Device: Samsung Galaxy S20FE Operating system: Android 13
So I was flying a route, LAX to SLC, and i have a speed warning for going mach 0.82, which is weird because i was going 319 knots, which is mach 0.48. Genuinely got a violation for ts. I’ll include the correct speeds up to mach one.
M 0.10 - 66.7 Knots
M 0.20 - 133.3 Knots
M 0.30 - 200 Knots
M 0.40 - 266.7 Knots
M 0.50 - 333.4 Knots
M 0.60 - 400 Knots
M 0.70 - 466.7 Knots
M 0.80 - 533.4 Knots
M 0.90 - 600.1 Knots
M 1.00 - 666.7 Knots
I got a violation for going mach 0.8 when i was going 319 knots make it make sense.
Quick tip, if you’re using Simbrief to generate a flight plan, look the the cruise speed when filling in the necessary information before generating the flight. It should say 320/M.85, meaning you shall cruise at M.85 which is 320 knots depending on the aircraft you’re flying.
On average, for most narrowbody aircraft, cruise at 295/M.78 and on widebody, cruise at 315/M.84.
Are you sure? From my experience, I don’t see that. You have to generate the flight before you can see your cruise speed unless you remember what speed you selected or preselected for the flight. Otherwise, it will set a CI number that you will see after you generate the flight. All of this will be on the briefing preview. It will show you your climb profile before you generate with something like 250/320/85, not after. I think that’s what you’re referring to. It doesn’t give specifics as to what IAS you would use in cruise, but it will tell you the expected TAS with the temperature for your given Mach number.
That’s not what that means… what the 320/M0.85 means is to accelerate to 320kts for the climb to cruise, and to switch to M0.85 at the mach transition altitude (28000ft/FL280 in-game).
Basically, if simbrief says 320/M.85, it means climb at 320kts from 10000-28000, and then switch to M0.85 at 28000ft, at which point airspeed will start decreasing while mach stays the same.
250/320/85 is exactly what they mean, it’s basically 250 knots under 10,000 ft then increase to 320 knots transitioning to Mach 0.85 at 28,000 ft as a350aviation explained. The 320 knots the OP explained in their Original Post is Mach 0.85, nowhere near the M 0.48 the OP thinks it should be.
For correlation to altitude, it is only related to the change in temperature relation to altitude (local speed of sound is independent of air pressure).
Mach speed is TAS relative to the local speed of sound.
Since you were at cruise altitude that 319kts must have been your IAS? Which means that your TAS would have been much higher, and as Mach speed is a measure of TAS relative to the speed of sound, your Mach speed must have been much higher.
The list of speeds you gave are in the special case where IAS and TAS merge at sea level so can both be related to Mach number only in that special case (where you have to have standard temperature and pressure, at 0 altitude).
I didn’t understand how Mach worked for quite some time either! But I didn’t have the guts to ask about it It’s definitely something worth asking about/looking into!
Your question is a great one I think. Sorting out why there are different aircraft speeds takes a bit of unpacking:
TAS (True Airspeed): relative to the air mass itself — wind doesn’t matter.
GS (Groundspeed): relative to the ground — wind does matter.
IAS (Indicated Airspeed): relative to the dynamic pressure of the air (what the wings feel). It differs from TAS because dynamic pressure depends on air density, which decreases with altitude and temperature.
Mach number: relative to the local speed of sound — important for avoiding compression shock waves and transonic effects.
I mean, our brain has to bounce between these depending on the situation. That’s why it’s such a worthwhile question!
In jet aircraft you’re often threading the needle between IAS (for lift and stall margins) and Mach number (to avoid compressibility effects), while still keeping an eye on groundspeed to track your progress over the Earth.
This part isn’t quite right: the speed of sound isn’t dynamic pressure. It’s a property of the air that depends only on temperature. TAS is the aircraft’s actual speed relative to the airmass, and Mach is TAS divided by the local speed of sound. Altitude only matters indirectly through temperature. The reason we reference speed of sound is that compressibility effects (which we need to avoid) depend on Mach, not TAS — that’s what puts the whole picture together.
It’s definitely something worth asking about/looking into!