Thursday, August 13, 2015

ADF Tracking and Homing (reprint)

ADF Tracking



Homing PigeonSee that critter to the left? That's a homing pigeon. They're also bred and trained for racing. For him, homing is good. For an aircraft, homing is not good. Let's take that procedure off the table right now.

Homing is Unacceptable

Homing is easy and instinctive, but it is also inefficient and potentially dangerous. Homing to a station simply means pointing the aircraft in the direction of the station. The easiest way to do this is to turn the aircraft in the direction of the ADF needle until the needle points to the top of the indicator.
The pilot compensates for the wind by keeping the ADF needle centered with heading adjustments. With the wind constantly pushing from one side, the pilot has to constantly change the heading as he proceeds toward the station to keep the needle on the nose. With homing the crosswind pushes the aircraft away from the direct course and the resulting path to the station will be curved.
The series of illustrations below graphically show why homing is undesirable. To the left the aircraft begins homing to the 090° NDB bearing with a 090° heading. The crosswind from the north blows the aircraft off course, to the south. The following images of the aircraft show how it's heading has to be adjusted to maintain the ADF needle on the nose as the wind blows from the North. As it nears the NDB the wind has blown the airplane so far off the inbound bearing that, to keep the needle on the nose, it must fly a heading of 020° instead of the desired 090°.

Homing - 1st 

With a crosswind, homing results in a curved flight path to the NDB.

Homing is unacceptable for IFR navigation because the aircraft strays too far from the intended course. The wide, looping course shown in this illustration could take it into a hill, a radio tower, or other obstruction at the minimum altitudes of an NDB approach.
Continually turning towards the wind to keep the needle centered as the aircraft approaches the beacon is sometimes called "Birdogging." In strong wind conditions ADFs gradually drift your aircraft heading toward the wind direction as you approach the station.

Tracking

Blown 10@deg off course
The only way to fly a straight course to a station is totrack to the station. Tracking means to establish a wind-correction angle that negates the drift caused by the crosswind.
Again, rely on the rule to turn toward the pointer to intercept any course being paralleled. This rule applies whether flying inbound or outbound.
Once you have intercepted the desired bearing, hold that heading and see what effect the wind has. Let's continue with the previous example, intercepting and tracking the 075° bearing to Provincetown's Runway 7—and see what happens.
The ADF gauge above shows that a crosswind from the left has blown our aircraft off course. Our heading is still 075°, but the airplane has drifted off the bearing by 10°. The bearing to the PVC beacon is now 065°—the needle points to 065°. A turn to the left, towards the needle, is necessary to return to the desired 075° bearing. But how much correction is needed to stay on course?
RMI, 055° hdg, 065° bearingRMI, 065° hdg, 075° bearingRMI, 070° hdg, 075° bearing

  1. To get back on course, double the drift first noted and turn toward the needle by that amount, in this case 20° relative, or to a 055° heading. You are reintercepting the bearing.
  2. Hold the intercept heading of 055° until the needle returns to 075°, the desired bearing to the station. Now reduce the correction by half—10° in this case—to a heading of 065° to compensate for the wind. You should also lead the turn back on track by two to five degrees, depending on how far you are from the station.
  3. This method of correcting for wind drift is called bracketing. You may have to "bracket" several times to establish a reference heading that keeps you on the desired bearing, especially if a long distance from the station. The initial wind correction may be too large or too small to stay on the bearing. If so, adjust the correction. In example C, if the 10° correction (065° heading) proves too much, reintercept the bearing and try a 5° correction with a 070° heading.
Chasing the needle is a common mistake in ADF intercepts, tracking and bracketing. It is so tempting to follow that moving needle. Resist that temptation! Hold the heading steady until the needle reaches the relative bearing that you want, then make the turn.
Near the station the ADF needle will become "nervous," start wiggling and become more sensitive. Again, don't chase the needle, just fly the reference heading. The needle will start to swing to the left or right on passing over a station.
Wait until the needle has definitely swung around to verify station passage—at least five to ten seconds past the ADF station. Then turn to the outbound magnetic heading to determine which side of the bearing you are now situated and how much you will have to correct.

Practice flights, tracking inbound

Tracking inbound really is a simple procedure as you have just read. The two flights next described will polish up your inbound tracking skills. Complete the Flight Planning Worksheet before beginning each flight.

