During an IFRIFRDefinition: Instrument Flight Rules...
flight, there are specific procedures to allow having a safe flight in all its stages.
Such procedures are:
SID
SID (Standard Instrument Departure) is the published procedure which the pilot must follow immediately after takeoff from an airport. SID is a coded procedure by which the pilot can reach the exit point of an airport's TMATMADefinition: Terminal Manoeuvring Area...
shortly after takeoff, based on the avoidance of obstacles, noise reduction (if necessary) and the overall traffic of the area.
A standard departure procedure involves a series of waypoints, which are defined by either geographic coordinates or by some navaids as VORVORDefinition: VHF Omnidirectional (Radio) Range...
and NDBNDBDefinition: Non-Directional (Radio) Beacon...
. It also includes a climb profile that must be followed by the pilot when passing through these waypoints. SID procedure ends at a waypoint on an airway which will be followed by the pilot in accordance with his flight plan. In each case the standard departure procedure can be overridden by the controller, by giving the pilot vectors to reach the endpoint.
At each airport, there are often several SID procedures, so every one of them has its own name. In most cases, especially in Europe, their names are based on the endpoint of the procedure which is the exit point from the TMA of the airport, usually followed by a number and a letter. The number indicates the serial number in a total of different procedures and the letter indicates the runway by which the pilot will takeoff.
STAR
STAR (Standard Terminal Arrival Route) is the published procedure which the pilot must follow after passing the last waypoint of his flight plan and ends by reaching the IAFIAFDefinition: Initial Approach Fix...
, which is the starting point of the approaching procedure for landing.
A typical standard terminal arrival route procedure does not differ much from a SID, as it also contains waypoints defined by geographical coordinates or by navaids VORVORDefinition: VHF Omnidirectional (Radio) Range...
and NDBNDBDefinition: Non-Directional (Radio) Beacon...
. It also contains a descent profile that pilot must follow when passing through these waypoints.
STAR procedures are not present on all airports. They mostly exist in large high-traffic airports or airports with difficult approaches eg to those located among mountains.
For each airport, there are various STAR procedures, depending on the entry points to the TMATMADefinition: Terminal Manoeuvring Area...
and airport's available runways. Their names differs from country to country. In Europe, their names are according to the name of the waypoint which the procedure begins, then followed by a digit, depending on the total number of those who have a common starting waypoint and a letter indicating the landing runway.
HOLDING
During the procedure of a holding pattern, an airplane is circling over an area in order to hold its position. Several times, ATC needs to keep some airplanes in a holding pattern due to heavy traffic and separates them in accordance with the requirements of the airport. Another reason that a pilot is forced to execute a holding pattern is to lose altitude, when he has such an altitude that he cannot follow the descent profile. In many cases the holding procedure can be contained in another IFR procedure eg a VOR/DME or an ILS approach.
Holding pattern procedure is always based on a holding fix. This fix may be a navaid such as VORVORDefinition: VHF Omnidirectional (Radio) Range...
or NDBNDBDefinition: Non-Directional (Radio) Beacon...
. It can also be any fix in area that is defined by a specific distance and radial from a VOR or a fix point with specific coordinates that can only be used by airplanes with a GPS system. Holding fix is the beginning of the holding procedure so it's the fix from which the aircraft should be pass to enter the holding pattern. simultaneously is the exit point of holding procedure.
Holding Execution
A holding procedure consists of 4 phases. Two turns of 180 degrees and two parallel straight legs. It may also be clockwise (standard holding pattern) or counterclockwise. When the airplane passes the holding fix, it must perform the first turn, then a straight leg (outbound), followed by the second turn and finally a straight leg (inbound) until the holding fix. Note that the turns are always in standard rate turn. The holding pattern is defined by whether it is clockwise or counterclockwise, the holding fix and the course of the outbound leg. A very important factor for the execution of the procedure is the execution time of each leg. Each standard rate turn lasts one minute. So the difference between holding patterns is the time of the inbound and outbound legs. In a standard holding pattern execution time is one minute, but this can also last longer period of time depending on the speed, the airplane type and the requirements of each procedure. In some cases holding procedure can be defined by distance and it's defined by how many miles the pilot will fly the inbound and outbound legs.
Holding Entry
An important parameter of the holding pattern, is the entry way that the pilot should select in order to enter the procedure. There are three entry ways available, Direct, Teardrop and Parallel. Choosing the right way depends on the current direction of the airplane when reaching to the holding fix.
