Electric backup AI

[jetdriven]

There really isn't a requirement for s standard rate turn anymore.  But 17 degrees of bank at 100 knots and 22 degrees at 150 knots is really close. 

[cliffy]

For use as a backup AI in place of a T&B instrument the Feds decided that in today's world indication of a standard rate turn was not important enough placed against the loss of vacuum and one vacuum AI. Secondly, as a backup AI it needs to have an ON/OFF flag internal. 

Below are cuts from AC 91-75 dealing with the subject:

d. An FAA-approved attitude indicator with a failure warning flag that monitors power supply is acceptable under this AC. This attitude indicator must have an independent power source from the primary attitude indicator. This provides an equivalent level of safety to existing rate-of-turn gyro arrangements.
 

However, in today’s air traffic control system, there is little need for precisely measured standard rate turns or timed turns based on standard rate. Maintaining a given bank angle on the attitude indicator for a given speed will result in a standard rate turn. Pilots using this AC to substitute an attitude indicator for their rate-of-turn indicator are encouraged to know the bank angle needed for a standard rate turn.
NOTE: The FAA preamble language for the 1970 amendment to section 91.33, re-codified to section 91.205, states: “[T]he FAA believes, and all other commenters apparently agree … the rate-of-turn indicator is no longer as useful as an instrument which gives both horizontal and vertical attitude information.”

 

 

 

[cnoe]

And in this case I firmly believe the feds got it right.

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[MB65E]

Ok, I'm splitting hairs in a gray area now. I have read the AC now several times. No where does it say the "electronic device" needs to be TSO'd. All it says is the unit must be stand alone with very very limited other functions. It even not need its own power source as long as voltage can be verified prior to take off. I have read all of the other ac's and Cfr's mentioned in the AC... Not one mentioned TSO'd certified Equiptment. Under the IFR regs in part 91 there is no mention of certified equiptment. Many argue that part 23 regs still apply to CAR 3 aircraft, but there is not much stating that. I will end up putting in a certified rca-2600-3. But there is way better experimental units available. It's  pretty strange that the FAA comes out with a do unmet clarification AC only for there to be more questions! Lol.

-Matt