Flying the coupled approach

FLYING THE COUPLEDAPPROACH

Purpose of this tutorial

To give the computer flight simmer a general idea of the methodsand practices utilized in flying an approach to a landing usingthe aircraft's autopilot. In aviation-speak, a "coupled approach"is one that utilizes the aircraft's autopilot to navigate theaircraft in the approach phase right down to the approach minimums,and, in some cases, on to the runway itself.

Background

It may have just been a long day, and you're tired from yourjourney. Or, your operation may require it, many airlines, realand virtual, do. Or, you're just beginning your training and arenot comfortable with your hand-flying skills yet. Whatever yourreason, using the autopilot to fly the approach can have its advantages.

However, there is a role change involved when you engage theautopilot to fly the aircraft's heading and navigational modes.You, the pilot, become to a degree a "systems manager".Whereas before you were controlling the inputs to the aircraft,now you must monitor the autopilot to be certain that it is doingit's job properly.

It's easy enough to sit back and "let George do it",but if you do not maintain your situational awareness it is possibleto end up in the land of total disorientation, rather than atyour destination airport.

This tutorial is not intended to instruct you on how to flya IFR (Instrument Flight Rules) approach, using all of the properprocedures. Instead, it is intended to give you sufficient informationon procedures and techniques using the autopilot, so that you,the flight sim pilot, can transfer them to your "virtualworld" and make your computer flight simulator time thatmuch more enjoyable.

Aircraft equipment required

First off, we know that you have an autopilot. As far as theinstruments go, that's kind of up to you and the aircraft thatyou are operating. In this short tutorial we'll cover the twobasic types of approaches, precision and non-precision. A precisionapproach is one that has lateral (left/right) and vertical (up/down)guidance. A non-precision approach is one that has the lateralguidance only.

Precision approach

Although there are other types of approaches that have verticalguidance, the ILS is the most ubiquitous, and is the one we willdiscuss .

The normal scenario is for Approach to vector (give you headingsto fly) your aircraft until you intercept the localizer, thenfor you to track the localizer inbound toward the airport untilintercepting the glideslope, then tracking the localizer and theglideslope down to approach minimums.

This is what we are looking at:

So there you are, flying along with good old George, the autopilot,in the "Navigation" and "Altitude Hold" modes,when Center tells you to "contact Approach on 124.75".You call Approach with "Good afternoon Approach, Red Baron123 is with you at 7,000, Delta". "Delta" is thecurrent ATIS (Automatic Terminal Arrival Information Service.)"Roger Red Baron 123, maintain 7,000, fly heading 040, vectorsfor the ILS runway 29 Left".

You reach up and set your "heading bug" to 040 degrees,and select the "Heading" mode on the autopilot. Theaircraft remains in the "Altitude Hold" mode.

Now you can go about setting your radios. Number One, the onethat drives the display right in front of you, should be set tothe ILS frequency, in this case 109.3. The Course Selector onyour HSI or VOR head should be set to the ILS "magnetic heading"(in this case 296 degrees) as shown on the approach plate, orin the approach word description. In most cases the runway andthe magnetic heading do not match. The runway may be "29L",but the actual magnetic heading may be 296 degrees. If you areunable to obtain the correct magnetic heading for the runway,set in the runway heading itself, in this case 290 degrees.

If you really want to set things up properly, and your aircraftis so equipped, you can do the following:

Set the ADF to the LOM (Locator Outer Marker) frequency, andplace it in the "ADF mode". This will help you to maintainorientation, as the ADF needle will be pointing at the Outer Markerduring your vectors from Approach. When flying an approach oninstruments, anything that you as the pilot can do to help yourorientation is of benefit.

If the weather is right down towards minimums, and you anticipatethe possibility of a Missed Approach (that's when you get downto minimums and cannot see the runway or it's "environment"),you can set your Number Two radio to the Missed Approach configuration,VOR frequency, course, etc.

