The two speeds every business jet has
Gulfstream quotes the G700 at 7,750 nautical miles and at 6,650. Both are correct. The difference is five hundredths of a Mach number, and it decides what a range figure is worth.
Gulfstream publishes two range figures for the G700. The aircraft will fly 7,750nm at Mach 0.85, or 6,650nm at Mach 0.90. Both numbers come from the manufacturer, both are accurate, and the gap between them is 1,100nm.
That is the entire range of a light jet, traded away for five hundredths of a Mach number.
Two speeds, quoted interchangeably
Every jet in this class has at least two published speeds, and they measure different things.
The first is the cruise speed a range figure is quoted at — the economical setting that produces the headline distance. The second is maximum operating Mach, or MMO: the certified limit, the number in the flight manual that the aircraft must never exceed.
For the G800, those are Mach 0.85 and Mach 0.935 respectively. The 8,200nm figure belongs to the first. The 0.935 belongs on a placard.
Quoting MMO as though it were a cruise speed is not lying, exactly. It is simply answering a different question from the one the buyer asked. Nobody plans a transatlantic sector at MMO, and if they did, the range figure printed next to it would no longer apply.
The unit problem underneath it
There is a second, quieter issue: manufacturers do not agree on what unit to publish.
Textron publishes knots. The Citation Longitude cruises at 483 ktas, the CJ4 Gen3 at 451 ktas, the Citation Latitude at 446 ktas. Those are directly comparable to each other and immediately legible.
Gulfstream, Bombardier and Dassault publish Mach numbers. The Falcon 8X has an MMO of Mach 0.90. The Global 7500 has a top speed of Mach 0.925.
Mach is not a speed. It is a ratio — the aircraft's speed relative to the local speed of sound, which varies with air temperature, which varies with altitude and with the day. Mach 0.85 at 45,000 feet on a standard day is a different number of knots from Mach 0.85 at 41,000 feet over the Gulf in August.
Converting one to the other therefore requires assuming an altitude and a temperature. Any published comparison that lists a Gulfstream's cruise in knots alongside a Citation's has made those assumptions on your behalf, silently, and probably has not told you what they were.
What we do about it
Our reference data stores speed in the unit the manufacturer published it in, and does not convert between them. Aircraft with a published knots figure have one. Aircraft published in Mach carry two separate fields — cruise Mach and maximum operating Mach — so the economical setting and the certified limit can never be mistaken for each other.
Where a manufacturer publishes only Mach, the knots field is empty. That is a gap by design. Filling it would mean publishing our own arithmetic as though it were the manufacturer's specification, and a reader comparing two aircraft would have no way of knowing which figures were reported and which were computed.
The practical version
If you are comparing aircraft on speed, three questions make the numbers usable:
- Is this the cruise speed the range figure was measured at, or the certified limit?
- If it is a Mach number, at what altitude?
- What does the range become at the faster setting?
The G700 answers the third question honestly and in public: 1,100nm. Most comparisons never ask it.