Indicator Replacement - Att / Heading

[bc-avi]

Hey everyone.

I'm an avionics tech looking to help a customer out with some modifications on their aircraft. We're hoping to change out the old Attitude and Heading indicators with something more modern like the Kelly Mfg RC Allen digital instruments (RCA2610 and RCA1510) in a VFR Bell helicopter.

The major mod section of CAR 571 Appendix A (2)(e)(10) says "affect instruments, or indicators that are installed as part of a system required by the approved type design" so replacing the primary attitude and heading indicators seems to be classified as a major modification. But then I start digging into the Type Certificate (FAA Type Cert: H4SW) and it doesn't seem to list any of the indicators or avionics that are 'required by the approved type design'.

The old indicators are the same size, function and TSO as the new ones we want to put in, but I don't really know what would stop us from doing the install. There would be no changes to the instrument panel or wiring, just an indicator swap. I've seen other aircraft of the same type with the digital indicators on the copilot side, installed using the manufacturers data manual / TSO. We don't have the capacity right now to develop an STC so that's not a route we're considering.

The regulations almost need a law degree to decipher

Thanks in advance!

[planenuts]

The TCDS is not going to list required indicators. The required ones are determined by the aircrafts certification. In your case - if you scroll through the TCDS you will find it is certified per 14 CFR 29. Looking at that certification you will find the requirements in there...

29.1303 Flight and navigation instruments.

The following are required flight and navigational instruments:

(a) An airspeed indicator. For Category A rotorcraft with VNE less than a speed at which unmistakable pilot cues provide overspeed warning, a maximum allowable airspeed indicator must be provided. If maximum allowable airspeed varies with weight, altitude, temperature, or r.p.m., the indicator must show that variation.

(b) A sensitive altimeter.

(c) A magnetic direction indicator.

(d) A clock displaying hours, minutes, and seconds with a sweep-second pointer or digital presentation.

(e) A free-air temperature indicator.

(f) A non-tumbling gyroscopic bank and pitch indicator.

(g) A gyroscopic rate-of-turn indicator combined with an integral slip-skid indicator (turn-and-bank indicator) except that only a slip-skid indicator is required on rotorcraft with a third attitude instrument system that—

(1) Is usable through flight attitudes of ±80 degrees of pitch and ±120 degrees of roll;

(2) Is powered from a source independent of the electrical generating system;

(3) Continues reliable operation for a minimum of 30 minutes after total failure of the electrical generating system;

(4) Operates independently of any other attitude indicating system;

(5) Is operative without selection after total failure of the electrical generating system;

(6) Is located on the instrument panel in a position acceptable to the Administrator that will make it plainly visible to and useable by any pilot at his station; and

(7) Is appropriately lighted during all phases of operation.

(h) A gyroscopic direction indicator.

(i) A rate-of-climb (vertical speed) indicator.

(j) For Category A rotorcraft, a speed warning device when VNE is less than the speed at which unmistakable overspeed warning is provided by other pilot cues. The speed warning device must give effective aural warning (differing distinctively from aural warnings used for other purposes) to the pilots whenever the indicated speed exceeds VNE plus 3 knots and must operate satisfactorily throughout the approved range of altitudes and temperatures.