Approach calls. "Red Baron 123, descend to and maintain5,000". You acknowledge with a "Red Baron 123 is outof 7,000 for 5,000". Depending on your installed autopilot,you either dial in 5,000 in the Altitude Hold window, or rollthe knurled knob on the autopilot out of the "Altitude Hold"detent and allow the aircraft to pitch down until it reaches 5,000feet, at which time you roll the wheel back into the "Hold"detent. In order to avoid giving two sets of instructions eachtime, we'll use the "Altitude Hold Window" in theseexamples.

Approach calls. "Red Baron 123, intercept the localizeron this heading and track it inbound, descend to and maintain3,000." "Roger, Red Baron 123 is out of 5 for 3, interceptthe localizer and track it inbound." Dial in 3,000 in theAltitude Hold and start your descent to 3,000. Depending on yourautopilot, you do one of two things. On some models you can pressthe "Heading" mode and the "Nav" mode at thesame time. Both annunciator lights will illuminate. The aircraftwill maintain the set heading in the "Heading" modeuntil the localizer is intercepted. At that time the autopilotwill switch out of the "Heading" mode and go into the"Nav" mode automatically. Or, in other models, you remainin the "Heading" mode until you see the ILS needle onthe HSI start to center. At that time switch to the "Nav"mode for ILS tracking.

Your aircraft is now in the "Nav" mode, trackingthe ILS inbound to the airport, level at 3,000 feet. Now thatyou are no longer in the "Heading" mode, this is a goodtime to reach up and set the heading bug to the Missed Approachheading. It never hurts to be prepared. If good old George theautopilot is doing his job, the localizer needle is centered rightin the middle of the gauge. The Boys down in Approach Controlare looking at their scopes saying "Man, this guy is good!He's flying that localizer dead nuts right down the middle!"

Then Old Charley strolls by and says "Nah, he's flyinga coupled approach." Well, they'll never know for certainanyway.

Approach calls. "Red Baron 123, 5 miles from the Marker,you're cleared the ILS runway 29 Left approach, contact the Towerat the Marker inbound." "Red Baron 123 is cleared theapproach, Tower at the Marker. Good day!" At this time, youshould have your approach power set, and your first notch of flapsdown. You watch as the glideslope slowly leaves it's peg at thetop of the gauge and descends towards the center of the HSI. Asit reaches the middle, depending on your autopilot, you will eitherwatch as the autopilot automatically switches out of "AltitudeHold" into the "Glideslope" mode, or you will haveto press the "Glideslope" button on the autopilot tomake it track the glideslope downward.

Shortly after glideslope intercept, the marker beacon goesoff with a "Dah, Dah, Dah" and the ADF needle swingsaround to point at the tail of the aircraft. You have just crossedover the Outer Marker. Gear down, adjust flaps and power as necessary.You monitor your aircraft until you reach the Descision Height(usually 200 feet above the end of the runway). Now it's decisiontime. Can you see the runway, or it's "environs" ? Environsinclude the runway lights, the REIL (Runway End Identifier Lights-those bright strobe lights aimed to flash at you, the pilot, duringperiods of low visibility), perhaps you see the white distanceto go markers on the runway. All of these count in the "environs"category. If you can see any of these things, disengage the autopilotand land.

If you cannot, it's time for the Missed Approach. Add climbpower, set the Altitude Hold to the published missed approachaltitude, press the "Heading" button (you already setthe Missed Approach heading, didn't you?), retract the gear aftera positive rate of climb is established, remove flaps in incrementsso that the aircraft does not settle downwards, and fly the publishedMissed Approach procedure.

Non-precision approach

In this type of approach there is no vertical guidance, I.E.no glideslope. This could be an ADF approach, a localizer approach,a VOR approach etc. For our example, we'll use a VOR approach,more specifically, a VOR/DME approach utilizing a VOR with DistanceMeasuring Equiipment. In this case, let's say that the runwayis once again 29 Left, and the VOR is located off of the field.The 292 degree radial of the VOR crosses the end of the runwayat exactly 11.2 miles from the station.

