PART 2 | It’s only when another Boeing 737 has a similar problem to the previous unresolved incidents – but doesn’t crash – that investigators crack the case open. The pilot of Eastwind 517, is on final approach into Richmond Virginia when, without warning, his 737 twice rolls sharply to the right. The pilot is able to recover and land the plane safely. NTSB investigators quickly determine that what happened on board Eastwind 517 is alarmingly similar to events on flights 427 and 585. The pilot’s testimony leads investigators to zero in on the 737’s rudder controls. After a series of gruelling tests, investigators discover that a key piece of equipment – a small hydraulic valve jams and then functions in reverse under the right circumstances. It means that any time a pilot tried to correct a rollover, by pushing on the rudder, the rudder might turn in the opposite direction, causing a fatal accident.

In the aftermath of the investigation, sweeping changes were made to improve the safety of the 737 and the entire aviation industry. New training protocols were designed to help pilots react to unusual inflight events, upset recoveries and advanced manoeuvre training. The FAA also directed Boeing to redesign the rudder’s dual servo valve to eliminate the potential for reversal. Boeing spent more than a billion dollars to replace the valves on thousands of 737’s around the world.

Click here for part 1 of this 'Hidden Danger' episode: https://bit.ly/3nbakFz

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From Season 4 Episode 5 “Hidden Danger”: US Air 585 Two 737 planes crash within several years of each other. The similarities are striking but investigators are stumped. It takes a third near miss, for investigators to get the break they need and crack the case.

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