Reverse Sensing? No Such Thing

I often hear comments from pilots about confusion over normal sensing and reverse sensing. To some it seems no big deal, but to others it is a source of worry and confusion. I am going to make what may seem to be a rather startling comment to some of you.

If you truly understand VOR navigation, there is no such thing as reverse sensing.

Okay, bear with me. The confusion arises because the majority of pilots have been taught to “fly towards the needle” when learning VOR navigation. That in turn gets interpreted to mean fly either right or left in order to get on the desired course. And therein lies the problem and the source of the confusion.

You do not fly towards the needle. Instead you fly towards a heading, and that may mean fly either right or left. It depends on where the nose of the aircraft is pointing.

In the above figure, the OBS is set to 360, same direction as the nose of the aircraft. So students have been taught to fly towards the needle, or to the left. But instead of right or left, think heading. Looking at the VOR display, a heading of 270° will take you directly to the selected course. In this case that does happen to be a turn towards the left. But now let’s spin the aircraft around, so it is flying south.

Notice the VOR display has not changed. The VOR head (as the VOR display is technically called) neither knows nor cares where the nose of the aircraft is pointed. The CDI is still deflected to the left. It is still saying that to get directly to the selected course, you need to fly a heading of 270 degrees. But now look at the DG (or heading indicator). A heading of 270° is towards your right – in the opposite direction of the needle. This, then, is the so-called reverse sensing. But if you think heading rather than right or left, there is no reverse sensing. Instead there is just a heading to fly, and that heading may be to your left or to your right.

This works for localizer as well as VOR courses. Let’s take a look at the ILS-18 into Lebanon, NH (KLEB). Here is what the instruments look like as the pilot is being vectored for the ILS, flying a heading of north. Look at the approach plate first and see where the aircraft is.

Now let’s look at the aircraft instruments. Note the aircraft is flying north, on the east side of the localizer. The VOR display says the pilot needs to fly towards the west to get to the localizer course. The DG (heading indicator) says this means a turn towards the left. Think heading, not right or left!

Now let’s look at tracking inbound on the localizer. Again, first look at the approach plate to see where the aircraft is.

Now let’s look at the instruments. Note that the aircraft is slightly west of the localizer course. The instruments show exactly the same thing – the aircraft is slightly west of course. Also note in both cases, the OBS for the VOR display is set to the final approach course. If you set the OBS to the final approach course, it results in less knob twisting, and in a busy cockpit, this is an advantage.

So you see that if you disavow yourself of the “fly right or left or towards or away from the needle” way of thinking, the entire concept of reverse sensing simply disappears.

I’ve shown it here for a localizer, since this notion of reverse sensing is very common when either flying a back course or tracking outbound on a localizer to do a procedure turn. But it works exactly the same way for tracking on a VOR approach.

Let’s look at the VOR-25/LEB. Below is a portion of the approach plate, showing the position of the aircraft being vectored for the approach.

Now let’s look at the instruments. The aircraft is being vectored on the east side of the final approach course. The OBS is set to the final approach course. The needle is deflected to the right and a heading of 330° would take us directly to the final approach course. But 330°is to our left, away from the needle. Think heading, not right or left.

Now let’s look at the picture as the aircraft has been given a heading that provides an intercept for the final approach course. First look at the approach and see where the aircraft is.

The aircraft is on a heading of 280°, just about ready to join the final approach course. This is what the instruments look like.

If you think heading rather than right or left, you can set the OBS to the final approach course, even if you are flying outbound to do a procedure turn. By the way, with an HSI you always set the course to the final approach course, sometimes called the front course, even if you are flying a Localizer-Back-Course approach.

If you are used to always setting the OBS to your heading, as students have been traditionally taught, then continue with the procedure if you are comfortable with it. However you decide to do it, though, think heading – not right or left.

I close this discussion with the following acronym.

IBOT

I have used it for a long time to help students remember what radial they are on.

I = inbound or “TO” flag on VOR head

B = radial is at the bottom of the VOR head

O = outbound or “FROM” flag on the VOR head

T = radial is at the top of the VOR head

So think “inbound bottom” and “outbound top.”

