How to calculate mach based on IAS?

There is something which I don’t understand. I am cruising at M 0.78 (290 kts IAS) at 30000ft and my ground speed is 457kts. However, when I use a converter, it says that M 0,78 is equivalent to 295 kts IAS. However, in IF this is Mach 0.79. Is there somehting which I’m doing wrong? Please help

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Ground speed is affected by other factors such as wind.


He is talking about IAS. It should measure to 295IAS however you have to remember that Mach is also dependent on air pressure. If they’re is a variation in the air pressure at FL280 then it may show up as M79. I’ve had it hit or miss between 295 being M78 and M79 often. For the most part though it usually ends up on the M78 side when I crossover at FL280

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The problem is that I can’t calculate stuff if this isn’t accurate. Could you tell me what M 0,54 is in IAS?

Help me someone!

May I ask what you need those speed information for? As normally we usually take the Mach speed during cruise and seldom really take the ground speed, since it is affect by multiple factors such as wind.


Also, the height affects the Mach speed.

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I’m trying to calculate the dash-8 cruising speed.

Would you like to take in Mach speeds or in terms of IAS?

Ground speed is unlikely to be a reference, since it is usually heavily affected by a number of factors.

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Well, it says the cruising speed is M 0,54. I need to know what IAS that is.

I am only good for commercial airliners, I’m sorry, but I know that commercial airliners cruise at Mach 0.86

When you fly the aircraft, and in cockpit HUD view. The left column will show the IAS.

It doesn’t show the cruising IAS.

Referring to your original post. You seem to have mixed up Ground Speed and Initial Air Speed. Are you sure that you have done the calculations correctly?

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I am using a converter

Which speed are you converting to?

And what speed result are you aiming for?

I want to see what IAS is M 0,54

@Philippe_Gilbert Are you talking about the Dash-8 calculations from your previous topic?

Ground speed is your speed relative to the ground. If you’re traveling in a car down the highway and look at the speedometer to see your speed, that’s ground speed. Your car is moving 60mph/100kmh relative to the ground.

IAS stands for indicated airspeed. This number will decrease as you gain altitude and increase as you lose altitude, even if your ground speed (speed relative to the ground) remains constant.

The Mach number is a percentage of the speed of sound. Mach 0.54 means 54% the speed of sound. As you increase altitude, the air becomes less dense, so sound travels slower. This means that even if you’re ground speed remains constant, your mach # will increase as you gain altitude.

Long story short, the IAS for M0.54 changes depending on what altitude you’re flying at.

You may find this tutorial helpful: Understanding different types of speeds

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Could you share the converter you are using as well as the information you are inputting?

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