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Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.

 

Note:   I have NO affiliation with ANY manufacturer or reseller.  All reviews and content are 'frank and fearless' - I tell it as I see it.  Do not complain if you do not like what you read.

I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).

 

All funds are used to offset the cost of server and website hosting (Thank You...)

 

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If you see any errors or omissions, please contact me to correct the information. 

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Thursday
Jun232016

RNAV, RNP, LNAV and VNAV Operations - Overview 

New flyers to the Boeing 737NG often become confused understanding the various terminology used with modern on-board navigational systems.

Although the concepts are easy to understand, the inter-relationship between systems can become blurred when the various types of approaches and departures are incorporated into the navigational system.

LEFT:  Collins Mode Control Panel (MCP) showing illuminated LNAV annunciation (click to enlarge).

This post will not provide an in-depth review of these systems; such a review would be lengthy, confusing and counterproductive to a new virtual flyer.  Rather, this post will be a ‘grass-roots’ introduction to the concept of RNAV, LNAV and VNAV.

In the Beginning there was RNAV  

RNAV is is an acronym for Area Navigation (aRea NAVigation). 

Prior to complex computers, pilots were required to use established on-the-ground navigational aids and would fly directly over the navaid.  Such a navaid may be a VOR, NDB or similar device.  Flying over the various navaids was to ensure that the flight was on the correct route.  Often this entailed a zigzag course as navaids could not be perfectly aligned with each other in a straight line - airport to airport. 

When computers entered the aviation world it became possible for the computer to 'create' an imaginary navigation aid based on a direction and distance from a ground-based navaid.  Therefore, a straight line could be virtually drawn from your origin to destination and several waypoints could be generated along this line.   The waypoints were calculated by the computer based on ground VORs and positioned in such a way to ensure more or less straight-line navigation.

Required Navigation Performance (RNP)

Simply explained, Required Navigation Performance (RNP) is a term that encompasses the practical application of advanced RNAV concepts using Global Navigation Satellite Systems (GNSS) which includes the GPS system.

Therefore; RNAV can be loosely defined as any 'straight line' navigation method similar to GPS.

LNAV and VNAV

LNAV and VNAV are parts of the Flight Guidance System, and are acronyms for Lateral Navigation and Vertical Navigation'.  Both these functions form part of the automation package that the B737NG is fitted with.

LNAV is the route you fly over the ground. The plane may be using VORs, GPS, DME, or any combination of the above. It's all transparent to the pilot, as the route specified in the clearance and flight plan is loaded into the Flight Management System (FMS), of which the Flight Management Computer (FMC) is the interface.

The route shows up as a magenta line on the Navigation Display (ND), and as long as the LNAV mode on the Mode Control Panel (MCP) is engaged and the autopilot activated, the aircraft will follow that line across the ground. LNAV however, does not tell the plane what altitude to fly, VNAV does this.

VNAV is where the specified altitudes at particular waypoints are entered into the FMS, and the computer determines the best way to accomplish what you want.  The inputs from VNAV are followed whenever the autopilot is engaged (assuming VNAV is also engaged).  

The flight crew can, if necessary alter the VNAV constraints by changing the descent speed and the altitude that the aircraft will cross a particular waypoint, and the computer will re-calculate where to bring the throttles to idle thrust and begin the descent, to allow the aircraft to cross the waypoint, usually in the most economical manner.

VNAV will also function in climb and take into account airspeed restrictions at various altitudes and will fly the aircraft at the desired power setting and angle (angle of attack) to achieve the speed (and efficiency) desired.

There is not a fast rule to whether a flight crew will fly with LNAV and VNAV engaged or not; however, with LNAV and VNAV engaged and the autopilot not engaged, LNAV and VNAV will send their signals to the Flight Director (F/D) allowing the crew to follow the F/D cue display and hand fly the aircraft the way the autopilot would if it were engaged.

Reliance on MCP Annunciators

LNAV and VNAV have dedicated annunciators located on the Mode Control Panel (MCP).  These annunciators illuminate to indicate whether  a particular mode is engaged. 

LEFT:  Flight Mode Annunciator (FMA) showing LNAV and VNAV Path Mode engaged.  The Flight Director provides a visual cue to the attitude of the aircraft while the speed is controlled by the the FMC.  CMD indicates that the autopilot is engaged (ProSim737 avionics suite).

