[DeTomaso] NPC air speed. indicators

[J. Sean Keane]

> Can the engineers or pilots on the list tell me why a 300 million jet like the Airbus uses a pieto tube to measure air speed instead of a GPS?  Seems like obsolete technology when a $125 unit from WalMart can do a better job and isn't subject to icing over.     Michael in Savannah
>   
You've already received the best answer, namely that the airspeed is 
what keeps the plane in the sky (or not) rather than the ground speed, 
but there are other good reasons.  GPS doesn't meet the FAA's 
requirements for accuracy, integrity, and availability.  As one example, 
valid GPS signals are not required to be available all of the time.  The 
U.S. Military can shut off the civilian GPS signal in an area of 
operations any time they want, while maintaining military use of GPS.  
There are a host of other issues which are being addressed by a system 
called WAAS.  Look up the Wikipedia article if you're interested.

In my opinion, the best reason to prefer pitot tubes over GPS is that 
the pitot tube is a simple mechanical system.  As long as it doesn't ice 
up, which can be prevented with a simple heating element, it works even 
if the plane loses electrical power.  Also, a pitot tube can't be jammed 
from the ground.  I'd prefer that any airplane I'm riding in isn't 
susceptible to failure from a terrorist with a homemade transmitter and 
a hand-held L-band dish.

Regards,

J. Sean Keane