Weather Explanations

Question: Can you please explain what "ground effect" is?

Answer: Ground effect is caused by the interference of the ground surface with the airflow pattern about the airplane in flight. When the wing is under the influence of ground effect, there is a reduction in upwash, downwash, and wingtip vortices. It can be detected and measured up to an altitude equal to one wingspan above the surface and is most significant when the airplane is maintaining a constant attitude at low airspeed close to the ground. A decrease in induced drag makes the airplane seem to float on a cushion of air beneath it, so if a power approach is being made, the power setting should be reduced as the airplane descends into ground effect to avoid overshooting your desired touchdown point. More information on this subject is discussed in the article "Ground Effect: Flying in the Realm of Altered Air Flow."

Question: Due to some favorable weather conditions during a flight the other day, I was able to operate above the advertised service ceiling that is outlined in the aircraft pilot's operating handbook. Nothing seemed to be awry with the operation, but I wondered if I might have been breaking some sort of regulation?

Answer: Indeed, it is possible that you may have, whether you knew it or not at the time. During an aircraft's certification process, operating limitations are determined based upon test flights in order to come up with safe aircraft operational parameters. FAR 23.1527 states, "The maximum altitude up to which operation is allowed, as limited by flight, structural, power-plant, functional or equipment characteristics, must be established." Additionally, FAR Part 91 regulations must followed. FAR 91.9 says, "...no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraf t Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry."

Question: What are the significant differences between cold and warm fronts?

Answer: Keep in mind that warm and cold fronts are relative terms with environmental variables that make up their characteristics and impact the weather. The two frontal types will vary in speed, composition, weather phenomenon, and prediction. Cold fronts move very quickly, generally 20 to 35 mph, in comparison to warm fronts, which typically move at 10 to 25 mph. Cold fronts also possess a steeper frontal slope due to their compacted, dense air make-up. Violent weather activity is commonly associated with cold fronts, and the weather usually occurs along the fontal boundary, not in advance of it; however, squall lines can form during the warmer seasons as far as 200 miles in advance of a severe cold front. Warm fronts will bring low ceil ings and poor visibility, provide warning of their approach (i.e., development of cirrus clouds overhead), and can take several days to pass through the area. More information on this subject is discussed in "The Weather Never Sleeps—Battle lines in the sky." Also read the AOPA Air Safety Foundation's WeatherWise Safety AEdvisor.

Question: I want to better understand detailed weather information. What resources can you recommend?

Answer: FAA Advisory Circular, Aviation Weather Services, is a good place to start. The information is published jointly by the FAA and the National Weather Service. It explains weather service in general and the details of interpreting and using coded weather reports, forecasts, and observed/prognostic weather charts. Section 5 of the publication provides an excellent outline of the many symbols used in surface analysis charts. Read more in the AOPA Pilot column "Wx Watch."