B737-300
Air Traffic Control Fully Certified
Confusion; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict
General None Reported / Taken
Procedure; Human Factors
Runways 30L/30R were in use at SJC. I took a point out from Lick Sector on a VFR Skyhawk 10-miles to the southeast of SJC; tracking northwest toward SJC with destination SQL or PAO airport. When the Skyhawk was 2-3 miles east of SJC at 2;000 FT MSL; the aircraft was tracking in a direction that would place it over mid-field SJC airport; so as to not be a factor for jet aircraft departing Runway 30R at SJC. The Skyhawk was on an 'N' tag as it approached SJC; indicating that Moffett (NUQ) would soon be in control of the aircraft. At this time; a B737 was told about the VFR Skyhawk at 2;000 FT; and that it would pass behind. The B737 was cleared for take off. After the B737 began its take off roll; the Skyhawk was observed making a right turn; tracking northbound instead of continuing its previous track toward NUQ as expected. I called NUQ and asked if they were talking to the C172; to which they replied negative. At the time the B737 was lifting off Runway 30R; the C172 was on the north side of the Runway 30R departure corridor; tracking north at 2;000 FT MSL. I then told the B737 that the traffic was passing off their right side; no factor; and to contact Norcal Departure. I told the B737 that traffic was no factor based upon the RADAR track of the C172. After the B737 was switched to Departure frequency; the RADAR track for the C172 immediately; and unexpectedly; began to turn toward my departure corridor; and toward the B737. I called Toga Sector; the sector who would be talking to the B737; to inquire about the C172 and advise them that I was not talking to the C172. Toga was not talking to the C172; nor was NUQ when I called Moffett back. Norcal later called SJC Tower to let us know that the C172 was instructed to cross SJC midfield westbound; as I had expected. Norcal said that the pilot of the C172 may be issued a pilot deviation. The RADAR targets of the two aircraft did not merge; however the proximity of the C172 to the B737 may have caused alarm for the two pilots. When I accepted the C172 point out from Norcal TRACON; I expected that the TRACON would keep the C172 clear of the departure corridor; because I had obtained releases for several jet aircraft which would fly through that protected corridor. I continued departures based on the fact that I had these releases and based on the track of the C172. The C172 made an immediate; unanticipated course change toward the B737; which was not evident on the RADAR when the B737 was changed to Departure frequency. I will exercise additional vigilance when aircraft are operating near my departure corridor; and I will remember to factor in the possibility of unexpected pilot actions; especially when I am not in direct communication with them. When communicating 'traffic no factor' I will remember to take into consideration that a RADAR track is slightly delayed information and that slower aircraft can change course much more rapidly than faster aircraft.
SJC Controller described a conflict between a VFR point out from NCT and an IFR Air Carrier departure from Runway 30R; the VFR traffic apparently not complying with airport crossing instructions.