# NTSB CEN18LA146: Cessna T303, N9746C, Pine Ridge, SD, April 24, 2018 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: April 24, 2018, 10:00 local (16:00 UTC) - Place: Pine Ridge, SD - Coordinates: 43.183055, -102.559997 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.1831&lon=-102.5600&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-descent: Structural icing](https://openairdocs.org/ntsb-events/210) - Highest injury: Minor injuries - Injuries: 3 minor, 1 uninjured - Status: Completed, report May 29, 2019 - Report: Approved by Office Director - NTSB office: Central Region - Parties: FAA - NTSB case key (mKey): 97102 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN18LA146 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/97102/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=97102 - Page: https://openairdocs.org/ntsb/CEN18LA146 ## Probable cause The airplane’s inadvertent encounter with severe icing conditions during descent, which resulted in structural icing, the pilot’s inability to maintain altitude, and an emergency landing. Contributing to the accident was an incomplete preflight weather briefing. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Temp/humidity/pressure: conducive to structural icing](https://openairdocs.org/ntsb-findings/03031025): Environmental issues › Conditions/weather/phenomena · Ability to respond/compensate (probable cause); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-findings/03031025/cases.md?model=2073820), [All aircraft, 103 cases](https://openairdocs.org/ntsb-findings/03031025/cases.md) - [Ceiling/visibility/precip: freezing rain/sleet](https://openairdocs.org/ntsb-findings/03035040): Environmental issues › Conditions/weather/phenomena · Ability to respond/compensate (probable cause); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-findings/03035040/cases.md?model=2073820), [All aircraft, 26 cases](https://openairdocs.org/ntsb-findings/03035040/cases.md) - [Aircraft](https://openairdocs.org/ntsb-findings/01030000): Aircraft › Aircraft structures · Capability exceeded (probable cause); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-findings/01030000/cases.md?model=2073820), [All aircraft, 72 cases](https://openairdocs.org/ntsb-findings/01030000/cases.md) - [Performance/control parameters: altitude](https://openairdocs.org/ntsb-findings/01062012): Aircraft › Aircraft oper/perf/capability · Attain/maintain not possible (probable cause); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-findings/01062012/cases.md?model=2073820), [All aircraft, 1,310 cases](https://openairdocs.org/ntsb-findings/01062012/cases.md) - [Planning/preparation: weather planning](https://openairdocs.org/ntsb-findings/02061020): Personnel issues › Task performance · Not specified (probable cause); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-findings/02061020/cases.md?model=2073820), [All aircraft, 156 cases](https://openairdocs.org/ntsb-findings/02061020/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Prior to flight: Preflight or dispatch event](https://openairdocs.org/ntsb-events/030); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-events/030/sequence.md?model=2073820), [All aircraft, 355 cases](https://openairdocs.org/ntsb-events/030/sequence.md) - [Enroute-descent: Structural icing](https://openairdocs.org/ntsb-events/210) (defining event); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-events/210/sequence.md?model=2073820), [All aircraft, 102 cases](https://openairdocs.org/ntsb-events/210/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Cessna T303, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=2073820), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Cessna T303, 3 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=2073820), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis Before the air taxi flight, the commercial pilot obtained a weather briefing via the company computer system and reviewed the weather information with the company chief pilot. The pilot stated that based on the computer briefing, which did not include icing conditions, he was aware of the forecasted weather conditions along the route of flight and at the intended destination. However, the briefing was incomplete as it did not contain any in-flight weather advisories, which would have alerted the pilot of moderate icing conditions expected over the flight route in the form of AIRMET Zulu. After takeoff and during the climb to 12,000 ft mean sea level (msl), the airplane encountered light rime ice, and the pilot activated the de-ice equipment with no issues noted. After hearing reports of better weather at a lower altitude, the pilot requested a descent to between 5,000 and 6,000 ft. During the descent to 6,000 ft msl and with the airplane clear of ice, the airplane encountered light to moderate icing conditions. The pilot considered turning back to another airport but could not get clearance until the airplane was closer to his destination. Shortly thereafter, the pilot stated that it felt “like a sheet of ice fell on us” as the airplane encountered severe icing conditions. The pilot applied full engine power in an attempt to maintain altitude. The airplane exited the overcast cloud layer about 500 ft above ground level. The pilot chose to execute an off-airport emergency landing because the airplane could not maintain altitude. During the landing, the landing gear separated; the airplane came to rest upright and sustained substantial damage to the wings and fuselage. