A nice saturday afternoon to everyone ;-)

 

At the moment I'm enroute on my MD-11 from EDDM to KJFK. Flying now anywhere over the North Atlantic I asked myself what are the three speeds showing on the PFD and the ND (see picture).

 

Its just a guess from myself, never tried to find out what they really are until now ;-). So:

 

On the ND the GS stands for Groundspeed? So the speed over Ground is 456 knots?

The TAS stands for True Airspeed? 478 knots, in this case higher because I have a Headwind?

 

Correct so far?

 

But what then is the speed shown on the PFD, the 275 knots. Always thought that is the airspeed? Why its around 200 knots lower than the TAS shown in the ND?

 

Thanks for any answers, Nicolas

Its indicated airpseed:

http://en.wikipedia.org/wiki/Indicated_airspeed

And its lower because the the air at higher altitudes has less density, less molicules in the air, so there less air to hit the Pitot.

 

So if there is less air goin into the pitot, there is less pressure inside of it :

 

Ground speed is the speed the aircraft is travelling over the ground. TAS=True Airspeed is is the actual speed the aircraft is travelling through the air calibrated for temperature and altitude, important for navigation. Indicated airspeed is the speed that is actually hitting the pitot static system and is in a sense, "raw," it is not calibrated and is directly fed to the aircraft.

The luxury of IAS is that 250 knots on sea level does the same stress to the aircraft as 250 knots at FL350. Just a small thing.

Thanks for the answers. Cleared up some things for me ;-)

 

Nicolas