Nct TRACON controller told an aircraft to fly heading 180. The pilot misunderstood the instruction a...

Narrative:

Training was in progress at the time. The departure sector pointed out an arrival on a right downwind visual approach so we knew that aircraft from the north were capable of seeing the field. This weekend was very busy due [to] an event generating 5-8 times the amount of departures and arrivals. To add to the complexity; a tfr was in effect south of mry. The runway 28L RNAV Y was the approach in use.aircraft X and other aircraft were incapable of that approach causing complexity and further burdening the departure sector for opposite direction procedures with consistent departure releases. We offered aircraft X; aircraft Y; and a few other aircraft vectors right traffic visual approach to facilitate the arrival flow. Aircraft X was first in line vectored at 4000 feet due to lowest MVA east of mry and cleared for a visual approach. The pilot questioned about a VFR aircraft approximately 3 miles east of the field already talking to the tower. Aircraft X was on a 3-4 mile right downwind. Aircraft Y was sequenced 6 miles behind at 4000 feet. Aircraft X was on the base leg still at 4000 feet; he was uncertain about the VFR aircraft to his right. I offered aircraft X to fly south for resequencing and told the pilot to fly heading 180. He read back 'roger right turn heading 180'; which we didn't catch. The aircraft made a complete 360 degree turn south in conflict with aircraft Y who was on the right downwind to follow aircraft X. We had to take immediate evasive actions to turn and climb aircraft Y out of the way.the biggest issue with mry; is that the RNAV Y runway 28L approach does not offer CAT D approaches and the runway 28L localizer/DME has been out of service for almost 2 years. These issues with the runway 28L approaches are constantly causing undue delay and complexity to these sectors.

Original NASA ASRS Text

Title: NCT TRACON Controller told an aircraft to fly heading 180. The pilot misunderstood the instruction and initiated a 360 degree turn putting it into conflict with traffic behind it on downwind.

Narrative: Training was in progress at the time. The departure sector pointed out an arrival on a right downwind Visual Approach so we knew that aircraft from the north were capable of seeing the field. This weekend was very busy due [to] an event generating 5-8 times the amount of departures and arrivals. To add to the complexity; a TFR was in effect south of MRY. The Runway 28L RNAV Y was the approach in use.Aircraft X and other aircraft were incapable of that approach causing complexity and further burdening the departure sector for opposite direction procedures with consistent departure releases. We offered Aircraft X; Aircraft Y; and a few other aircraft vectors right traffic visual approach to facilitate the arrival flow. Aircraft X was first in line vectored at 4000 feet due to lowest MVA east of MRY and cleared for a Visual Approach. The pilot questioned about a VFR aircraft approximately 3 miles east of the field already talking to the Tower. Aircraft X was on a 3-4 mile right downwind. Aircraft Y was sequenced 6 miles behind at 4000 feet. Aircraft X was on the base leg still at 4000 feet; he was uncertain about the VFR aircraft to his right. I offered Aircraft X to fly south for resequencing and told the pilot to fly heading 180. He read back 'roger right turn heading 180'; which we didn't catch. The aircraft made a complete 360 degree turn south in conflict with Aircraft Y who was on the right downwind to follow Aircraft X. We had to take immediate evasive actions to turn and climb Aircraft Y out of the way.The biggest issue with MRY; is that the RNAV Y RWY 28L approach does not offer CAT D approaches and the RWY 28L LOC/DME has been out of service for almost 2 years. These issues with the RWY 28L approaches are constantly causing undue delay and complexity to these sectors.

Data retrieved from NASA's ASRS site 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	1381885
Time
Date	201608
Local Time Of Day	1201-1800
Place
Locale Reference	NCT.TRACON
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Medium Transport Low Wing 2 Turbojet Eng
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Light Transport Low Wing 2 Turbojet Eng
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Approach Instructor
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 13
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Clearance Deviation - Track / Heading All Types

Nct TRACON controller told an aircraft to fly heading 180. The pilot misunderstood the instruction and initiated a 360 degree turn putting it into conflict with traffic behind it on downwind.