However, reliance on the MCP annunciators to inform you of a mode’s status is not recommended.  Rather, the Flight Mode Annunciator (FMA) which forms part of the upper area of the Primary Flight Display (PFD) should be used to determine which modes are engaged.  Using the FMA will eliminate any confusion to whether VNAV (or any other function) is engaged or not.

This post explains the Flight Mode Annunciators (FMA) in more detail.

Summary

In summary, RNAV is a method of area navigation that was derived from the use of VOR, NDBs and other navaids.  RNP through it use of GNSS systems has enabled Area Navigation to evolve to include LNAV and VNAV which are sub-systems of the Flight Guidance System -  LNAV is the course across the ground, and VNAV is the flight path vertically. 

Historically, navigation has been achieved successfully by other methods, however, the computer can almost always do things better, smoother and a little easier – this translates to less workload on a flight crew.  

In my next post, we will discuss RNAV approaches and how they relate to what has been discussed above.

References

The information for this article came from an online reference for real-world pilots.

Acronyms and Glossary

Annunciator – Often called a korry, it is a light that illuminates when a specific condition is met
DME – Distance Measuring Equipment
FMA - Flight Mode Annunciator
FMC – Flight Management Computer
FMS – Flight Management System
Gotcha - An annoying or unfavorable feature of a product or item that has not been fully disclosed or is not obvious.
GPS – Global Positioning System
GNSS - Global Navigation Satellite System
LNAV – Lateral Navigation
MCP – Mode Control Panel
ND – Navigation Display
NPA - Non Precision Approach
RNAV – Area Navigation
RNP - Required Navigation Performance
VNAV – Vertical Navigation
VNAV PTH – Vertical Navigation Path
VNAV SPD – Vertical Navigation Speed
VOR – VHF Omni Directional Radio Range

Thursday
May262016

Trim Wheel Nut Tool - New Design

A potential problem when using an OEM Boeing throttle unit, is removing the nut that secures the trim wheels to the side of the throttle.  The nut has been designed in such a way that loosening it can only be done with a specialised tool.  Attempting to use a screwdriver or pliers may burr the nut, or slip causing damage to the trim wheel.

LEFT:  The redesigned Trim Wheel Nut Tool (click to enlarge).

In an earlier post I examined how a simple tool had been designed to easily remove the nut from the spline shaft that holds the trim wheels in place.   Although this tool was functional there was room for improvement in its design and manufacture.

New Design and Improved Engineering

The tool, has been redesigned and incorporates an aluminium cylinder that has been produced from a solid block of aluminium using a milling machine.  The inside of the cylinder has been milled and a set screw securely inserted.  

The outer flange, adjacent to the set screw has then been machined so that two ridges, approximately 1mm in height are either side of the set screw.  The set screw mates with the female located on the end of the spline shaft while the ridge provides extra purchase by mating with the indents in the nut.  In addition, a circular hole 8mm in diameter has been drilled through the cylinder enabling a similar sized piece of metal, or the shaft of a screwdriver to be inserted.  This allows additional purchase and leverage should the nuts be difficult to loosen.   Finally, the aluminium on the outside of cylinder has been slightly scoured to facilitate better grip.

Round and Round

The trim wheels are continually rotating back and forth as the aircraft is trimmed.  This rotation causes the nut, that secures the trim wheels to the spline shaft to, over time, become tighter and therefore more difficult to loosen.  This firmness is often exacerbated if working on a throttle unit removed from a real aircraft, that has not had the spline nuts removed for several years; corrosion and caked grease can easily cement the nuts in place.

LEFT:  New design has easier mating which enables greater purchasing power for removing tight spline nuts (click to enlarge).

This tool, although not an OEM part, is more than adequate to loosen the most determined nut.

Thursday
May122016

Knobs Aren't Knobs - Striving for the Perfect Knob

In Australia during the early 1980’s there was a slogan ‘Oils Ain't Oils’ which was used by the Castrol Oil Company.   The meaning was simple – their oil was better than oil sold by their competitors.  Similarly, the term ‘Knobs aren’t Knobs’, can be coined when we discuss the manufacture of reproduction knobs; there are the very good, the bad, and the downright ugly.

Boeing Knobs

As a primer, there are several knob styles used on the Main Instrument Panel, forward and aft overhead, various avionics panels, and the side walls in the B737-800 NG

If you search the Internet you will discover that there are several manufacturers of reproduction parts that claim their knobs and switches are exactly identical to the OEM knobs used on Boeing aircraft – don’t believe them, as more often than not they are only close facsimiles.