Long Island to Meriden, Connecticut

Silver Chalice
"What's going on in Long Island?" I asked the Boss. His message on my pager said to call, urgent.
"It's Counter, again," he replied. "Seems his Administrative Assistant is threatening to quit. His A.A. has a passion for hand-made silver and so Counter wants to fly to Meriden this afternoon."
"Meriden?"
"Yeah," the boss interrupted. "It earned the title of 'Silver City of the World' for the great hand-made stuff there. Counter figures if he can get there fast enough and buy something really cool, his A.A. won't quit. I don't understand the big deal, I mean, isn't the A.A. a clerk, a dime a dozen?"
"I think Counter's A.A. has more talents than that," I suggested. I had seen her and she was a knockout. Scuttlebutt had it that she had been a finalist in a local beauty-queen pageant a year or so back.
"Yeah, you're probably right. They get to know the inner workings of the company—that increases their value."
I didn't see the need to bring him up to speed. "The weather on the Sound isn't looking too good ... overcast and lousy visibility."
"Counter said he'd pay a bonus if you get him there and back today," the Boss offered, sensing my reluctance.
I hung up and headed for the airport. It seemed like I was now Mr. Benjamin Counter's private airline.

  1. Today's weather is poor. Set in 1500 ft. overcast with a visibility of 3 miles. Start the timer at the beginning of your takeoff roll. Depart from The Gabreski airport, KFOK, on Long Island, New York, using Rwy 33. Your destination is Meriden, Connecticut, KMMK. Tune in the Meriden NDB—"MMK"—on 238 kHz. On departure turn right to the 001° bearing to MMK, 41 nm. distant. You may not receive the MMK NDB until three or four minutes after departure. Climb to 3000 ft. Your flight time will be 25 minutes at 110 kts. cruise. Fifteen minutes into the flight begin a 500 fpm descent, maintaining 110 kts. Slow to approach speed on reaching 1000 ft., 500 ft. below the overcast. Continue tracking inbound on the 001° bearing until sighting the airport and Rwy 36 then execute a visual landing. Field elevation is 101 ft.
  2. Same route, same weather, but the wind has picked up. It's now 30 kts from 310°. Note: prior to starting your takeoff roll your airspeed indicator will read about 28 kts. That is from the strong surface headwind which will considerably shorten your takeoff run (but lengthen the flight).
    Total Distance of flight41 NM
    Time to climb to 3000 ft @ 700 fpm4.2 minutes
    Ground speed during climb68 kts
    WCA During Climb15° L
    Magnetic Hdg during Climb346°
    Distance during climb5 NM
    Distance for Cruise & Descent36 NM
    Ground Speed during Cruise & Descent89 kts
    WCA during Cruise & Descent12° L
    Magnetic Hdg during Cruise & Descent349°
    Time to Cruise 36 NM at 89 kts24 minutes
    Total Time En Route28 minutes
    With these numbers, now proceed as in the previous flight.
NOTE: Obviously one doesn't descend at 110 kts all the way to the runway threshold, but slows to enter the traffic pattern. Adding five minutes to the calculated ETE gives a good approximation of your actual flight time.
These flights will be pretty well under control after you fly each of them two or three times. You will be a busy pilot en route, too.
It is extremely important that you listen to the Morse-code identifier for any beacon that you are tracking to or from and verify that it is the proper NDB. Since NDBs operate in the LF band they can have great range. Click the center of the face of the radio for the ident function. A second click discontinues the ident.

The words GUESS and KNOW when used in
flying may produce entirely opposite results
.

Outbound Bearings from the NDB

Blown 20@deg off course
The procedures to intercept, track, and bracket outbound NDB bearings are very similar to those used on inbound bearings. The difference is that we work with reciprocals of the headings.
Limit outbound maneuvers to course corrections to compensate for crosswinds. It's not smart to intercept an outbound bearing en route because no information exists on where you are ... one nm. from the beacon or 30 nm. from the beacon? One traditionally enters an outbound leg at station passage, i.e., from a known position.
Assume that the last leg of your flight tracks outbound on the 078° bearing from the FFF beacon to Provincetown's Runway 7. The bearing from your aircraft to the beacon will be the reciprocal, or 258°, which is where the ADF pointer should be. Here the ADF indicator shows the aircraft's heading is 078°. But the ADF needle, pointing behind you to the FFF beacon, isn't on 258°. It's on 278°—you've drifted 20° off course.
Point number one. Just as tracking inbound to a beacon, if you are paralleling the desired path outbound, the pointer arrow shows you which way to turn to get back on course. Here the arrow points to the left so turn the aircraft to the left
Follow the same procedure as when intercepting an inbound bearing, Double your 20° error and turn towards the POINTER of the ADF needle, to the left by 40°.
RMI Outbound - Intercept headingRMI Outbound - at desired bearingRMI Outbound - tracking on  desired bearing

