With today’s glass cockpits, “partial panel” now probably means reverting to a backup gyro artificial horizon, either electric or vacuum driven. Even some six pack-equipped aircraft (with vacuum primary gyros) have had their old-fashioned turn coordinators replaced by backup electric-powered gyro horizons — much better because they afford pitch and bank information as well as rate of turn. I haven’t heard any war stories, yet, from pilots who have lost power to their glass suites and had to revert to what the rest of us have been using since the 1930s. But they will surely come. One difference with glass panels is that if they should fail, there will be no doubt. I don’t believe it is possible for the system of sensors and the display to fail gradually, as is the case with a failed gyro that is slowly spinning down. Most pilots who come to grief following gyro failure are likely misled to continue dutifully following the failed instrument’s erroneous indication until it is too late and the aircraft is either stalled or in a pilot-induced, steep spiral dive.
Even without the ensuing sense of panic, recovering from unusual attitudes under partial-panel situations is a much greater challenge. Peter Dogan, founder of Professional Instrument Courses, wrote in his Instrument Flight Training Manual, “The most dangerous [partial-panel] unusual attitude is the descending turn.” He recommended a three-step recovery strategy:
1. Reduce power. 2. Level the wings (rather than raising the nose, which would steepen a bank even further). 3. Only after wings are level would you raise the nose, and then only if the altimeter and vertical speed indicator continued to show a descent.
Dogan wrote, “The nose will tend to rise [on its own], and without a direct indication of pitch attitude, it is easy to overcontrol, which could cause a high pitch attitude and a near-stall condition.” With so much less information available to the pilot under partial panel situations, Dogan further pointed out it is necessary to speed up the instrument scan among the dials that are left, and focus that much more acutely on interpreting the indications. Still, with airspeed, altitude, vertical speed and rate-of-turn information — and the reliable old whiskey compass — losing gyro instruments need not be irrevocably fatal. World War II pilots were taught a simple sing-song that they were to repeat over and over if faced with partial panel in the clouds: “Needle, ball and airspeed. Needle, ball and airspeed.” And in an environment where instruments were prone to failure from “lead poisoning,” that little ditty saved a lot of lives.
