Accident Analysis: Rose Without a Thorn

Anticipating that inexperienced pilots might opt for the airspeed indicator as a safeguard against inadvertent stalls, Schiff disdained the airspeed indicator as redundant once you’ve learned to “feel the wing” (easy for him, not always for others). He had good things to say about an oil temperature gauge as the most basic indicator of engine health, but his first choice—surprising to many—was the magnetic compass (see “Old Reliable,” p. 50). His reasoning was simple: Once beyond sight of the airport, it’s good to know which way you’re going.

Early mariners recognized the value of being able to identify magnetic north without the need for landmarks, and in Europe the first practical nautical compasses were in use by the twelfth century. (The Chinese had them even earlier.) Their mechanisms have been refined enormously over the centuries, but the basic principle of mounting a magnet in a frictionless medium so it remains aligned with the Earth’s magnetic poles is as essential in the age of GPS as it was to Prince Henry the Navigator.

How’s that? Well, start with the fact that it’s the one navigational instrument that always works no matter what has happened to the vacuum or electrical systems (although at night, you might wish you’d remembered those fresh batteries for your flashlight). Airplanes with horizontal situation indicators lose all other navigation capability in the event of a total electrical failure. The compass saved the pilot of an HSI-equipped Cessna 210 whose battery died 20 minutes after the alternator quit in low instrument conditions. Knowing there was worse weather to the north, mountains to the west, and restricted airspace to the south, he turned east and made a successful forced landing after a gradual descent through the clouds.

In aviation, compass references are so universal that they’re easily overlooked. The airplane’s directional gyro; VOR radials and the airways and approach courses they define; and GPS tracks are all based on the compass rose (the latter corrected from magnetic to true north). Runways are identified by their rounded compass headings. An automotive GPS that just tells the driver to “turn left” and maybe “proceed southbound” is disconcerting if you’re conditioned to expect “Turn left heading 170.”