What happened
The pilot was returning to Santa Monica Airport (SMO) from a cross-country flight when the destination runway was closed due to a disabled aircraft on the field. The crew diverted to Van Nuys and, after the runway reopened, filed an instrument flight rules (IFR) plan to continue the flight at 5000 feet, departing at night.
During departure, Air Route Traffic Control Center (ARTCC) controller AR-3 provided radar vectors for a clearance altitude of 3000 feet. At 1926:39, the AR-4 controller acknowledged and accepted an automated handoff via an ARTS-III computer keyboard entry. AR-3 continued to provide additional vectors to the flight, with the last instruction being a heading of 080 degrees at 1929:12. However, the controller did not instruct the pilots to change to AR-4's frequency.
At approximately 1933, both AR-3 and AR-4 controllers were relieved and began briefing their replacements. Shortly thereafter, the flight passed over the Airport Surveillance Radar (ASR) antenna and was displayed on the radar scope in coast mode. It reappeared with a data tag that erroneously indicated another facility had control of the flight. The relieving controllers saw the full data block on their scopes but disregarded it due to the erroneous control symbol. Subsequently, the aircraft struck mountains at the last assigned altitude of 3000 feet. The commercial flight instructor (CFI) had recently moved from Florida to California and was on his second day of employment in the state.