hi, i have some questions rergarding the decision height on the PMDG 747-40Xfirst, how can i determine it?second, what's the difference between RADIO and BARO on the EFIS??please sugest me, since i use FS2Crew a lot i really need those informations

hi, i have some questions rergarding the decision height on the PMDG 747-40Xfirst, how can i determine it?second, what's the difference between RADIO and BARO on the EFIS??please sugest me, since i use FS2Crew a lot i really need those informations

-You can get the DH from the approach charts- a 747 is a CAT D aircraft.- RA Radio Altimeter Height- works similar to an echo lot on a ship - For a CAT 1 approach it will be a BAROMETRIC Altitude- usually 200ft above MSL Mean Sea Level- lets say airport elevation is 2000ft than you would set 2200ft.For a CAT 2/3 approach it is RA; i.e.: CAT 2 ~ 100ft above ground level, CAT 3a ~50ft, CAT3b ~ 20ft.This is depending on the aircraft as well as on the company. I am NOT familiar with 744 though!

As you might know, the decision height is a set height at which you must initiate a Missed Approach if you cannot see a visual reference for the runway by the time you have descended to that set height (there's a bit more to it than that in the exact rules, but that's the gist of it). This is actually a legal limit and is generally determined by equipment at the airport which determines the visability at the airport with electro-optical sensors to give an official Runway Visual Range (RVR). Visibility limits for landing are sometimes specific to airports and are listed in the aerodrome booklet and approach charts as the 'published minima'. However, some of these limitations are also dependent on the currency and the ratings of the pilots and the equipment on board the aircraft, for example, in a full 'pea souper' Cat IIIc landing where you can't even see the windscreen wipers, your aircraft generally has to have the ability to maintain tracking on the runway centreline after touchdown and keep guiding straight as it rolls out to a standstill (which is why the radio beacons for ILS are at the far end of a runway).Since we are talking about the 747, we can assume that your aircraft has all the necessary fancy equipment to do full Cat landings and that you are 'qualified' for those types of approaches (in a simulated sense). Therefore, you can use the following (going from toughest to easiest):In zero visability, no decision height necessary (this makes it a Cat IIIc landing)With runway visual range at between 75 and 150 metres, your decision height should be 50 feet (this makes it a Cat IIIb landing)With runway visual range at between 150 and 200 metres, your decision height should be 100 feet (this makes it a Cat IIIa landing)With runway visual range at between 350 and 550 metres, your decision height should be 200 feet (this makes it a Cat II landing)With runway visual range at 550 metres or more, your decision height should be greater than 200 feet (this makes it a Cat I landing)Typically, these are classed as 'precision approaches' because they use both lateral and vertical guidance (i.e the localiser and the glideslope). Other factors which determine the Category of landings a runway can handle include the level of redundancy in the equipment, for example, when operating full Cat landings in really crappy weather, the airport has to have several back up systems in place to ensure the integrity of the ILS signal, such as spare generators for radio beacon power. Other less obvious stuff includes such things as vehicles on the airport not being allowed to use their radios when near the transmitters for the ILS signal. It is these things which cause aircraft to divert to alternate airports, since if either the airport, the flight crew or the aircraft they are in are not legally equipped and qualified to fly those sort of approaches, they have to go elsewhere, which is why your have an alternate and 45 mins of spare fuel.So, you will need to know what the runway visual range (RVR) is at your destination airport. You can get that a number of ways, in the real world it would be told to you over ATC, or you could determine it from the airport's ATIS frequency (which is why you have two comms radios), also, when FS ATC vectors you for a landing, it should put you on a runway with the correct category for the weather in FS or if it is below minimums tell you to go elsewhere. But it doesn't always do that since it cannot read what equipment your aircraft has and doesn't 'know' how skilled you are, so a more reliable method is to look on an approach chart for the published minimums and categories a particular runway is able to handle, and then get a weather report for the destination. I use Flight Keeper's ACARS gauge for that to get a weather report in flight, but many weather add-on programs can generate a similar report at various stations and at a push, you can use the map and weather tools in FS to determine it too.When you know what your DH should be, setting it on the panel and checking it with your 'co-pilot' is of course part of your landing checklist and briefing. In really crappy weather and tricky conditions, it is very often the case that one pilot will 'fly the needles' of the ILS approach and the other will look out of the window for the visual reference and when he/she spots it, will call out 'my aircraft' at which point the pilot on the needles will confirm 'your aircraft' and the pilot with the visual on the runway will take over the landing, whilst the guy on the needles will continue to monitor the instruments and give altimeter call outs.Radio alt and barometric alt are what the aircraft is using to determine its height. Barometric alt should be an accurate gauge of your height providing you have a current QFE (field elevation pressure reading) from the airport, but it is no use if you are on QNH (height above sea level) unless you know the height above sea level of the airport. So you also have radio altimeters which bounce a signal off the terrain below to tell you how high up you are. You might remember the recent crash of a Turkish Airlines B737 on approach to Schiphol, which it is suspected was caused by a faulty radio altimeter being used on approach. The faulty radio altimeter incorrectly reported that the aircraft was down on the runway when it was still several hundred feet up. The autopilot then used that mistaken info to close the autothrottles thinking the aircraft was down on the deck when it was not, and the resulting loss of thrust caused the aircraft to semi-stall and belly into a field short of the runway.Radio altimeters are of course only useful if the terrain elevation is relatively flat below you when you are on finals, so some airports are not suitable for that data source when landing, for example Prague's Ruzyne airport in the Czech Republic has quite an incline up to one of its main runways on the last few miles of the final approach, making it a tricky airport to land at when in poor visability. This incidentally, is one of the reason why I'm hoping the new PMDG 737 NG for FSx will feature the Vertical Situation Display (VSD), as to get that capability I currently have to use the DBS Profile Radar add-on.This is all a very 'quick and dirty' guide to things, and there is a bit more to matters in real life, but it should get you on the right track, so I hope it helps.Al

Alan, you should copy this to an AVSIM wiki article. Nice job.

Alan, you should copy this to an AVSIM wiki article. Nice job.

Alan: may be recheck before you do that: CAT 2 with a DH of 200ft??, CAT3a with 100ft??

As I said on the post, it was a 'quick and dirty' guide from memory, so it might not be the letter of the law, but was rather intended to provide a 'quick assist' to the original poster which would be good enough to get them going.Feel free to tweak it for complete accuracy and stick it on the AVSIM tutorials if you like, everyone should have a crack at doing a tutorial.Al