Prc controller described loss of separation event when failing to hear an incorrect read back result...

Narrative:

Taxiway alpha pattern [was] in use. Second R22 [was] given taxi instruction to hold short of A1 on alpha contact ground. Read back [was] incomplete. [I] didn't correct. The first R22 cleared option runway 21R. [I] noticed the second R22 holding short of runway 21R at A1. I gave crossing instructions to the second R22 to cross runway 21R at A1. As he was crossing I noticed the first R22 holding on the numbers of runway 21R on his option. Recommendation; correct read back errors or omissions. Slow down. Scan runway. Locate all applicable traffic.

Original NASA ASRS Text

Title: PRC Controller described loss of separation event when failing to hear an incorrect read back resulting in an aircraft crossing Runway 21R with an aircraft in the process of an 'Option' landing/takeoff.

Narrative: Taxiway Alpha pattern [was] in use. Second R22 [was] given taxi instruction to hold short of A1 on Alpha contact ground. Read back [was] incomplete. [I] didn't correct. The first R22 cleared option Runway 21R. [I] noticed the second R22 holding short of Runway 21R at A1. I gave crossing instructions to the second R22 to cross Runway 21R at A1. As he was crossing I noticed the first R22 holding on the numbers of Runway 21R on his option. Recommendation; Correct read back errors or omissions. Slow down. Scan runway. Locate all applicable traffic.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	923449
Time
Date	201012
Local Time Of Day	1201-1800
Place
Locale Reference	PRC.Tower
State Reference	AZ
Aircraft 1
Make Model Name	Robinson R22
Flight Phase	Initial Climb
Route In Use	None
Aircraft 2
Make Model Name	Robinson R22
Flight Phase	Taxi
Route In Use	None
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Conflict Ground Conflict Less Severe

Prc controller described loss of separation event when failing to hear an incorrect read back resulting in an aircraft crossing runway 21R with an aircraft in the process of an 'option' landing/takeoff.