The key here is to not put oneself in the position of having to attempt this 'last' ditch maneuver.
If the aircraft and/or pilot are not IFR certified and current then one should not put oneself in this position. I know this sounds simple and self-evident, but the accident statistics prove otherwise. If conditions change from when the flight is planned then turn around or find a place to land in plenty of time to avoid IMC. I know - I'm guilty of doing it myself once or twice, but as they say in the magazine - NEVER AGAIN. There is no such thing, IMHO, as accidently flying into a cloud. Roy ________________________________ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Ed Burkhead Sent: Thursday, June 19, 2008 12:39 PM To: ety Subject: [ercoupe-tech] desperation GPS or magnetic compass as emergency blind flying instrument Importance: Low This is a cross-post from the FlyChallenger forum that looks valuable. I've heard this method from other sources and kept it in the back of my mind as a final, desperate-situation backup technique for when it's do something or die. This guy seems to know what he's talking about and so I present it for discussion. I'd suspect that anyone doing this as OTHER than a last-ditch method is probably an idiot. Also, this method is difficult and seriously worth practicing under the hood. Ed -----Original Message----- From: steve Sent: Thursday, June 19, 2008 1:58 PM Desperate do something or die use of GPS or magnetic compass as emergency blind flying instrument I have flown IFR w/ compass only in several light aircraft. If you stay on a relatively constant course, the wings must be staying relatively level. It is absolutely critical to choose a heading that is relatively close to magnetic south (if you are flying in the northern magnetic hemisphere). On such a heading, the compass errors work in your favor and exaggerate small deviations in yaw so you can fix them. Don't try headings of east or west where in theory there is no error--if you accidentally deviate to a heading that contains a magnetic north component then you lose control. Once you lose control you cannot regain it w/ compass only. I.e. the wings will break off in the spiral dive that ensues. When flying with primitive instrumentation, you will be disoriented and will tend to over-control the aircraft. In practice it works best to control heading with rudder only, relying on yaw-roll coupling to indirectly control bank. Don't expect the ball or yaw string to be centered - at many airspeed/ power combinations, it will not be. That's ok. If conditions are smooth enough, trim for airspeed and keep your hands off the stick. If you need to make pitch corrections to hold airspeed, hold the stick low and brace your hand against your leg to avoid excess stick movement, and try not to make any roll inputs at all w/ the stick. Expect to be very disoriented. Due to the way a conventional aircraft compass is laid out you have to remember to step "opposite" the position of the target heading on the compass dial. (Example: your target heading is magnetic S, you accidentally deviate to magnetic SSE, the "S" emblem is now to the left of the lubber line on the compass, you must step in the opposite direction, on the right rudder pedal.) It sounds obvious but will be extremely disorienting in cloud w/o prior practice. [Suggestion: think about using your foot to push the LINE on the compass back toward the letter S.] (Some compasses are laid out so you look across the dial and read the heading at the back of the dial, or read the heading at the top of the vertical card, these don't suffer from this particlar problem.) In rough air--forget it. The point of all this-- if I actually had to use a Garmin 496 or similar to descend through a cloud layer, I would choose a heading near magnetic south if at all possible, so I could use the aircraft's magnetic compass as a backup if the batteries failed. If I had something more primitive like a Garmin Etrex or 76S I would use the aircraft's magnetic compass as my primary instrument, not the GPS-derived heading display on the handheld. As long as the heading is near magnetic south and the air is not too rough and the pilot can remember to "step away" from the target heading on the compass dial, the aircraft compass outperforms this type of GPS as a heading guidance instrument. These GPS's simply don't update fast enough to give any realistic hope of keeping an aircraft under control in cloud--the once-per-second update rate is just not enough. But again, remember, with a magnetic compass, once you lose control there is no hope of regaining it, with even a primitive GPS maybe you do have some microscopically small chance of regaining control after initial loss of control. Never try to use the magnetic function on the GPS, if it has one. Know how to make sure it is switched off and will stay off. It suffers from errors that are even worse than a conventional mechanical compass. Does anyone know, does the (cheaper) Garmin GPS 196 have a similar update rate to the Garmin GPS 496? Thanx Steve
