WPR22FA151

The pilot’s failure to maintain altitude during an instrument approach, which resulted in a descent below the approach path and impact with a vent stack. Also causal was the failure of the processing plant to correctly paint the vent stacks, which had been determined by the FAA to be a hazard to navigation due to their proximity to the landing approach path. Contributing to the accident was the likely distraction/illusion/obscuration created by steam from the processing plant, which intermittently obscured the runway.

The pilot flew two RNAV (GPS) runway 20 instrument approaches at the Burley Municipal Airport, Burley, Idaho in instrument meteorological conditions (IMC). The accident occurred during the second approach. For the first instrument approach, the pilot configured the airplane with flaps up and flew the final approach segment at speeds above the operator’s training standard of 120 knots indicated airspeed (KIAS).The pilot flew a low pass over the runway, most likely to assess the landing conditions in accordance with company policy, determined the conditions were acceptable, initiated the missed approach and requested to return flying the same approach. The pilot elected to not use flaps during the second approach but slowed the approach speed during the final approach leg. Reported weather had improved and visibility had increased to about 2.5 miles. During this approach, the airplane intercepted and remained on the glide path to the stepdown fix. The last automatic dependent surveillance - broadcast (ADS-B) equipment plot recorded the airplane about a mile past this fix, or about 0.6 nautical miles (nm) from the displaced threshold, on the glide path, and at an estimated 85 knots calibrated airspeed (KCAS), which was slower than the airplane’s 95-knot minimum speed for flaps up in icing conditions. Shortly afterward, the airplane descended about 130 ft below the glide path, striking an agglomerate stack atop a potato processing plant, fatally injuring the pilot and substantially damaging the airplane. A witness reported seeing the airplane come out of the clouds and immediately enter a steam cloud coming from six other stacks before striking the accident stack. A security camera at the processing plant captured the last moments of the airplane’s flight as it came into view in a wings-level, flaps-up, nose-high descent and just before it impacted the stack. While snow and visible moisture were present, the agglomerate stack was always in clear view during the video, with only partial sections obscured. The witness’s account of hearing the engine noise increase and then the nose lift-up may have been the pilot’s attempt to avoid the obstacle. The Federal Aviation Administration’s (FAA) Aeronautical Information Manual advises pilots to avoid overflight of exhaust stacks; however, the accident stack was directly underneath the instrument approach course and overflight would be expected. Postaccident examination of the airplane, conducted hours after the accident, revealed no structural icing on the wings and empennage. Examination of the airframe and powerplant revealed no mechanical malfunctions or failures that would have precluded normal operation. The flaps were up, and a review of the manifest revealed the airplane was loaded within the specifications of the manifest and within the center of gravity limits. Between 2016 and 2017, the FAA conducted two aeronautical studies regarding the stack structures. In the first study, the FAA determined that many of the stack structures were a hazard to air navigation that required mitigation by the processing plant. As an interim measure, the FAA placed the runway 20 visual approach slope indicator (VASI) out of service because the stacks penetrated the obstruction clearance surface and were deemed hazardous to aviation. After determining that they needed to increase the height of the stacks, the plant then modified their proposal; the proposed height increase necessitated a second study. The second study determined the agglomerate stack and the row-of-six stacks exceeded the Code of Federal Regulations (CFR) section 77 standards and provided mitigating actions that included painting the stacks with high visibility white and aviation orange paint and equipping the stacks with red flashing warning lights. The control measures also included the permanent removal of the VASI. On the day of the accident, the agglomerate stack and row-of-six stacks had not been painted to the standard required by the FAA. The warning lights had been installed, and five of the row-of-six stacks were equipped with flashing red lights. The agglomerate stack warning light was stolen following the accident, so an accurate determination of its operating status could not be made. The existing paint scheme and the visible moisture emitted by the stacks provided a low contrast to the environmental background. This low contrast and the lack of a visual glide slope indicator may have caused difficulty for the pilot in maintaining a safe altitude during the visual portion of the approach to the runway. A white and aviation orange paint scheme, as identified in the regulations, may have offered a higher contrast and thus an adequate warning once the pilot transitioned to visual conditions.

