The weather observation is a piece of critical information that a pilot needs to have in making his decision to land,stated Thomas Anthony, director of the University of Southern California’s Aviation Safety and Security Program, following the May 2025 fatal Cessna Citation S550 accident near San Diego. The tragedy, which resulted in six fatalities including several well-known music industry personalities, was not an error of a single event but a chain of technical failures, regulatory failures, and difficult human factors.
As the Cessna descended toward Montgomery-Gibbs Executive Airport in the darkness before dawn, an essential element of situational awareness was absent: Montgomery-Gibbs’ Automated Surface Observing System (ASOS) had been down since the previous night. The Federal Aviation Administration had made no Notice to Airmen (NOTAM) regarding the outage, a regulatory failure that deprived the pilot of immediate, real-time weather information for the field. By FAA rule, a NOTAM must be issued if ASOS information is in error or unreliable. The lack of this notice compelled the pilot to use weather observations from surrounding airfields, an imperfect alternative due to the microclimates within the San Diego basin.
The weather was merciless. Visibility and ceiling were reported at half mile with a 200-foot ceiling from Marine Corps Air Station Miramar, only four miles to the north. Such conditions are well below the minimums for a Category B aircraft like the S550, which typically requires at least three-quarters of a mile visibility and a decision altitude no lower than 673 feet for RNAV approaches. The pilot, Dave Shapiro, acknowledged the poor conditions but pressed on, stating, “That doesn’t sound great, but we’ll give it a go,” in a conversation with air traffic control.
Adding to the difficulty, the airport’s Runway Alignment Indicator (RAI) lights had been dark since March 2022, waiting for repairs held up by an environmental study. Although other runway lights were functional, the RAI system essential for the orientation of pilots making low-visibility approaches was dark. The pilot tried to switch on the pilot-controlled lighting system by keying the microphone seven times, but since the RAI was unavailable, the approach lighting environment was incomplete. According to the NTSB preliminary report, this gap in visual cues may have played a role in the pilot’s situational awareness during the final approach.
Instrument approach procedures are designed with layers of redundancy and safety margins. For RNAV approaches, the minimum crossing altitude (MCA) at the PALOS waypoint is 1,380 feet MSL, providing obstacle clearance over the terrain and man-made structures. ADS-B data indicates the Citation passed PALOS at a mere 1,190 feet MSL short by almost 200 feet of the prescribed minimum. This is a critical deviation since the final approach path overflies high-voltage power lines suspended between towers at about 90–95 feet AGL, 1.8 nautical miles from the runway threshold. The aircraft impacted the lines, chopping off its tail surfaces and causing it to crash into the residential area beneath.
Why did the pilot go below minimum? Investigators are looking at a number of possibilities. One is that there was no current altimeter setting for Montgomery-Gibbs. If the pilot’s altimeter was calibrated to the standard 29.92 inHg instead of the local 29.89 inHg, the discrepancy would be approximately 30 feet short of alone accounting for the full difference, but possibly troublesome in conjunction with other factors. The pilot’s judgment was probably impaired as well by fatigue; the flight had departed late the previous evening from New Jersey and made a stop in Kansas to refuel, and the final descent was at 3:47 a.m. Pacific time after many hours’ worth of overnight flight.
The omission of precision approach alternatives made things worse. The Instrument Landing System (ILS) and the related glideslope of the airport were not operational, so there was a need to use a non-precision RNAV approach that has greater minimums and no vertical guidance. According to minimum crossing altitude guidelines, pilots are not allowed to descend below published altitudes unless the runway environment is in sight, and this condition was not met due to the stated ceiling and visibility.
From a systems engineering standpoint, pilot-controlled lighting system reliability is of utmost concern in non-towered, low-visibility conditions. The microphone-keying system, being well-designed, is no stronger than the foundation lighting infrastructure. Here, the delay in repairs caused by the environmental study created a critical lag. As NTSB investigation revealed, all other runway lighting was available but perhaps the missing RAI cues contributed to spatial orientation or misjudgment during the approach.
The investigation is also made more difficult by the fact that there is no flight data recorder (FDR) on the Citation S550. Although a cockpit voice recorder (CVR) was recovered and analyzed, the absence of FDR data restricts the reconstruction of the aircraft’s exact flight path, control inputs, and system states. As detailed by the National Transportation Safety Board, FDRs record dozens of parameters altitude, airspeed, direction, and others giving investigators a rich digital account of the last moments of a flight. In light aircraft, CVRs are usually the only required recording device, with gaps in the technical record.
The combination of technical malfunctions, procedural uncertainty, and human error in the San Diego crash serves to illustrate the inherent vulnerability of safety margins in instrument flight. The lack of an expeditious NOTAM announcing the ASOS outage, the out-of-service RAI lighting, the pilot’s penetration below minimum crossing altitude, and the lack of full-flight data recording all added layers of risk. Each was manageable alone but combined were catastrophic.
