I recently received the December edition of EAA’s Sport Aviation magazine. As is my custom, I always check out Steve Krog’s “The Classic Instructor” commentary first. His article about density altitude brought back a memory of a long-ago flight.
As a 500-to-600-hour private pilot, I thought I had an understanding of density altitude and its effects on an aircraft’s performance. But that understanding changed on a hot, humid July day in northern Alabama!
In the mid 1990s, a buddy suggested that he, his wife, and I fly to Talladega, Alabama, in my Cessna 172, to attend the July NASCAR race. It sounded like a grand adventure, and I was all for the idea. Our flight from western New York was pretty uneventful until departing from our second fuel stop in northern Alabama. There, without much consideration, I did as I always had and told the fueler to top off the tanks. I was completely unaware of the lesson I would soon learn.
The subsequent takeoff began normally enough—I didn’t necessarily notice if we became airborne a little farther down the runway than normal or not. But once airborne, I slowly became aware that things weren’t going as expected. After liftoff, the climb rate of the 172 was downright anemic to say the least. It was clawing the air trying to climb, but without much success. We were barely climbing, but we weren’t skimming the rooftops either, and at least we weren’t descending.
I also noticed that the airspeed wasn’t increasing. In fact, to achieve whatever climb rate I did have, it was hovering somewhere just above stall. I was working hard, trying to coach the plane to climb by attempting to find the right pitch angle where the wings would produce the best lift, while hopefully at the same time maintaining an airspeed somewhere above stall. The goal was to slowly accelerate in order produce a better climb rate.
About now, there are readers that are wondering, how heavy were they? What was he thinking when he had the tanks topped off?
Obviously, I wasn’t thinking about performance or density altitude. It probably isn’t a newsflash that Alabama in July is hot and humid. But none of that information was considered as part of my planning because the airport elevation was relatively low, probably somewhere between 800 and 1500 feet.
In retrospect, I lacked a true understanding of the whole density altitude topic. I have decided that my lack of understanding stemmed from the fact that when density altitude was discussed during training, it was discussed as being an issue when high, hot, and humid.
Because all my flight training and flying up to this point had been in the east, I thought to myself, “Self, since I am flying in the East and density altitude presents a problem at high elevations (like if I was flying out West), then except for the written test. I don’t need to remember or apply any of this because it won’t affect me here where I fly.”
As I continued to build flying hours and I didn’t experience any issues with density altitude, it just reinforced that thought… until that day in July down in Alabama!
If I had thought about density altitude, here is generic example of what it may have been that day:
So, how/why did my thought processes take me down such an erroneous road?
For what it is worth, here is my take. When learning something new, or when our brains become overwhelmed with information, mine (and possibly yours) tends to “weed out” extraneous information. It decides what information is not important and what information it does consider important.
We then remember what was deemed important and the remaining extraneous information “gets shelved” in the back of our minds somewhere or is discarded completely.
As a result, we end up believing we have an understanding of a subject, procedure, or situation when we don’t. We usually aren’t even aware of the misunderstanding until we get that unexpected wakeup call. Hopefully, one that doesn’t end up resulting in a bad outcome.
As Steve Krog reflected in his article, “In order to protect ourselves from the effects of density altitude, we must first understand what it is and how it impacts flight.” This is true concerning all aspects of our flying. We must ensure that we first understand the subject, procedure, or situation. We must not allow ourselves to settle for what “we think we understand.”
As for that long-ago trip, it added to my experience, it is a great memory, and we had a great weekend. I am not sure my friends even realized that our takeoff was any different than any other. Talladega was as exciting and unpredictable as always, but boy was it low, hot, and humid during the race.
Editor’s Note: This article is from our series called “I Can’t Believe I Did That,” where pilots ‘fess up about mistakes they’ve made but lived to tell about. If you have a story to tell, email us at: [email protected].