A recent highly publicized accident in Missouri involving a Cessna 335 has focused the FAA regulatory spotlight on potential deficiencies in aircraft equipped with dual vacuum systems. The FAA states that there are 1,990 reports of vacuum system component failures on the Service Difficulty Report database. An undetected failure of components of an aircraft vacuum system can result in total or partial loss of attitude and directional indications, and could possibly lead to spatial disorientation when operating in Instrument Meteorological Conditions (IMC).
In an effort to preclude the possibility of an undetected vacuum system failure, the FAA published an Airworthiness Concern Sheet (ACS) applicable to "All twin reciprocating engine small airplanes certificated under CAR3 or 14 CFR Part 23 that have gyroscopic instruments which are powered by single or dual vacuum sources." The ACS indicated the FAA was considering an Airworthiness Directive mandating repetitive vacuum system check valve inspections and replacements and solicited input from AOPA, aircraft type-clubs, and other organizations. In response to the ACS, AOPA and aircraft type-clubs opposed an AD mandating repetitive inspections and parts replacements, pointing out that a simple preflight check at engine start-up could completely preclude the possibility of an undetected vacuum system failure. The FAA, in reaction to the recommendations of AOPA and others, opted out of an AD, and instead issued an SAIB recommending a simple preflight verification of the vacuum system's integrity.
AOPA thanks the FAA for affording the General Aviation community an opportunity to participate in their effort to mitigate this airworthiness concern. AOPA believes that the FAA has taken the best possible action by avoiding unnecessary mandatory maintenance actions through the issuance of an SAIB. The quality of industry comments in response to this ACS is an example of how the practical knowledge and expertise of owner's organizations and aircraft type-clubs can result in practical and affordable alternatives to draconian AD actions. AOPA looks forward to continued successes using the airworthiness concern process.