Sct controller described MVA event when an aircraft descended below the issued altitude of 4;200 to ...

Narrative:

Aircraft X was told to turn to 230 intercept the cno localizer and maintain 4;200. He read back descending to 4;300 turning to 230 to intercept the localizer. I corrected him by saying negative maintain four thousand..forty two hundred. He read back four thousand..forty-two. I saw him descend to 4;000 MSL and said 'verify four thousand two hundred.' he said negative I thought you said four thousand forty two. The MVA was 4;200. My phraseology was misleading. I should have said maintain four thousand two hundred...forty two hundred; but I didn't complete the first part which caused confusion. It never occurred to me that a pilot would fly 4;042 ft and think that it was an assigned IFR altitude. That's why I didn't correct him when he said descending to forty two.

Original NASA ASRS Text

Title: SCT Controller described MVA event when an aircraft descended below the issued altitude of 4;200 to 4;042; the reporter acknowledging phraseology utilized was misleading.

Narrative: Aircraft X was told to turn to 230 intercept the CNO localizer and maintain 4;200. He read back descending to 4;300 turning to 230 to intercept the localizer. I corrected him by saying negative maintain four thousand..forty two hundred. He read back four thousand..forty-two. I saw him descend to 4;000 MSL and said 'verify four thousand two hundred.' he said negative I thought you said four thousand forty two. The MVA was 4;200. My phraseology was misleading. I should have said maintain four thousand two hundred...forty two hundred; but I didn't complete the first part which caused confusion. It never occurred to me that a pilot would fly 4;042 FT and think that it was an assigned IFR altitude. That's why I didn't correct him when he said descending to forty two.

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	887596
Time
Date	201005
Local Time Of Day	1201-1800
Place
Locale Reference	SCT.TRACON
State Reference	CA
Aircraft 1
Make Model Name	MU-2 Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Approach
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Sct controller described MVA event when an aircraft descended below the issued altitude of 4;200 to 4;042; the reporter acknowledging phraseology utilized was misleading.