around simulator-land.

Airways

Because of their versatility and their lack of propagation problems, VOR's are used to define airways in the airspace system. Just as Otto connected the NDB's with lines to form his route, the FAA has predefined airways by connecting the VOR's for us and giving the lines names, like V34 or J18. A single route number will actually pass over many VOR's from beginning to end. Think of them as analagous to highway route numbers, because that's essentially how they're referred to. Instrument flights use these airways whenever possible to easily navigate to their destination.

Airways that begin with the letter V are called Victor airways, and apply below 18,000 feet MSL. The J airways, for flight at and above 18,000 feet MSL are called Jet airways for obvious reasons, although even jet traffic must ususally use part of the lower Victor system during climb and descent. Airplanes enter the jet airway system as they climb to altitude, and pretty much stay on them until it's time to descend for approach and landing.

VOR combined with DME (Distance Measuring Equipment)

Now, VOR's are usually (but not always) linked with Distance Measuring Equipment, or DME, on the same site. Simply stated, DME will tell the pilot how far he is, in nautical miles, from the DME facility. DME is a system which measures the time difference required for the DME signal to make a round trip from the airplane to the DME and back. The greater the time required, the further the aircraft is from the DME facility. All this DME stuff is actually going on not on the frequency of the VOR, but on an ultra-high (UHF) frequency between 962 and 1213 MHz. that is paired with a given VOR frequency. The pilot need only tune the VHF navigation receiver; the radio "knows" to look for the DME on the proper paired frequency. By the way, a VOR combined with DME capability known as either a VOR/DME or a VORTAC.

So if the DME is located in the same place as the VOR, Otto can get both a radial and a distance from the VOR site and plot his current position with excellent accuracy on a chart! If his receiving equipment tells him he's on a 080 radial from the Johnstown VOR, at a DME of 14, Otto simply uses a special protractor called a plotter to draw a line out from the VOR at 80 degrees from magnetic north. Then he measures, again using the plotter which has a scale for nautical miles, 14 units from the VOR out along the line he just drew. That's his current position. He sure couldn't do that with his ADF listening to a single NDB!

If Otto's navigation equipment didn't have DME capability, he could use two VOR's in his reception range to fix his position: he just draws the first line, changes the receiver frequency to the other VOR, gets his radial, and plots the second line. Where the two lines intersect is Otto's location.

VHF Omni Ranges (VOR's)

Now we come to the very heart of modern aeronautical navigation. Not only are VHF Omni Ranges used as the basis for the airway system as we know it, but even sophisticated airplane- and satellite-based systems which do their own navigation calculations depend on VOR's to "keep them honest"; in other words, to verify their own internal accuracy.

As the name suggests, VOR's operate on the VHF Air Band, specifically between 108.0 and 117.95 MHz. That makes the reception of VOR's a line-of-sight affair; the pilot must have a straight line between the VOR and his aircraft in order to receive a usable signal. Although that may seem like a disadvantage, the truth is there are so many VOR's out there, strategically well-placed, that there's almost always one or two that the pilot can tune in and use to navigate. Also, VHF radio is not normally susceptible to the problems of wierd propagation, interference, and fading. That's what makes them ideal navigation devices: they're consistently easy to receive and predictable to use.

To get an understanding of how a VOR works and how our pilot friend Otto uses it, think of our old compass rose sitting on top of a map. The center of the compass is directly on top of the VOR site, and the top of the rose (zero or 360 degrees) corresponds to magnetic north. Naturally, 90 degrees is "mag" east, and so on.

Now some of you may know of a concept in radio electronics called phase. Essentially, when the two wave components of radio energy, current and voltage, follow each other step for step, they are said to be in phase. The current peaks and ebbs exactly when the voltage does. We can say that the phase difference between current and voltage is zero; i. e., there is no phase differential.

What happens, though, when the current and voltage are out of step with each other? Suppose the voltage peak occurs at the same time as the current trough? In other words, that the highest voltage occurs at the same instant as the lowest current reading. Now we say that the current and voltage are 180 degrees out of phase. Remember that...180 degrees...as in "south".

We can manipulate our VOR's transmitted radio signal to be in or out of phase by any amount from zero to 359 degrees by manipulating the transmission circuitry and antenna system. We can then install a receiver in Otto's airplane that will measure what the phase difference in the received signal is. Are you starting to get the picture?

