Hi Everyone:Simple question - If I am on the ground at an airport above sea level (i.e. - Chigaco KMDW at 640 ft), how can a pilot tell when they are at a fixed point above the airport if I reset the altimeter? For examle, if I reset my altileter at Chicago's KMDW airport, it tells me that I am 640 ft above seal level when I am sitting on the runway. But if I want to turn on the Autopilot when I arrive at 1,000 ft AGL for example, how do I know instantly that I am at 1,000 ft? Do I just calculate in my mind that it will be when I reach 1,640 feet & just "remember" this when I get up to that altitude? If I were to turn it on when the altimeter reads 1,000, I would really only be at 360 ft. AGL and not 1,000. What about on descending? How will I know to turn off the A/P at, let's say, 200 ft AGL? When will that be? Do I just have to know to watch for 840ft on my altimeter? OR, am I supposed to reset the altimeter first & then scroll the altimeter knob ("Kollsman knob?") down until the altimeter reads zero? In short, there are specific times I seem to need to know what the AGL is, but Ground level for this airport is not 0, but 640. How do pilot's handle such a thing?Thanks.Chris Catalano

Not to sound silly Chris or to be a smary pants but install a radar altimeter to your cockpit or build a window for one.If you cant do this or dont know how, just drop me an email at [email protected] and I will build you one (a seperate window and gauge) and give a simple source to copy and paste into any panel config. This will give you a fairly accutate AGL reading in all but the most ragged of mountains.JimPS And "yes" most of us real pilots still use "simple old arithmetic done in our heads.

Or if you are flying some advanced aircraft you will see a RA readout on the PFD which is active for a certain altitude about the ground..[h4]Randy J. Smith[/h4]AMD 64 4000+|ASUS K8V DELUXE|SAPPHIRE ATI X800XT PE|MUNCHKIN 3200|80 gig SATA|DELL 1905FP 19" LCD|TRACKir PRO|PFC JEPPESEN MOONEY YOKE|CH PRO PEDALS|

And most show up to 2500 AGL if I recall correctly. My mind hasn't been storing the info too well lately. Probably because it doesn't pertain to me in the real-world yet so it all goes in one ear and out the other. If I hit 200knots in any of the aircraft I'll be flying in the next 4-6 years, I'll be riding a wingless fuselage down. :-lol----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

do the math, don't touch that knob! :-)that's the fun, no?

One option is to set the local (I think is QFE? but might be QNH?) which is to say zero the indicated elevation at your desired airfield.This is OK if you are flying locally and for shortish durations.You now have an altimeter which reads AGL at field,we do this frequently during local glider flights.Note:This method does not need a RA but is totally unsuitable for flights to other airfields or of long duration where a presure change is possible Best WishesAshley Sear(G4MGD-Licensed since 1981)http://www.jdtllc.com/images/rcv4bannerbeta.jpg

Real pilots always set their altimeter to the local sea level pressure (if available) below 18,000 MSL, so the altimeter should always read MSL (though Ashley's example can work ok for those extreme-local flights)You almost always use MSL when flying since the ground level varies so much. For things where you do use AGL such as a traffic pattern or decision height, you have to do the math, though for the DH, your chart will tell you both the MSL and AGL altitude.

Thanks Randy - Also - is the PMDG 737-700 such an aircraft where I can get a readout of Radio Altimeter, and if so, how do I calibrate it so it reads 0 when I am on the ground?Thanks.Chris

Not sure since we don't use it in the US (well, the nearby AFB's METARs have QNH), but might the FE in QFE mean field elevation?----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

The Radio Altimeter isn't set and, as far as I can figure, it's just a downward pointing radar that measures the distance to what ever it hits below you. On the PMDG 737NG series, it'll be in a black rectangle with white text that pops up on the lower portion of the ASI in PFD/ND display configuration. For the EFIS/MAP display configuration, I'm not sure off hand.----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach