Understanding the weather conditions behind the Kobe Bryant helicopter crash


A weather camera image shows the top of the surrounding cloud layer at the approximate time of the crash. Pilots should not count on finding breaks in this type of low, stratus cloud deck. NTSB Image

A little over a year after a Sikorsky S-76B helicopter crashed in Calabasas, California on Jan. 26, 2020, killing nine people including Kobe Bryant, the National Transportation Safety Board (NTSB) determined that the probable cause of the accident was “the pilot’s decision to continue flight under visual flight rules into instrument meteorological conditions [IMC], which resulted in the pilot’s spatial disorientation and loss of control.”

Weather reporting sites Kobe Bryant crash
A map of ceiling and visibility reporting weather stations along and nearby the accident aircraft’s route of flight on Jan. 26, 2020. The crash occurred in the Santa Monica Mountains, where rising terrain met the low cloud layer. NTSB Image

Obviously, the weather conditions in coastal Southern California were of paramount importance in this accident. Over the course of a relatively short flight, the aircraft, which took off in marginal visual meteorological conditions (VMC), encountered IMC although the weather conditions themselves were well forecast and did not significantly change over the time of the flight. Here is a closer look at the weather on that day.

On the morning of Jan. 26, this area of Southern California was covered by what is known as the “marine layer.” Off the coast of California, we have cool water temperatures (in the range of 50 F / 10 C) due to the cold California Current. Air sitting over this water becomes cool and moisture-laden. Above the marine layer, we have warm, dry, sinking air, the result of subsidence on the east side of the Hawaiian or Pacific High pressure area. This sets up an inversion layer separating the two very different air types. The marine layer itself is very shallow, typically only a few thousand feet in depth.

With the excessive moisture, the marine layer is normally associated with a low, stratus cloud deck which frequently occurs at the top of the layer, just below the inversion. For aviation interests, this cloud deck is often very dense with few if any breaks. It is, however, usually shallow, sometimes only 1,500 feet thick with clear skies above.

With any type of onshore, westerly flow, which is typical on the West Coast, the marine layer with its cloud deck will come ashore. The eastward progression of this shallow air mass is usually blocked by the coastal mountain ranges, with the interior valley regions staying warm and cloud-free. Again, for aviation interests, it should be noted that the mountains themselves are within the marine zone and its cloud cover. Any peaks, even just over 1,000 feet mean sea level (MSL), could be obscured in the clouds.

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The marine layer is generally much more of a weather factor in the summer. The low-level air off the ocean is much cooler than the hot air over the land. Weather systems which could alter this stable situation have followed the jet stream well to the north, thus allowing for the prolonged summer dry season. Typically in the winter, the jet stream makes incursions this far south, allowing low pressure areas and fronts to affect the area, now in the winter wet season.

However, January 2020 was not like this. Most of the significant weather systems stayed well to the north, and there was little precipitation that month. The coastal marine layer was much more of a factor.

Soundings in the area that morning were indicative of the situation. A dense but shallow layer of stratus clouds could be seen in a saturated zone between 1,000 and extending to just above 2,000 feet (2,400 feet was the actual cloud layer top). Below this to the surface, the air was very moist with little wind, thus being prone to fog, mist, or haze. Above the stratus layer was a strong capping inversion with warmer, drier, cloud-free air of considerable depth. Still higher up there was another moist layer indicating high clouds above 15,000 feet (which were apparent on satellite imagery).

AIRMETs Calabasas crash
AIRMETs for IFR conditions and mountain obscuration were active at the time of the accident. The accident location is indicated by the red dot. NTSB Image

All relevant TAFs showed a ceiling holding at 1,000 feet MSL or slightly higher and visibilities between two to four statute miles. The National Weather Service Aviation Weather Center did issue an Airmen’s Meteorological Information (AIRMET) SIERRA advisory for IMC due to mist and fog, and for mountain obscuration in areas including the ultimate accident location. Even without an AIRMET, pilots familiar with the area should know to expect visibility issues in the mountains due to cloud cover in these situations.

Ara Zobayan was the pilot for the flight, which was to depart from Santa Ana at about 9 a.m. with a destination of Camarillo, a direct distance of about 75 miles (120 kilometers) northwest. He completed a flight risk analysis at approximately 7 a.m., indicating that the flight would be within the company’s low-risk category. As required by his company, Zobayan would have to remain in VMC at all times. His plan was to fly between 400 and 600 feet above ground level (AGL), staying in the cloud-free zone below the main cloud deck.

When the helicopter took off from John Wayne-Orange County Airport at 9:07 a.m. in Santa Ana, there was a ceiling of low clouds based at 1,000 feet AGL with a station elevation of 56 feet MSL. Visibility was four statute miles in mist. Flying to the northwest, Zobayan had little difficulty sticking to his flight plan. Weather observations from airports along the way showed that the ceiling remained at 1,000 feet or slightly greater.

The problem arose when he approached Calabasas, a city 22 miles (35 km) northwest of downtown Los Angeles and in the Santa Monica Mountains. These mountains have numerous peaks above 2,000 feet MSL, with Sandstone Mountain being the highest at 3,111 feet. Complicating the situation was the fact that the Santa Monica Mountains are an east-west mountain chain as opposed to most mountain ranges in the U.S., which are north-south. This made the mountains much more of an obstacle for a northbound flight. And in this case, the mountain tops were obscured in the cloud deck.

In addition, the land itself was rising as he continued northward. The city of Calabasas sits at an elevation of 928 feet. Even U.S. Route 101, which he was following, has to go through the Cahuenga Pass with an elevation of 745 feet. What was a cloud ceiling of 1,000 feet when he departed was now closing down on him.

Weather cam Calabasas
A west-facing Bloomsky network camera image from around the accident time. While the FAA is gradually expanding its official weather camera roll-out, many unofficial weather cams are already online and can provide pilots with additional information to consider during flight planning. NTSB Image

The NTSB investigators located regional cameras which showed low clouds with some fog or haze in the area. The images gathered came from the ALERTWildfire network, which had numerous cameras in the area; the Bloomsky Weather Network; and the City of Calabasas Weather Cam. All of these can be accessed online in real time.

Flying at 450 feet AGL and now entering the clouds, Zobayan radioed air traffic control (ATC) to tell them he was initiating a climb to get above the clouds. He was climbing at a rate of 1,500 feet per minute, which meant he would be above the clouds in only a minute or so. Perhaps he believed that in such a short period of time, spatial disorientation would not be a problem.

The helicopter reached 2,370 feet MSL (1,600 feet AGL) and was probably within a hundred feet of breaking through the top of the cloud layer when it began to descend rapidly. When ATC questioned Zobayan, his response was that he was climbing to 4,000 feet MSL (about 3,200 feet AGL) to get above the clouds (and the mountaintops). The NTSB concluded that a somatogravic illusion due to spatial disorientation made him believe he was ascending when in fact he was spiraling rapidly downward. Within seconds, the aircraft crashed into the side of a nearby mountain. All of the above transpired in just two minutes.

The accident is a reminder that a pilot cannot extrapolate conditions near sea level as existing in mountainous terrain. VMC at low levels can quickly turn into IMC as the terrain rises — with deadly consequences.

Sourcing note: Much of the meteorological information referred to came from the NTSB docket for accident DCA20MA059.

  
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