FLYING ON INSTRUMENTS

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FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sat Aug 11, 2018 11:19 am

Radio Navigation Aids

Having achieved a high standard in attitude flying using the flight instruments, it is now time to apply this ability to cross-country navigation on instruments.

It is, in fact, possible to fly cross-country using attitude flying only, without referring to any radio navigation instrument in the cockpit, simply by following instructions passed to you by a radar controller.

Instructions such as “Turn onto heading three four zero, and descend now to eight hundred feet”, can be followed, even to the point of a cloud break for a straight-in landing on a particular runway.

Radar is the first of the radio navigation aids, or radio navaids, that we will consider in this series, since it does not involve a great deal of understanding before you can benefit from it. As well as explaining how radar can be of use to you, we will also discuss the basic theory of its operation, together with the transponder in the aircraft.

VHF direction finding (VDF), which, like radar, does not require additional instrumentation in the cockpit, may also be used for cross-country flying.

Radio navigation aids covered in this series, that do not require cockpit instruments include:-
The non-directional beacon (NDB) and automatic direction finder (ADF) combination. The ADF has various cockpit presentations, such as the relative bearing indicator (RBI) and radio magnetic indicator (RMI)
The VHF Omni range (VOR)
• Distance-measuring equipment (DME), and
• The instrument landing system (ILS)
• GNSS (Global Navigation Satellite System) or GPS (Global Positioning System)
There are also some rapidly developing RNAV (area navigation) systems – pseudo-VOR/DMEs, Loran-C and GPS.


…….to be continued
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sat Aug 25, 2018 4:48 am

RADAR
Most air traffic control in busy airspace occurs in a radar environment. This means that the air traffic controller has a radar map of the area showing the position of the various A/C within it, bringing enormous advantages such as:-
• A significant reduction in the amount of air-ground communications. For instance, there is no need for pilots to transmit regular position reports
• The ability to handle an increased number of aeroplanes in the same airspace, with reduced, but still safe, separation distances.
• The ability to fix an aircraft’s geographic position
• The ability to radar vector an aeroplane along various tracks by passing headings to steer to the pilot
• The ability to feed aeroplanes onto final approach to land, either to the commencement of an instrument approach such as an ILS (Instrument Landing System) or until the pilot becomes ‘visual’, without the need for excessive manoeuvring, and with more than one aeroplane on the approach at any one time.
This use of radar is known as surveillance radar. Wide areas of some countries have radar coverage, and you may, even if operating in uncontrolled airspace, take advantage of services such as Lower Airspace Radar Advisory Service (LARS - UK example) or other similar facilities in your area.

Next……..SSR Transponders
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sun Aug 26, 2018 1:19 am

SSRT (Secondary surveillance radar transponder)

Most aeroplanes are now fitted with a transponder, which transmits a unique signal in response to a radar signal from the ground, thereby allowing the radar controller to identify a particular aeroplane on a radar screen. You are probably familiar with the operation of the transponder. The name transponder is derived from transmitter/responder.

RADAR VECTORING

Radar vectoring is when a radar controller passes a heading to steer a pilot with an instruction such as: “November 26, turn right HDG 070”. Bear in mind that the radar controller is trying to get you to achieve a particular track over the ground and, because he does not know precisely what the wind at your level is and the amount of drift that it is causing, he will occasionally request a modification to your heading whilst radar vectoring your aeroplane.
No radar navigation instruments are required in the aeroplane for it to be radar vectored, but radio communication is necessary. The pilot concentrates on attitude flying (maintaining the desired heading, altitude and airspeed), while the radar controller concentrates on the aeroplane achieving the desired track over the ground. This is not to say that you should not be very aware of where your track is taking you, especially if high terrain is in the vicinity, and you should always maintain a picture of where the aeroplane is with respect to the aerodrome. This is essential in case of radio communication failure.
The termination of radar vectoring is indicated by the phase: [i]“radar service terminated" and/or "resume own navigation”.
[/i]Radar vectoring is a very useful procedure in busy Tracon/Terminal areas where an aeroplane may be vectored quite efficiently onto final approach to land. Radar vectoring by the controller may cease once the aeroplane is established on a visual approach or on an instrument approach, such as an ILS. The radar controller will most likely radar vector you followed by a reason, such as: “turn left heading 070, vectors for final approach”
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Tue Aug 28, 2018 5:19 am