Try out some of the ideas I’ve presented here yourself. You will find out they work, and they can significantly reduce the amount of confusion that occurs when doing VOR navigation.

True, False or Maybe

Instrument flying is chock full of rules and regulations. However it is also replete with gray areas, where a clear definitive answer is not spelled out. These areas are always good to spark a lively debate among pilots. Instructors are no different – we have our ideas too about the gray areas. So let’s look at a few things that are not clearly spelled out and are sure to provoke some debate.

Question 1:

Scenario: you are flying towards the IAF for the NDB or GPS RWY 34 at Cambridge (KCBG). You have been cleared for the full approach, your direction of flight is northwest and your altitude is 4000’ MSL.

After passing over the IAF, you must get established on the outbound leg with a heading of 170° in order to do a procedure turn. Which is the true statement?

· You must make a right-hand turn to get established on the outbound course because that is the protected side shown for the hold.

· It doesn’t make any difference whether you turn right or left because you are at MVA and not in any danger of colliding with an obstacle.

Question 2:

For the same approach, for various reasons you are at an altitude of 8,000’ and need to lose a lot of altitude in order to fly this approach. ATC tells you to hold south of the NDB IAF as published and descend in the hold until you reach 3,000’.

You do as directed and reach 3000’ as you are approaching the IAF on the inbound leg of the hold. ATC clears you for the full approach.

True or false:

· You must intercept the outbound leg in order to fly out and do a procedure turn.

· You can simply extend the outbound leg of the hold for two minutes or so and then turn inbound in the elongated holding pattern.

· Both procedures are acceptable.

Bonus question:

· What is DUMDY? (Hint – it is not shorthand for Descend Undercarriage Mixture Descend some more and Yippee there’s a runway in sight)

Question 3:

Now let’s look at another approach, this one is the GPS-28 approach into Maple Lake (KMGG). Scenario: you are approaching NAZMY from the east. ATC has cleared you for the approach.

You are pretty much lined up with the final approach course but the approach plate doesn’t specify NoPT coming from this direction and the 1-minute hold depicted at NAZMY is clearly meant to serve as a procedure turn.

True or false:

· You must do a turn around holding because NoPT is not specified

· You don’t have to do a turn around holding because you are more or less lined up with the final approach course

Question 4:

You are flying the full VOR-A approach into KMIC (see IAP below). You have completed your outbound leg on the procedure turn and are ready to do a 180° turn to a heading of 121° to intercept the inbound course.

You happen to glance at your DME and it reads 9 nm. The profile view clearly states the procedure turn must be done inside of 10 nm. Which of these statements is true?

· You must turn right because that is how the procedure turn is depicted on the approach plate.

· It makes no difference which way you turn, so make a left-hand turn to 121° in order to stay within the 10 nm range for the procedure turn.

Second bonus question:

You are flying single-pilot IFR and are trying to get the weather at your destination. But just about the time the ATIS report is giving the winds, ATC starts talking again so you turn down the volume on the ATIS frequency in order to hear the controller. After several attempts to get the weather, you still don’t have the pertinent information and are getting closer and closer to your destination.

What is your best course of action?

· You never leave the ATC frequency, so just hang in there and keep trying. Maybe you’ll get lucky.

· Ask ATC for permission to leave the frequency to get the weather at your destination

Answers:

As I said at the start, these are areas that can provoke a lot of discussion among pilots, so here is my two cents worth.

Question 1:

It makes no difference which way you turn in order to get established outbound.

Question 2:

Both procedures are acceptable.

First bonus question:

DUMDY is a procedural waypoint for an IFR GPS. An IFR GPS starts scaling down to 0.3 nm sensitivity two miles before reaching the FAF. However this approach does not have a FAF; you simply start to descend when established inbound. DUMDY serves as a virtual FAF for an IFR GPS. Two miles before reaching DUMDY the GPS starts scaling down to 0.3 nm sensitivity. And as a sidebar, if flying this as a GPS approach, you had better not start your procedure turn until you are south of DUMDY.

Question 3:

The second answer is correct. ATC is not expecting you to do a procedure turn. In the AIM, this is clarified, and controllers will often clear you straight in for the approach. If there is any doubt in your mind, however, query the controller about it.

