Every once in a while I run across an article that I print out and actually put in my flight bag. This is one of them. Rules of thumb I have found are critical to aeronautical decision making in flight. That being said, use sound judgement when to use a rule of thumb and when it pays to use the a more precise instrument.
Plane & Pilot Magazine Top 10 Rules of ThumbAmy Hoover's article on Rules of Thumb
My favorites:
Rule of thumb; DA: To determine Density Altitude at a given Pressure Altitude, add 60 feet to the existing PA for every 1° F above standard temperature for that altitude. (Remember: Standard temperature at sea level 15° C / 59°F and decreasing at 2°C/3.5°F per 1000 feet of altitude above sea level). If altimeter setting is above29.92 inches mercury, add another 100 feet of density altitude for each 10th of an inch below29.92 or subtract 100 feet for each 10th of an inch above 29.92. Because the precise effect of humidity involves complex calculations one can compensate by raising DA by 1000 feet on hot humid days and assuming a performance hit by a fudge factor 10%.
Rule of thumb; Abort:An aircraft should achieve 70% of its flying speed by the time it has consumed 50% of the runway or an abort is in order.
Descend rule of three: Number of miles out times three gives you your AGL height (in hundreds of feet) above the airport for a 3 degree descent path
Estimate chart distance: Bend the fingers on your right hand into a U Shape. One of the middle segments will represent 10 miles on a sectional chart (check which one comes closest), or five miles on a terminal chart. Use it to measure approximate distances.
This shot was taken on the way down to Watsonville along the Monterrey Bay coast.
