Question: In what month was the crash that Dennis Nielsen is most widely known for having participated in the rescue effort for?
Sentence (from "United Airlines Flight 232"): United Airlines Flight 232 was a DC-10, registered as N1819U, that crash-landed at Sioux City, Iowa in July 19, 1989 after suffering catastrophic failure of its tail-mounted engine, which led to the loss of all flight controls.
Relevant evidence: Yes