June 1, 2004
Teresa J. Foden
It's summer, the season of lazy days and flights into endless skies. But for the unwary pilot, danger lurks behind the mask of clear blue.
High altitude, high temperatures, and high humidity translate into high density altitude, or "thin air." Melissa Huettel, an AOPA aviation technical specialist and CFI, says, "Departure from standard temperature and pressure will have a direct effect on density altitude, and you won't be flying in standard day conditions."
As temperature and altitude increase, air density decreases. The less dense the air, the less lift, the more lackluster the climb, and the longer the distance needed for takeoff and landing. Fewer air molecules in a given volume of air also results in reduced propeller efficiency and therefore reduced net thrust. These are real-world flight conditions, often a far cry from the standard day, standard atmosphere conditions that the manufacturer's performance numbers are based on, says Huettel.
While pilots generally become acquainted with density altitude during training, a lack of practical application may result in common misconceptions, she says. A pilot, for instance, may assume that high density altitude plays a role only at high-altitude airports in the West — but even airports at low elevations may present high density altitude-related challenges with sufficiently high temperatures or humidity levels.
The potential for high density altitude should be a part of preflight planning for every flight in the summer. Consulting the aircraft operating handbook alerts you to safety factors that are within your control. Think about reducing the aircraft's load if you're planning a flight from the lowlands to the high country on a blistering hot day in mid-August, for instance. A lighter load improves the airplane's relative performance and may ensure that you can take off again once you've landed.
Also consider the following suggestions for minimizing the effects of high density altitude:
Answers to frequently asked questions about your AOPA membership
Q. What's the best way to communicate with AOPA through e-mail, and how long does it take for someone to respond?
A. Just send your e-mail to firstname.lastname@example.org! Our Member Services and Aviation Services representatives answer e-mails from 8:30 a.m. to 6 p.m. Eastern time, Monday through Friday. E-mails are usually answered by the close of the next business day, but in many cases you will get a same-day response.
Q. I only fly recreationally once or twice a month. Why do I need the AOPA Legal Services Plan?
A. Pilots who fly less frequently can find themselves unaware of FAA rule changes and new regulations, making them more vulnerable to violations. The plan provides valuable services you may need as a pilot, no matter how infrequently you fly, such as unlimited legal consultation on covered plan matters, review of your key aviation documents, and much more. At $26 per year, it's an affordable way to protect your certificate and guarantee aviation legal assistance. To enroll, call 800/USA-AOPA (872-2672) or visit the Web site ( www.aopa.org/legalservices.html).
Q. If I encourage others to join AOPA do I receive any benefit?
A. Yes! In addition to helping another pilot obtain access to valuable information and services through AOPA membership, you will be rewarded through our Member-Get-A-Member program. If you help recruit three new members into AOPA, you'll be rewarded with a free year of membership. Just have your friend mention or note that you referred them when they call to join, or when they respond to one of our mailings.
Telephone: 800/USA-AOPA (872-2672), 8:30 a.m. to 6 p.m. (ET) Monday through Friday After hours: Renew your membership, reset your Web password, or enroll in Automatic Annual Renewal using our self-service touch-tone telephone option.
Web: Update your personal information, renew your membership, and much more by clicking on My AOPA in the left column of our home page (www.aopa.org).
For more information on density altitude, check this aviation subject report. www.aopa.org/members/files/topics/density.html
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