Chapter 12: Advanced Functions of X-Plane for the iPhone and iPod Touch
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Flying an Approach Using the Instrument Panel
All of the airplanes in the mobile X-Plane applications have basic navigation radios and instruments built into them, and all of these are used in more or less the same way. We will go through an example for flying an ILS approach (that is, an approach using an instrument landing system) in the Southern California region in the X-Plane 9 and X-Plane Airliner applications, but similar steps can be used for any airport in any application.
Note that instrument navigation is not for the faint of heart. X-Plane Mobile is as realistic a flight simulator as possible, and navigation is no exception. This section is by no means a complete guide to airplane navigation (there are plenty of 400-page books available that claim that), but it will go into quite a bit of detail. We will discuss a great deal of side information needed to fly all approaches, but we will always come back and relate it to flying the example approach into San Bernardino International (found in the Southern California region of X-Plane 9 and X-Plane Airliner).
Note: This chapter assumes prior familiarity with the workings of the view options and the Settings menu, as well as with the standard flight instruments. All of this is described in Chapter 2 of this manual.
To fly an instrument approach, users will first need to know the local navigational aid (NAVAID) frequencies. To find this, tap the center of the screen to make the various menu options appear, then click the Settings button (highlighted in red in the image below).
The map in the window that appears shows the ILS, LOC, VOR, and VORTAC frequencies for the area. Zoom in and out of the map by placing two fingers on the screen and dragging them farther apart (to zoom in) or closer together (to zoom out). To pan the map, place one finger on the map and drag it, and to rotate it, place two fingers onto the map and twist them in a circular motion.
Let's discuss the specifics of each of these types of navigational aids (NAVAIDs)
Types of NAVAIDs
The earliest type of navigation modeled in X-Plane Mobile is based on VOR signals (that is, signals from a Very high frequency Omnidirectional Range transmitter). VOR transmitters work by sending a series of 360 discrete little carrier tones on a main frequency. Each of these carriers is oriented along a different radial from the station, one of 360 just like on a compass rose. Thus, when one is flying along and tunes in the main VOR frequency, one then fine tunes the navigation display to tell which of the 360 radials the aircraft is flying and also whether the transmitter station is in front of or behind the plane.
In the X-Plane Mobile maps, a VOR beacon is labeled as in the following image.
A specific type of VOR, a VOR-DME, combines the lateral guidance (that is, guidance left and right) of a VOR with the distance guidance of a DME (distance measuring equipment). In X-Plane Mobile, this is labeled as in the image on the following page.
Another type of VOR beacon, a VORTAC, is also found throughout the X-Plane maps. This is a transmitter that combines both VOR and TACAN features. TACAN (or tactical air navigation) provides special information to military pilots similar to a civilian VOR. However, for our purposes, this is functionally identical to a VOR-DME. A VORTAC in X-Plane is labeled as in the following image.
A LOC (or localizer) transmitter provides guidance to the centerline of a runway. It works by sending out two signals on the same channel, one of which modulates at 90 Hz and the other of which modulates at 150 Hz. One of these signals is sent out slightly to the left of the runway, while the other sent out slightly to the right of it. If an aircraft is picking up more of the tone modulated at 150 Hz, it is off to the left. If it is picking up more of the tone modulated at 90 Hz, it is off to the right. The course deviation indicator (or CDI) in the instrument panel then indicates this so that the pilot can correct it. When both tones are being received in equal amounts, the craft is lined up with the physical centerline of the runway. In X-Plane Mobile, a LOC transmitter is marked as in the image below.
An ILS (or Instrument Landing System) combines the functionality of a localizer, which provides lateral guidance, with a glideslope transmitter, which provides vertical guidance to the runway. The glideslope beacon functions similarly to the localizer, sending out two tones that have the same frequency, but different modulations. The difference is that the glideslope tells the plane that it is either too high or too low for its distance from the runway. The pilot uses this information to push the craft's nose up or down as needed. The ILS will allow a pilot to fly on instruments only to a point that is a half mile from the end of the runway at 200 feet (depending on the category of the ILS) above the ground. If the runway cannot be clearly seen at that point the pilot is prevented from executing a normal landing. If this happens, the pilot in real life is required to fly a "missed approach" and climb back to altitude in order to try again or go somewhere else.
In X-Plane Mobile, an ILS transmitter is marked as in the image below.
For our example approach, we’ll be flying into San Bernardino International Airport (KSBD, found in the Southern California region). Zooming into the map screen near this airport shows that the ILS signal is coming from runway 06 (as seen in the image at the top of the following page). Not coincidentally, there is a button here in the map screen to put the aircraft on a final approach to this runway. As seen in the screenshot below, the frequency we need to tune for KSBD's runway 06 is 109.30.
