Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.") It's part of what makes aviation so exciting for all of us... just when you think you've seen it all, along comes a scenario you've never imagined.

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators, and as representatives of the flying community. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

It is our unabashed goal that "Aero-Tips" will help our readers become better, safer pilots -- as well as introducing our ground-bound readers to the concepts and principles that keep those strange aluminum-and-composite contraptions in the air... and allow them to soar magnificently through it.

Look for our daily Aero-Tips segments, coming each day to you through the Aero-News Network. Suggestions for future Aero-Tips are always welcome, as are additions or discussion of each day's tips. Remember... when it comes to being good pilots, we're all in this together.

Aero-Tips 02.07.06

More and more owner-flown airplanes are capable of flight above 18,000 feet—in the "flight levels." If the Very Light Jet movement catches on a whole lot more of us will be flying "up high." Several things change when passing through 18,000 feet. Most noticeably, altimeters are always set to 29.92 inches of mercury.

Why? The assumption is that airplanes in the flight levels cruise at high airspeeds. This would mandate very frequent altimeter setting updates if the local altimeter setting was used. To make it easier for everyone, high-speed, high altitude pilots use a common, one-size-fits-all altimeter setting.

Unusable Flight Levels

There are times when this rule creates "unusable flight levels." Remember, it’s legal to fly under Visual Flight Rules (VFR) right up to Class A airspace (beginning above 18,000 feet). The "hemisphere rule" recommends VFR cruise at altitudes plus 500 feet, meaning that the highest VFR cruising altitude should be 17,500 feet. If the local air pressure is lower than standard (29.92 adjusted for sea level), then a VFR airplane using the local altimeter setting may be cruising at an altitude that conflicts with an airplane using 29.92 in Class A airspace. To prevent this conflict Air Traffic Control makes the lower Flight Level cruising altitudes "unusable" when the local surface air pressure is below standard. Flights in Class A airspace will not be cleared to level off at an unusable flight level.

The Aeronautical Information Manual (AIM) charts the lowest usable flight level during times of low air pressure:

Aero-tip of the day: Don’t be surprised if your requested flight level of 180 to 200 is declined if the local altimeter setting is lower than standard.

FMI: Aero-Tips