In this article, I will primarily refer to the General Purpose Knobs (GPK) which reside for the most part on the Main Instrument Panel (MIP).  Boeing call these knobs Boeing Type 1 knobs.

Why Original Equipment Manufacturer (OEM) Knobs Are Expensive

Knobs are expensive, but there are reasons, be they not be very good ones.  

LEFT:  The real item – a Boeing Type 1 General Purpose Knob (GPK) and issue packet.  There can be nothing more superior to an OEM part, but be prepared to shell out a lot of clams (click to enlarge).

The average Boeing style knob is made from painted clear acrylic resin with a metal insert. On a production basis, the materials involved in their manufacture are minimal, so why do OEM knobs cost so much…   Read on.

There are two manufacturers that have long-term contracts to manufacture and supply Boeing and Airbus with various knobs, and both these companies have a policy to keep the prices set at an artificially high level.

Not all flight decks are identical, and the requirements of some airlines and cockpits are such that they require knobs that are unique to that aircraft model; therefore, the product run for knobs for this airframe will be relatively low, meaning that to make a profit the company must charge an inordinate amount of money to cover the initial design and production costs.

A high-end plastic moulding machine is used to produce a knob, and while there is nothing fancy about this type of technology and the process is automated, each knob still requires additional work after production.  This work is usually done by hand.

Once a knob has been produced, it must be hand striped and finished individually to produce a knob that is translucent and meets very strict quality assurance standards.  Hand striping is a complex, time consuming task. 

Additionally, each knob must undergo a relatively complex paint spraying procedure which includes several coats of primer and paint, and a final clear protective coating.  Spray too much paint and the translucent area (called the pointer) inside the twin parallel lines will not transmit light correctly.  Spray too little paint and the knob can suffer from light bleed.  There is a fine line during production when it is easy to ruin an otherwise good knob with a coat of thickly applied paint. 

Finally, any part made for and used by the aviation industry must undergo rigorous quality assurance, and be tested to be certified by the countries Aviation Authority.  Certifying a commercial part is not straightforward and the process of certification takes considerable time and expense.  This expense is passed onto the customer.

Replicating Knobs - OEM Verses Reproduction

It’s not an easy process to replicate a knob to a level that is indiscernible from the real item.  Aside from the design and manufacture of the knob, there are several other aspects that need to be considered: functionality, painting, backlighting, robustness and appearance to name but a few. 

LEFT:  Often disregarded during the manufacture of reproduction knobs is the inner metal sleeve.  The sleeve protects the material from being worn out from continual use (click to enlarge).

Backlighting and Translucency

To enable the knob to be back lit calls for the knob to be made from a translucent material.  Unfortunately many reproduction knobs fall short in this area as they are made from an opaque material.

The knob must also be painted in the correct colour, and have several coats of paint applied in addition to a final protective layer.  The protective layer safeguards against the paint flaking or peeling from the knob during normal use.  In the photograph below, you can see where extended use has begun to wear away part of the knob's paint work revealing the base material.

Set Screws and Metal Inserts

Often lacking in reproduction knobs is a solid metal set screw (grub screw).

The task of the set screw to secure the knob against the shaft of the rotary so that when you  turn/twist the knob it does not rotate freely around the shaft.  Plastic set screws can be easily worn away causing the knob to freely rotate on the shaft of the rotary encoder. 

LEFT:  Detail of the grip and metal set screw.  The set screw is important as it enables the knob to be secured against the shaft of the rotary.    This knob previously was used in a Boeing 737-500 (click to enlarge).

The position of the set screws on the knob also deserves attention.  Correctly positioned set screws will minimize the chance of rotational stress on the shaft when the knob is turned.

Of equal concern is the hole on the underside of the knob where the rotary shaft is inserted.  The hole should be sheathed in metal.  This will increase the knob’s service life.  If the hole does not have a metal sheath, it will eventually suffer from wear (disambiguation) caused by the knob being continually being turned on its axis.   Finally, the knob must function (turn/twist) exactly as it does in the real aircraft.