Some little hints and tips – contributions from other pilots are welcome

DME and Slant Distance
Distance-measuring equipment (DME) can provide you with extremely useful information: the distance of your aircraft from a DME ground station. DME uses radar principles to measure this distance, which is the slant distance rather than the horizontal distance (or range). For most practical purposes, the DME distance can be considered as range, except when the aeroplane is within a few miles of the DME ground station.
Passing directly over the DME ground station, the DME indicator in the cockpit will either show the height of the aeroplane in nautical miles (1nm = 6000ft approximately), or the DME indication will drop out.

DME Arcs
A DME arc is a curved path flown at a specific distance from the DME station. It is usually flown as a series of short straight legs, or small segments of the arc, rather than a steady curve. The DME arc is often used to transition from the en route phase of a flight to the intermediate approach or final approach segment of an instrument approach.

VOR/DME Pairing
Where this occurs, each VOR frequency has a specific DME channel paired with it. For instance, VOR frequency 116.80 has DME channel (TACAN) 115X paired with it, so that the VORs associated DME will automatically be interrogated when you select the VOR frequency 116.80 on the VHF-NAV. The purpose of this pairing is to reduce your workload in the cockpit, with only one selection instead of two required, and to reduce the risk selecting the right VOR but the wrong DME station. It is normal for only co-located VORs and DMEs to be frequency paired. Co-located VORs and DMEs will have the same Morse code ident.

ILS/DME Pairing
Many instrument landing systems (ILS) have their localiser frequency paired with a DME located very close to the runway threshold. This provides you with very useful information during an ILS or localizer approach to the runway; for example, distance fixes for key positions on the approach (such as the final approach fix), as well as the distance-to-run to the runway threshold. Example ILS or LOC RWY 16C at KSEA – frequency 111.7 and channel 54
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Fri Sep 14, 2018 12:14 am

THE NDB and the ADF

The non-directional beacon (NDB) is the simplest form of radio navigation aid used by aircraft. It is a ground-based transmitter that transmits radio energy in all directions, hence its name – the non-directional beacon.

The automatic direction finder (ADF), fitted in an aeroplane has a needle that indicates the direction from which the signals of the selected NDB ground station are being received. This is extremely useful information for pilots flying in instrument conditions and/or at night. In days past, the combined ADF/NDB system was referred to as the radio compass.

Flying to an NDB in an aeroplane is similar to following a compass needle to the North Pole – fly the aeroplane towards where the needle points and eventually you will arrive overhead. Flying away from the North Pole however, with the magnetic compass needle pointing behind, could take the aeroplane in any one of 360 directions. Similarly, flying away from the NDB using only the ADF needle will not lead the aeroplane to a particular point (unlike flying to an NDB). The aeroplane could end up anywhere! Further information is required.

……….for that, see the next instalment to follow.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sat Sep 15, 2018 1:59 am

THE ADF and the Direction Indicator (DI)

The extra information required by the pilot, in addition to that supplied by the ADF needle, comes from the magnetic compass, or more commonly, from the DI. Accurate navigation can be carried out using the aircraft ADF needle which points at an NDB ground station, and a DI which indicates the aeroplane’s magnetic heading (MH).

Note: - Since a DI will most probably drift slowly out of alignment, it is essential that you realign it periodically with the magnetic compass in straight flight at a steady speed, say every 10 or 15 minutes.

The NDB/ADF combination


Before using an ADF’s indications of the bearing to a particular NDB, the aeroplane must be within the promulgated range of the NDB and you must have:-
Correctly selected the NDB frequency;
Identified its Morse code ident; and
Tested the ADF needle to ensure that it is indeed ‘ADFing.

If the NDB is 40 degs to the left of the aeroplane’s MH, say MH 070 degs M, then the NDB, since it is 40 degs left of the nose, will have a magnetic bearing (MB) of 30 degs M from the aeroplane.

