Impostors in the Cockpit

Sunday, June 15, 2014 at 05:51 PM ET

Verified

** Even in the sun-drenched Maldives, low
pressure will produce negative density
altitudes — but not negative densities.**

Key Takeaways:

Pilots frequently use "proxy scales" (e.g., density altitude, pressure altitude) to simplify complex physical properties, which can sometimes lead to misunderstandings, though concepts like negative density altitude are normal.
The article advises against deploying flaps during turns due to added complexity, clarifying that flaps lower (not raise) stall speed and do not affect turn coordination.
The most critical and potentially dangerous proxy is airspeed, as it obscures the vital "angle of attack" (AoA), which is the most important information for low-speed flight.
The author advocates for greater adoption of AoA instruments, noting recent FAA approval changes, urging pilots to choose this superior measurement over the proxy of airspeed.

See a mistake? Contact us.

One of the pleasures of this job is hearing from readers. Some write to correct my errors or to note my omissions. Some are hostile, though the population recommending my immediate consignment to the infernal fires has for some reason dwindled in recent years. Maybe they went first. Some ask questions. Some of the questions are standard ones, but some are ones that would never have occurred to me and get me thinking about stuff in new ways.

Last winter, for example, cold spells in the mid-Atlantic states produced reports of negative density altitudes in places where they aren’t usually seen. A reader wrote to inquire what a negative density altitude meant and what effect it would have on his flying.