To all Sim Pilots I'd like to say hi !

Hi again
Capt Steve here with another Tech Tip.

Subject: Transition Altitudes and ISA

This month I would like to talk about Transition Altitudes and ISA. It is important to know that in the U.S. that the Transition Altitude is 18000 feet, but in Europe every country has its own Transition Altitude. I worked for Mcdonnel Douglas years ago and helped in the delivery of new aircraft to Europe and Asia. When in Holland I flew with the first flight crews on the new Martinair MD-11's and I noticed right away that they entered a different transition altitude, 10000 feet! I found out later that different countries use different Transiton Altitudes: In Ireland it's 5000 feet QNH and in the UK it is 6000 feet. Transition Altitudes are set for the specific country and give 1000 feet separation between aircraft and the highest point in the country. Transition altitudes are the highest altitudes you can fly in controlled airspace before you must change to 1013.25(29.92), any higher and you'll be referring to flight levels. Now it is very important to understand that aircraft altimeters measure air pressure, not altitude. Especially today when just about every pilot uses a GPS; it is also important to remember that an aircraft flying at a specific pressure altitude may note a different altitude displayed on his or her GPS(which by the way measures actual distance above mean sea level). In some cases this difference is small...but it might be enough to cause a mid air collision if a pilot was using the GPS instead of pressure altitude. This now brings me to the 1976 International Standard Atmosphere or (ISA). This was developed to provide a common reference for temperature and pressure based on 59 degrees F and a baro of 29.92inHg.,(under these exact conditions the Density Altitude is equal to the Pressure Altitude). In the lower atmosphere (below 36000 feet) the standard pressure lapse rate per 1000 feet =1.00 inch/Hg, and the temperature rate is 2 degrees C or (3.5F). Remember that the altitude setting in the Kollsman window refers to the correct "Geometric Altitude" only, and that Density Altitude means Air Density, and is neither "Pressure Altitude" nor "Mean sea Level", but strickly "Density Altitude". So Density Altitude is the altitude at which the ISA Density is the same as the density of the air being evaluated., i.e. calculating Density Altitude is to calculate the actual density of the air, and then find the altitude at which that same air density occurs in the Standard Atmosphere. ISA temperature Deviation, (different than ISA Density) is used to forecast in flight route temperatures, the formula goes something like this..........If the ground temperature is 20degrees C you would have 20C - 15C =ISA DEV of +5C. The 15C comes from the Standard day temperature. Well thats it for now, till next time..........

Good flying , see ya next month
Capt Steve

Till next time, great flying to you,
Capt Steve