History of Flight
On July 13, 2022, about 1852 mountain daylight time, a Cessna 208B airplane, N877FE, was substantially damaged during an accident at Salt Lake City International Airport (SLC), Salt Lake City, Utah. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 cargo flight, specifically CPT 7727, a Federal Express Corporation feeder flight.
The flight departed Friedman Memorial Airport (SUN), Hailey, Idaho, about 1729 and climbed to 15,000 ft mean sea level (msl). The en route portion was uneventful. About 1817, the airplane began descending into SLC. The pilot checked in with Salt Lake Terminal Radar Approach Control (TRACON) at 12,000 ft msl and was cleared to descend to 11,000 ft msl with waypoints for the approach. About 1835, the controller transmitted that light to moderate precipitation was expected once abeam the airport. By 1845, the pilot reported the airport in sight and was told to expect landing on runway 34R.
About 1846, the controller instructed the pilot to follow a heading of 150° and descend to 8,000 ft msl. A PIREP indicated a windshear gain of 20 knots on an 8- to 9-mile final. The pilot was then instructed to follow a Boeing 757 on final for runway 34R, cautioned about wake turbulence, and cleared for the visual approach.
About 1848, both approach and local controllers transmitted a windshear alert for runway 34L, citing a 15-knot loss 2 miles out. The pilot contacted SLC tower and was told he was following a Boeing 757 on a 5-mile final, with wind from 300° at 18 knots gusting to 29 knots, and cleared to land on runway 34R. The controller solicited a PIREP from the Boeing 757 crew, who reported windshear of ±10 knots on final. The controller then transmitted a windshear alert for runway 34R arrivals and departures, indicating a 15-knot loss over the runway.
The pilot reported flaring when the controller relayed the 757's windshear encounter. During the flare, the airplane began moving sideways across the runway. The pilot elected to go around due to loss of directional control from left wind and informed the controller. After adding power and climbing to about 30 ft agl, the pilot lowered the left wing to counteract drift. He then encountered a downdraft pushing the airplane toward the ground.
Surveillance video showed the airplane impacting terrain off the right side of the runway in a left-wing-low, nose-down attitude. The tail rose to near-vertical and settled back. The airplane came to rest on its belly and right main landing gear; the nose and left main landing gear collapsed.
Meteorological Information
The pilot checked weather using Aviation Digital Data Service and reviewed terminal forecasts, METARs, and radar. He did not use onboard weather radar. As the airplane approached SLC, some weather was occurring over mountains west of the airport moving slowly east. ATIS information changed several times, mostly due to barometric pressure updates, with northwest wind at 20 to 30 mph. The pilot was not provided wind information after being cleared to land.
SLC had an ASOS augmented by a certified weather observer. At 1833 (19 minutes before the accident), wind was from 340° at 16 knots gusting to 21 knots, visibility 10 miles or greater, thunderstorm, few cumulonimbus at 11,000 ft agl, broken ceiling at 24,000 ft. The thunderstorm began at 1827 with cumulonimbus southwest moving northeast. At 1854 (2 minutes after the accident), wind was from 300° at 29 knots gusting to 48 knots, visibility 9 miles, thunderstorm with light rain, broken ceiling at 14,000 ft agl. The thunderstorm ended at 1842 and began again at 1850 with cumulonimbus overhead moving northeast.
The National Weather Service issued three airport weather warnings between 1800 and 1900: at 1817 for outflow gusts of 30 mph (26 knots) or greater; at 1826 for lightning within 5 miles through 1845; and at 1845 extending the lightning warning to 1900.
The GFA valid at 1800 indicated VFR surface visibilities, scattered thunderstorms, and southwest surface wind at 10 knots gusting to 15 knots. Cloud forecast indicated clouds above the accident site. At 1354, the Storm Prediction Center issued a convective outlook with areas of general thunderstorms.
Weather radar base reflectivity images between 1836:37 and 1854:11 showed reflectivity values between 20 and 40 dBZ moving from southwest to northeast over the accident site. An increase in windspeed toward the accident site was noted. The base reflectivity core descended toward the accident site at the accident time. Fifty lightning flashes were reported within 25 miles in the 10 minutes before and after the accident, with the closest flash 1 mile west of the flight track at 1850:46.
AIRMET Sierra was valid for the accident site, forecasting mountain obscuration. Convective SIGMET 66W was valid, forecasting thunderstorms with little movement and cloud tops above flight level 450. SIGMETs indicate potential for windshear, lightning, and severe turbulence. Rain showers and convective clouds can produce downdrafts, microbursts, outflow boundaries, and gust fronts. According to the FAA Aeronautical Information Manual, microbursts are typically less than 1 to 2.5 miles in diameter, with strong divergent winds and downdrafts reaching 6,000 ft per minute. They can be found in and beneath convective clouds, often embedded in heavy rain or virga.
Video imagery around the accident time showed virga descending toward the accident site with gusting winds and rain. About the time of the accident, the SLC tower wind sensor reported a gust of 16 knots. The Integrated Terminal Weather System and windshear displays provided no microburst alerts until about 10 minutes after the accident.
Wreckage and Impact Information
Postaccident examination revealed the outboard 6 ft of the right wing bent up about 30°, the outboard 5 ft of the left wing bent up about 5°, and the left side of the fuselage crumpled aft of the cargo loading door. The cockpit was undamaged. The flap lever was in the UP position, and the flap jack screw correlated to flaps UP. The left main strut was bent inward about 45°.
Additional Information
FAA Advisory Circular 00-54, “Pilot Windshear Guide” (November 25, 1988, since canceled), defined windshear as any rapid change in wind direction or velocity, and severe windshear as changes causing airspeed changes greater than 15 knots or vertical speed changes greater than 500 ft per minute. The guide focused on windshear associated with convective weather and identified microbursts as a concentrated, powerful downdraft. Microbursts can occur anywhere convective weather occurs; about 5% of thunderstorms produce a microburst. Downdrafts are typically a few hundred to 3,000 ft across, with outflow regions 6,000 to 12,000 ft across. Horizontal vortices may extend to over 2,000 ft AGL.
A review of the NASA Aviation Safety Reporting System (ASRS) found no windshear events involving a Cessna 208 in the 10 years preceding the accident; the most recent was in 2006. In the same period, three windshear-related events at SLC were reported, including go-arounds and significant airspeed fluctuations.
Corporate Air, founded in 1981 and headquartered in Billings, Montana, operated a fleet of about 34 Cessna 208 Caravans. The company’s Flight Operations Training Manual listed windshear as a special operations training topic. The General Operations Manual stated that airborne thunderstorm detection equipment was not required, but if inoperative, crews should select a route to avoid hazardous weather, maintain VFR, or delay the flight. The Flight Operations Manual provided guidance on windshear recovery, including applying firewall power, rotating toward a target attitude of 15°, and using the red bug to visualize stall margin. The manual emphasized that avoidance is primary and advised never penetrating thunderstorm outflow below 1,000 ft agl.