Navigation Instruments
Before we begin, let’s review the instruments used in navigation. This section assumes familiarity with the panel view as described in Chapter 2.
Instruments in the Piston-Engined Aircraft
The image above is the panel view in X-Plane's piston-engined aircraft (that is, the craft with propellers) after scrolling down to view the navigation radios. The omni-bearing indicator (or OBI—the most important instrument in navigating approaches like this) is marked with a 1. The broken yellow arrow going across its face is called the course deviation indicator (or CDI). Each end of the CDI touches the directional gyro, which serves the same function as a compass. The yellow rectangles on the outside of the directional gyro are the glideslope indicators. We'll discuss the OBI more in a moment.
Below the OBI are the navigation radios. The NAV 1 radio is marked with a 2 in the image above, and the NAV 2 radio is marked with a 4. Between the two is the navigation source selector switch (marked with a 3).
To navigate using any of the previously listed NAVAIDs (VOR, LOC, ILS, etc.), that NAVAID's frequency must first be tuned in to one of the navigation radios. It doesn't matter which radio is used as long as it is selected with the source selector switch. The two knobs on each radio are used to tune them. The knob on the left is used to tune the integer (or "counting number") portion of the frequency. The knob on the right is used to tune the decimal portion of the frequency.
For instance, imagine we want to fly the ILS into San Bernardino International airport using the NAV 2 radio below.
Above, we found that the KSBD ILS is transmitting at 109.30 Hz. Of course, we could use the NAV 1 radio that's already tuned to that frequency, but that would defeat the purpose of the example!
To tune the NAV 2 radio down to 109.30 Hz, we will first tap below its left knob six times. This will bring the frequency to 109.20. From here, we'll tap above its right knob twice, bringing it up to the required 109.30.
With that done, we need to make sure the navigation source selector switch is set to the radio we want to use. In the previous image, it is set to NAV 1. We will tap it once to switch it over to NAV 2. At this point, we are all set to fly San Bernardino International's ILS using our NAV 2 radio.
With the navigation radio set, assuming we are on an approach to the ILS we just tuned (which can be done using the KSBD 06 Final button found on the Map screen), the CDI should begin to move. Remember that the CDI (course deviation indicator) is the broken yellow arrow found in the OBI.
For instance, in the image at the top of the next page, the center bar of the CDI has moved to the left of the rest of the arrow. This indicates that the aircraft has moved to the right of the localizer course (recall that the localizer portion of the ILS is responsible for guiding the craft left and right). To get back on course, the aircraft needs to turn left—in other words, it needs to follow the line on the CDI.
Also note the glideslope indicators, the two rectangular yellow bars along the outside of the heading indicator. They are rather high above the center of their travel in the image above. In order to stay on the glideslope, the aircraft will need to pull its nose up—in other words, it needs to follow the glideslope indicators. When those rectangular yellow bars are in the center of their travel, the craft is right on course.
Let's talk about the OBS, the omni-bearing selector. In the image at the top of the next column, this is the knob with a red box around it. This knob is used to turn the CDI to point to a specific heading.
For example, if we looked at a navigational chart for San Bernardino International Airport (or use an airport database like AirNav), we would see that runway 06 that we're flying into has a magnetic heading of 057. It would be a good idea to use the OBS to turn the CDI so that it points at 57 (or a little less than 60) on the directional gyro. That way, when the craft was directly on course, the CDI would be pointing straight up.
Tap above the OBS to turn it clockwise, and tap below it to turn it counterclockwise.
That's all the knowledge required to begin flying an instrument approach in a piston-engined aircraft. Let's now discuss the instruments used in jet-engined craft. Users not interested in the jets should skip ahead to Flying the Approach.
Instruments in the Jet-Engined Aircraft
The image above shows the panel view as seen in X-Plane Mobile's jets. The attitude indicator is marked with a 1. In addition to displaying the aircraft’s pitch and roll attitude, this instrument combines functionality from the horizontal situation indicator, or HSI. For our purposes, the HSI serves the same function as the OBI in the piston-engined aircraft panel; it simply displays the information differently.
The course deviation indicator (CDI) portion of the HSI is represented by the vertical purple line in the image above. It is in the center of the attitude indicator, meaning that the aircraft is lined up almost perfectly with the physical centerline of the runway. The glideslope indicator portion of the HSI is represented by the horizontal purple line. In the previous image, the line was a bit above the aircraft's nose, indicating that the craft needed to pull up slightly in order to intercept the glideslope.
Below the attitude indicator is the directional gyro. This, like the CDI and glideslope indicator, is normally a part of the HSI. In the interest of conserving screen space, the CDI and glideslope indicator have been moved to the attitude indicator. This leaves room on the screen for about a third of the directional gyro to be visible.
