NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The twin engine airplane collided with rising mountainous terrain while in cruise flight on an IFR clearance. The airplane, N304PA, was on a night IFR flight and was number four in a trail of five company airplanes flying the same route. The time separation between each airplane was about 5 to 10 minutes. The airplane directly ahead of N304PA was N434PA. After being handed off from Los Angeles Center, the flight crew of N304PA contacted the TRACON sector controller at 2043:48 PDT, reporting level at 8,000. The TRACON sector controller instructed the pilot to fly heading 260 after the Julian VOR and intercept the localizer. At 2045:47, the TRACON sector controller told the pilot of N434PA to descend to 6,000 feet. The pilot of N434PA acknowledged the clearance. At 2047:55, the sector controller transmitted, "Seminole four papa alpha descend and maintain five thousand two hundred." The pilot of N304PA responded, "Down to five thousand two hundred for three zero four papa alpha." According to information provided by the TRACON sector controller, this clearance was intended for N434PA. The controller did not recognize that the clearance had been acknowledged by N304PA rather than N434PA. At 2049:55, the pilot of N304PA reported that he had ATIS information Zulu and the sector controller responded, "Seminole three zero four papa alpha thank you very much." At that time the data block on the TRACON controller's display was showing N304PA descending through about 6,600 feet. The Minimum Enroute Altitude for the airway segment being flown was 7,700 feet. At 2050:27, the sector controller again cleared N434PA to descend and maintain 5,200 feet. A Minimum Safe Altitude Warning (MSAW) alert on N304PA was presented to the Center controller at 2049:03. The aircraft's data block remained on the Center controllers display until the radar controller forced it off at 2050:07. The Center controller did not notify the TRACON sector controller that he was receiving a MSAW alert as required by FAA directives. The TRACON's MSAW system generated two predicted altitude alerts on the accident airplane at 2050:46 and 2050:51. According to FAA MSAW documentation, two consecutive predicted alerts will initiate an MSAW warning to the controller working the affected aircraft. Collectively, these alerts would have caused a 5 second aural alert to the sector controller beginning at 2050:51, along with a flashing red "LA" in N304PA's data block from 2050:51 until about 2051:06. The aircraft then descended below radar coverage, the track went into coast status, and the alert terminated. The wreckage of N304PA was located on a ridgeline 200 yards south of the Julian VOR at 5,537 feet msl. No preimpact airplane mechanical anomalies were identified.