Tower controller described a loss of separation event when a departing aircraft assigned 20 continue...

Narrative:

The bonanza departed runway 15 with an assignment to climb to 020 and turn left to heading 050 after departure. These instructions were assigned by the flight data position; and the pilot read back the instructions. No other departure instructions were given to the pilot. Upon commencing the left turn; the person I was training issued traffic to the bonanza on a low level helicopter about 3 miles from his position. Subsequently; the altitude read out on the radar was unavailable for a moment for the bonanza. So; the trainee asked the bonanza to say altitude to ensure safety between the bonanza and the helicopter prior to switching the bonanza to the departure controller. The pilot said 'passing through two thousand' (which he had not yet done according to the altitude read out that came back up on our screen). I believed the pilot had said 'to' not 'through'; however; upon listening to the tapes; it is clear that the pilot stated the word 'through'. The controller I was training switched the aircraft to the departure controller with the bonanza indicating 019. We observed the bonanza indicating 021. We observed the target of the bonanza merge data tags with an aircraft flying over our airspace at 030. We were unable to read any of the data tags until they unmerged; at which point the bonanza was indicating 023. I thought it was possible for the departure controller to have climbed the bonanza; because at that point they had passed the position of the over-flying jet. So; I did not realize that an unsafe event had actually occurred. Upon review of radar feed; the bonanza climbed to within 400 ft of the over-flying jet before beginning a descent. Phraseology change to differentiate between two almost identically sounding words could prevent a re-occurrence; to vs. Through. We could have asked the pilot to 'say again'. Additionally; the pilot could have maintained the altitude that he was assigned by the flight data controller; and the event would have never occurred.

Original NASA ASRS Text

Title: Tower Controller described a loss of separation event when a departing aircraft assigned 20 continued to climb and conflicted with overflight traffic; the misunderstanding of the words 'to' and 'through' listed as contributing factors.

Narrative: The Bonanza departed Runway 15 with an assignment to climb to 020 and turn left to heading 050 after departure. These instructions were assigned by the Flight Data position; and the pilot read back the instructions. No other departure instructions were given to the pilot. Upon commencing the left turn; the person I was training issued traffic to the Bonanza on a low level helicopter about 3 miles from his position. Subsequently; the altitude read out on the RADAR was unavailable for a moment for the Bonanza. So; the trainee asked the Bonanza to say altitude to ensure safety between the Bonanza and the helicopter prior to switching the Bonanza to the Departure Controller. The pilot said 'passing through two thousand' (which he had not yet done according to the altitude read out that came back up on our screen). I believed the pilot had said 'to' not 'through'; however; upon listening to the tapes; it is clear that the pilot stated the word 'through'. The Controller I was training switched the aircraft to the Departure Controller with the Bonanza indicating 019. We observed the Bonanza indicating 021. We observed the target of the Bonanza merge Data Tags with an aircraft flying over our airspace at 030. We were unable to read any of the Data Tags until they unmerged; at which point the Bonanza was indicating 023. I thought it was possible for the Departure Controller to have climbed the Bonanza; because at that point they had passed the position of the over-flying jet. So; I did not realize that an unsafe event had actually occurred. Upon review of RADAR feed; the Bonanza climbed to within 400 FT of the over-flying jet before beginning a descent. Phraseology change to differentiate between two almost identically sounding words could prevent a re-occurrence; to vs. through. We could have asked the pilot to 'Say again'. Additionally; the pilot could have maintained the altitude that he was assigned by the Flight Data Controller; and the event would have never occurred.

Data retrieved from NASA's ASRS site as of July 2013 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	996331
Time
Date	201202
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
State Reference	US
Aircraft 1
Make Model Name	Bonanza 33
Operating Under FAR Part	Part 91
Flight Phase	Initial Climb
Flight Plan	IFR
Aircraft 2
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Person 1
Function	Local Instructor
Qualification	Air Traffic Control Fully Certified
Person 2
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Altitude Overshoot

Tower controller described a loss of separation event when a departing aircraft assigned 20 continued to climb and conflicted with overflight traffic; the misunderstanding of the words 'to' and 'through' listed as contributing factors.