Question 4:

The second one is preferred. It makes no difference which way you turn, and a left-hand turn will more likely keep you within the 10 nm limit.

Second bonus question:

The second course of action is preferable. You won’t read this in any book, but I have had both controllers and DPEs tell me they would prefer pilots ask for a frequency change to get the weather. Otherwise you are trying to listen to two frequencies at once and risk missing a call or not getting the weather (or both).

In the future I’ll try to delve into some of issues and questions like this. Your suggestions for future topics are welcome.

Silence

I have not been posting for a long time. Busy is about my only excuse. But I've had many requests to start posting again. So I will start again in the near future.

It is very nice to know that many people read the blog and that it has proven helpful in some ways.

Linda

Audio Panels Demystified

As instructors we are sometimes quite guilty of assuming “everyone knows that”, whatever “that” may be. Just a simple question from a student however can quickly make us realize it’s a false assumption. So it was a question from a student concerning the operation of an audio panel made me realize that it is probably worth offering some explanation about its operation.

The audio panel in question was the KMA 24, probably one of the most common audio panels found in planes.

In an overall view, the KMA 24 audio panel has two rows of buttons, flanked on the left by marker beacon lights and on the right by a rotary knob whose principle function allows the user to select COM 1 or COM 2. The top row of buttons directs the selected audio output to the speaker in the aircraft. The bottom row of buttons directs the selected audio output to your headset.

1. Marker beacon lights are used in many ILS instrument approaches. If the ILS approach has marker beacons (not all of them do), the most common ones are the outer marker (the blue light marked “O”) and the middle marker (the amber light marked “M”). The inner/airway marker (the white light marked “A”) is generally only installed at major airports. Marker beacons emit a 75-Mhz signal. When the aircraft passes over an outer marker, the blue marker beacon light is seen. A middle marker beacon illuminates the amber marker beacon light. In addition, an audible tone may be heard. If you want the audible signal to come through the speaker, press MKR (#9) on the top row of buttons. If you want it to come through your headset, press MKR on the bottom row of buttons.
1. The 75 Mhz signal transmitted by the marker beacons is a carrier frequency. This carrier frequency is modulated into a 400 hz, 1300 hz or 3000 hz signal for the OM, the MM, and the IM respectively.
2. TST - test the marker beacon lights. Pressing this button causes all the marker beacon lamps to illuminate. SENS - the button just to the right of the amber marker beacon lamp selects the sensitivity of the marker beacons. HI allows the marker beacon signal to be detected approximately one mile before passing over the beacon. At this point, if you had HI sensitivity selected, you would want to switch to LO sensitivity. A word of caution concerning the TST button. Bendix King notes that the TST button should not be pushed when the autopilot is coupled on an ILS approach. Some autopilots, including Bendix King models, use the marker beacons to change the sensitivity of the autopilot. Next to the “O” marker beacon lamp is a photoelectric cell which controls the brightness of the marker beacon lamps.
3. TEL – controls audio for a radio telephone. Alternately some KMA 24 audio panels replace the TEL function with HF, for operation with a high frequency transceiver. Note that this function, either TEL or HF, must also be selected on the rotary knob on the right side of the audio panel.
4. 1 COM – controls audio received from COM 1 communications radio. Again, the top row button directs output to the aircraft speaker, and the bottom row button directs it to your headset.
5. COM 2 – controls audio received from COM 2 communications radio.
6. 1 NAV – controls the audio received from the NAV 1 radio. This includes any weather information, such as HIWAS as well as the Morse code IDENT. Many nav radios have a switch on the radio for IDENT. This must be selected in addition to selecting either speaker or headset for the audio.
7. NAV 2 – ditto for the NAV 2 radio.
8. DME – allows you to hear the Morse code identifier for any DME that is co-located with VOR or localizer stations. Most DME receivers have the ability to enter a frequency separately from the nav radios. However the most common method of operation is to remote the DME receiver to either nav 1 or nav 2.
9. MKR – allows you to hear the marker beacon audio signals.
10. ADF – allows you to hear the Morse code identifier of an NDB station. During an NDB approach, most instructors teach their students to keep the Morse code identifier for the NDB on during the entire approach to verify integrity of the signal. Unlike VOR receivers, ADF receivers do not display an OFF flag, so the Morse code is the only way to ensure the data being received by the ADF receiver is valid.
11. AUTO – this is probably the most confusing button for pilots when they first work with the audio panel. The rotary switch on the right side of the KMA 24 can be set for either COM 1 or COM 2. The rotary switch controls the transmission frequency. So if you have COM 1 selected with the rotary switch, when you push the transmit button, you are transmitting on COM 1. The AUTO button allows you to automatically slave the received audio information to whichever frequency you have selected with the rotary switch. By pressing the AUTO button in the bottom row (headset), you will automatically hear the transmissions from either COM 1 or COM 2, depending on which one has been selected by the rotary switch. So with AUTO selected, you may switch back and forth between COM 1 and COM 2 with the rotary switch without having to reselect COM 1 or COM 2 using the push buttons. If you desire to hear audio from the other com radio, you may do so by simply pressing the appropriate button for either speaker or headset. For example you are listening and transmitting on COM 1 but would like to listen to ATIS at the same time. You may do this by putting the ATIS frequency in COM 2 and pressing the COM 2 button for either speaker or headset. Warning – it can be confusing to try to listen to two frequencies at the same time.
12. The rotary switch on the right side is used to select the desired transmitter for the cockpit microphones. COM 1 and COM 2 have been previously discussed. The INT position selects cabin intercom. This allows the crew to address the passengers over the cabin speaker. The EXT position allows the crew to address people on the ramp through an external ramp hailer speaker, if one is installed.

