Imagine yourself in the captain's seat of this DC-3 (see photo below), flying in instrument meteorological conditions (IMC) and hard on the gauges. Which instrument on this airline-standard panel of the 1940s and '50s is directly ahead of you? It's the turn-and-bank indicator. This is a throwback to the earliest days of instrument flight, when the U.S. Post Office flew the mail and attempting all-weather operation often proved deadly ... with the most common cause of death a loss of control soon after entering the clouds. What many modern pilots don't realize is that proper use of a rate-of-turn indicator is the best way to recover from unusual flight attitudes even to this day.
Howard Stark and the Sperry Gyroscope
Howard Stark was a World War I veteran who, after the war, paid $500 for a surplus Curtiss Jenny and, as was common in the day, taught himself to fly. By 1926 Stark owned a Stinson cabin biplane -- very modern for its day -- which he leased to Colonial Airways to fly the mail between New York and Boston ... with himself as the pilot.
Frequent fogs and low clouds in the Northeast made the N.Y.-Boston route particularly deadly in the early day of air mail. Rapid loss of control after losing sight of the horizon was not unique to civilian operations, and when Sperry Gyroscope Company invented a device they called the Turn Indicator, the U.S. Army detailed two pilots to evaluate them for "blind" flying use. After a year of testing the pilots published their findings, concluding it was impossible to fly continuously by reference to the Turn Indicator, and indeed -- if one tried that -- loss of control would occur within about three minutes of entering clouds or fog.
Howard Stark's Stinson was equipped with a Sperry Turn Indicator, and Stark had the advantage of not having heard of the Army's work. The Stinson was very stable and Stark noticed if he kept his hands off the controls and steered only with his feet, using the magnetic compass for direction and the Turn Indicator to hold course, he could fly the entire distance between Boston and New York by reference to instruments. All that remained was altitude control, which he accomplished with small changes in elevator trim in lieu of movement of the control stick. Stark learned to judge ground speed and to adjust trim up as he neared a ridge on his route, then down again once clear on the other side -- perhaps the first "standard instrument procedure." As long as he kept the wings level on course using this technique, without turns, the self-taught Stark could regularly complete his route when ex-military pilots also flying the line were forced to set down or turn back because of weather.
Stark 1, 2, 3
But like other pilots, if Stark tried to turn in the clouds, he would quickly lose control. Wisely, he conducted his experiments at altitude, with plenty of clear air between the bases of clouds and the surface in which to recover from the steep spirals he'd invariably find himself in. Then Stark had an epiphany -- "blind" flying requires a pilot to ignore his/her veiled sensations of movement that quickly lead to vertigo, and instead trust the instruments to reflect true motion. Using instrument cues, Stark devised a means of recovering from unusual flight attitudes:
- Stop the turn (with rudder pressure based on the turn needle indication);
- Level the wings (by centering the slip/skid ball with the turn stopped); and
- Control the airspeed (with careful application of elevator based on the airspeed indicator's trend)
If what he called the "Stark 1, 2, 3 System" worked to recover from a loss of control, Stark concluded, it could be used to anticipate control loss and therefore permit prolonged instrument flight without losing control in the first place. He soon found his theory worked.
Stark and his wife penned a pamphlet describing the Stark 1, 2, 3 System and sold it by mail. He instructed other Colonial Airways pilots in the technique. Word spread quickly and soon airlines across the U.S. and in Europe were using Stark's technique, several hiring Stark to personally teach it to their pilots. Charles Lindbergh credited Stark in making his trans-Atlantic flight possible.
It was only a few years before Sperry developed gyroscopic attitude and heading indicators, making modern instrument flight possible -- but it was Howard Stark who taught the world to fly in IMC. Stark died on a transcontinental flight, but not from loss of control. He was forced down in the mountains in a heavy snowstorm, and froze to death trying to walk out.
(With information from John M. Miller, Flying Stories, ©2002 American Bonanza Society Air Safety Foundation)
Those Cagey Attitude Indicators
My first real flight instruction was in mid-1960s Cessna 172s, with large, vacuum-driven attitude indicators (AIs). A required step in preparation for steep turns and stalls was to "cage" the AI -- you pulled a knob that stopped the gyro and kept the AI from "tumbling" at high pitch and bank angles. A tumbling AI does exactly what the term implies: The AI's horizon line wobbles up and down, unusable as a pitch reference. Certainly a tumbling AI would be completely unusable in an unusual attitude recovery by reference to instruments.
More modern AIs are much less likely to tumble, but they are not immune from the hazard. In a rapid rate of pitch, bank and/or yaw change it's possible even a brand-new AI may become unusable in an unusual attitude recovery. Following the AI in an extreme nose-up or -down attitude, especially with a steep bank, might make matters even worse if the AI begins to tumble in the maneuver. The errant horizon line will provide no inkling it's failed.
That's one reason why most instructors teach unusual attitude recoveries by reference to instruments other than the attitude indicator. (The main reason is that a failed AI is probably the most likely reason an instrument-rated pilot would find him/herself in an unusual attitude in the first place). In anything other than the mildest of attitude excursions, it's best to regain control using the "partial panel" references of rate of turn, airspeed and altimeter, then cross-check the AI once under control to confirm whether it's still providing truthful information.
Turn and Bank vs. Turn Coordinator
Sperry's original gyroscopic Turn Indicator eventually developed into two types of instruments: the turn & bank (T&B, or "turn needle") and the later turn coordinator (TC). Both incorporate a gravity "ball" slip/skid indicator, or inclinometer, to indicate the "quality" of the turn. Many pilots feel the T&B provides a more obvious indication of rate of turn, while rate-based autopilot systems require a TC in order to function.
TCs look something like an attitude indicator and sometimes there's confusion about what they really show, so much so that many TCs have the words "No Pitch Information" written right on the face of the instrument. "Glass cockpit" airplanes that include a rate-based autopilot like the KAP140 or the S-TEC line still require the TC, but may hide it behind the instrument panel, out of view.
Whether it's a T&B or a TC, however, the different mounting of the rate-of-turn's drive gyroscope (compared to an attitude indicator's required orientation) make the rate-of-turn immune to tumbling in unusual attitudes. Nose high or nose low, wings level or steeply banked, you can trust your rate-of-turn to help get you back under control. Proper recovery from unusual attitudes is less a question of which type of rate-of-turn indicator the airplane has than it is the pilot's training and currency using the rate instrument in unusual attitude recoveries.
FAA Advisory Circular 91-75 authorizes replacing a T&B or TC with a back-up attitude indicator, subject to some rules about redundant power supplies and retaining a requirement for a slip/skid indicator (inclinometer) in the primary instrument scan. The backup AI is generally considered an improvement over the original rate-of-turn indicators, and it's easier to fly precisely using a backup attitude indicator than "traditional" partial-panel techniques should the primary AI or its drive system fail.
Given the tendency of AIs to tumble in unusual attitudes, though, and for pilots who don't own the airplanes they fly (and have no say in how they are equipped), it might be a good investment to train to proficiency on unusual attitude recoveries using the T&B or TC and the Stark 1, 2, 3 method. In fact, installing a small turn and bank instrument near the primary flight display (PFD) of a glass cockpit airplane, or moving a hidden turn coordinator from behind the panel to a spot in full view in airplanes with rate-based autopilots, might look like a step backward in panel design but would add a much-needed level of redundancy in the event of a PFD failure.
No matter what indicators you use, remember the key to recovering from unusual flight attitudes:
- Stop the turn;
- Level the wings;
- Control the airspeed
It's as easy as Stark's 1, 2, 3.
Fly safe, and have fun!