This is what we are looking at:

You're flying along in your trusty Red Baron, on autopilot,when Center calls. "Red Baron 123, fly heading 140, maintain7,000, contact Approach on 123.75". "140 on the heading,maintain 7,000. Good Day!" You reach over to the headingbug and set it to 140 degrees. If you are in the "Nav"mode, switch to the "Heading" mode. Now that you arebeing vectored by Approach, set your radios up for your approach.The VOR frequency is 115.7, the small "d" by the VORname shows that it has DME (Distance Measuring Equipment). Infact, you will be shooting a VOR/DME approach, one that requiresthe DME to be in operation. If it is not, or if your equipmenthas failed, you may not shoot this particular approach. (Thisisn't totally correct. If Approach is willing, you can tell themthat your DME has failed, and request that they "call"the appropriate DME points on the approach for you. Dependingon their radar coverage and work load, they may do this for you.This is perfectly acceptable and legal.) Once the radio is tunedto the right frequency, set your Course Selector in the HSI oron the VOR head to the final approach course, 292 degrees.

Pop Quiz: If your aircraft is as shown on the diagram above,and you tune in the Beavr VOR, and your Course Selector is setto 292 degrees, what does the "TO/FROM" indicator show?What about the CDI (Course Deviation Indicator)? Will it be tothe left, or to the right on your HSI (Horizontal Situation Indicator)?

If this question totally throws you, you may want to read thetutorial on "UnderstandingVOR's". Spatial orientation is extremely important whenflying, especially so when you're in the "soup" gettingready to commence an approach.

Back to the Pop Quiz. With the situation shown in the diagram,the "TO/FROM" indicator will show "FROM".How about the CDI? The needle will be pegged to the far left sideof the HSI.

(Oh, and why do I keep spelling the "Beavr" VORTACthat way? In the U.S. the FAA started converting all intersectionsto five-letter designations some time ago. Some VOR's were changedtoo. Hence, the "Beavr" vs. Beaver. Call it a smallhomage to Ward and June.)

Having an excellent spatial relationship with your aircraftand the airspace that it operates in, you realize that Approachis going to "widen you out" to the East before "turningyou back in" for the approach. If you were to maintain yourpresent Southbound heading it would require too tight of a turnto establish your aircraft on the approach radial to the airport.

This is a good time to review the approach procedure, and setup your Number two radio for the Missed Approach if the weatherappears questionable.

Approach calls. "Red Baron 123, turn farther left, heading120, descend to and maintain 4,000." "Out of 7 for 4,120, Red Baron 123." You reach up and set the Heading Bugto 120 degrees, and set the altitude hold to 4,000 feet. Levelingat 4,000, Approach calls. "Red Baron 123, turn right heading270 degrees." "Right to 270, Red Baron 123." Youreach up and set the Heading Bug to 270 degrees.

Approach calls. (Incessant, aren't they?) "Red Baron 123,intercept the inbound radial for the runway 29 Left approach onthis heading, descend to an maintain 3,000." "Out of4 for 3, intercept the radial, Red Baron 123." Once again,depending on you type of autopilot, you will either press boththe "Heading" mode button and the "Nav." modebuttons for an automatic transfer from heading to navigation whenthe radial is intercepted, or wait until the CDI swings into thecenter of the HSI and then press the "Nav." button onthe autopilot.

The CDI centers. You are on the reciprocal radial of 292 degreesfrom the Beavr VOR, the 112 degree radial, level at 3,000 feet.The "TO/FROM" arrow is pointing "TO" , andthe CDI is centered in the HSI. The autopilot is in the "Nav."mode, and the Altitude Hold is at 3,000 feet. The DME readoutshows 5 miles to the Beavr VOR. It's time to get your pre-landingcheck list completed as much as possible for this stage of thegame. Power should be set at your approach settings. This shouldput the good old Red Baron in the flap operating range on theairspeed indicator. Hold off on the flaps for the time being though,no sense in dragging this out and eating up that expensive avgas.The DME now shows 2 miles to the Beavr VOR. Might as well dropthat first notch of flaps at this point.