Reproduction knobs may fail in several areas:

(i)    The knob has various flaws ranging from injection holes in the molded plastic to being the incorrect size or made from an inferior plastic material;
(ii)    The knob does not use metal set screws, and the set screws are not located in the correct position on the knob;
(iii)    The knob has a poorly applied decal that does not replicate the double black line on NG General Purpose Knobs.  The adhesive may not be aligned correctly and may peel away from the knob;
(iv)    The knob is made from a material that does not have the ability to transfer light (translucent pointer);
(v)    The knob does not appear identical in shape to the OEM part (straight edge rather than curved);
(vi)    The paint is poorly applied to the knob and peels off.  OEM knobs have several thin coats of paint followed by hard clear coating of lacquer to ensure a long service life;
(vii)    The colour (hue) of the knob does not match the same hue of the OEM product; and,
(viii)    The circular hole in the rear of the knob, that connects with the shaft of the rotary encoder does not have inner metal sleeve.  

The time it takes to manufacture a knob is time consuming, and to produce a quality product, there must be a high level of quality assurance throughout the manufacturing process.

Older Classic-style Knobs

It's common knowledge that many parts from the classic series airframe (300 through 500) are very similar, if not identical to the parts used in the Next Generation airframe.  Unfortunately, while some knobs are identical most are not.

The knobs may function identically and be similarly designed and shaped, but their appearance differs.  Knobs used in the Next Generation sport a twin black-coloured line that abuts a translucent central line called the pointer, classic series knobs have only a central white line.

Rotary Encoders

Although not part of the knob, the rotary encoder that the knob is attached deserves mention.

A fallacy often quoted is that an OEM knob will feel much firmer than a reproduction - this is not quite true.  Whilst it is true that an OEM knob does has a certain tactile feel, more often than knot the firmness is caused by the rotary that the knob is attached to.

Low-end rotary encoders that are designed for the toy market are flimsy, have a plastic shaft, and are easy to turn.  In contrast, rotaries made for the commercial market are made from stainless steel and are firmer to turn.

Also, low end rotaries and knobs are made from plastic and with continual use the plastic will wear out prematurely resulting in the knob becoming loose.

Final Call

Whether you use reproduction or OEM knobs in your simulator is a personal choice; It doesn't play a huge part in the operation of a simulator.  After all, the knobs on a flight deck are exactly that – knobs.  No one will know you have used a reproduction knob (unless low end reproductions have been chosen).

LEFT:  Many reproduction knobs fit the bill, and for the most part look and feel as they should.   It's easy to criticise the injected plastic being a little uneven along the edge, but this is unseen unless you are using a magnifying glass.

However, the benefit of using a real aircraft part is that there is no second guessing or searching for a superior-produced knob.  Nor is there concern to whether the paint is the correct colour and shade, or the knob is the correct shape and design – it is a real aircraft part and it is what it is.  But, using OEM knobs does have a major set-back - the amount of money that must be outlaid.  

But, second-hand OEM NG style knobs are not easy to find and often there is little choice but to choose the ‘best of the second best’. 

BELOW:  Cross section of a Boeing Type 1 General Purpose Knob.

Tuesday
Apr192016

Increasing Paint Longivity - Avionics Panels

One of the most important items in a simulator is the panel; after all, you spend a lot of time looking at panels, and a scratch or major blemish can be rather off-putting.  

LEFT:  Testers Dullcote.  Although it can be applied by a brush, a better approach is to use an airbrush and spray a thin coat onto the panel. When applying Dullcote to a panel, it is best to spray an even thin coat.

It is unfortunate, that the final grey-coloured coat of paint on many reproduction panels does not conform to the same level of quality assurance that Gables or Smiths provide on an OEM item. 

Some reproduction panels can easily be scratched and chipped, and after installing and removing a panel several times, or using it for a few months, the panel quickly can appear to look like a well-used item. 

Quality assurance is a term frequently used to discuss the quality of an item.  Many manufacturers of reproduction panels only apply one or two coats of paint which may or may not be applied over a primer.  The strength and longevity of the paint depends upon whether a primer has been used, the thickness of the paint, the quality of the paint and the number of applications.  Three thinly applied coats of grey-coloured paint over primer base is far better than one or two thick coats of paint without a primer. 

The final paint finish should not be shiney but be non-reflective.

So how can you improve the durability of paint after it has been applied? 

A product called Testers DullCote has been used in the modelling arena for many years.  Modelers apply a layer of Dullcoat to their models prior to applying other painting effects which may be damaging to the underlying base coat.   Dullcote dries to a clear matt texture that adds a layer of protection to the base coat of paint.  

The application of Dullcote can be either by rattle spray can, airbrush or by a standard modeling brush.  Whatever application method is chosen, always trial the product on a lesser item prior to applying to an expensive avionics panel.

