On September 14, 2015, the FAA published policy statement PS-ACE-03-08, “Replacement of Vacuum Driven Attitude Indicators in 14 CFR, Part 23/CAR 3 Airplanes.” This will make replacing a vacuum-driven attitude indicator with an electronic attitude indicator a “minor alteration” in most instances (for Part 23 aircraft weighing less than 6,000 pounds). The new policy attempts to create a workaround to the current part 23.1311 regulations requiring electronic displays to have independent sources of altitude, airspeed and attitude instrumentation, in case of power failure to the PFD. An unintended consequence of this regulation prevented the replacement of vacuum-driven altitude indicators by electronically driven altitude indicators. The new policy provides relief from having to install an independent standby attitude instrument as required by §23.1311
The non-regulatory policy is meant to increase flexibility of improving aircraft safety quickly and efficiently with new technological advances. Many, including AOPA, consider the decision a move in the right direction, signaling a shift towards more commonsense policies by the FAA.
In its statement, the FAA references its 2001 Safer Skies initiative that identified vacuum system failures as a significant cause or contributor to fatal accidents under IMC conditions. Failed bearings, primarily caused by contamination due to dirty air supply can lead to pump failure, rendering the AI inoperable. Loss of AI function in IMC flying can be catastrophic without a backup, especially since the devices can degrade slowly, making it difficult to recognize a failure. Replacing vacuum driven AI with solid-state electronic versions gives an extra margin of safety, increases reliability and decreases maintenance costs. Electronic gyros eliminate the problem of bearing failure since they are solid-state gyros (with no spinning bits).
Electronically driven systems also improve functionality by providing:
- More precise attitude indication
- Greater internal error-checking ability
- Internal redundancy
The policy change allows the replacement of a vacuum-driven AI with an electronically driven AI with backup battery that can include a secondary function, such as a turn-and-slip indicator. The only caveats are that the new unit must be positioned to allow for partial panel operations in the event of instrument failure and that it must include a dedicated circuit breaker.
There are several electric and electronic AIs on the market:
At $650, this battery-based emergency power supply is designed to provide an hour of auxiliary power to an electric AI or DG and up to 6 hours of power to the RCA 2600 Digital Horizon. Easily mounted behind the instrument panel, it provides an extra margin of safety when you need it.
The Castleberry Series runs from $2300 to $3800, depending on model. This high quality electric attitude indicator replaces the turn and bank and may be installed in the same panel location, freeing up crowded panel space. Installation of these units is straight-forward.