The ADF/NDB combination, in conjunction with the DI, can be used:
To track to the NDB on any desired track, pass overhead the NDB, and track outbound on whatever track is desired; or
To fix the aeroplane’s position.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Fri Sep 21, 2018 4:18 am

The ADF in the aeroplane should, whenever possible, be selected to an NDB relevant to the desired path of the aeroplane. If tracking en route between two NDBs, the point of transfer from one NDB to the next would reasonably be the half-way point, depending of course on their relative ranges.
If the NDB is ahead, the ADF needle will point up the dial; if the NDB is behind, the ADF needle will point down the dial. As the aeroplane passes overhead the NDB, the ADF needle will become very sensitive and will swing from ahead to behind.
The ADF can also be used for more advanced procedures such as:


……………….to be continued
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sat Sep 22, 2018 5:25 am

The ADF can also be used for more advanced procedures such as:
• Flying an accurate ‘racetrack’ holding pattern based on the NDB; or
• Using the NDB for guidance when manoeuvring in the vicinity of an aerodrome, either as a let-down or cloud break aid in its own right, or as a lead-in to a precision approach aid such as an ILS (instrument landing system).
An example of a NDB published approach can be viewed at KGRF – the NDB RWY 15 approach. The GRAYE (GRF) NDB frequency is 216 and this NDB is also an IAF (initial approach fix) and NDBs are available as:
*A point at over which to hold in a racetrack pattern;
The sole tracking aid on an NDB let-down;
As an additional tracking guide when using a RWY ILS, and as an outer marker (LOM) or check point on an ILS approach
*Some NDBs are not available for holding or for instrument approaches, but only for en route navigation.
The NDB/ADF combination is the simplest form of radio navigation in theory, yet it takes a good instrument pilot to use it accurately. Other more advanced systems, such as the VOR are more complicated in principle but easier to use.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Fri Sep 28, 2018 2:46 am

The NDB

The non-directional beacon (NDB) is the ground-based part of the combination. It is called non-directional because no particular direction is favoured or differentiated in its transmissions; the NDB radiates identical electromagnetic energy in all directions.

Each NDB transmits on a given frequency in the low-frequency or medium-frequency LF/MF bands (somewhere between 200 to 1,750 kHz). The transmission aerial is either a single mast or a large ‘T-aerial’ slung between two masts.

To avoid confusion between various NDBs, and to ensure that the pilot is using the correct beacon, each NDB transmits its own particular identification signal (or ident) in the form of a two-or-three-letter Morse code signal, which you should monitor periodically in the cockpit.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sun Sep 30, 2018 2:15 am

NDB RANGE
For long-range en route navigation where no other aids are available, a fairly strong NDB with a range of 100 nm or more is usually required. Some NDBs used for long-distance overwater tracking, for instance in the Pacific area, may have a range of 400nm.

For manoeuvring in the vicinity of aerodromes, only lower-powered NDBs are required. NDBs used for approaches are sometimes referred to as Locators. If a locator is co-located with an outer marker that serves to fix a position as an aircraft proceeds down an instrument landing system (ILS) approach, then it will be depicted on the chart as LOM (locator outer marker), and as OM (outer marker) on some charts.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sun Sep 30, 2018 2:35 am

The ADF

Note:- NDB – Monitor the ident frequently if an NDB is the only Navaid you are using, as a signal failure will not be indicated on the ADF display!

The airborne partner of the NDB is the automatic direction finder, usually referred to as the ADF. It operates on the radio compass principle whereby the ADF needle indicates the direction from which the signals are coming.

The automatic direction finder has three main components;
THE ADF RECEIVER, which the pilot tunes to the frequency of the desired NDB and verifies with the ident.
THE AERIAL SYSTEM, consisting of a loop aerial (or its modern equivalent), plus a sense aerial, which together determine the direction from which the signal is coming.
THE ADF COCKPIT DISPLAY, either a fixed-card or a rotatable compass card with a pointer or needle indicating the direction from which the signals are coming. The cockpit instrument is fitted into the instrument panel , usually to the right of the attitude flight instruments, with the top of the dial representing the nose of the aeroplane, and the bottom of the dial representing its tail. Ideally, the ADF needle will point continuously and automatically towards the NDB ground station.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Thu Oct 04, 2018 1:20 am

