Plane & Pilot
Saturday, May 1, 2004

Worst-Case Weather Scenarios

If you find yourself in hazardous situations, nothing helps you more than having a plan

worst weather scenariosThere is absolutely no excuse for beginning or continuing a flight into known hazardous weather—“hazardous” being defined as any weather condition that exceeds the limitations of your pilot ratings and currency and/or those of the airplane as it’s certified, equipped, maintained and inspected. Our responsibility as pilots in command is painstakingly clear when it comes to weather planning and flight in adverse conditions.
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Worst-Case Weather ScenariosHow To Survive Severe Turbulence
If you fly into severe or extreme turbulence, including mountain waves, make sure to do the following:
• Tighten all safety belts and secure loose objects.
• In retractable-gear airplanes, increase the stability by lowering the landing gear.
• Establish Va and trim.
• Keep flaps up; lowered flaps reduce the maximum G loading that the airplane can withstand.
• Turn off an autopilot’s altitude hold (“attitude hold” and heading/nav modes are helpful to leave on).
• Maintain the power setting and attitude; accept altitude and airspeed deviations (tell, don’t ask, air traffic control that you need a “block altitude”).
• Keep the wings level to hold the G loading to a minimum.
• Land as soon as it’s practical after leaving the area of turbulence. Have a mechanic thoroughly check the airplane for damage before anyone flies it again.

Worst-Case Weather ScenariosHow To Survive Airframe Ice Accumulation
If you’re flying an airplane that isn’t equipped with de-icing devices and you encounter ice, or if the rate of accumulation is so great that even the constant use of de-icing equipment won’t keep the airframe clear, heed the following steps:
• Turn all anti-ice and de-icing devices on.
• Retract flaps and the landing gear to prevent ice accumulation on them.
• Maintain “ice penetration” airspeed; airplanes certified for flight in icing conditions have published speeds producing angles of attack that prevent ice from building on the underside of the wings and fuselage. Without precise POH guidance, maintain your best speed when you’re in icing conditions, no less than about 10% above your normal approach speed—you may have to put the airplane in a descent, obstacles permitting, to minimize ice accumulation.
• Get out of visible moisture or change to a non-freezing altitude. This may mean climbing (if you’re able), descending or turning around to escape.
• Aim for the nearest airport with a runway that is longer than about 4,000 feet for single-engine airplanes or 5,000 feet for twins—you’ll be landing fast and long, and the runway may be slick, as well.
• If you’re still accumulating ice while landing, use the power to maintain ice penetration speed until your flare.
• If you’re not accumulating any additional ice, but your airframe is still contaminated, carefully test the airplane control at progressively lower air speeds (we suggest doing tests at five-knot increments).
• Establish a minimum landing speed by using the zero-flaps landing speed or 1.2 times the speed at which you get the very first indication of control difficulty or impending stall, whichever is higher.
• Do not extend flaps—flaps increase the horizontal stabilizer’s angle of attack and may lead to an unrecoverable tail stall.
• In retractable-gear airplanes, delay the gear extension to avoid building ice and do not retract the gear once it’s extended in ice—the landing gear may freeze up in the wells.
• A go-around or missed approach isn’t an option—you’re committed to land.


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