Direct Entry
With direct entry the pilot all he has to do is to pass the holding fix and then to continue the procedure by turning and follow the outbound leg.
Parallel Entry
When the pilot must choose the parallel entry, he should pass the holding fix and then continue flying parallel the inbound leg but having the outbound course. Continues for one minute and then turning to the protected area of the holding pattern by turning again inbound to the holding fix. Then he starts executing normally the holding pattern procedure.
Teardrop Entry
With the teardrop entry, when passing the holding fix, we turn at a 30 ° angle difference from the outbound leg, left or right but always to the protected area of the holding. After a minute we start turning to follow the inbound leg.
Choosing Holding Entry
There are several methods for the pilot to choose the entry way. We will describe an easy one, to avoid be distracted while you have other more important issues in the cockpit. Please note that this method is based on the case that we fly to the holding fix. We don't need to use pencil and paper, we just have to advice the heading indicator. We draw an imaginary line with our fingers on the instrument, which performs an angle of 70 degrees with our course. Starting from the top right side of the instrument, when it's clockwise (figure A) and left when it's counterclockwise (figure B). For more convenience you can use a pen. We observe that along the line of our course, our instrument is divided into three sections. If we know which is the outbound course of holding all we need is to look in which section belongs.
Examples:
Α. We perform holding pattern clockwise with outbound course 90 degrees. If our heading is 20 degrees, basis of figure A, if we put 20 in the head, we see that 90 is in the area of direct. So we will enter holding pattern with direct entry.
Β. We fly with heading 220 and we should go into counterclockwise holding pattern with outbound course 200. Based on figure B and putting heading 220, we see that 200 is in red area so we have to perform teardrop entry.
However, the best way is the one that works best for us and one that we are most familiar with. Please also note, some limitations on the speed with which we perform a holding pattern (Applies to U.S. civil aviation).
- Up to 6000ft MSLMSLDefinition: Mean Sea Level...
the MHSMHSDefinition: Maximum Holding Speed...
is 200 KIASKIASDefinition: Knots-Indicated Air Speed... - From 6000ft up to 14000ft MSL the MHS is 230 KIAS
- From 14000ft MSL and above the MHS is 265 KIAS
ARC DME
ARC DME is each circular route that an airplane makes while flying, with constant radius and centered on a waypoint VORVORDefinition: VHF Omnidirectional (Radio) Range...
or NDBNDBDefinition: Non-Directional (Radio) Beacon...
. ARC DME may be part of the approach or the departure from an airport. The characteristics of the ARC route that a pilot has to execute, are contained in the published charts of the relevant airport. To be able to have an ARC DME, it is of course necessary the present of a DMEDMEDefinition: Distance Measuring Equipment...
instrument together with the navaid which is involved.
In execution of this procedure is necessary for us to know : The navaid located in the center of the procedure and its frequency, the radius of the ARC that we will fly in nautical miles, the altitude that we should have and the entry and exit points. The entry and exit points, usually are defined by specific radials. To enable the pilot to perform an ARC / DME, the airplane should be equipped with VOR and DME indicators. The protected area of an ARC / DME is 2 nm from both sides of the course, however it's recommended for the pilot to remain in a range ± 1 nm.
ARC/DME Execution Methods
Let us now try to understand the two ways in which we can execute successfully an ARC / DME procedure. There are various techniques to enable you to carry out such a procedure. The best way is always the one that suits us best.
So let's put a hypothetical scenario ( Figure 1 ) executing an ARC around the VOR KRK at Corfu airport (LGKR). Coming from the waypoint PITAS with course 155, we should join the ARC / DME (16 nm) until the radial 268 where we have to turn to the VOR.
We will also assume that wind is calm. So to be able to do this procedure, we should always be tangent to the route of the arc.
1st Execution Method : Using VOR indicator ( Rule ± 10 / ± 10)
To enable the execution of an ARC / DME procedure with this method, our airplane needs to be equipped with VOR and DME indicators. We see in Figure 2 that we separate the ARC / DME procedure in arcs of 10 degrees. Every time the airplane passes the noted radials, we should turn by 10 degrees heading and turn 10 degrees the course of the VOR indicator. Let 's see how we do this:
We are established on the radial 335 with course 155 degrees inbound the KRK VOR and we have put on the top of the VOR indicator course 155 degrees. Observing the figure, we see that 18 miles inbound the VOR, we should turn right to enter the ARC. We first reduce 10 degrees on the VOR indicator, so we put 145 that corresponding to radial 325 (325-180 = 145). Then we turn to the right so that when crossing radial 325, to be tangent to the ARC and vertically to the radial ( 325-90 = 235). We also watch the DME indicator and we try to keep our distance from the VOR at 16 miles.
