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Aug 3, 2010

This week marked the 25th anniversary of the crash of Delta flight 191 at Dallas-Forth Worth airport, a tragedy that killed 135 people and lead to vital improvements in detecting and avoiding the microburst or wind shear hazards that destroyed a Lockheed Tristar on that terrible day.

Coincidentally, that anniversary, on Monday, came only five days after a closed seminar at Melbourne Airport at which an Australian wake and microburst detection system was reviewed by aviation regulators, airport and airline managers and other interested parties.

This patented system has been under development and field testing by the Australian owned Sondei Group for much of the decade. It has been generating real time acoustic technology images of transient aircraft wake turbulence features in unprecedented detail at Melbourne Airport for the last two years.

But will it suffer a similar fate to the ‘black box’ flight recorders invented by David Warren, who recently died, and fall on barren ground in this country and become yet another involuntary export of Australian genius to shrewder foreign investors?

The Sondei system uses acoustic techniques to measure in high definition the often severe, chaotic and fast moving cells of air turbulence caused by the wake of passing aircraft, and by nature, in the form of sudden downdrafts or micro-bursts such as those generated by the stormy conditions encountered by DL 191 as it approached Dallas-Forth Worth.

In the Melbourne trials Sondei has been providing instant images of the meteorological and man made micro climatic conditions inside and near the airport from ground level to 500 metres up, giving safety authorities their first accurate measures of transient forces that are now blamed for the deaths of many hundreds of people in a string of crashes throughout the jet age.

The system’s main purpose is to improve the efficiency and safety of airports through the closer spacing of arrivals and departures that is possible when the formation and dispersal of wake turbulence and microbursts is known with certainty rather than estimated with the need for significant margins of uncertainty.

The circumstances of the crash of DL 191 are recounted in detail in this entry in Wikipedia.

At about 1500 feet above ground level (460 m), First Officer Price mentioned to Captain Connors that he saw lightning in one of the clouds ahead.

At 800 feet (240 m) above ground level, the airspeed increased without crew intervention. Although the aircraft was supposed to land at 149 knots IAS (276 km/h), its airspeed instead increased to 173 knots IAS (320 km/h). Price tried to stabilize the aircraft’s speed, but Connors had recognized the aircraft’s speed increase as a sign of wind shear, and he warned Price to watch the speed. Connors told Price, “you’re going to lose it all of a sudden, there it is.” Suddenly, the airspeed dropped from 173 to 133 knots IAS (320 to 246 km/h), and Price pushed the throttles forward, giving temporary lift. The airspeed then suddenly dropped to 119 knots IAS (220 km/h); on the cockpit voice recording Connors can be heard saying “Hang on to the son of a bitch!” In addition to the sudden tailwind, the aircraft also experienced a downdraft of more than 30 feet per second. This downdraft would reverse itself several times over the final moments of the flight.

As Price struggled to maintain control of the aircraft through rapidly changing wind conditions, it was hit by a sudden sideward gust, causing a rapid roll to the right and an increase in the aircraft’s angle of attack. Price attempted to regain control by pushing the aircraft’s nose down to avoid a stall, but the severe wind conditions continued to force the airplane towards the ground. Its descent rate reached 5,000 feet per minute at 280 feet above ground level. Price pulled the aircraft’s nose up forcefully just before impact as the captain called “TOGA” (“Take Off/Go Around”), reducing the airplane’s descent rate to 10 feet per second at the initial touchdown.

Delta Flight 191 first struck the ground on a field about 6,300 feet north of the approach end of runway 17L and bounced back into the air. Then, while crossing State Highway 114, it came down again, with an engine striking a black 1971 Toyota Celica vehicle, killing its occupant, William Hodge Mayberry. The aircraft also struck a highway light pole near its wing root, igniting the wing fuel tank, before skidding onto the airfield in Irving, colliding with two 4-million US gallon water tanks at a speed of 220 knots, and exploding into flames. Most of the survivors of Flight 191 were located in the rear, smoking section of the aircraft, which broke free from the main fuselage before the aircraft hit the water tanks.

The Delta 191 memorial dedicated at the Founders Plaza, DFW, on Monday
The Delta 191 memorial dedicated at the Founders Plaza, DFW, on Monday

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