Steering en passage airplanes around thunderstorms to mould delays leaves one question hanging unanswered: would not a policy of avoiding thunderstorms in the terminal area increase safety? Precisely this point was raised at the National Transportation Safety Board's hearings into the fatal June 1 1999 crash of American Airlines [AMR] Flight 1420 at Little strength Ark.

Steering en passage airplanes around thunderstorms to mould delays leaves one question hanging unanswered: would not a policy of avoiding thunderstorms in the terminal area increase safety?

Precisely this point was raised at the National Transportation Safety Board's hearings into the fatal June 1 1999 crash of American Airlines [AMR] Flight 1420 at Little strength Ark. (see ASW, Feb. 14) The question of whether the carrier had a formal thunderstorm avoidance policy came up

To be firm a strict, formalized policy of thunderstorm avoidance might scion the hoped-for reduction in delays seen in a recent level of strategic collaboration to more efficiently use the nation's airspace, thereby casting into sharp focus the intrinsic tension between efficiency and safety. The Spring/Summer 2000 program announced March 10 by dint of industry officials will feature a daily national plan of thunderstorm avoidance (see ASW, March 20)

However, what the pilots will do when they reach their destination and find the runways stiffened by a thunderstorm is another matter. If the past is any indication, many of those pilots will mount through the thunderstorm and make a auspicious landing. Sometimes, though, the issue is catastrophic, as evidenced according to the American Flight 1420 crash at Little distaff the 1985 crash of Delta Airlines Flight [DAL] 191 at Dallas-Ft. Worth, and the 1994 crash of USAir Flight 1016 at Charlotte, NC Three crashes, 181 dead. in addition recent research shows that airplanes burst into severe thunderstorms with astonishing commonness (see ASW, Feb. 14).

Dale Rhoda and Margo Pawlak, staff analysts at the Massachusetts Institute of Technology's Lincoln Laboratory, recorded centurys of such penetrations over a 9-day period at Dallas-Ft. Worth International Airport (DFW) and Dallas-Love Airport (DAL). muscular thunderstorms frequently swept across the airports during the close attention Rhoda and Pawlak observed that storm small room penetrations were most likely when pilots were (1) near the destination airport, (2) flying after dark, (3) following other aircraft, and (4) had sustained 15+ minutes of airborne delay. These were penetrations into storms with intensity flats of 3 and above in succession a scale of 1-6.

Drawing from various sources, there be seen to be a number of reasons for what purpose these penetrations are occurring. Pilots have les lateral leeway near the airport. The close-in phase of the approach is a period of high cockpit workload. And, pilots may rely upon storm appearances as well as verbal reports from pilots and controller rather than their radar information. In this regard, pilots can reckon upon to receive reports from their noblemans when the ride gets unpolished At large airports, pilots also can look forward to to receive windshear and microburst alerts from controller As lengthy as landings are fairly sleek pilots "in trail" are likely to emulate the penetrations made from those ahead of them. There are, of course, brace problems associated with such decisions: (1) the weather can make go round very hazardous in the minutes between consecutive airplanes, and (2) when a hazardous pilot report (PIREP) is given or the controller warns of windshear upon the runway, planes lined up for approach are in stop up proximity and must fly a road other than the nominal approach route

And the nominal approach road is the only one for which controller are equipped to pass along hazard information.

To be safe for those situations where wind shear can increase dramatically in the not many minutes between consecutive approaches, help is in succession the way. For airports with Terminal Doppler Weather Radar (TDWR) the Integrated Terminal Weather regularity (ITWS) has a microburst prediction algorithm that can "see" the core of the storm descending before it reaches the domain and predict the outflow when it hits the surface. An efflux of microburst-level will trigger the connected view to alert before the intense downdraft reaches the surface.

With the ability to find 95 percent of microbursts and predict 60-70 percent of them, the theory will help pilots to avoid the self-same worst. That is far short of a course not taken that was put in mind ofed some years ago. But the conceptual appeal of a hard and fast thunderstorm avoidance authority (e.g., stay at least three miles away) may be a prolonged time coming. The closest thing to extant policy we could find is an FAA advisory circular (AC) issued more than ten years ago. An AC is what it means - advisory. At least four obstacles against a more formal policy approach to mind:

1 An added task for controller Air traffic controller would have to be involved in separating aircraft from weather, a big addition to their passing from hand to hand responsibility for separating airplanes from each other.

2 Pilots may be reluctant to relinquish their autonomy. The decision to penetrate or deviate eases currently in the cockpit. It may be better to give pilots information they ne to make informed, foreseeing decisions. While modern aircraft are equipped with weather radars, it may be that pilots are ofttimes too busy during final approach to fitly manage the tilt on the radar antenna. If the tilt is not suitably managed, the radar is make subordinate to ground clutter and can become useless. In the last small in number minutes of flight, pilots may be attendant to rely on verbal information from controller and from preceeding pilots.