After reaching and passing radial 325, we turn our airplane left by 10 degrees to course 225 and we turn the VOR indicator -10 to radial 315. We continue with this course and when passing radial 315 we follow the same tactic, by turning left again the aircraft by 10 degrees and turn in our indicator again -10 degrees to radial 305.
So, every 10 radials we subtract 10 degrees from the heading of the aircraft and 10 degrees from the VOR indicator1. In each phase of this procedure, we always check the distance from KRK VOR, to be close to 16 miles. If therefore we see that we move away from the VOR, then we must fix it immediately before grown more. All we have to do is to correct our course little earlier before we are established to the VOR, by reducing the radius of our turn.
Otherwise if we see that distance is reducing from the VOR, then we delay to do the correction to the heading and the course, letting aircraft move away in order to get back the 16 miles. Continuing with this method and having reached the radial 275, we put 88 degrees to our course in VOR indicator and we begin to turn left to establish radial 268 inbound VOR .
1 In clockwise ARC, this process is changing and instead of reducing, we add 10 degrees to heading and 10 degrees to the course of VOR indicator.
2nd Execution Method: Using RMI
It is obvious that in order to perform an ARC using the instrument RMIRMIDefinition: Radio Magnetic Indicator...
, it should be included in the equipment of our airplane. Also there should be a DME instrument in our cockpit. Knowing that the RMI shows us the direction in which is the VOR, when entering the ARC, after we tune the frequency of the VOR, we try to keep the needle of the RMI vertically to the course of the airplane (see Figure 3).
As ARC is counterclockwise, the needle is on the left side of the instrument, as VOR is left of the airplane. Of course at regular intervals, we should confirm with the DME indicator, that our distance from the VOR is about 16 miles. If during the execution of the arc, we find that we are away from the distance defined in ARC procedure (in our case 16 nm), we should bring our course at an angle less than 90 degrees, by about 10 degrees with the indication of RMI. This means that we will see the needle of the instrument entering the left upper quadrant (see Figure 4).
We will stay in this configuration until we reach again at 16 DME distance.
Then we turn back at a vertical course inbound the VOR. If we find that we are more close and we move towards the center, we just keep a steady course until we reach again the target of 16 miles. Completing that, our entrance to the ARC / DME, is the same as we described in the first method.
ILS Approach
ILS (Instrument Landing System) is a ground-based approach system, which provides information on the airplane to approach the runway and to land safely, under specific meteorological conditions, such as low visibility due to fog or heavy rain. It's based on radio signals that are sent from a ground station and these signals show the correct course and angle of descent that the airplane should have in order to land safely.
Basic principles
ILS is a system of radio transmitters which send signals to the airplane. Airplane undertakes to decode these signals and following them, to reach the desired point on the runway. Many airplanes, through their autopilot, can follow these signals automatically without the intervention of the pilot.
ILS consists of two subsystems. Localizer which gives direction on the horizontal axis and the glide slope that provides guidance on the vertical axis.
Localizer (LOC or LLZ) is a series of directional antennas, located 1,000 feet beyond the end of the runway. These antennas are transmitting two signals. One formed at 90Hz and another at 150Hz. Each antenna transmits in this signal, a thin beam of 3-6 degrees, one from the right side of the runway and the other from the left respectively. Then the receiver is taking these signals and calculates the difference in depth of modulation of the two frequencies. When this difference is stronger on one frequency (90Hz) or the other (150Hz), then the airplane is outside the centerline of the runway. This is illustrated in the instrument of the cockpit and showing the pilot if he needs to move left or right to align perfectly with the centerline.
Glide slope (GS) is a directional antenna that is located on one side of the runway, next to the TZ (Touchdown zone) at a distance of 750 to 1,250 feet from the beginning of the runway. Glide slope is also based to the operating philosophy of the localizer. From the antenna are transmitted two different signals, with a frequency of 90Hz and 150Hz. In this case GS signals are sent from antenna one over the other with a difference of 1.4 degrees. In the center of this dispute is the glide path, an imaginary line that should be followed by the airplane to approach the touchdown zone. The pilot during descent, should be seeing in his instrument the glide slope to be in the center.
In ILS systems at airports, there is often a DMEDMEDefinition: Distance Measuring Equipment...
system too. With this, we can also have information on our distance from the threshold in nautical miles.
