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How airspeed indicator works

how airspeed indicator works


©Hal Stoen, Stoenworks, Inc. September 4, 2000

Purpose of this tutorial

To give the flight simmer an idea of what IFR procedures are. What IFR is, how it differs from VFR, how to fly IFR enroute, what IFR approaches are, definitions, and how to "shoot" the various instrument landing procedures. This is not an "IFR Tutorial". For the correct procedures to use in the IFR environment, see Andrew Ayer's tutorials on IFR procedures.

The discussion herein are based on those used in the United States. Other countries vary on details, but the central theme is similar.

About the author

I soloed in 1966 and received my Commercial license several months later. For the next 20-some years I made my living flying airplanes: flight instructing, charters, mail, commuter airline, and ending up as a corporate pilot for the last 15 years or so. In that time I accumulated over 6,000 hours while operating a variety of aircraft ranging from the single engine Cessna 150 to the four engine DeHavilland Heron. During my time, I received my Commercial, Multi-Engine, Flight Instructor Instrument licences and ratings. I retired from aviation in 1988, and now ride in the back like most everyone else- and yes, I am a poor passenger.

What is this thing called "IFR"?

"IFR" stands for Instrument Flight Rules, as opposed to "VFR" which stands for Visual Flight Rules. These are the two basic divisions of flying IFR, or VFR. For all intents and purposes, to fly VFR the weather must be a "ceiling" of at least 1,000 feet above the ground, and the visibility must be at least 3 statute miles. Just to muddy up the waters, there is another category named "special VFR", but we'll stay with the two basic divisions.

For VFR flight, it's see and be seen, hop in your aircraft and go. As long as you stay away from "controlled airspace" you can go and do what you want to- as long as you don't violate any regulations of course.

For IFR flight, you must have the permission of ATC, Air Traffic Control, to operate in controlled airspace.

Glossary (an attempt at "non-tech" definitions)

ARTCC : Air Route Traffic Control Center. Often called "Center". The United States is divided into divisions, roughly based on the amount of traffic that they control. Thus, New York Center's geographic airspace is smaller than Minneapolis' airspace. Within the various Centers are more divisions that are usually worked by a single controller.

ATIS : Automatic Terminal Information Service. A continuous broadcast of the airport conditions. As conditions change, the change is noted by an alphabetical increase in the name of the broadcast. Information "Charley" becomes information "Delta", etc.

ADF : Automatic Direction Finder. A low frequency device that can point at a radio station. The term "ADF" can sometimes refer to the tuner head that tunes the ADF frequencies, or the display head. (see the illustrations that follow)

Ceiling : The height from the surface to the lowest layer of clouds that are reported as "broken", "overcast", or "obscuration", but not classified as "thin" or "partial".

Center : A common abbreviation for ARTCC.

Clearance : 1. Your IFR clearance for your intended route, or approach.

2. An abbreviation for Clearance Delivery, a feature that is available at larger airports. Clearance Delivery has a devoted radio frequency that you can use to get your IFR clearance. Once you have obtained it, you then contact Ground Control for taxi instructions.

Controlled airspace : Just about all of the airspace in the United States. There are several categories.

Continental Control Area : Covers all of the "lower 48" plus most of Alaska. Extends from 1,501 feet above the surface up to infinity, or the base of the PCA, the Positive Control Area.

Control Zone : The area around an airport that has a control tower. Usually a 5 statute mile circle around the airport, and any extensions necessary for instrument approaches. It extends from the surface to the base of the Continental Control Area.

Positive Control Area : The airspace extending from 18,000 feet MSL to Flight Level 600 (for all intents and purposes 60,000 feet).

TCA : Terminal Control Area. Airspace around larger airports. VFR or IFR, you need permission to be in there.

Controller : A person that works at a control tower or at ARTCC.

CDI : Course Deviation Indicator on the HSI.

CTAF : Common Traffic Advisory Frequency. A radio frequency that is used to broadcast on when the controlling facility for an airport, the tower for example, is not in operation.

DA : Decision Altitude. Minimum descent altitude on a precision approach, in feet above sea level (msl).

DH : Decision Height. Minimum descent altitude on a precision approach, in feet above the ground (agl).

DME : Distance Measuring Equipment. The readout on your DME will give the distance from the station that your nav. radio is tuned to.

FAF : Final Approach Fix. The point from which the final approach (IFR) to an airport is executed. It is shown on some approach plates as a Maltese Cross for non-precision approaches, and by the glide slope/path intercept point on precision approaches.

IFR . Meteorological conditions that are less than VFR. IE: ceilings less than 1,000 feet and visibility less than 3 statute miles.

ILS : Instrument Landing Sysrem. An approach that provides both vertical (glide slope), and horizontal (localizer) information.

LOM : Locator, Outer Marker. A NDB that is co-located with the Outer Marker associated with an ILS. This allows using the ADF for orientation on the approach.

MAP : Missed Approach Point. That point at the end of an approach where, if you cannot see the runway to land, you terminate the approach, and go into the Missed Approach mode.

MDA : Minimum Descent Altitude. The lowest altitude (msl) that you can descend to on a non-precision approach.

Missed Approach : The segment flown between the MAP (see above) and the Missed Approach fix.