  1. With a 40° turn to the left for intercept, the aircraft heading will be 078°–040° or 038°. Notice that the pointer has swung farther away from the tail of the plane. That confirms that your turn was in the correct direction when flying outbound.
  2. Maintain a 038° heading until the ADF needle nearly reaches the desired 258° bearing from the aircraft to the beacon.
  3. Turn right to 058°, one-half of the initial correction angle, and track outbound with the pointer on 258° to the station. If you continue to drift off course, repeat the bracketing steps until the track is correct. Bracket outbound the same as on an inbound leg, except determine the wind correction necessary using reciprocals.
In actual practice, one would not drift so far off course as this example, to require a 40° intercept angle. Large numbers were used here so that the procedures would be clearly visible on the ADF indicator. Run through these procedures two or three times on your Flight Simulator to make everything click together.
Remember that the needle always points to the station. Never put the needle on the tail by changing the heading. This will cause you to miss the bearing completely and, as you will see during an NDB approach, if you lose that outbound bearing, you miss the airport.

Norwood, Massachusetts to Falmouth, Massachusetts

University
I was in the pilot's lounge relaxing after a tough IFR flight. We had been in the soup the whole time. I lapsed into a day-dream about my last CAVU flight—Ceilings and Visibility Unlimited—when our receptionist tapped me on the shoulder. I looked up and she nodded in the direction of the Boss's office. Without a word I got up and walked over.
"Is your aircraft fueled?" he asked before I could sit down.
"Yep, topped up, oil checked and windscreen polished," I replied, lowering myself into a battered chair.
"Good," he responded. "because I just got off the phone with Mr. Airline-CEO Counter. He missed his commuter flight to Falmouth, Massachusetts this morning, and there won't be another until tomorrow morning, which would be embarrassing."
I contemplated that for a moment but nothing came to mind that would embarrass Counter.
The Boss went on, "Counter is the scheduled Commencement speaker tonight at his alma mater, Downhome University of Hillsdale. They requested him to speak because of his rise in industry and his insistence that business success is directly tied to punctuality. It will not send a good message if he misses that commitment because he over-slept his flight. He requested your services because you can keep your mouth shut, whatever on earth that's all about."
A picture of his administrative assistant flashed across my mind and some of the destinations where the two had met for "business" purposes.
"He's in Norwood, Mass., so leave for there as soon as you can get the engine cranked up and get him to Falmouth. There's a bonus for both of us if you can make it look like the charter was planned from the start," the Boss said with finality.
I rose to leave when the Boss added, "And it doesn't help his humor or increase his desire to charter our services if you remind him of his alma mater's initials."
Downhome University of Hillsdale. What could I say?

Practice flights, tracking outbound


Two practice flights are listed below that will sharpen your skills at intercepting and tracking an outbound radial using the ADF. Although the routes are the same, the flights differ. Try to fly each flight once a day until you have nailed the procedures. That will happen very quickly.
Concentrate on staying on the 151° outbound bearing. In case your calculator is broken, the reciprocal of 151° is 331°. A one-degree deviation puts you off course by 0.6 NM. at the end of the 38 NM outbound leg from OW NDB. This is a long distance to track outbound, especially to arrive at a runway. That's why these are such good practice flights.
Enjoy the flights. It will be a busy 24 minutes.
  1. Tune your ADF to 397.0 kHz, STOGE NDB (OW), and tune Nav-1 to 115.8 MHz, (FMH). FMH is a TACAN Station, and your VOR needle will not respond; we use this signal for DME information only. Wind is calm. Start the timer at the beginning of your takeoff roll. Depart from Rwy 17, KOWD, Norwood, Massachusetts, climbing to 3500 ft. Destination is Otis Air National Guard Field, KFMH, Falmouth, Massachusetts, with field elevation of 131 ft. Fly direct to OW NDB, then turn left and track the 151° radial outbound from STOGE NDB to Otis ANG Field. RMI Needle will point to 331°. You will track almost 38 NM outbound from OW NDB, landing Otis Rwy 14. ETE from Norwood Memorial Airport is 24 minutes. Begin your 400 fpm descent 15 DME from FMH VOR (TACAN). Leave your ILS OFF during this flight!
  2. Same route as above, except that we add some complexity and reduce the visibility to 3 miles and the cloud cover to overcast, base at 1100 ft. Set in a 20 kt wind, from 130°. Calculate your WCAs and Ground speeds for Climb and Cruise before departure. Same en route details as previous flight, except altitude will be 3000 ft. and begin your 400 fpm descent 13 DME from FMH VOR (TACAN). Land Rwy 14. Leave your ILS OFF for this flight!