If applied correctly, Dullcote will minimize the chance of a panel being scratched or blemished and provide a clear, durable, and flat texture that can easily be cleaned.  Additionally, if Dullcoat is applied to an OEM annunciator, the application will enhance the appearance of the annunciator making it appear clearer than possibly what it is.

Glossary

Gables and Smiths – Two manufacturers of OEM Boeing 737 avionics panels
Light Plate – The actual plate that contains the lighting array to backlight the cut-out sections on a panel
OEM – Original Equipment Manufacture aka real aircraft part
Panel – Used loosely to mean a avionics panel or module (for example Fire Suppression Panel or radio panel)

Friday
Mar112016

BRT / DIM Functionality - Lights Test Switch

The annunciators in the Boeing 737 are very bright when illuminated, and the reason for the high intensity is justified - the designers want to ensure that any system warnings or cautions are quickly noted by a flight crew.

However, when flying at night for extended periods of time the bright lights can be tiring on your eyes.  Also, during critical flight phases such as during a night-time approach, the bright lights can become distracting.  At this time, the flight deck is usually dimmed in an attempt to conserve night vision. 

For example, the three green landing annunciators (Christmas tree lights), speed brake and flaps extension annunciators are all illuminated during the final segment of the approach.  At full intensity these annunciators can, at the very least, be distracting.

LEFT:  Lights Test switch.  The three way switch located on the Main Instrument Panel (MIP) Captain-side is used to toggle the intensity of connected annunciators.  The panel label reads TEST, BRT and DIM.  The switch in the photograph is an OEM switch which has been retrofitted to a Flight Deck Solutions (FDS) MIP.

To help minimize eye strain and to enable night vision to be maintained as much as possible, pilots can select from two light intensity levels to control the brightness output of the annunciators. 

Anatomy of the Lights Test Switch

The switch (a three-way toggle) which controls the light intensity (brightness level) is called the Lights Test switch.  The switch is located on the Main Instrument Panel (MIP).  The switch is not a momentary switch and whatever position the switch is left at it will stay at until toggled to another position.  The switch has three labelled positions: Lights Test, BRT and DIM. 

(i)           UP controls the lights test (labeled Lights Test);

(ii)          CENTRE is the normal position which enables the annunciators to illuminate at full intensity (labeled BRT); and,

(iii)         DOWN lowers the brightness level of the annunciators (labeled DIM).

OEM annunciators have a built-in Push-To-Test function, and each annunciator will illuminate when pushed.  The brightness level is pursuant to the position the Lights Test switch (DIM or BRT). 

The Lights Test will always illuminate all the annunciators at their full intensity (maximum brightness). An earlier article explains the Lights Test switch in more detail.

Special Conditions

When the Light Test switch is set to DIM, all the annunciators will be display at their minimum brightness.  The exception is the annunciators belonging to the Master Caution System (MCS), which are the master warning, fire bell and six packs, and the Autopilot Flight Director System (AFDS).  These annunciators will always illuminate at their full intensity because they are construed as primary caution and warning lights.

Variable Voltage

There is nothing magical about the design Boeing has used to allow DIM functionality; it is very simplistic.

Annunciators for the most part are powered by 28 volts; therefore, when the Lights Test switch is in the neutral position (center position labeled BRT) the bulbs are receiving 28 volts and will illuminate at full intensity.  Moving the switch to the DIM position reduces the voltage from 28 volts to 16.5 volts with a correspondingly lower output.  In the real aircraft, the DIM functionality (and Light Test) is controlled by a semi-mechanical system comprising relays and zener-type diodes that vary the voltage. 

Two Controlling Systems - your choice

The DIM and Lights Test functionality can be achieved in the simulator by using one of two systems - software or mechanical.

Software Controlled

The avionics suites developed by Prosim-AR, Project Magenta and Sim Avionics have the ability to conduct a full Lights Test in addition to allowing DIM functionality.  However, depending upon the hardware used, the individual Push-To-Test function of each annunciator may not be functional.  The DIM functionality is controlled directly by the avionics suite software; it is not a mechanical system as used in the real aircraft.

In ProSim737 the DIM function can be assigned to any switch from the configuration/switches and indicators menu.  In Sim Avionics the function is assigned and controlled by FSUPIC offsets within the IT interface software.

Mechanically Controlled

I have chosen to replicate the Lights Test and DIM functionality in a similar way to how it is done in the real aircraft. 

