The first aeronautical charts, part II (U.S. sectionals)
US aeronautical charts known as sectionals have been around for a long time. How long?
- over 30 years
- over a half century
- over the last 70 years
- a few years shy of a full century
All Shook Up
As you are about to flare for landing, just when you reduce propeller rpm, you feel a slight shudder go through the airplane, the cockpit, and you. Is there anything wrong?
- No (although it depends upon how you define normality). Many piston aircraft engines have some degree of inequity in the fuel distribution of the induction manifold, which induces power differences among the engine cylinders.
- Yes, although the malady isn’t catastrophic. Although almost no piston engine crankshaft is balanced to absolute perfection, after a decade or so, about half of the crankshafts will need at least some dynamic balancing. (Again though, smoothness is subjective.)
- Yes. This can happen most often when reducing power below 1800 rpm, while still above idle speeds (between 1200 and 1800 rpm). While not serious, this is most often because of a propeller imbalance. The majority (over three quarters, by one estimate) of general aviation propellers are, at least to some measurable degree, out of balance. What you may feel occurs when a slight vibration of an out-of-balance prop is picked up by the inherent harmonic “dampening” frequency of the engine mounts themselves.
- No. You’re feeling the interaction of the propeller slipstream and the increased airflow above the wing when entering ground effect.
Hold It
True or false: A controller is permitted to issue airborne holds only to IFR traffic.
The Answers…
The first aeronautical charts, part II (U.S. sectionals)
Answer: The need for aerial mapping of the U.S. was made quite obvious when airmail flights began during the last few months of World War I (first by the U.S. Army, then the Post Office). Pilots made do with whatever maps they could find (or in the case of enterprising pilots like Elrey Jeppesen, compile, from their own experience). The U.S. Army Air Service began photographing all routes to aid pilots in their orientation, and commercial firms such as Rand McNally produced “Air Trails” maps as early as 1928. When the US Government began printing aerial maps, at first they took the form of strip charts of principal air routes, similar to an AAA “Trip Tik” and were in use as early as 1923. In 1926, the Navy’s Hydrographic Office printed coastal charts of North and Central America. Upon passage of the Air Commerce Act in 1926, placing civil aviation under the Commerce Department, the Coast and Geodetic Survey produced additional aerial maps. It reached the point where the country was covered somewhat haphazardly by different types of charts from various agencies; some areas of the country received no coverage whatsoever, while others were mapped multiple times in different ways. Finally, a committee representing these agencies met in 1929 to resolve the issue. They found that more flying was done off the airways, and not on them, and also that for military purposes, the country needed something more all-inclusive. The new chart, called a sectional chart, was a conic projection on a 1:500,000 scale, and most of them each covered six degrees of longitude (about that of today’s sectionals) and two degrees of latitude, which is half that of current sectionals. (That’ s not to be confused with the term used in surveying, where a “section” is the unit or subdivision of a township with one mile square rectangular boundaries, containing 640 acres.) The first sectional charts appeared in 1931 (so it’s choice C). They were initially issued every two months, and there were roughly 87 of them (more than twice the present number). A more recent historical note is that on October 1 2000, the National Aeronautical Charting Office (NACO) and its 300-plus employees became a part of the Federal Aviation Administration, Aviation System Standards, as a result of an agency transfer of the Office of Aeronautical Charting and Cartography from the National Oceanic and Atmospheric Administration (NOAA).
All Shook Up
Answer: C. Other symptoms include vibrating engine needles, a magnetic compass that continues shuddering and doesn’t ever calm down, or even a numbing sensation in one’s hands and feet from continual contact with vibrating surfaces, in more extreme cases.
Hold It!
Answer: False. They actually do so on a fairly regular basis; they just don’t sound like IFR holds. Whenever Approach Control tells you to hold “North of the freeway, and call back in five minutes” those are holding instructions. If you’ve ever flown to Oshkosh in late July, you already know about VFR holds.
