A federal safety official says the pilot of a plane involved in a mid-air collision over the Hudson River read back the wrong radio frequency to an air traffic controller but wasn't corrected.

Nine people were killed in the Aug. 8 crash between the single-engine Piper and an air tour helicopter.

Click here for exclusive photos.

PHOTOS: Grim Recovery Effort (WARNING: Graphic)

National Transportation Safety Board Chairman Deborah Hersman told a congressional committee Wednesday that an air traffic controller gave the plane's pilot the radio frequency for Newark Liberty International Airport in New Jersey, but the pilot read back the wrong frequency.

She said there is no indication the pilot was corrected and he never contacted Newark. Later attempts to contact the pilot were unsuccessful.