Lion Air Crash: initial reports of possible windshear


Initial reports are pointing to a possible wind-shear, that pushed the Lion Air flight into the ocean, short of the runway at Ngurah Rai Airport in Bali. Wind-shear can be concentrated in micro-burst events that can, and have, literally pushed aircraft into the ground when on final approach (slow and close to the ground).

A micro-burst can best be described as a narrow shaft of very strong air coming out of a storm cloud base going straight down. Like a water hose pointed straight down the wind dissipates in every direction at impact. So that on approach initially the crew will get strong head winds forcing them to push over the nose and pull back the thrust. In this attitude and power state, the aircraft then hits the violent down draft and if immediate action is not taken will impact the ground.

There are conflicting reports on the weather and winds:

“The captain says he intended to go around but that he felt the aircraft dragged down by the wind; that is why he hit the sea,” said the source, who was briefed on the crew’s testimony.
“There was rain coming east to west; very heavy,” the source said, asking not to be named because no one is authorized to speak publicly about the investigation while it is under way.
However, Erasmus Kayadu, the head of Ngurah Rai Airport’s weather station, said there was no rain during the crash period and that visibility was 10 km (6 miles).
The weather station’s data showed the wind speed was 11 kph with lots of low cloud cover, including dense storm clouds, said Kayadu, who is involved in the investigation.

It is still very early in the investigation. The Boeing 737 involved was a brand new aircraft; modern aircraft are equipped with soft ware that first warns of possible wind-shear and then directs “ESCAPE” when it determines that the aircraft has entered an event. There was no mention of the warning or (mandatory) escape directive.






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