Accident analysis: Radio silence

The temptation to fall back on familiar patterns grows particularly strong when fatigue makes a fresh assessment seem like too much trouble—exactly the point at which a pilot’s internal alarms ought to be blaring warnings to pause and reconsider, and when the consequences of succumbing to that temptation may prove especially grim.

The disaster

At 12:23 a.m. on October 24, 2004, a Learjet 35A configured as an air ambulance took off from San Diego’s Brown Field Municipal Airport (SDM) to return to its base at Albuquerque International Sunport Airport (ABQ). Two minutes later, just after the captain established radio contact with the Southern California Tracon, the jet flew into a mountainside eight miles east of the airport at an elevation of 2,256 feet, creating a 48-foot impact crater and a 500-foot-wide debris field. All five on board—two pilots and three medical crew members—were killed.

The flight

The accident flight was the crew’s fourth in the span of 11 hours. They originally departed from Albuquerque at 3:20 p.m. Pacific time on a positioning leg to El Paso, Texas, where they picked up the third member of the medical crew. From El Paso, they flew to Manzanillo, Mexico, to board one patient and an accompanying passenger, landing at 6:25 p.m. They launched for San Diego around 8:40 p.m., landing at Brown Field at 11:24 p.m. The patient and passenger disembarked, and the crew cleared Customs during a ground stop of about an hour.

Two minutes after midnight, one of the pilots filed an IFR flight plan to Albuquerque with the San Diego Flight Service Station, giving a planned departure time of 12:20 a.m. Routing was direct to Palm Springs and then direct to destination, with an estimated time of 1 hour 15 minutes at Flight Level 370. The caller did not request a briefing, a clearance, or an IFR void time.

The flight crew’s radio transmissions and cockpit conversation during the next 20 minutes were captured by the Learjet’s cockpit voice recorder (CVR). The recording showed that the crew tuned in San Diego’s ATIS broadcast, but shut it off after the “remarks” portion without listening to the weather. (Cautions about the higher terrain to the east were added to Brown Field’s ATIS transmissions after the accident, but were not provided at that time.) A surface observation recorded at 11:53 p.m. included calm winds and eight miles visibility under an overcast layer at 2,100 feet above the ground, or about 2,600 feet mean sea level.

The first officer tried to radio San Diego ground control to pick up their IFR clearance but received no response—the tower had closed more than two hours earlier. He mentioned the possibility of calling for IFR clearance while airborne, adding “I don’t want to do it, but….” He then tried the San Diego FSS’s remote communications outlet frequency, the Tijuana tower, and a second FSS frequency, but was unable to make contact on any of them. After the fourth unsuccessful attempt, the captain said, “All right, let’s just go VFR.”

The captain chose to take off from Runway 8L, both to avoid overflying downtown San Diego and to head directly toward their destination. During the ensuing discussion, neither pilot brought up the mountains immediately to the east and northeast. The NTSB’s report notes that during the six minutes of conversation, the CVR recorded the first officer yawning five times. In response to the first officer’s request for a briefing, the captain answered, “Uh, let’s see…will be standard callouts tonight and, if you can’t punch up through a nice hole then just, uh, you know, stay at a reasonably safe altitude and, uh, underneath 250 knots, and I’ll do the best I can to get somebody’s attention.”

The Learjet took off from Runway 8L at 12:23 a.m., climbing straight out until it leveled off at 2,300 feet msl. The captain contacted Southern California Tracon, was given a squawk code, and told to ident. At 12:24:55 a.m., the controller acknowledged radar contract and told the pilots to turn left to a heading of 20 degrees, maintain VFR, and expect their clearance after reaching 5,000 feet. The captain’s readback was the flight’s last radio transmission.

Four seconds later the controller’s radar screen began issuing minimum safe altitude warnings, but the controller didn’t attempt to warn the flight crew for almost another minute—34 seconds after radar contact had been lost.

Contributing factors

San Diego’s obstacle departure procedure for Category C and D aircraft using Runways 8L/8R required a climbing left turn to a 280-degree heading—nearly opposite the direction of takeoff—to intercept the 160-degree radial from the Mission Bay Vortac. The crew chose not to follow it when taking off toward poorly lit rising terrain under an overcast layer at night. Although they didn’t listen to the weather portion of the ATIS, the captain’s suggestion that they “punch up through a nice hole” suggests that they were aware of the relatively low ceiling.

Perhaps even more surprising is that they never tried to telephone FSS to get their clearance, although according to the airplane’s operator both a cellphone and a satellite phone were on board. It seems unlikely that both devices’ batteries had been drained. There was no mention of using a phone on the CVR, suggesting that neither pilot—both of whom had by that time been awake for more than 16 hours and on duty for 11—remembered that they had that option. (Cellphones were far less ubiquitous in 2004.) As the NTSB report notes, “people who are fatigued become less able to consider options and are more likely to become fixated on a course of action or a desired outcome.”

The report also was sharply critical of the tracon controller, who although familiar with the mountains east of the airport and aware of the overcast layer, not only failed to warn the crew but actually vectored the jet onto a heading toward the peaks. He explained these lapses by asserting that under VFR, terrain avoidance is the pilot’s responsibility. However, FAA Order 7110.65P establishes issuing safety alerts as a controller’s first priority whether the flight is VFR or IFR. The same order states that when a controller issues an instruction—such as a heading—to a flight requesting an IFR clearance while maintaining VFR below minimum IFR altitudes, responsibility for terrain clearance is transferred to the FAA. When interviewed after the accident, the controller claimed to be unaware of this. In a concurring statement, NTSB member Kathryn O’Leary Higgins noted that the controller had worked an eight-hour morning shift, then returned for the night shift seven and a half hours later without having slept. Fatigue might also have figured into his neglecting the safety of the only aircraft he was working at the time.

As complex as the machinery is, catastrophic aircraft accidents often can be traced to simple things. Staying over until morning, flying the obstacle departure procedure, even making a telephone call could have been enough to save five lives.