August 2009 Issue

More Attitude and Backing Up a Vacumm/Pressure System

When your primary attitude reference fails, it’s too late to go shopping for some backup. Adding redundancy depends on what you have already.

Anyone planning to do for-real, piston-airplane IFR work also needs to plan for the inevitable gyro instrument failure. As too many accidents have shown, depending on your rusty partial panel skills to get you home ain’t gonna cut it for much more than descending through a thin overcast. For most of us flying behind air- or vacuum-powered gyros, that means at least a backup pump of some kind or an electric attitude indicator (AI). Those lucky enough to have glass panels in a certified (i.e., non-LSA) airplane probably already have some kind of backup. It could be an electric AI, or an instrument powered by the airplane’s essential bus, something we’ll explore in a moment. And it needs to be in your main scan, not on the other side of the panel, as is often the case with backup instruments in piston aircraft. To accurately assess whether you need a backup instrument, you need to know what powers your primary gyros, the likelihood of that system failing and decide whether existing backup instrumentation, if any, is both up to the task and in a location designed to maximize the ease with which you can transition to it in for-real situations.

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