Plane & Pilot
Tuesday, December 7, 2010

Beware The Downburst


An insidious risk that can undercut airspeed and drive you into the ground


Delta 191 wasn’t the first wind shear accident. An Eastern Airlines jet approaching JFK Airport in New York had crashed 10 years before, killing all aboard, and a Pan Am 727 had crashed on takeoff from New Orleans in 1982, again fatal to all aboard. Both accidents had been attributed to wind shear.

As the pilots of flight 191 taught us, the only solution is avoidance, because once you’re caught in wind shear, you may become nothing more than a passenger. The forces generated are often too strong for even many military fighters to overcome. To that end, several manufacturers have developed Doppler radar capable of predicting major shifts of wind direction and velocity well ahead of an appropriately equipped aircraft.

Trouble is, you and I will probably never fly behind such equipment. The radar systems are so expensive that it’s unlikely they’ll ever trickle down to general aviation. We’re left with warnings generated by other sources. So far, 45 major airports, principally those that support airline traffic, are equipped with ground-based Doppler wind shear warning systems. These allow controllers to detect possible wind shear and warn all aircraft of potentially dangerous wind situations. NEXRAD uplink also can provide information on wind shear.
Many pilots have been caught in downdrafts of varying intensity, and the phenomenon is definitely not fun.
Of course, the best advice when flying around thunderstorms is the age-old adage, “Don’t.” This doesn’t address situations when you’re already en route and thunderstorms spring up unexpectedly. The good news/bad news about wind shear is that it normally occurs close to the ground. Even if you did encounter the phenomenon at cruise altitude, you’d probably have time to recover.

If you encounter what seems a strange updraft on final approach in convective weather that tempts you to reduce power and follow the glideslope to avoid increasing speed, be aware that you may be about to fly through the mother of all downdrafts in a few seconds. It’s probably safer to climb above the glideslope just in case you’re about to be forced downhill by a microburst.

Perhaps the only good thing about a downburst is that it usually provides some warning of what’s about to happen. Considering what’s at stake in a downburst and the fact that the forces unleashed may countermand any amount of skill, you need to understand the warning signs. Unlike me, you may not be allowed a second chance.

Pilot precautions for handling wind shear are fairly simple. If thunderstorms are in the area and you’re flying adjacent to significant convective activity, be aware that you may be required to take evasive action to avoid being seduced by a downburst. In Albuquerque, I had the luxury of landing long. That’s a good option if you’re operating into an airline airport with runway to spare.

Don’t blindly follow the ILS in VFR conditions, and don’t allow a controller to coerce you into landing short with an order to expedite your approach for traffic behind you. That’s a rare occurrence these days, anyway, as controllers have been educated to the dangers of wind shear and will do everything in their power to avoid a hazardous situation.




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