The directional gyro works like a compass in that it indicates the aircraft's heading. For instance, in the image below, the craft had a heading of 059 (note that the arrow is pointing just a little to the left of the six, representing 060).
If we looked at a navigational chart for San Bernardino International Airport (or use an airport database like AirNav), we would see that runway 06 that we're flying into has a magnetic heading of 057. This means that, according to the previous image, we are pointed two degrees to the right of the runway.
In the image above, the panel's moving map is marked with a 1. The green bar on this map is identical to the yellow CDI from the panel of the piston-engined aircraft. Because it performs the same function as the CDI in the jet panel's attitude indicator (and because its function was described in the piston-engined section above), we won't describe it here.
Important to note, though, are the light blue airports indicated in this map (for example, L67, KSBD, and L12 from the image above). The locations of these airports are shown relative to the aircraft, which is represented as the white triangle in the center of the map.
Localizers are represented on the moving map as triangles for pilots to fly down. Recall from prior in this chapter that a localizer provides the lateral (left and right) guidance in an instrument landing system (ILS).
When flying a localizer, the pilot starts at the widest part of these triangles. The center line of the triangle is the desired course and the right and left edges correspond to full scale right and left deflections of the course deviation indicator. This means that this is the width that one could fly to either side of the CDI's center line and still get accurate guidance. The path comes to a point at the end of the approach (corresponding to the end of the runway). Consequently, it gets much more difficult to stay on course at the end of the approach because a very small deviation off course will give the pilot a full scale deflection on the CDI. So, pilots fly into the fat part of the arrow and, hopefully, right down the center line, keeping the CDI centered the whole time by making progressively smaller and smaller corrections left and right to keep the needle centered.
Additionally, note that the knob labeled 2 in the image above (marked OBS) provides the same function as the OBS in the piston-engined aircraft. In this case, it will rotate the green CDI found in the moving map to line up with whatever heading the pilot specifies—for our example approach to San Bernardino International, we would want it pointing a little to the left of the 6 found at the top of the map (for a heading of 057).
Finally, the knob marked 3 in the image above controls the level of zoom in the moving map. Tap to the left of it to zoom in, or tap to the right to zoom out.
As the navigation radios work identically in the jet-engined aircraft as in those with piston engines, we will not describe them again here.
Flying the Approach
Now that we've discussed the different types of NAVAIDs in the mobile X-Plane applications, as well as how to use the navigation instruments in all the aircraft, let's begin flying the actual approach.
For our example instrument approach, we'll be flying into San Bernardino International Airport (KSBD), which is found in both X-Plane Airliner and X-Plane 9. It is near the northeast corner of the Southern California region. According to the map (shown in the following image), KSBD has an ILS navigation system. This means that an instrument approach to the airport can take advantage of both horizontal (left and right) and vertical (up and down) guidance, thanks to the ILS's localizer and glideslope beacon, respectively. The map shows that the ILS frequency for runway 06 is 109.30.
For simplicity's sake, rather than taking off from one airport and flying to San Bernardino, press the Final button for KSBD runway 06 (marked with a red box in the image above).
Now that we're on the approach, select the instrument panel view. Slide the panel up using your finger to see the NAV (navigation) radios. Tune one of the radios to the desired ILS frequency (in this case, 109.30). Make sure that the radio that was tuned is also selected with the navigation source selector switch. For instance, if the NAV 1 radio is tuned to 109.30, the source selector also needs to be pointing to NAV 1.
In the real world, we would look at an approach plate to determine what heading we should be flying to get to the runway. As not everyone has a set of approach plates for southern California, the AirNav database can be consulted for the heading. Scrolling down on that web page to the Runway Information section reveals that Runway 06 has a magnetic heading of 057. Additionally, the page lists the runway's elevation as 1084.6 feet above sea level. This information will become very important once we get close to the runway, for obvious reasons!
With this information, click above or below the OBS knob until the CDI is pointing to 057 degrees, as shown in the images below. On the left is the OBI in the piston-engined aircraft, and on the right is the moving map in the jets. While this step is not absolutely necessary, it does make it easier to follow the CDI.
Note that in the images above, the CDI (a yellow arrow in piston-engined craft, green in jets) is pointing just a little to the left of the "6," denoting a heading of 060.
At this point, the CDI will begin to wander left or right to indicate which direction the craft needs to move in order to point down the centerline of the runway. Aim toward the deflection to intercept the localizer course; when the CDI wanders right, point the aircraft's nose right, and so on.
Additionally, the glideslope indicator will begin to move. If its needles are above the center of the instrument then the craft needs to fly up, and if they are below the center of the instrument, it needs to fly down to intercept the glideslope. The goal is to keep the localizer CDI centered to stay on the localizer, and the glideslope CDI centered to stay on the glideslope.