At airports, along with ILS systems, very often we find the system marker beacons. The marker beacon is an audio signal that comes from a beacon and gives the pilot the ability to control the correct descent path according to the distance from the runway. These signals, except the alarm, are activating a system of three lights too (if it's installed in the aircraft). There are three different marker beacon signals:
A) Outer marker is located 3.5 to 6 nm from runway's edge. This signal is modulated at a frequency of 400Hz and is in Morse code with two dots on each second. By the time the aircraft passes over the transmitter, the pilot hears this code and into the cockpit illuminates a blue light indicator.
B) Middle marker is located 0.5 to 0.8 NM from threshold. The sound of this signal is at 1400Hz and two dashes per second. When the airplane passes over the middle marker, pilot hears the sound and illuminates a yellow light indicator.
C) Inner marker is in front of the runway's threshold. The sound of this signal is at 3000Hz. The identification is six dots per second and the light is white color. Inner marker is used only to airports with ILS category II and III.
When we are in an approach procedure to the runway, on the glide path there is a altitude noted in charts, called decision height and measured from the ground. At this height the pilot should has the required visual contact with the runway or lights, to decide whether to continue the approach, or to perform a missed approach, by trying again the same or a different approach or even diverting to the alternate airport.
Categories
There are three categories of ILS systems in accordance with the global organization ICAOICAODefinition: International Civil Aviation Organization...
CAT I
In this category the minimum DH is 200 feet and with RVR 548 meters or 1800 feet . In this case the airplane should be equipped with systems for IFRIFRDefinition: Instrument Flight Rules...
flights and of course an ILS instrument.
CAT II
In this category the minimum DH is 100 feet and with RVR 365 meters or 1200 feet. An airplane to be able to approach with this class ILS, should have a radio altimeter receiver or marker beacon, autopilot and two pilots.
CAT III
In this category, if the airplane is equipped with appropriate systems, can make an auto land, without intervention by the pilots.
CAT IIIa
In this category we can have an auto land. The minimum DH is 100 feet and with RVR 213 meters or 700 feet.
CAT IIIb
In this category, the airplane lands only by using the ILS. The DH is less than 50 feet and with RVR 45 meters or 150 feet.
CAT IIIc
In this category, the airplane lands only with the use of ILS. Theoretically there is no DH and RVR is at 0 meters. The airplane in this case can even taxi to the runway after landing, but since the pilot has no visual contact with the ground, it would be unable to vacate the runway. For this reason until now, no airport is certified for this type of approach.
History
First tested ILS system was at 1929 at U.S.A. In this experiment, the pilot guided towards the runway by Morse signals. In 1932 for the first time Albert Hegenberger manages to land the airplane safely under no visibility of the runway, using an ILS system based on radio signals and a system that displayed the correct climb and descent angle inside the cockpit. The first passenger airplane ILS approach was made in 1938 with a Boeing 247D. In the second world war, was widely used by Americans, a low visibility landing system, called ground control approach (GSA). GSA was using two CRT monitors, where the controller was seeing on the first, the airplane's position on the horizontal axis and to the second the vertical one. In these terms, he was guiding the pilot on the right path through the radio. Later the system was used at many airports. The first successful fully automatic ILS landing happened at Bedford 's airport, in March of 1964, with a BEA Trident airplane.
VOR/DME & NDB Approach
VOR - VOR/DME Approach
VOR or VOR / DME approach, is an IFR procedure followed by the pilot, to approach the runway. In this procedure there is always a VORVORDefinition: VHF Omnidirectional (Radio) Range...
station present. If there is a VOR / DME available, then of course we have the ability to calculate the distance from the VOR. In equipment of the airplane is necessary to have a VOR indicator and a DME when required.
The procedure should be followed, is published in a special chart, which is marked as "VOR" and then the runway in which we approach, for example VOR RWY 06. At large airports with heavy traffic we encounter many times more than one VOR approaches to a runway. In this case there is also a letter (Z, X, Y, W) followed to the chart's name, to distinguish between them. The VOR / DME approach, is characterized as "NON-PRECISION APPROACH". This is because while we have the opportunity to perform with precision our course, established on a radial as our charts indicates, that thus may not have accurate indications of our necessary descent path, as is available for example on an ILS approach. Also in the final phase of the approach, we are not always aligned with the runway and the pilot should bring the aircraft on track to land on the runway.
In large airports also, we can meet the procedure separated in initial and final phase. So the first phase starts from the IAFIAFDefinition: Initial Approach Fix...
which is the starting point of the approach to the airport and reaches the final phase, where starts the final descent to the runway.
