Originally Posted by BobTurner
The requirements for a standard category airplane are not just in the FARs; there are a lot of additional requirements hidden in the type certificate process. e.g., until the recent faa exemption for certain efis units, you had to install a TSOíd AI in a type certificated airplane. Thatís not in the farís, itís in the type certificate rules. Likewise, you will not find any normally certificated aircraft with a Type Certificate for ifr that has only one power source for attitude info.
show me the source of your info. FAR91.205 dictates what equipment is required for IFR flight. looking at type certificate 3A12 which is the type certificate for the cessna 172. since there are a lot of models,and getting into the newer models requires digging into the cessna manual, I will use the 172 - 172Q models. you will find this in the data pertinent to all models sections:
The basic required equipment as prescribed in the applicable airworthiness requirements (see
Certification Basis) must be installed in the aircraft for certification. This equipment must include
a current Airplane Flight Manual effective S/N 17271035 and on.
now going to car 3 which is the certification that the aircraft was certified under you will find under section 3.665 basic equipment, which is mostly the same things you will find in far 91. in in section 3.668 you will find the requirements for Gyroscopic indicators (air-driventype) the only mention of two sources is for multi engine aircraft.
the only redundant source is that cessna used a electric turn and bank, or T/C in their aircraft for certification.
there is nothing in the FARs that says a TSO'ed anything must be installed in a part 91 aircraft. there are systems that must "meet" the requirements of the TSO. A TSO does not permit the installation of anything in a type certificated aircraft, it is only one way of showing that a part can be installed on an aircraft.
there are thousands of pipers,cessnas,and beeches flying around with two air driven gyros and a electric T/C and even then, under car 3 there was nothing that said that the T/C or turn and bank needed to be electric.
again, if you can show me a certification document, or regulation requiring two independent source of power for IFR I would love to see it.