However, even modern glass avionics sometimes have bad days, and the associated failures can be multiple. While logical, data comparing this perceived reliability is illusive. This instrument panel closely approximates the description in the accompanying table of aircraft Bīecause of a lack of mechanical gyros and spinning vacuum pumps, solid-state avionics are perceived to be more reliable. In the latter situation, the turn coordinator had to be retained. However, this exchange resulted in losing the slip/skid ball and impacted an associated rate-based autopilot. With Advisory Circular 91.75 (June 2003), the FAA allowed the exchange of the turn coordinator with an electric attitude indicator. To avoid the single-point-of-failure mode, some airplanes have been fitted with a second vacuum pump, electrically or engine driven. Newer panels were fitted with a visible indicator that the vacuum pump failed, an improvement over the nondescript peanut-sized suction indicator. In IMC, it’s a true emergency, especially in turbulence, because aircraft attitude had to be inferred from these remaining instruments-a high workload. In the above situation, we were left with the airspeed indicator, altimeter, electric turn coordinator, vertical speed indicator (VSI), and a magnetic compass. As the gyros slowly wound down to a dead stop, along the way they would indicate “interesting” attitudes on the AI and result in even more interesting flight excursions. While a practical way to simulate vacuum pump failures, realistically, such a failure would be more insidious.
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