Approach calls. "Beaver 123, I show you 2 miles from theBeavr VOR, you're cleared the VOR/DME approach to the Oxford Airport,contact the Oxford Tower at Beavr inbound." "Clearedthe approach, Tower at Beavr, Red Baron 123." Now the CDIis really sensitive, as the radial you are navigating "closes"on the VOR. The autopilot tries to keep up, and finally quitssearching, "knowing" that it will be able to track theradial after you cross this "zone of confusion" whereall of the radials compress into such a small area. The "TO/FROM"arrow flips at this point from "TO" to "FROM".

You have just crossed over the Beavr VOR. Reach over and setyour "Altitude Hold" to the "Minimum Descent Altitude",let's call it 1,000 feet for this example. Gear down, mixturesrich, check power settings, flaps set as necessary, check listcomplete, call the Tower.

Remember, fly the airplane first, communicate second.

"Oxford Tower, Red Baron 123 is at Beavr inbound"."Roger Red Baron 123. Not in sight, cleared to land 29 Left.""Cleared to land, 29 Left, Red Baron 123."

Note that for this approach the end of the runway is at 11.2DME from the Beavr VOR. Let's say that the MAP (Missed ApproachPoint) is at the 10.0 DME point, in effect about one mile of visibilityis required for the approach. You want to be certain that youraircraft is at the MDA of 1,000 feet before you get tothe MAP of 10.0 miles from the Beavr VOR. This assures that youwill have the maximum opportunity to "look around" forthe runway environment. If you descend so as to reach the MDAand the MAP at the same time, you will only have a split secondto look and make your decision as to "Yes, there's the airport,I can land." or "Nothing out there, going Missed Approach."Don't worry about descending too fast, this is all taken intoaccount when the FAA (in the U.S.) lays out the approach.

Back to the cockpit of your Red Baron. You are level at 1,000feet. The DME reads 9.0 miles. Gear and flaps are down and set.You're looking out the window, through the murk, trying to findthe airport. There it is! You disengage the autopilot, maneuveras necessary to line up with the runway, and land your trustybird in a perfect squeaker.

Or, you don't see it. The DME clicks down to 10.0 miles andthere is nothing but the view from the inside of a bottle of milk."Oxford Tower, Red Baron 123, Missed Approach." "RogerRed Baron 123, Missed Approach, contact Approach on 123.75."(You did set that frequency on Comm. 2 just in case, didn't you?)You contact Approach. "Approach, Red Baron 123 is with you,missed approach at Oxford."

Unless you have advised Approach of your alternate intentionsbefore, this is the guaranteed reply that you will receive:"Roger 123, what are your intentions?" You had besthave an answer. Never shoot an approach where theoutcome is in doubt without having a plan "B". Grindingaround in the soup on a Missed Approach, reconfiguring your airplanefrom the approach mode to the climb mode, is not the timeto try to figure out what you are going to do next. If it appearsthat a "miss" is likely, advise Approach at some timeprior to shooting the approach that "If Oxford is below minimums,and we go missed approach, we would like vectors over to Big CityAirport for the ILS 30 approach." Now that's a plan "B".When flying airplanes, always, always, have a plan "B".Sometimes, depending on the circumstances, you may want to extendeven farther down the alphabet.

What happens if you start to go Missed Approach, and then seethe airport down below you? Well, unless you have stumbled intoa very large clear area that allows you to maneuver the aircraftin a normal fashion, at normal pattern altitudes(not too likely) you must continue on your Missed Approach. The"Circle To Land" minimums for an instrument approachare much higher than those for the Straight In approach that youjust shot.

You do not want to be flying low to the ground, circling aroundtrying to get back to the approach end of the runway. People stallairplanes and hit the ground doing that kind of thing, it willruin your entire day. And, just in case you do pull it off andmake it on to the runway, the friendly fellows in the Tower willask you to call them on the telephone, and will start fillingout forms for a violation . Most likely you will lose your ticket.

Don't do that.

Conclusion

I hope that this has been helpful to you in understanding howthe autopilot can be used in approach and landing situations.If there are any errors, or if I didn't explain something to yoursatisfaction, please contact me.

Have fun flying.

This tutorial is available on aCD

This tutorial, along with additional content, is availableon a CD. Click here formore information.

Hal Stoen

revised, 26 August, 2000

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