For example, in the image below, the CDI is deflected a little to the left (indicating the craft needs to turn to the left) and the glideslope indicators are quite high (indicating that the aircraft needs to raise its nose a good deal).
In the image below, the CDI is deflected to the right (indicating the aircraft needs to bank to the right) and the glideslope indicator is high (indicating the craft needs to raise its nose).
Follow the guidance of the localizer and glideslope until the craft reaches an altitude of about 300 feet above the runway. Remember from when we looked up the runway information on AirNav that its elevation is 1084.6 feet; therefore, our key altitude will be 1385 feet. When the aircraft's altimeter reads 1385, tap the center of the screen and select the HUD view.
At this point, if everything was done correctly, the runway will be right in front of the aircraft. If the landing itself was managed properly, the aircraft will be its stalling speed plus 30% with the gear and flaps down (remember that gear, flaps, and throttle are still visible in the panel view) as it comes in for a landing. In the Cirrus Vision, this is about 90 knots. In the Cessna 172, it's about 65 knots, and in the Boeing 747, it's about 140 knots.
Using the Autopilot
The autopilot is one of the most asked about features in X-Plane—indeed, in real world planes, too. The fact is that many real aircraft owners never take the time to learn to use their autopilots. The basic autopilot functions available in the mobile X-Plane applications, however, are really not too difficult to understand once the user has taken the time to learn about them.
In a real aircraft, there are three levels of autopilot functionality:
- Off, with no autopilot functions active,
- On, where the autopilot servos take over the flight controls and fly the airplane, and
- Flight Director, where the autopilot displays a set of "wings" on the attitude indicator to show the pilot where to fly.
If the pilot follows the flight director wings perfectly, the airplane will behave just like when it has the autopilot servos on. If the pilot does not follow the wings, it will be as if the autopilot were off completely.
The X-Plane Mobile applications do not have this flight director mode. Therefore, whenever the autopilot is switched on (using the switch at the top of the panel view, highlighted in the following image), it will automatically take control of the flight controls.
Available Autopilot Functions
The following functions are available in many of the X-Plane Mobile aircraft, including most of those with jet engines.
ROLL and PTCH
These are the roll and pitch hold modes, respectively. When the autopilot is switched on, these two are turned on automatically. They will hold the current roll and pitch attitudes of the aircraft. For example, if the craft has its nose pitched down ten degrees and is in a five degree left bank when the autopilot is switched on, ROLL and PTCH modes will hold this ten degree down, five degree left attitude. These modes are shown in the following image.
ATHR
This is the auto-throttle button. When this button is pressed, the autopilot will attempt to maintain the craft's current airspeed by increasing or decreasing the throttle. It will not, however, attempt to control the craft's speed using any other method, such as pitching the nose up or down or adding or subtracting flaps. Therefore, the auto-throttle will be able to put the throttle anywhere between its maximum or minimum, but it will not be able to maintain an excessively high or low airspeed (such as one obtained by pitching the nose excessively low or high).
The ATHR is turned on (as indicated by its button being lit yellow) in the following image.
In the image above, the auto-throttle is set to hold 108 knots (indicated by the number in green located above the ticking airspeed tape). The craft's current airspeed is 101 knots, so the craft will keep increasing the throttle until it gets closer to 108 knots.
With the ATHR button pressed, the other autopilot functions can be disengaged by turning the autopilot power switch to off. This allows the pilot to pitch and roll the craft freely while the auto-throttle maintains the same speed.
Also, note that when auto-throttle mode is engaged, it will start the throttle at its minimum, then slowly bring the throttle up to the point where it holds the selected airspeed. This results in a drop of around ten knots when the AHTR button is first pressed, but this drop in speed is not permanent.
HDG
This is the heading hold button. Pressing this button will set the autopilot to follow the heading currently displayed on the directional gyro (recall that the directional gyro is the partial circle found at the bottom of the left EFIS display). It will follow this heading by rolling the aircraft left and right. For this reason, when the HDG button is pressed, heading hold mode will replace roll hold mode.
For instance, in the image below, the HDG button was pressed when the craft was pointed at heading 314 (indicated by the number in green by the directional gyro). Since a heading of 270 is due west, and a heading of 360 (or 0) is due north, the autopilot will be flying the aircraft northwest.
HOLD
This is the altitude hold button. Pressing this button will cause the autopilot to hold the current altitude by pitching the nose up or down. This mode automatically replaces pitch hold mode.
For instance, in the image below, the HOLD button was pressed when the craft was at an altitude of 24,730 feet (indicated by the number in green above the ticking altitude tape). Since the craft is currently at an altitude of 24,850 feet, the autopilot will gently (and momentarily) nose the craft down before leveling off.
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