Now all that's left to do is to transmit the signal from our VOR station (the center of our compass rose) in such a way that the direction of the signal travel will correspond to the phase difference of the signal going in that direction (fortunately there is a way to do this that does not require 360 transmitters and antennas.) The signal transmitted to the magnetic west of the VOR will have a phase difference of 270 degrees. The signal transmitted to mag north will be an "in-phase" signal. If Otto is mag north of the VOR, regardless of his distance from it (as long as he can still receive the signal), his VOR receiver will read zero or 360 degrees.

Notice that, unlike the non-directional beacons we looked at, the VOR reading on Otto's receiver does not depend on the position of his airplane's nose relative to the navaid, in this case the VOR. HIs VOR receiver will read the proper "spoke" from the VOR "hub" regardless of whether his airplane's nose is pointed north, south or whatever.

As Otto flies across the sky, of course, his VOR radial indication will change, unless he's traveling directly inbound to or outbound from a particular VOR.

Company Radio: Fuel and Weight

On the company frequencies you may hear many conversations relating to fuel. But you'll almost never hear a reference to gallons of fuel; it's almost always expressed in pounds.

The reason has to do with the simple fact that as an airplane flies, it's constantly losing weight: fuel is being burned by the engines and converted into forward thrust and exhaust gases. All of the calculations that are involved in loading and planning the flight are simply easier to accomplish if everything, including fuel, is converted to pounds and kept that way.

Here's a simple arithmetic "ladder" of sorts which may help explain the concept of flight load planning. Follow at the top of the ladder and move downward, line by line. We'll explain as we go along. The terms in bold are the ones you're likely to hear on the air. We've got a Boeing 757-200, planning a flight from Miami to Boston, a distance of 1100 nautical miles. Here's the table of weight limitations from the airplane's flight manual:

Boeing 757-200
Maximum Taxi Weight	231,000 pounds
Maximum Takeoff Weight	230,000 pounds
Maximum Landing Weight	198,000 pounds
Maximum Zero Fuel Weight	184,000 pounds

Now let's look at the ladder of weight calculation. Just follow along as we do the math, going down this chart.

Take Operating Empty Weight (also known as Basic Operating Weight)	135,000 pounds	Operating Empty Weight (or OEW) refers to the total weight of the empty airplane and all items necessary to complete the flight: pilots, flight attendants, meals, etc. but excludes passengers, cargo, and fuel. Empty airplanes are periodically weighed in a hangar using appropriate scales to determine the proper empty weight for that airplane alone. This weight is kept updated and used for calculations until the next weighing.
...add Payload	40,000 pounds	Payload refers to the total weight of all passengers, baggage and cargo (average weights for passengers and their bags are used...passengers are not normally weighed).
...equals Zero Fuel Weight	175,000 pounds	The airplane's weight without fuel is therefore 175,000 pounds. The airplane is never really drained of all its fuel, of course; this is a calculation.
...now compare Zero Fuel Weight to Maximum Zero Fuel Weight	175,000 pounds is less than MZFW of 184,000 pounds	Compare 175,000 pounds to the maximum of 184,000 pounds: no problem for this flight. As you may expect, you can never exceed Maximum Zero Fuel Weight--you would have to remove either payload or "dead weight" such as serving carts or meals to get Zero Fuel Weight below 184,000 pounds.
...now take Zero Fuel Weight and add Fuel Load	175,000 pounds + 35,000 pounds	The fuel load is also called the release fuel, the total weight of the fuel the airplane is released or dispatched with. Using the conversions provided elsewhere in this blog, this equates to about 5,200 gallons of fuel.
...equals Gross Takeoff Weight (also known as Brake Release Weight)	210,000 pounds	This is the total weight we're planning for the airplane at the beginning of the takeoff roll.
...compare Gross Takeoff Weight to Maximum Takeoff Weight	210,000 pounds is less than MTOW of 230,000 pounds	Compare 210,000 pounds to the maximum of 230,000 pounds: again no problem with this flight. Maximum Takeoff Weight may sometimes be less than 230,000 pounds depending on a variety of factors, including runway length and the airplane's configuration. But today, from Miami's long runways, this is not a factor.
...now take Gross Takeoff Weight and add Taxi Fuel	210,000 pounds + 800 pounds	We plan that 800 pounds of fuel will be burned to taxi from the gate to the runway where takeoff will commence.
...and get Ramp Weight (also known as Taxi Weight)	210,800 pounds	Total weight of the airplane when it departs the gate under its own power.
...then compare Ramp Weight with Maximum Ramp Weight	210,800 pounds is less than 231,000	Compare 210,800 to the maximum of 231,000, again no problem. There's one more weight calculation to make.
...take Gross Takeoff Weight and subtract Fuel Burn	210,000 pounds minus 24,000 pounds	We plan that 24,000 pounds of fuel will be burned from brake release at Miami until landing at Boston. We calculate fuel burn by using our flight plan data to get fuel burn information from the airplane's manufacturer. Notice we've planned on 11,000 pounds of Reserve Fuel or Arrival Fuel (35,000 pounds released - 24,000 pounds plan burn).
...and get Landing Weight	185,500 pounds	Planned weight of the airplane upon arrival in Boston.
...finally compare Landing Weight to Maximum Landing Weight	185,500 pounds is less than MLW of 198,000 pounds	Our weight checks are complete.