In putting this discussion together, I found a good pilot guide to operation of the KMA 24 audio panel on the Bendix King website. It is a downloadable pdf file, and the web address is

Pilot Guide to the KMA 24 Audio Panel

Goodbye old WINGS, hello new WINGS

The old Wings safety program that we all knew is now officially gone. This has come as a shock to many pilots who relied on it for their flight reviews. In its place however is a new and improved version of the program, one that addresses some of the issues and shortcomings of the old program.

The new WINGS is a web-based program that tracks your training and promotes personal proficiency. The old WINGS program was time based; go to an FAA safety seminar and do the three hours of training. No standard of proficiency was specified. The new WINGS program is based on both knowledge and proficiency. It is modeled on consistent recurrent training to PTS standards, a paradigm that has proven successful in both airline and corporate flying. As with the old program, it is entirely voluntary. In order to participate, you need to have a pilot license and a current medical. Student pilots may participate in the program, but they will not be able to receive credit for training.

Training is broken down into three phases — basic, advanced and master. Completing the requirement for the basic phase will count as a flight review. Within the phases there are core elements and elective elements. Completing the requirements for the basic phase constitutes a flight review.

How do you, both flight instructor and pilot, participate in the new WINGS Pilot Proficiency Program?

• Go to the website (FAASafety.gov) and register. You must hold an FAA license and a current medical.
  
• Complete the pilot profile for the type of training you wish to do. This does not necessarily have to reflect your certificates. It may be tailored to the type of flying you do.
  
• Complete the required and elective training requirements.
  
• Submit your completed credits for validation.
  
• Use the system to track your proficiency.
  

As with the old system, you must fly with an instructor in order to complete your training. Both the flight instructor and the pilot must be registered in order to obtain credit. If the flight instructor is not registered, the flight training must be verified by a registered instructor.

The instructor doing the training must put an endorsement of training in the pilot’s logbook.

“I certify that [pilot], holder of pilot certificate number [number], has satisfactorily demonstrated proficiency in all tasks as outlined in the WINGS Pilot Proficiency Program activity course number [number] on [date].
Name, certificate number, date, signature”

I have made it my goal to do my flight review, which expires in May, by working my way through the Basic phase of the new WINGS Pilot Proficiency Program. This should give me a much better understanding of the program, and I am looking forward to doing it.

Substituting GPS for DME and ADF

I work with a lot of plane owners, and I have found the trend is to install an IFR GPS and skip having a DME in the plane. After all, the IFR GPS can be used in place of DME – right? Yes it can, but you had better have a clear understanding of how that substitution is to be done if you want to stay squeaky clean with the FAA.