There are no benefits or advantages to either system – they are just different methods to achieve the same result.

Two Meanwell power supplies are used to provide the voltage required to illuminate the annunciators.  A 28 volt power supply enables the annunciators to be illuminated at their brightest intensity, while the less bright DIM functionality is powered by a 16.5 volt power supply (or whatever voltage you wish).

A heavy duty 20 amp 28 volt relay enables selection of either 28 volt or 16.5 volts.

DIM Board

A small board has been constructed from ABS plastic on which is mounted a 20 amp 28 volt relay and a terminal block. The board, called DIM is mounted behind and beneath the MIP. This facilitates easy access to the required power supplies mounted within the Power Supply Rack (PSR)

LEFT:  The DIM Board is surprisingly simple and comprises a single terminal block and a heavy duty 28 volt relay.  Wires are coloured and tagged to ensure that each wire is connected to the correct terminal (click to enlarge).

An important function of the DIM board is that it helps to minimise the number of wires required to connect the DIM functionality to the various annunciators and to the Lights Test switch.   

Interfacing and Connections

Prior to proceeding further, a very brief explanation is required to how the various panels receive power. 

Rather than connect several panels directly to a power supply, I have connected the power supplies to two 28 volt busbars - one busbar is located in the center pedestal and other is attached to the rear of the MIP.  The busbars act a centralised point from which power is distributed to any connected panels.  This allows the wiring to be more manageable, neater, and easily traceable if troubleshooting is required.

Likewise, there is a lights test busbar located in the center pedestal that provides a central area to connect any panel that is lights test compliant.  Without this busbar, any panel that was lights test compliant would require a separate wire to be connected to the Lights Test switch in the MIP.  To read more about this feature, navigate to the page that deals with the lights test busbar.

The below mud schematic may make it easier to understand.  To view the schematic at full size click the image.

A 28 volt busbar located in the center pedestal is used as a central point from which to connect various panels to (lower pale blue box).  

The busbar is connected to the terminal block located on the DIM board.  Wires from the terminal block then connect to a 16.5 and 28 volt power supply located in the PSR (orange boxes). 

The 28 volt relay is also wired directly to the terminal block on the DIM board and a single wire connects the relay with the Lights Test switch located in the MIP (green box). 

From the Lights Test switch, a single wire connects with the lights test busbar located in the center pedestal (pale blue box).  The purple box represents any panel that is Lights Test compliant - a single wire connects between a panel and the lights test busbar.

Although this appears very convoluted, the principle is comparatively simplistic.

How it Works

When the Lights Test switch is toggled to the DIM position the relay is closed.  This inhibits 28 volts from entering the circuit, but allowing 16.5 volts to reach the 28 volt busbar (located in the center pedestal); any annunciators connected to this busbar will now only receive 16.5 volts and the annunciators will glow at their lowest brightness level.  Conversely, when the switch is toggled  to BRT or to Lights Test, the relay opens and the busbar once again receives 28 volts.

Which Annunciators are Connected to DIM Functionality

The annunciators that connect with the DIM board are those in the fire suppression panel, various panels in the center pedestal, the forward and aft overhead, and in the MIP.  If further annunciators in other systems require dimming, then it is a matter of connecting the appropriate wires from the annunciator to the 28 volt busbar, and to the and lights test busbar, both of which are located in the center pedestal.

BELOW:  A rather haphazard video showing the two brightness levels.  The example shows the annunciators in the OEM Fire Suppression Panel (FSP).  The clicking sound in the background is the Lights Test switch being toggled from BRT to DIM and back again.  Note that the colour of the annunciator does not alter - only the intensity (brightness).  The colour change in the video, as the lights alter intensity, is caused by a colour temperature shift which is not visible to the naked eye but is recorded by the video.

Glossary

Annunciator - A light that illuminates under set conditions.  Often called a Korry.
Busbar - A bar that enables power to distributed to several items from a centralised point.
Mud Schematic - Australian colloquialism meaning a very simplistic diagram (often used in geological mapping / mud map).
Push-To-Test Function - All annunciators have the ability to be pushed inwards to test the circuit and to check if the globe/LED is operational.
OEM - Original Equipment Manufacturer aka real aircraft part.
Panel/Module - Used interchangeably and meaning an avionics panel that incorporates annunciators.
Toggled - A verb in English meaning to toggle, change or switch from one effect, feature, or state to another by using a toggle or switch.