Company Radio: a Glossary

Here we are at the high end of the VHF band, 128.8 to 132.0 MHz., for the purposes of listening in on those frequencies allocated to commercial aviation companies: airlines. This is where you'll hear communication between airline pilots and their operations, maintenance, dispatch and weather personnel. This makes for some fascinating listening as the logistics involved in the day-to-day movement of people, cargo and airplanes unfolds in your VHF receiver. This is where you'll be introduced to the many professional men and women who support the flight crew to ensure a safe and reliable air operation.

Here are some common terms you may hear on company radio.

MEL - Minimum Equipment List. This is an approved list of items on the airplane that may be inoperative while still allowing the aircraft to be dispatched. Often, an MEL item carries with it an operational constraint or performance penalty that must be accounted for.

CDL - Configuration Deviation List. Much like the MEL, but this consists more of aerodynamic fairings and panels that are removed or missing. Again, there's usually a performance-related weight penalty that must be applied.

RON - Remain over night. Can apply to airplanes and/or crews.

ETR - Estimated time of repair. The time, usually given in Zulu time or UTC, that an aircraft is expected to return to service.

Ferry Flight - A flight without any revenue on board (no passengers or cargo). Ferry flights are usually used to get airplanes back to a maintenance facility, or to position an airplane to pick up a line of flying.

Line of Flying - The "line" of flight numbers that an aircraft is scheduled to operate in a day. For instance, a typical line of flying for one 727 aircraft may look like this:

• Aircraft remained overnight (RON) in Boston.
• Aircraft makes up flight 32 from Boston to Atlanta to Montego Bay, then...
• Flight 994 from Montego Bay to Charlotte to Chicago to Las Vegas, then...
• Flight 711 from Las Vegas to Albuquerque to Dallas/Ft. Worth to Charlotte, then...
• Flight 52 from Charlotte to Cincinnati to Detroit.
• Aircraft RON in Detroit.

The next morning, the aircraft makes up the next line of flying starting from Detroit. Notice that the flight number changes with each general change in direction of flight.

Tail number - Registration number of the airplane. Not the same as the flight number.

Minimums - The weather requirements (visibility and ceiling) for takeoff or landing on a given runway. Visibility is ususally expressed as an RVR (runway visual range) number, which is essentially how many feet you can see lighted objects on the runway. Ceiling is the height, in feet, from the runway surface to the lowest major layer of clouds. For instance you may hear a flight crew being told, "Runway two eight left RVR is five thousand, ceiling three hundred". NOTE: this is a very simplified explanation; there's a lot more to it, but that's the basics.

Crew Legality - Both flight crews and cabin crews are bound by regulations and company policy or contract, to adhere to rest, meal, and other non-flying time minimums. When flights are delayed or cancelled, a crew may not be legal for their intended trip. Either the crew or the flight itself may be adjusted to maintain legality.

Segment - One takeoff and landing, i. e., one nonstop flight.

VFR - Visual Flight Rules. Means that the ceiling is 1000 feet or better, and the visibility is 3 miles or better. More often than not, it's simply used as a short way of saying "the weather's pretty good".

IFR - Instrument Flight Rules. Means visibility and ceiling are poor; the opposite of VFR.

What frequencies should I be listening to? Part two

Since VHF is only audible in line-of-sight communications, it's completely ineffective for trans-oceanic flights. That's where High Frequency (HF) comes in.