NDB Approach
NDB or NDB / DME approach is the procedure where we approach to the airport, with the help of NDBNDBDefinition: Non-Directional (Radio) Beacon...
navaids. If there is also a DME available, the procedure is called NDB / DME and we can calculate its distance from our station. The NDB stations can be found at the airport or in the surrounding area around it.
For each NDB approach there is a published chart, which describes the entire procedure. The name of these charts is given in accordance with the landing runway. The NDB approach procedure is also a non-precision approach. The indications we have from the NDB, are only where is its direction. So to be able to know in which radial we are established relative to the NDB station, we must advise our magnetic compass.
The NDB procedure, as the VOR one, begins from IAFIAFDefinition: Initial Approach Fix...
, where the STARSTARDefinition: Standard Terminal Arrival Route...
procedure ends. In the final stage of this procedure and after MAPMAPDefinition: Missed Approach Point...
, ( the point where we must decide whether to continue with the procedure or to execute a missed approach), the flight is now continuing by sight and we should continue the approach only on good visibility conditions, allowing us to have runway in sight.
More information on IFR procedures, refer to section of IFR charts.
VOR Navigation
VOR to VOR Navigation
With the use of VORVORDefinition: VHF Omnidirectional (Radio) Range...
navaids, we can navigate from one point to another, with absolute precision. The use of VOR started in the early '50 and even today is one of the most popular ways of navigation. This method is based on the ability of the station to show us the radial at which we are established and also the distance from it. With this information we can calculate our flight and follow it with absolute precision. Obviously, to perform a VOR navigation, we need at least one VOR indicator on our airplane.
Let's now look at the basic principles of the VOR. It is a beacon which transmits information to the VHF radio band. The signals transmitted are omni-directional, forming a circle of radials around it, starting from the first one, which is oriented to the magnetic north. The number of these radials is 360, one for each degree of the circle. When the VOR indicator is tuned to the frequency of the beacon, it calculates the combination of the signals transmitted and can calculate the angle formed by the position of the airplane and the magnetic north. In this way it can inform us in which radial we are established, in relation to the VOR station.
Inbound to VOR
Let's see how to use a beacon VOR, to follow a course inbound it. With the VOR indicator we have the ability to choose one of the 360 radials and be established with it. We assume that the radial of our choice is 230 and we want to move inbound the VOR. The course we will follow, would be the exact opposite ( 230-180 = 050). So we put this value in our instrument with the regulator that is on it.
In the center of a VOR Indicator, there is an indication which moves from right to left of the instrument. When the airplane is to the right of the selected radial (phase 1), the indication is left than the center. So we know that we should move to the left to establish (phase 2). If we are left than the radial (phase 3), we will see the indication on the right side of the instrument. So we should move to the right to establish on the radial (phase 2).
Outbound from VOR
Let us now see how we follow a radial, outbound from a VOR.We assume that the radial to follow is 030. We put theVOR indicator course to 030 and we aim the indication to be in center.
If we are left from radial we will see that the indication is to the right of the center so we have to move to the right. Similarly when we are right from the radial, we will move to the left to establish and maintain our course.
VOR to VOR Example
Knowing the usage of the VOR and understanding how we can maintain a steady course with it, we can navigate a route using these navaids.
We suppose that we are in Limnos Airport (LGLM) and that we want to go to the airport of Chios (LGHI). At this stage we will not deal with the usage of the airport's charts on departure and arrival and also we will not go into details about reading enroute charts. From Limnos to Chios we are going to use 3 VOR. LMO, LSV and MES.
From website www.skyvector.com, we make a route as shown in Figure.
Leaving LGLM after we have tuned the frequency 109.2 we will get to LMO VOR and from there we will move for 41 miles outbound, following the radial 146. So we will reach NILVA waypoint, where we will change the frequency 114.2 to tune with LSV VOR. Then we will set 95 course in VOR indicator and we will move inbound it for 23 miles, following the radial 275. Reaching over LESVOS VOR, we will change course again in 198 to fly about 64 miles to the radial 198 and get to MESTA VOR.
When we are about half of our distance (about 30 miles) it's good for us to tune in MES VOR 117,6 MHz without changing course in VOR indicator, so to become established in the radial 019 inbound to MESTA VOR. The reason we tune from one VOR to another is to reduce error indications due to with distance from the first VOR.
For FlightSimmer.GR
Giannis Evagelinos