The ADF Control Panel

ADF units vary from type to type, so you must become familiar with the set you will be using prior to flight. You must be able to select and positively identify the NDB that you want to use, and then verify that the ADF needle is indeed responding to the signals from that NDB. The correct procedure, any time a new NDB is to be used, is to confirm (verbally if so desired):
Selected
Identified; and
ADFing (and giving a sensible bearing).
The Mode Selector or Function Switch
The mode selector switches between ADF modes of operation:
OFF. Switches the ADF off
ADF. The normal position when you want bearing information to be displayed automatically by the needle. Most NDBs can be identified with the mode selector in this position (and the volume knob adjusted suitably).
ANT or REC. Abbreviations for antenna or receiver. In this position, only the signal from the sense antenna is used, with no satisfactory directional information being available to the ADF needle. The reason for this function position is that it gives the best audio reception to allow easier identification, and better understanding of any voice messages. Never leave the mode selector in this position if you are navigating using the ADF – the ADF needle will remain stationary with no obvious indication that it is not responding! It is possible, however, to identify most NDBs with the mode selector in the ADF position (which is a safer position), and for the ANT position to be avoided.

………………..to be continued
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Fri Oct 05, 2018 5:45 am

TEST. Switching the mode selector to the TEST position will deflect the needle from its current position. Placing the mode selector back to ADF should cause the needle to swing back and indicate the direction of the NDB. This function should be tested every time as part of the selected, identified, ADFing tuning procedure.
Some ADF sets have a separate TEST button which only needs to be pressed to deflect the needle, and then released to check the return of the needle.
NOTE On some ADF equipment, the TEST function is achieved using the ANT/REC position, which drives the needle to the 090 position. Returning the mode selector to ADF should see the needle start ‘ADFing’ again.
VOL. The volume knob will probably be separate from the mode selector. With audio selected to the pilot’s headset or to the [mod-man parts]-pit speakers, the VOL should be adjusted so that the ident or any voice messages on the NDB may be heard. If signal reception is poor in ADF, then try ANT/REC; if there is no signal reception, try BFO/CW. But remember to return the mode selector to ADF!

Frequency Knobs
NDBs transmit on a frequency in the range 200-1,750 kHz, the most common band being 200-400 kHz. To allow easier and accurate selection of any particular frequency, most modern ADFs have knobs that allow digital selection, in 100, 10 and 1 kHz steps. Some ADFs may have a band selector (200-400; 400-1600 kHz), with either a tuning knob or digital selection for precise tuning.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Mon Oct 08, 2018 5:56 am

ADF Cockpit Displays

The basic purpose of an automatic direction finder in an aeroplane is for its needle to point directly towards the selected NDB ground station.

The ADF cockpit display is a card or dial placed vertically in the instrument panel so that:
• If the needle points up, the NDB is ahead;
• If the ADF needle points down, then the NDB is behind;
• If the ADF needle points to one side, then the NDB is located somewhere to that side of the fore-aft axis of the aeroplane.
To convey this information to the pilot, various presentations are used, three of which include:
1. The fixed-card ADF, or relative bearing indicator (RBI);
2. The rotatable-card ADF (the poor man’s RMI); and
3. The radio magnetic indicator (RMI).
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Tue Oct 09, 2018 4:55 am

The Relative Bearing Indicator (RBI)
A fixed-card display has an ADF needle that can rotate against the background of a fixed azimuth card of 360 degs with a 000 deg (360 deg) at the top, 180 deg at the bottom, and so on. The fixed-card ADF is also known as the RBI, and is common in many GA aircraft.

On the fixed-card ADF, the needle indicates the relative bearing of the NDB from the aeroplane.

The relative bearing of the NDB from the aircraft is the angle between the aircraft’s heading and the direction of the NDB. Usually relative bearings are described clockwise from 000 degs to 360 degs, but it is sometimes convenient to describe the bearing of the NDB relative to the nose or tail of the aeroplane.

Each time the aeroplane changes its magnetic heading, it will carry the fixed-card with it. Therefore, with each change of magnetic heading, the ADF needle will indicate a different relative bearing (RB).
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