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G7USL

The PMDG 744 Experience

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Let me start by commenting on the DVD ITVV video of the Virgin Atlantic 747 flight is the most instructional tution video of all the programs I have seen.Secondly, (but should have been first I suppose? :-)) PMDG's 747 simulation is the best there is, of any aircraft and I simply can't get enough of it. Thanks to the team for providing the ultimate for us.As I have said, I have been using this sim for a long time but, there's still some things I still haven't found answers too?They are; 1. What decides the DH 'Decision hieght' setting? I know what it does and it's function but just wonder why maybe its 100 but mainly 200 on the 747?2. 'BUS' - BUS bars and BUS tie's. What does 'BUS' stand for, does anyone know please? I understand its the electrics switch.3. What is the purpose of the 'Storm Light'. When is it used?Lastly, I have learnt so much from a freind 'Craig Read' via 'Skype' who did a superb tutorial on what was basicly a simulation of the 'ITVV' Virgin Atlantic flight from Heathrow to San Francisco and seems to know the 747 like the back of his hand. We are all thankful for guys like him and the PMDG squad for their help in enjoying the chance of flying this great aircraft.To conclude, I wish PMDG the very best of success for all they do, (I have them all) and will continue to be a regular customer while they turn out this exceptional quality. Thanks again PMDG, your the TOPS, IMO.


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Decision height is based on current weather and visibility conditions I believe. When pilots get to the decision height, they decide whether its fully safe to land the aircraft, usually they announce "landing" or something simular. If they get to the decision height, and somethings not right, like they can't see the runway they should perform a missed approach.As for the storm light, this is taken directly from the PMDG 747-400 Aircraft Systems manual. "Storm Lights: The storm light switch is anoverride switch that sets all interior cockpitlights to a high brightness setting in order tocombat night blindness resulting fromlightning in close proximity to the airplane.This switch function is not modeled in thePMDG 747-400."An electrical bus is basically a hub where many electrical systems or devices connect to one electical connection so each device can communicate with each other more efficiently. A good example is that a bus connects your CPU and graphics card to your motherboard.

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Dave,100% Agree with you: the PMDG 744 is simply the ONLY one.About Decission Height (DH). It refers to Precission Approachs (with lateral and vertical guidance), those are typically ILS approaches.Every runway with an ILS has an approved and published plate. There you will find the specific DH for that runway depending on the ILS category (catI, catII or catIII), the aircraft category and the minimum RVR (runway visual range). You will find the value of DH in BARO or RADIO altitudes (the use of autopilot and radioaltimeter is compulsory for catII-III approaches).Hope it helps.Jose Luis.


signed: José Luis

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The BUS TIES are nothing to do with electrical components like computer processors or electronics.. These are data buses and there isn't really any point in being able to disconnect them and reconnect them.. If you don't want a device on a bus simply turn it off or don't communicate with it..The BUS you are talking about is an electrical power rail.. BUS actuall is short for BUSBAR..http://en.wikipedia.org/wiki/BusbarWhat you are doing by turning them on or off is effectively isolating the electrical power generator system from the power rail that feeds the electrics on the aircraft.. The 4 BUS TIES are for the generators from the engines I believe.. If there is a spike the generator control breaker would trip off anyway and isolate it automaticallly from the power system. There are two main power rails in the 747, BUS 1 and 2 run the first and BUS 3 and 4 run the second. They are seperated by a SSB Breaker which isolates the seperate power rails, if you closed it they would function as 1 but you'd lose some degree of your redundancy. Each of the rails powers all the systems, with the breaker off (as normal), the configuration means the aircraft has two independent power supplies, which in turn have two independent generators. I would assume (although not modelled in the PMDG?) that it would be possible to close the SSB and have all the rails powered by just one generator through just one BUS TIE if you needed to, perhaps a failed connection on power rail 1 means you want to power rail 2 with a BUS on rail 1... (look at the EICAS display and it will make more sense)..This is one of the reasons the APU has 2 generators and also why there are two external supply points. EXT 1 and APU 1 run the first power rail, APU 2 and EXT 2 run the second. Both supply rails, although independent supply power to ALL the systems be they utility (electrics, lights, panels, doors, tvs, seats, etc etc) or galley. If one failed (assuming all generators are working) you wouldn't notice any change as the other would still provide the power to the various units. However EICAS would alert you. On the ground often only one supply is set, either EXT 1/2 or APU 1/2.. you don't need both to operate the aircraft systems.. Powering both simply fires up both rails giving you redundancy at the ramp.. which isn't really necessary.. but I do it anyway..Hope that isn't too unclear.. lolCheersCraig


Craig Read, EGLL

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Thanks to everyone that replied to my questions. This hobby has the same 'camerarderie' as I enjoyed when I used to enjoy my previous hobby of Motorcycling and racing.Thanks again.


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When and under what circumstance would the 'Bank Limiter' be used? I have found no information regarding it's use?


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Dave:The bank limiter can be left in Auto in most cases, except-1) When you are heavy (to REDUCE bank angles)2) Later on the flight when you are not, and you are below FL180 where ATC usually expects all turns be made at 25 degrees of bank (to ensure/INCREASE bank angles).Usually good to use it to REDUCE bank angles (auto limits between 12-25 degrees) on departures with significant lateral course changes, and until about 320T; and then again good to use before descending through FL180 for approach.Perfectly acceptable to stay in Auto for the cruise, and even for departures/climbs with shallow turns or direct routings or at lighter weights.Hope this helps.....Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png


Best-

Carl Avari-Cooper

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Just to add to that, the bank limiter only works in HDG mode, i.e. not when in LNAV.


/Tord Hoppe, Sweden

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Thanks again guys.


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Guest joyschtik

Jepps WWT Intro 4, 27 July 2007Decision Altitude/Height (DA/H) (ICAO)A specified altitude or height (A/H) in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established.Note:a. DA is referenced to mean sea level (MSL) and DH is referenced to the threshold elevation.b. The required visual reference means that section of the visual aids or of the approach area which should have been in view for sufficient time for the pilot to have made an assessment of the aircraft position and rate of change of position, in relation to the desired flight path.Decision: to continue the approach or execute a go around.Bank angles:

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Thanks 'Joyshtick' (What's, your name), I bet a lot of fans didn't know that either?That explains a lot and you put it into laymans language. Thanks again.


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Guest joyschtik

Hi Dave,No probs at all mate. I'm still learning as there are many unknowns and unanswered questions that only Boeing and the original developers/designers/programmers know. We'll have to keep digging, I guess..;).To answer your first question; "What decides the DH 'Decision height' setting?" Landing MinimaMost regulatory authorities require visibility for landing minima. Ceilings are not required. There are limits on how far an aircraft can descend without visual contact with the runway environment when making an approach. Descent limits are based on a decision altitude/height DA(H) for approaches using a glide slope or certain approaches using a VNAV path; or a MDA(H) for approaches that do not use vertical guidance, or where a DA(H) is not authorized for use. Most agencies do not require specific visual references below AH.Approach charts use the abbreviation DA(H) or MDA(H). DA(H) applies to Category I, II and certain fail passive Category III operations. A decision altitude

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Thanks again Pete, what a wealth of knowledge there is on here. ;-)


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