Experienced Black Hawk pilot and crew chief:
"The single-greatest error in this accident was the decision to fly without a second Crew Chief on the left-hand side of the Blackhawk, who could have provided an extra set of eyes to 'look out-and-up' to see the approaching American Airlines Passenger plane.
That is from the article but this anon also believes ATC was much to blame for not giving enough warning to the helicopter.
https://www.thegatewaypundit.com/2025/01/wayne-root-here-is-best-explanation-ive-heard/