The July/August issue of FAA Safety Briefing featured an interesting article (“Climbing into Thin Air”) discussing density altitude – an invisible danger for high-altitude mountain flyers on hot summer days. The FAA article began by providing this description of density altitude:
There is a thief among us! Without warning, it can sneak into your airplane and rob you of precious lift, thrust, and power. And, if you’re not careful, it can quickly put you in a deadly spot during your next flight.
The culprit here is not something particularly obvious, nor is it something pilots who routinely fly at or near sea level are used to dealing with.
The article then related the story of a fatal accident that recently occurred in Arizona where a pilot failed to attain and maintain an adequate airspeed during takeoff in high density-altitude conditions. This resulted in an aerodynamic stall.
The article continued by noting that when density altitude is high as a result of temperatures that are above standard at a given altitude, the air is less dense than normal. Hence, an aircraft will perform as if it were flying at a higher altitude with decreased climb performance and acceleration ability. This can be a big problem if you are flying on a hot and humid summer day and if you are operating from a short runway that has a few tall pine trees at the end of it.
However, a hot day can have an affect on aircraft performance at any altitude. Hence, the article quoted one flying expert who suggested that pilots need to become familiar with the weight-and-balance along with the performance and limitations sections of a pilot’s operating handbook (POH) or airplane flight manual. In addition, avoiding takeoffs and landings at midday when temperatures are usually at their highest and instead taking advantage of cooler mornings or evenings will also help to avoid performance surprises.
In other words and if you plan on doing any summer flying, be aware that humidity and temperatures can impact your aircraft’s performance and be sure to plan accordingly.