NDB Approaches

There are two types of NDB approaches: an inbound approach, if the station is on the field; and an outbound approach if the station is some distance from the field. The next section discusses each of these approaches in detail.

Holding Patterns

Holding patterns, you may remember, was not among the navigation procedures listed earlier that would be reviewed. In the late 1940s they were important and frequently used. Circumstances still exist today when they are required. But holding patterns are not covered here because they usually are in response to an ATC instruction or, in the event of a missed approach, while awaiting an ATC instruction. Since interactive voice communication with Flight Simulator is limited to On-Line Flying, VATSIM, holding procedures in response to an ATC instruction will not be reviewed here.

Credits


thank-youAlthough I did the keyboarding for this site it contains the fine contributions of many people.

With no prior experience in building a website I was overwhelmed at the generosity of those that I asked for permission to either reproduce their work, or for their technical help, or to use their designs, artwork and descriptions.
Many thanks to those listed below in alphabetical order, who so willingly shared their talent so that I could assemble these webpages:
Bob Austin, of Mission Viejo, California. A scenerio in the VOR Approaches section required an over-kill list of mountaineering equipment for Mr. Benjamin Counter. Counter intends to "scale" southwest New Hampshire's 3165 ft. Mt. Monadnock, the second-most climbed mountain in the world, behind only Mt. Fuji in Japan. Since Florida's highest "mountain" just reaches 345 ft. I had to look elsewhere for an expert. Bob Austin jumped right in, providing an awesome equipment list, which I had to shorten. Any omissions are my work, not his. Bob has the credentials to provide an accurate and complete list, too. In his climbing he's completed six big-walls including two El Capitan routes—The Nose and Triple Direct. Thanks, Bob. Just reading your equipment list I could imagine the wind fiercely blowing off the face of the mountain, daring any climber to move higher.
Wagner Beskow, for his Handy Sheet 3.0. Wagner, a Brazilian in New Zealand taking his Ph.D., assembled this one-page compendium of useful facts for the flight-simmer. "It takes a while for a beginner to find all that information and when he does it's all scattered and difficult to refer to. The idea was to produce something useful that could stay around without cluttering the 'cockpit' too much." Thanks, Wagner. I wish I could say my cockpit was uncluttered now.
Boeing Company, photo of 40-A mailplane. The 40-A, a fabric-covered mail plane, was Boeing's first commercial success. Built in 1927 (the year Charles Lindbergh crossed the Atlantic), it carried mailbags and—load permitting—two passengers. http://www.boeing.com/companyoffices/gallery/boeinghistcom.html
Tom Christine, Electrical Engineer, Federal Aviation Administration. Tom was very helpful on specifics about present-day Non Directional Beacons, including their power levels, uses, their friendly coexistence with GPS, and frequency limits of the LF band. Thanks Tom.
Mario Corral, Sydney, Australia, who sent me the sketch of the homing pigeon. Mario patiently explained to me some similarities and differences between homing pigeons, racing pigeons, and carrier pigeons. Thanks Mario for keeping me on the right track.
Rick Covington, photos of the Piedmont DC-3 in the "On the Beam" section. Thanks Rick ... an excellent photo. You can find more of his photographic expertise at www.airliners.net. He photographed the Piedmont shown here in Durham, N.C.
Mike Genovese for the finest interior shot I've seen of any aircraft. "The shot was taken in Nassau in the early 90's... the plane was just sitting there unattended as we (crew of a major airline) walked by on the ramp... I could not resist the opportunity for the 'Kodak Moment!' ... " Great pic Mike and keep your camera handy as you jet to all those tough destinations. See www.airliners.net for more of Mike's work.
Jesse Kempa for his virtual E6-B calculator program. This program does it all, and best of all, it's freeware. Input True Course, TAS, wind speed and direction and on the click of a button it returns the Wind Correction Angle and Ground Speed. It will calculate distances between points with known lat. and long. coordinates, and on and on. Thanks Jesse for a great utility.internet.oit.edu/~kempaj/e6b.htm
Brian Kostick, the gauge programmer of the very-useful digital Elevator Trim indicator. With it the pilot has repeatability in elevator trim settings. Thanks to Brian, Br5an@aol.com, for an instrument that I rely on and for his quick willingness to let me use it in this panel.
Paul Lutus ... who wrote the freeware HTML editor "Arachnophilia" which I used in assembling these webpages. Arachnophilia is a full-featured, nearly perfect editor—and now v4.0 is even better with a 120,000 word spell-checker. Paul has an outstanding philosophy on life, too. Thanks, although we've never "met." www.arachnoid.com