BYI had an automated surface observation system (ASOS). Automated BYI weather at 0810, about the time of the first approach, was wind from 190° at 8 kts, visibility 1 mile, light snow, mist, broken ceiling at 2,300 ft agl, overcast skies at 2,800 ft agl, temperature of -3° C, dew point -5° C, and an altimeter setting of 29.96 inches of mercury (inHg). Remarks: automated station with a precipitation discriminator, a trace of precipitation since 0753 MDT, temperature -3.3°C, dew point -5.0°C. Automated BYI weather at 0840, about the time of the second approach, recorded wind from 210° at 8 kts, visibility 2.5 miles, light snow, broken ceiling at 3,000 ft agl, overcast skies at 4,700 ft agl, temperature of -3° C, dew point -6° C, and an altimeter setting of 29.97 inHg. Remarks: automated station with a precipitation discriminator, a trace of precipitation since 0753 MDT, temperature -2.8° C, dew point -5.6° C. The 0900 MDT High-Resolution Rapid Refresh (HRRR) sounding for the accident site indicated an unstable to conditionally unstable environment from the surface through 11,000 ft with a stable layer between 6,750 ft and 7,250 ft. Clouds were indicated by RAOB analysis program between 5,700 ft and 10,000 ft. Moderate or greater icing potential was indicated by RAOB between 5,300 ft and 9,500 ft. Geostationary Operational Environmental Satellite visible and infrared data were obtained from an archive at the Space Science Engineering Center at the University of Wisconsin-Madison in Madison, Wisconsin, for the period from 0600 MDT through 1200 MDT and reviewed. (Figure 5) Figure 5. GOES-17 visible image at 0830 MDT at 2X magnification with the accident site highlighted with a red square and cloud cover indicated above the accident site. The cloud cover was moving from west to east with cloud cover remaining over the accident site. A regional view of the National Weather Service National Reflectivity Mosaic is included as Figure 6 for 0830 MDT with the approximate location of the accident site marked by a red circle. The image depicted 10 to 20 dBZ echoes above the accident site. Figure 6. National Reflectivity Mosaic for 0830 mdt. There were text Airmen’s Meteorological Information (AIRMET) advisories Sierra and Zulu valid for the accident site at the accident time. Text AIRMETs Sierra and Zulu issued at 0410 and 0245 MDT, respectively, forecasted mountain obscuration conditions due to clouds, precipitation and mist, and moderate icing between the freezing level and 16,000 ft. An autopsy of the pilot was performed by the Minidoka County Coroner’s Office, Rupert, Idaho. The cause of death was multiple blunt force injuries. According to the operator’s Operations Specifications, the accident airplane was authorized to conduct commuter and on-demand operations in IFR/VFR and day/night conditions. The airplane was not equipped with a cockpit voice recorder or a flight data recorder, nor was it required to be. The airplane had an S-1 Icing Supplement to the Pilot’s Operating Handbook that was applicable to airplanes equipped with the TKS Ice Protection System and a cargo pod, such as the accident airplane. “Icing conditions” are defined in the Supplement as “visually detected ice, or the presence of visible moisture in any form at an OAT [Outside Air Temperature] of 5° C (41° F) or below.” The airplane’s two approaches to runway 20, conducted in temperatures below 5° C in light snow, met this definition of “icing conditions,” and consequently the limitations listed in the supplement applied. The limitations in the Icing Supplement included a minimum airspeed of 95 knots indicated airspeed (KIAS) flaps up, and 85 KIAS at flaps 10°-20°, and maximum 20° flap setting for landing. The airplane was equipped with a Low Airspeed Awareness System (LAA). The LAA was designed to warn the pilot when airspeed falls below 97.5 knots while operating in icing conditions. When the system is operational and the airspeed drops below 97.5 KIAS, the BELOW ICING MIN SPD annunciator will flash between amber and white, and the stall horn will sound intermittently until the speed is increased above 97.5 knots. An NTSB Performance study included calculations to determine the visibility of the stack from an exemplar airplane at various seating heights. To evaluate the effect of varying eye positions on the visibility of the stack, the azimuth and elevation angles of the cockpit windows and other airplane structures were computed for three different eye heights in the cockpit. This study presented recreations of possible views from the cockpit created by a flight simulation program using sky and terrain graphics including the exhaust stack, and assuming the nominal or average eye position. The time and date were set to those of the accident (0832:30 MDT on April 13, 2022), which resulted in the correct placement of the sun in the sky. The weather options were set to match that of the accident time, and the airplane’s attitude (heading, pitch, and roll) were based on the accident approach trajectory. The results of the simulation revealed that at an average eye position the airport runway could be seen just above the instrument panel, while the accident stack was obscured by the instrument panel from about 29.5 to 3.3 seconds before impact (Figure 4). According to the Chief Pilot for the operator, the accident pilot had no problems seeing over the instrument panel. Figure 4. Flight simulation using accident weather conditions and airplane attitude, showing the airport visible above the instrument panel while the stack is concealed by the instrument panel. A note in the Supplement directs the pilot to multiply normal POH/AFM landing distances by 2.1 for flaps 10°, and to multiply the POH/AFM landing distances by 2.0 for flaps 20°. The note did not provide a multiplier for flaps up. The note did advise pilots to expect the activation of the LAA when slowing to land to include the illumination of the BELOW MIN ICING SPD annunciator and the aural warning to sound [intermittent stall horn]. A review of records revealed that on April 9, 2022, the pilot was on duty between 0630 and 1000 and flew a roundtrip from SLC to BYI and logged a total of 2.4 hours in the CE-208B (N928JP). On April 10, 2022, the pilot was off duty. On April 11, 2022, the pilot was on duty between 0600 and 1900 and logged a total of 5.0 hours (no routing information was provided). On April 12, 2022, the pilot was on duty between 0600 and 1030 and was scheduled to fly a roundtrip from SLC to BYI. According to Gem Air LLC interviews, the pilot had to divert from BYI to Joslin Field/Magic Valley Regional Airport (TWF), Twin Falls, Idaho due to "ground icing conditions" at BYI. The pilot logged a total of 3.2 hours in the CE-208B (N928JP) for the day. On April 13, 2022, the day of the accident, the pilot went on duty at 0600. The pilot completed initial CE-208B training on November 16, 2021. On February 17, 2022, the pilot successfully completed 14 CFR 135.293, 135.297 and 135.299, proficiency, instrument, and line checks. The Gem Air pilot training program included standards for performing non-precision instrument approaches. According to the operator’s Flight Maneuvers Description Manual, the non-precision approach section stated, in part, “if you are approaching an airport, without current weather reports, even if the approach is straight-in, you may wish to plan on circling over the airport to check the winds and runway condition.” The document’s standard for airspeed after passing the final approach fix was 120 knots indicated airspeed (KIAS). According to the Chief Pilot, Gem Air did not teach the pilots to follow the Garmin vertical flight path indicator but did teach pilots to use it as advisory guidance. Gem Air taught pilots to use the autopilot on non-precision approaches in both VNAV and Approach mode. If engaged, the autopil