CHICAGO (CBS) — Opponents say they have new ammunition in their fight against a helipad at the new Children’s Memorial Hospital complex, which is now under construction in Streeterville.

As WBBM Newsradio’s Bob Roberts reports, opponents have forwarded to federal transportation officials an anonymous one-paragraph letter, purporting to say four senior University of Chicago chopper pilots will not use the new helipad, because of the proximity of nearby buildings and the inability to land anywhere nearby in case of an emergency.

LISTEN: WBBM Newsradio’s Bob Roberts reports

The Illinois Department of Transportation in October approved plans for the helipad, which will sit atop a 22-story hospital wing.

The hospital issued a statement, in which it said expert testimony squarely addressed the pilots’ concerns.

The planned helipad has been drawing criticism from neighbors ever since it was first proposed in 2006. Neighbors in the high-density community were concerned about noise and safety.

But Children’s Memorial said the helipad was approved after a three-year review by IDOT experts. The hospital pointed out that it has operated a helipad for more than 20 years at its current campus in Lincoln Park.

Upon moving to its new location, Children’s Memorial Hospital will be renamed the Ann & Robert Lurie Children’s Hospital of Chicago. The hospital at 225 E. Chicago Ave. will open in June 2012.