Preliminary Accident Reports

May 2019 Issue

Losing Attitude

There’s really no excuse today for not having backup attitude instrumentation when flying hard IFR.

All other things being equal, one of the benefits of a primary flight display (PFD, which presents flight instrumentation on an electronic panel) is its use of a solid-state attitude and heading reference system, sometimes known as an AHARS. By using an AHARS to determine which side is up and in which direction the airplane is pointed, the vacuum-driven system is avoided and usually only an electrical system failure or failure of the display itself can eliminate the flight instruments. (Certification rules require backup flight instruments when a PFD is present but not when steam gauges are energized by a vacuum pump.)

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