REFLECTOR:Attitude Indicator vs Turn coordinator

[reflector@tvbf.org]

In a message dated 12/8/2003 4:07:40 PM Eastern Standard Time, rdugas@bayou.com writes:

> He states the FAA has agreed to allowing a second AI run off
> a separate power source to be installed in the place of a
> Turn Coordinator.

I think I remember reading that in the AOPA magazine. Don't know where you could confirm it though. 

> The idea is that a failed AI places one in partial panel
> flying and a TC is not as good as a second AI.  

I am leery of this concept though for two reasons. 

1) Stec AP's run off the TC. Since TC's have very, very low failure rates I like that. Whichever AI you slaved your AP to could fail and roll you over. (conversely when your AI fails you can still use your TC driven AP to keep you shiny side up until you get VFR.) 

2) I just use the TC too much to throw it away. Ever notice how you have have to reset your DG every now and then due to precession but you never have to reset your AI? that is because the AI has a pendulum based system that is continuously trying to erect the gyro. So after a 1 minute turn in a hold or a procedure turn the AI is off by several degrees. So when you roll level the AI will say you are one wing low. If you level by the AI then the DG keeps moving. That can be very disorienting. Since the TC has no pendulum it's always accurate. When you center the TC you are NOT turning. 

So I always roll into and out of every turn with reference to the TC. Sure, I am still keeping the AI in the scan but the fine tuning gets done with the TC. 

IMHO, having a secondary AI will be a very good thing on those rare occasions when you loose the primary. However, loosing the TC for every other flight would be a big loss and would make everyday IFR flying that much more difficult. At least to me. 

Rob



Rob