Greetings, When an aircraft manufacture posts on their website that the range of an aircraft is XXXX nm, at xxx knots, at what altitude are they talking about? For example, the Gulfstream G550 has an Range of 6,750NM, at a cruise speed of 459 KTS. Is there a set altitude that aircraft companies test their aircraft for maximum range? Thanks J.R. Duda

It's generally like cars for City/Highway miles per gallon. At what speeds? Is it 50, 60, or 70 miles per hour they're going on the highway. They just find which get's them the best range, and which gets them the best speed.----------------------------------------------------------------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

There is a lot more to range than the little information on the Gulfstream website.6,750 nm @ .80 Mach - 8 pax + 4 crew + NBAA IFR reserves6,000 nm @ .85 Mach - 8 pax + 4 crew + NBAA IFR reserves5,000 nm @ .87 Mach - 8 pax + 4 crew + NBAA IFR reservesInitial cruise altitude - 41,000Maximum cruise altitude - 51,000Maximum payload - 6,200 lbsPayload with maximum fuel - 1,800 lbsMy company is looking at the planned purchase of a G-550 or a Global Express in the next year - and the flight dept view is 5,500-5,750 as the max effective range of either aircraft.There are some very interesting charts on the Cessna web site.Their charts have aircraft weight, altitude, speed (KTAS) and Fuel Flow (lbs/hr) - those numbers give a much more accurate representation of the aircraft performance cababilities.I especially like their Range/Payload charts - very informative.But getting back to your basic question - from the information I can find a G-550 would climb quickly but slower than normal to FL410 then do slow step climbs as they burned off weight up to FL510 for a short time, then a long slow descent to landing. That profile should maximize the range of the aircraft.That assumes 8 pax @ 170 lbs each & 4 crew @ 170 lbs each - I don't see a baggabe allowance - so any carry on and stowed baggage would have to fit within the 170 lbs per person weight - 1980 lbs total payload weight. However since the max weight with full fuel is 1,800 lbs - some one must be on a diet.These numbers come from computer calculations - not testing. The science of aircraft design, the known performance of engines at altitudes - those can all make the calculations accurate with a few tenths of a percentage.The range numbers are published long before the aircraft flies.The critical factor is always how to calculate and control the fuel flow in pounds or kilograms per hour.