Hi. I have a problem with PMDG 747 Airspeed Indicator. The problem is that during the flight the Airspeed Indicator shows for exaple 356 knots while the Ground Speed shows 512 knots. I was wondering if this a bug or there might be a soloution to this issue. By the way I have FSX on my PC.Thanks

Hi. I have a problem with PMDG 747 Airspeed Indicator. The problem is that during the flight the Airspeed Indicator shows for exaple 356 knots while the Ground Speed shows 512 knots. I was wondering if this a bug or there might be a soloution to this issue. By the way I have FSX on my PC.Thanks

That is normal, they are two different speeds. 356 is 'indicated' and 512 is indicated adjusted for altitude and wind. Thats the simple explanation, you can get more info onthe different types of airspeeds online.

Don't worry, nothing is broken, it should be like that.There are two reasons why the indications differ, the first is that indicated airspeed is not the same as true airspeed. Essentially your aircraft reads its airspeed from the pressure differential between the air pressure at the static port on the side of the aeroplane, and the pressure at the pitot tube on the nose or wingtip. You can see this for yourself on a light aircraft; sit in the cockpit and have someone gently cover the end of the pitot tube with the palm of their hand, as they do so, it will push a bit of air down the pitot tube and you'll see the ASI needle move in the cockpit (note: don't ever be tempted to blow down a pitot tube to check that out, it can damage it!)The strength of the air pressure pushing down into the open end of the pitot tube is calibrated to the airspeed dial, and the faster the air is going in (as you rush through the sky), the higher your airspeed reads, but, since the density of the air decreases as you get up higher (that's what your altimeter detects to work out your altitude, a bit like a barometer), there is less air to press down the tube to move the ASI needle, so your ASI under-reads at altitude. But it is only the instrument that is under-reading, and you are actually traveling through the airspace at a higher speed.What also adds to the problem is the fact that the mass of air you are travelling through can also be on the move (you feel that when on the ground as the wind). Since the air can be, and usually is, moving over the ground, even if you were in a hover in that air, you would still have a groundspeed, because you would be travelling across the ground in the moving air (that's why aircraft try and find favourable tailwinds).Modern aircraft such as your 747 can work out the groundspeed by triangulating their position from various ground-based and satellite signals, then measuring how those signals shift, and it is this calculation which you see on your primary flight displays. In the old days it was a bit trickier, and on less fancy aircraft it still can be!There are formulas to work out your true airspeed from what your ASI is displaying, but you will need to know your altitude above sea level and the air temperature to get a precise figure. Generally speaking you can simply trust the ASI to indicate a safe flying speed and regard the increased groundspeed as a bonus.Hope that helps a bit. Al

I assume that you haven't read the manual for the 747 yet. I suggest reading it as you may be missing many excellent features and descritions that PMDG has put into the plane, it only makes it that much better when you can fully understand all the systems. Best of luck.