MSL : Mean Sea Level. The average height of the world's oceans.

NDB : Non-Directional Beacon. A low frequency radio beacon that radiates it's signal in all directions.

OM . Outer Marker. A beacon that radiates a signal that is received in an aircraft shooting the approach. The Outer Marker is usually about 5 miles from the end of

the runway.

Non-Precision approach : An approach without a glide slope.

Precision approach : An approach with a glide slope.

Special VFR : When authorized by ATC, VFR flight with at least 1 mile visibility, and remaining clear of clouds.

TACAN : Military format for azimuth and distance.

VFR : Ceilings more than 1,000 feet and visibility three miles or greater.

VOR : Very-high Omnidirectional Range. A VHF station that gives azimuth information for aircraft navigation. See "Understanding VOR's" for more information.

VOR/DME : A VOR that has DME capabilities also.

VORTAC : A VOR that has DME available in addition to TACAN. Don't worry about the TACAN part. Unless you have military receivers you won't get the signal. From a civilian standpoint, regard VORTAC's the same as a VOR/DME station.

What training do I need, as a sim. pilot, to fly IFR?

You should be able to fly your airplane of choice solely by the instruments on the panel, without looking out the windows. In addition, you should be familiar with navigation procedures. (If you have not read Understanding VOR's. and How to navigate. I would suggest that you do so when time permits.)

In addition, you should have a good working understanding of how the various instruments on the aircraft's panel operate and how to set them up for navigation.

What equipment do I need in my airplane to fly IFR?

(all of the instruments shown below are discussed in detail in the "How to fly computer flight simulators " tutorial)

The short of it: magnetic compass, Needle and Ball, airspeed indicator and an altimeter. "Needle and Ball" refer to the Turn and Bank indicator.

With these basic instruments you can fly IFR. It wouldn't be pretty, but you could do it.

Let's make up a more functional group and discuss them just a little. You don't need everyone of the following items, but in this tutorial I will refer to various procedures as if your aircraft has at least the following items.

magnetic North. A "wet" compass floats in a kerosene-like fluid, while a "dry" compass is just that. They require no outside information. The compass is a difficult instrument to use for heading information due to a whole bunch of turning moments that are induced into it by the aircraft's acceleration and turning. But, it is a 100% back-up, just in case a more complex heading instrument fails.

So, how do you "become" an IFR flight?

Two ways, basically. You can file an IFR flight plan, then "pick it up" from Clearance or Ground Control before you depart, or you can file in the air by contacting Center and telling them what you want to do.

Ah, then how do I get "out" of an IFR flight?

Several ways. If you land at an airport with a Control Tower, your IFR is automatically cancelled upon landing. If you land at an airport without a Control Tower you will have to request that your IFR is cancelled either by using your radio, or making a telephone call once on the ground. And, of course, if the weather is VFR and you're not in controlled airspace, you can cancel IFR just by telling Center. "Center, Red Baron 123 is cancelling IFR at this time."

OK, how do I figure out how to get from "here" to "there"?

This example will be for going from where you are, to an airport that is within the area shown on the X-Plane built in chart. Go up into the menu and find the charts. You will be able to zoom in on the airport you are located at. Note the name and frequency of the nearest VOR that is along your intended path to your destination airport. Zoom in or out as necessary to locate the airport that you intend to land at, and the nearest VOR. File your flight plan from the airport you are at to the VOR nearest that airport, then to the VOR nearest your destination airport, then to the airport that you want to land at.

In its simplest form, that will get you from "here" to "there". Well great, what if you want to go from Los Angeles to New York? In that case you will have to locate some charts that show the routes available between those two points. Sim charts are available on the net at several locations, or you can purchase charts through the mail or at your local airport. If you have not done so, now would be a good time to read Understanding VOR's and How to navigate .

Alright, I understand VOR's and how to navigate. How do you fly all of those various instrument approaches?

In this segment we'll cover that. The subjects covered will be: Transitioning from enroute to the approach phase, SID's and STAR's,VOR approaches, VOR/DME approaches, NDB approaches, Localalizer approaches, the ILS, and lastly the Back Course approach.

Transitioning from enroute to the approach phase

As you near your destination airport, Center will call and either give you a lower altitude or instructions to contact Approach Control, or a combination of both of these instructions. Something like "Red Baron 123, descend to and maintain 7,000.", or "Red Baron 123, descend to and maintain 7,000. Contact Approach on 124.7."

SID's and STAR's

These are printed guides that show in graphic and text form the standard departure and arrival routes for a given airport. Not all airports have them, usually only the busiest ones do.

A SID is a Standard Instrument Departure. If you are issued a Sid as a part of your departure clearance, you are expected to follow the instructions on the chart. The example below is for Tucson International Airport, KTUS.

A STAR is a Standard Terminal Arrival Route. If you are issued a STAR as a part of your arrival clearance, you are expected to follow the instructions on the chart. The example below is for Tucson International Airport, KTUS.

This ends the "Introduction to IFR" tutorial. See the Tutorial Section for further guides on various approaches.

This narrative, along with aditional content, is available as a CD or an eBook.

For CD information click here. For eBook information click here .

© Hal Stoen, September 4, 2000

Category: Forex

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