The altimeter read 1,000 feet as the pilot of a Piper PA-32 single-engine airplane flew the traffic pattern at a Texas airport—but the view below must have been startling indeed.
“Instead of approaching at an altitude of 1,600 MSL, my altitude was 1,000 MSL, putting me only 200 feet above the ground and surrounding homes. [This was] a mistake that will not happen again,” the pilot wrote in a filing with the Aviation Safety Reporting System. Filing a so-called NASA report may offer a pilot protection from an enforcement action provided the violation involved was inadvertent and not deliberate.
Details count. Student pilots learn that some information reviewed during flight planning is expressed in values above ground level (agl); other details are presented in relation to mean sea level (msl).
Sometimes both values are given. Take obstructions plotted on sectional charts. Two values are shown, one for the “elevation of the top above mean sea level,” and another, in parentheses, indicating the obstacle’s height above ground.
Time for a spot quiz: Without checking a chart, when does the size of a chart symbol for an obstruction change? When the obstruction is below 1,000 feet agl, or below 1,000 feet msl? If you can’t recall the answer, ask yourself which value would more useful as you fly in the vicinity of the obstruction. (Answer: agl).
Such concepts are fairly easy to remember once you familiarize yourself with the definitions.
Here’s a more challenging question—a matter of interpretation of a note about runway lighting in an airport’s listing in the chart supplement. The note says: "preset medium ints dusk-dawn, to incr ints and ACTIVATE twy lgts—CTAF."
Based on the note, are these runway lights on or off as you approach the airport between dusk and dawn? Or does the note mean the runway lights come on at medium intensity when you activate them on the common traffic advisory frequency?
The question was posed to an experienced local pilot.
“I thought I knew the answer,” he replied by email. On checking with the airport manager, however, he learned that “the runway lights stay ON all night, at medium intensity, with the latter controllable via CTAF. The taxiway lights are normally OFF, but can be activated via CTAF.”
Was that your “take”?