The HF bands are audible with a shortwave receiver capable of single sideband mode reception. Good, portable shortwave receivers are available for less than USD $200 and will also pick up AM and FM broadcasts.

Although you might hear some aviation communications with the built-in whip antenna, a good outdoor long-wire antenna will go a long way toward helping you to hear signals in these bands.

High Frequency (kHz)	Mode	Purpose	What you'll hear
2850 to 3155 3400 to 3500 4650 to 4750 5450 to 5730 6525 to 6765 8815 to 9040 10005 to 10100 11175 to 11400 13200 to 13360 15010 to 15100 17900 to 18030 20005 to 21000 21850 to 22000 21964 22720 to 24890	Upper Sideband (USB)	Voice communication	Long-haul flights, air-to-ground, air-to-air

The low frequency range can be heard with most shortwave receivers that cover the low frequency band. There are very few navigation aids (navaids) in use in this band anymore, however. If you do listen to this frequency range, make sure you have long wire antenna of some kind to attach to your receiver.

Low Frequency (kHz)	Mode	Purpose	What you'll hear
200 to 415	AM (Morse Code three-letter identifiers)	Non-Directional Beacons (NDB's)	Navaids (no voice communications)

Two great links with more detail about Aviation frequencies are here and here.

What frequencies should I be listening to? Part one

Very High Frequency (MHz)	Mode	Purpose	What you'll hear
108.000 to 117.950	FM	VHF Omni Range's (VOR's) and Instrument Landing System (ILS's)	Navaids only, no voice communication
118.000 to 121.400, also 123.600 to 128.800 MHz	FM	Air Traffic Control	Voice communication
121.500	FM	Distress Frequency	Emergency voice communication
121.700 and 121.900	FM	Ground Control	Voice communication
122.000 to 123.575	FM	Uncontrolled airports, Flight Service Stations (FSS's), air shows, various air services	Voice communication
128.800 to 132.000	FM	Airline communications, ramp control, dispatch	Voice communication

The VHF band is the "meat" of aviation listening. The best way to listen to the VHF band is to use a programmable scanner with a decent VHF receiving antenna, although if you live near an airport the scanner's built-in whip antenna may give you some reception.

As you scan, save the frequencies that are "hits" for you in your scanner's memory. Later you can scan only the memory frequencies instead of the whole ranges listed above.

Av-speak, part six: Landing

Now we come to the landing phase. The approach controller has done his or her job in getting all these arriving aircraft on the ILS or visual track for landing, properly spaced and at appropriate speeds and altitudes. Each one in turn is handed off to the tower.

"Midway Tower, USAir 221 is with you for two-two left."

"USAir 221, Midway tower, number two, wind two-two-zero at ten." A minute or so later, "USAir 221, runway two-two left, clear to land."

"Clear to land, USAir 221."

A lot of "two's" in there, huh! USA221 checks in with Midway tower and is advised it is "number two", in other words, there is one arrival ahead of USAir on the approach for 22L. The tower lets USA221 know that the wind is right on the runway heading; that is, there's a straight-on headwind of ten knots at this time.

"Delta 909, turn left when able at the next high-speed."

"Turning left, Delta 909." Then, "Delta 909, contact ground point niner, good day."

Many runways have one or more high-speed taxiways, angled away at 45 degrees or less from the runway, that allow landing aircraft to clear the active runway while still rolling at a pretty good clip. In other words, by utilizing the high-speed taxiway, they need not come to an almost complete stop to turn 90 degrees onto an intersecting taxiway. Traffic behind the landing airplane can then be given clearance to land. High speed taxiways are a great tool to maintain the rate of landing aircraft.

As for the "ground point niner", this is a shorthand way of saying that the Ground Control frequency is 121.9 MHz. The overwhelming majority of airports' ground controllers are either on 121.7 or 121.9; this is one of those "assumed" things that can confuse the casual listener. Now you know.

After the taxi ride to the gate, led by directives from the ground controller, the aircraft parks at the arrival gate where passengers deplane, and the aircraft is serviced for the next leg of flight. At large hub airports, there may be one more intermediary between the ground controller and the gate area: this is called ramp control or the ramp coordinator, or something similar. It is usually staffed by the major airline at that airport, and its main function is to manage the large number of airplanes and gates that must be matched up to ensure a smooth hub operation. More on company communications in the next installment.