The 2007 AIM, section 1-1-19 has information that every pilot flying with an IFR GPS should take the time to read. Specifically 1-1-19(f) talks about the substitution of an IFR GPS for DME or ADF. Before jumping into this discussion, it must be noted that your GPS must have a current database card.

Let’s look at the DME requirements first. Let me offer a caveat up front. I confess to having a difficult time following the AIM numbering scheme. Having said that, I will jump into this discussion, hoping I have the numbers right.

The first point to note is in AIM 1-1-19(f)(5). It says that in order to use the GPS for DME, the course deviation indicator (CDI) must be set to terminal sensitivity. This is normally 1 nm full-scale deflection. In most situations, the GPS receiver will already be in terminal mode. However, if it isn’t, then you will need to manually select terminal mode. To do this with the Garmin 400-500 series, go to the Aux 3 page and select CDI/Alarms.



This will allow you to manually select the CDI sensitivity. Select the 1.00 nm scale.



The caveat here is that you must not forget to restore it to AUTO once you no longer need it forcibly set to 1.0 nm sensitivity.

To manually select the CDI scale for the KLN89B, go to the NAV1 page. Turn the cursor on. Position it on the CDI Deviation Indicator and press CLR until it says CDI scale. Use the small knob to select the 1.0 nm sensitivity (ARM mode). Press CLR to return the display to the CDI Deviation Indicator and turn the cursor off. When the KLN89B is in Approach mode, it is not possible to select a less sensitive scale that the current one. The default sensitivity is 5.0 nm. Unlike the Garmin units, there is no AUTO mode.



The KLN94 CDI sensitivity is selected in the same manner. For both the Garmin and the KLN units, if the sensitivity has been manually set to 1.0 nm, the unit will go to a more sensitivity setting (approach mode), but it will not go to the enroute sensitivity (5 nm) until it has been reset to AUTO (Garmin) or 5.0 nm (KLN).

AIM 1-1-19(f)(c)(2)(b) talks about using GPS to fly a DME arc, and this is the one that is probably most frequently violated, albeit unintentional. It says, in part, with the boldface type from the AIM itself:

“You must select from the airborne database the facility providing the DME arc as the active GPS waypoint.
Note: The only acceptable facility is the DME facility on which the arc is based. If this facility is not in your airborne database, you are not authorized to perform this operation.”

What that means is you can’t just merrily load the approach and fly the arc using the Map page display and the suggested headings provided by the GPS, sequencing along from waypoint to waypoint. You have to keep the DME facility as your active waypoint. It is generally possible to do this and keep the waypoints, including the arc, visible in your Map display.

Let’s look at the VOR/DME-27 into Anoka (KANE) as an example of how to do this.





This approach incorporates a couple of different examples of using GPS for DME. To get started, let’s examine the use of the GPS to fly the DME arc. The first step in doing this is to load the approach into the GPS. By loading the full approach into the GPS, we get most of the waypoints as well as the arc displayed on the Map page. Also note that the GPS is in terminal mode sensitivity.



The problem however is that GEP, the facility that provides the DME information, is not the active waypoint. It is however the MAP waypoint for the hold. We can make it the active waypoint by going into FPL0, highlighting GEP and doing a DIRECT-TO.




By doing this, we still have the waypoints displayed on the Map page, but we have now satisfied the requirement to have the DME facility as the active waypoint. The arc can be flown using the Map for positional awareness and the waypoint distance to keep us within the proper arc distance.



Turning inbound on the final approach course, we are in VLOC mode and GEP is still the active waypoint. Now that we are no longer on the arc, we can go back to using the GPS waypoints. AIM 1-1-19 f(c)(1)(b) states:

“If the fix is identified by a five-letter name which is in the airborne database, you may select either the named fix or the DME facility as the active waypoint.”

This means that the fixes in the approach (TOURI, VOR10 and RW27) may be used in lieu of GEP and the DME distance.



By going to PROC and selecting Activate Vectors-To-Final, we can replace GEP with TOURI, the FAF, and start waypoint sequencing again. But be forewarned; because this is not a GPS approach, you must leave the CDI in VLOC mode so that guidance is being provided by GEP.