Alice Marks ... for the extraordinary sketch of McGirr field. That picture is the essence of the intermediate fields that Air Mail pilots aimed for when facing an emergency. Her artistry instantly backed me onto McGirr field—into the new era of Air Mail, with the wind sweeping across the plains, striking me in the face. But then, it should have because Alice Marks's father was McGirr field's caretaker and Alice grew up there. She has a wonderful first-person account of the activities at the field that beats anything you'll read in stuffy history books. Take five and go to her site and relive the experience. http://www.halcyon.com/cliffsan/airmail/air_mail.html. Thanks Alice, twice ... for sketching McGirr field to keep that kernel of history alive and for letting me share it with others.
Ned Preston, Agency Historian, Federal Aviation Administration. Ned provided the chronology on when VORs were introduced, a whole wealth of information on the four-course radio range and on the light-beacon system used to identify the airways at night before radio navigation facilities were in place. Never met a more helpful person. Thanks Ned.
Bill Rambow for his many e-mails answering so many questions. Bill designed the incomparable dual panel for the Douglas DC-3 / R4D / C-47. A restored, flyable U.S. Navy R4D at the Mid Atlantic Air Museum in Reading, Pa. was the model for his work. A finer piece of work I've never seen. Thanks for the encouragement, Bill.
Tom H., "Rumple," a gentleman who always sets his work aside to answer the other fellow's questions. I reaped the benefits of his very-methodical air-file testing. He also designed the manifold pressure gauge for the training panel in my Virtual Airline. Tom is very visible on newsgroups and forums patiently answering questions that are asked over and over. Thanks for being there, Tom.
Sarah at Airline History Website for the photo of the KLM Douglas DC-5 which opens the VOR Navigation section. I only recently learned that a DC-5 had ever existed and wanted to include a picture of it. Since Sarah's site has 350 Airline Histories, 1700 Airline Pictures, and 150 Airliners from 1920 to 1999, I knew it would be there. Why is Sarah interested in all this stuff? ... because she's a pilot—and more. She writes software for and sells IFR flight Simulator programs for real IFR training. Thanks Sarah for the great work that you put into your site.airlines.freeuk.com/airlines
Chris Sheldon, fwog@mindless.com, from the U.K. He photographed G-AMPZ at Manchester Airport, and it appears here in the IFR Charts section. The aircraft belongs to Atlantic Airways (previously called Air Atlantique) who are based at Coventry Airport. The first letter in the registration number, "G," denotes a U.K. aircraft. Chris exhibits his work at www.airliners.net. Thanks Chris.
Russ Strine, Mid Atlantic Air Museum in Reading, Pa. Here's another fountain of information. A very busy man at the museum, he pushed his papers aside and spoke with me for an hour on the telephone about aviation in the old days and VORs and NDBs and answered questions that I just wasn't savvy enough to ask. He gave me some anecdotal stuff, too, that you can't find in books. Thanks for your time, Russ, and all the information. www.maam.org
Barry Thomas, Silversmith, who created the magnificent chalice pictured in the section on tracking ADF's inbound. That section's lead-in story centers around Mr. Benjamin Counter's desire to fly to Meriden, Connecticut, 'The Silver Capital of the World' to buy some silverwork. The chalice pictured was not created in Meriden, nor even in the U.S. Barry Thomas is a silversmith in rural Derbyshire, England. Meriden earned the Silver-Capital title in the late 19th century and it is doubtful that it still retains the rights to that sobriquet. Thanks Barry for the great picture, too. More of his masterpieces can be found athttp://easyweb.easynet.co.uk/bthomas.
Rod Watson, for his stunning photograph of the Gay Head Lighthouse on Martha's Vineyard, Massachusetts. Rod has visited over 170 lighthouses in the US. and the Lighthouse Gallery section of his website, Rod's Photo Gallery, includes photographs of most of those lights, organized by geographic locations. He photographs more than lighthouses, too. Thanks, Rod, for a great picture.Rod's Photo Gallery
Roland Zuiderveld, from Sweden, for his totally awesome picture of a DC-3 descending out of the clouds at dusk to land. Roland also displays his work onwww.airliners.net. Thanks Roland, and if you take any more pictures like this one I want to hear about them.
Many others contributed to my virtual airline webpages and were just as generous. They are identified on that site. Assembling a webpage is so much easier with the assistance of people like these.
With thanks,

Charles Wood 

No comments:

Post a Comment