Nothing was stranger than floating down a perfectly centered ILS approach in the soup with the compass indicating you were in a 30-degree crab. I once flew a Piper Warrior with that problem. “Were you struck with lightning on the last flight?” I joked, knowing from experience that a jolt like that, though it won’t knock a metal airplane out of the air, will magnetize the airframe, causing all kinds of erroneous heading indications. So why did the headings generated by the magnetometers and a whisky compass not add up? Had we somehow lost calibration on both magnetometers? And our compass suddenly needed a swing? All at the same time? That was pretty unlikely. The wind computation was clearly off because of erroneous heading information being fed into the air data and heading reference system (ADHRS) computer by two highly sensitive magnetometers (one for each unit). The backup iPad GPS agreed, too, as did the secondary GPS on the EFIS motherboard. We were right on the magenta line the computer had generated depicting our GPS track to our first waypoint, and our clear view of the landmarks below concurred with the moving map. This did not bring a smile to my co-pilot/AMT’s face. “And look, the headings don’t agree at all between the two ADHRS, either,” I noted. This airplane, with this powerplant, will never see that paint-blistering number in real life. If the wind computer was correct, our TAS would have been closer to 230 knots. It was highly unlikely that our true airspeed was much above 180 knots at 23 inches/2400 rpm/11 gph fuel flow. “It says we’ve got a 100-knot crosswind, which I assure you, with this groundspeed, we do not,” I asserted. “Hon’, that wind can’t be right,” I affectionately elbowed my co-pilot, who also happens to be the AMT who installed the avionics as well as my husband.

It was my scan (yes, I have the same instrument scan for VFR that I have for IFR flight) that clued me in to a potential issue. We fly a relatively new airplane, equipped with dual electronic flight systems (EFIS). There wasn’t a cloud in the sky and all systems were nominal, or so I thought. The setting was bucolic enough: We were flying straight and level on a cool summer’s morning somewhere west of the Black Hills and near Devil’s Tower, above Wyoming. I recently learned the hard way how failure of the heading sensor(s), usually a magnetometer, may not be a failure at all, depending on how the equipment is designed and installed. In many situations, losing heading information isn’t the end of the world-especially if GPS navigation remains available-but it can have a ripple effect on the panel’s various other systems and capabilities. One of these new-tech failure modes involves the way in which they determine the aircraft’s heading, along with other information, most of which firmly belongs in the nice-to-have-but-not-critical category. Along with their additional capabilities and accuracy, glass panels also bring different failure modes to the cockpit.

Through the “magic” of a software-driven display supported by various sensors, modern flight instrumentation can provide easy-to-read attitude information and a wealth of other data that simply wasn’t available before.īut there’s no free lunch. The latest-technology glass panels do many more things than the old, tried-and-true “steam gauges” with which many of us grew up.

Piper cherokee 180 glass cockpit