Now let’s look at another approach that might trip the unwary user depending on GPS to substitute for DME. Consider the ILS-27 into Anoka.



The trap here lies in the localizer-only approach. If you load this approach from the GPS database, the step-down fix KOGGE will not be one of the waypoints in the approach. This means that you must rely on DME to identify this fix, but the facility providing the DME is the localizer, I-ANE, rather than a VOR. You can get the proper DME distance by doing DIRECT-TO IANE in your GPS. Both the Garmin and the KLN units think IANE is an intersection, but it does give you the proper DME distance for a localizer-only approach. I did talk to Jeppesen about this approach. They do not include waypoints for step-down fixes for localizer-only approaches. However Jeppesen indicated there is some thought as to possibly including them in the future.

When substituting GPS for an ADF, it is not so detailed on instructions. The AIM says the NDB must be selected from the database and the receiver must be in terminal sensitivity. This might lead you to believe you can fly a pure NDB approach using the NDB as the active waypoint in the GPS and placing the unit in OBS (non-sequencing mode). Take the case of the NDB-28 approach for Osceola (KOEO).



By now you are probably asking yourself why would anyone choose to do this when there is a GPS-28 for Osceola? Well, for quite a while there was indeed an approach plate for GPS-28/OEO but there was no corresponding GPS approach in the database. Why? Because of a runway extension, the GPS-28 approach was NOTAM’ed as NOT AUTHORIZED. In this case, you had only one choice – the NDB-28. So trying to conform to the guidelines in the AIM, the NDB-28 approach is loaded. But now you run into yet another problem. AIM 1-1-19 (f)(b)6) says:

“Charted requirements for ADF and/or DME can be met using the GPS, except for use as the principle instrument approach navigation source.”

Now the conundrum – that ancient ADF receiver in your plane hasn’t worked in years. And even if it did work, you know that loading OEO into the GPS as the active waypoint, putting the receiver in OBS mode, and forcing it to terminal sensitivity is going to do a far better job of getting you into Osceola than that old ADF receiver. But unfortunately the AIM seems to say the FAA doesn’t see it that way.

This basically means that you can hold over a compass locator or NDB using GPS, and you can use it to identify a compass locator on an ILS or LOC approach. Returning to the ILS-27 into Anoka, the primary holding fix is GEP. But there is an alternate holding waypoint at the PNM NDB, which is about 30 nm northwest of Anoka.




You can use GPS to substitute for ADF in doing this hold. Again, the receiver must be set to terminal sensitivity. At the MAP waypoint for the ILS-27 into Anoka, the GPS receiver stops sequencing and waits for instructions from the pilot. If you press OBS on the Garmin units, it automatically brings up the waypoint for the published hold, which in this case is GEP. However you don’t want to go to GEP. So instead press DIRECT-TO. The GPS will display the waypoint for the published hold in the DIRECT-TO dialogue box, with the cursor on. All you have to do is put in PNM for the desired waypoint. The DIRECT-TO works on the KLN units as well.



So now you can head off to Princeton (KPNM) and enter the alternate hold. You can either do it by placing the GPS in OBS mode and flying the hold with raw data, so to speak, or you can load the NDB-15 approach at Princeton (KPNM) and go to PNM for the missed approach, since it is the same hold. Personally I would opt for the latter, since it depicts the hold.



To summarize substitution of an IFR GPS for DME and/or ADF:

• Current database card
  
• For use on a DME arc, the active waypoint must be the facility providing the DME
  
• For DME waypoints (other than an arc), if the DME waypoint has an associated name in the database, you may use the database waypoint. If not, the waypoint must be identified using the DME facility as the active waypoint
  
• The GPS may substitute for an NDB or compass locator except if it is the primary navigation source for an instrument approach
  
• For use in lieu of both DME and ADF, the GPS must be in at least in terminal sensitivity (1 nm)
  

So now you have the nuts and bolts of substituting your IFR GPS for DME and/or ADF. Find a friend and go practice this ahead of time. Or better yet, find a good sim with a GPS and go practice these skills. Flying in the soup with a controller issuing rapid-fire instructions is not the time to be figuring out which buttons you need to push to substitute your GPS for DME or ADF.