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation and that the airplane was within its maximum gross weight. Structural icing was observed on the airframe after the landing. Based on the weather information, which indicated the probability of icing between 5,000 and 9,000 ft over the region and a high threat of supercooled large droplets between 5,000 and 7,000 ft, it is likely that the airplane, which was equipped for flight in icing conditions, inadvertently encountered severe icing conditions consistent with supercooled large droplets, which resulted in structural icing that exceeded the airplane’s capabilities to maintain altitude. ## Factual narrative On April 24, 2018, about 1000 mountain daylight time, a Cessna T303 airplane, N9746C, impacted terrain during an emergency off-airport landing after encountering severe icing conditions near Pine Ridge, South Dakota. The commercial pilot and two passengers sustained minor injuries, and one passenger was not injured. The airplane sustained substantial damage to the wings and fuselage. The airplane was registered to and operated by Aberdeen Flying Service, Aberdeen, South Dakota, as a Title 14 Code of Federal Regulations Part 135 on-demand air taxi flight. Day instrument meteorological conditions (IMC) prevailed, and an instrument flight rules flight plan was filed for the flight. The flight departed Aberdeen Regional Airport (ABR), Aberdeen, about 0930 central daylight time, and was destined for the Pine Ridge Airport (IEN), Pine Ridge, South Dakota. Prior to the flight, the pilot obtained a weather briefing via the company computer system and reviewed the weather information with the company chief pilot. The pilot stated that based on the computer briefing, which did not include icing conditions, he was aware of the forecasted weather conditions along the route of flight and at the intended destination. After takeoff and during the climb to 12,000 ft mean sea level (msl), the airplane encountered light rime ice, and the pilot activated the de-ice equipment with no issues noted with the equipment. After crossing over the Pierre Regional Airport (PIR), Pierre, South Dakota, the pilot heard via the radio reports of better weather at a lower altitude, and the pilot requested a descent to between 5,000 and 6,000 ft. During a descent to 6,000 ft msl, the airplane encountered light to moderate icing conditions. Prior to the descent, the airplane was clear of ice accumulation. The pilot thought about turning back to PIR but could not get clearance until the airplane was closer to IEN due to poor radio coverage. Shortly thereafter, the pilot stated it felt "like a sheet of ice fell on us" as the airplane encountered severe icing conditions. The pilot applied full engine power in an attempt to maintain altitude. The airplane exited the overcast cloud layer about 500 ft above ground level (agl). The pilot decided to execute an off-airport emergency landing because the airplane could not maintain altitude. The airplane touched down in a field about 25 miles from IEN. During the emergency landing, the landing gear separated, and the airplane came to rest upright. The pilot reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation, and the airplane was below its maximum gross weight. A review of photograph images obtained by the operator confirmed the airplane retained structural icing after the landing. At 0852, the IEN Automated Surface Observation System (ASOS), located 19 miles west-southwest of the accident site, reported wind from 350° at 15 knots gusting to 22 knots, 5 miles visibility inunknown precipitation and mist, ceiling overcast at 1,200 ft agl, temperature 2° C, dew point 1° C, altimeter 30.43 inches of mercury (Hg). At 0952, IEN ASOS reported wind from 360° at 11 knots gusting to 20 knots, 6 miles visibility in unknown precipitation and mist, ceiling overcast at 1,300 ft agl, temperature 2° C, dew point 1° C, altimeter 30.45 inches of Hg. The National Weather Service Aviation Weather Center Current Icing Products, which were available online for the preflight briefing, reported the probability of icing at 5,000 ft, 7,000 ft, and 9,000 ft, as follows: the probability indicated a greater than 75% probability of icing over South Dakota from below 5,000 ft through 9,000 ft. In addition, the icing intensity was depicted as light to moderate intensity, with a high threat of Supercooled Large Droplets at 5,000 ft and 7,000 ft over the region. The preflight weather briefing did not include any inflight weather advisories, which would have alerted the pilot of moderate icing conditions expected over the flight route in the form of airmen's meteorological information (AIRMET) Zulu that was issued at 0700 and valid for 0900. AIRMET Zulu included moderate ice between 5,000 ft and flight level 180 with conditions continuing beyond 0900. The preflight weather briefing did include a pilot report which indicated light rime icing conditions encountered by a commercial airplane climbing through IMC conditions between 3,500 ft and 10,000 ft. There was no current significant meteorological information (SIGMET) to prohibit the flight from operating at the time of the accident. According to the Federal Aviation Administration's Instrument Flying Handbook FAA-H-8083-15B; Chapter 10 on page 10-24: "The very nature of flight in IMC means operating in visible moisture such as clouds. At the right temperatures, this moisture can freeze on the aircraft, causing increased weight, degraded performance, and unpredictable aerodynamic characteristics. Understanding avoidance and early recognition followed by prompt action are the keys to avoiding this potentially hazardous situation … Structural icing is a condition that can only get worse." ## Aircraft - Registration: [N9746C](https://openairdocs.org/aircraft/N9746C), registered now, S/N T30300210 (OpenAirDocs) - Reported make and model: CESSNA T303 (NO SERIES) - Registry model: [Cessna T303](https://openairdocs.org/model/cessna-t303) (registry code 2073820) (OpenAirDocs) - Registry engine: [Continental GTSI0-520-F-K](https://openairdocs.org/engine/continental-gtsi0-520-f-k) (registry code 17031, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: T30300210 - Year built: 1983 - Airframe hours: 8929 - Engines: CONT MOTOR TSIO-520-AE 250 horsepower reciprocating; CONT MOTOR LTSIO-520-AE 250 horsepower reciprocating - Damage: Substantial damage - Flight: Part 135 - Operator: Aberdeen Flying Service - Registered owner: Aberdeen Flying Service - Airworthiness certificate: Standard, Normal - Last inspection: Annual, March 30, 2018, 6 hours before - Departed: ABR, Aberdeen, SD - Destination: Pine Ridge, SD - Flight plan: IFR - Equipment: Auto-pilot, Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 28; injuries: minor; commercial, flight instructor; airplane ratings: single-engine sea, single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review January 19, 2018; seat: left; restraint: 3-point; flight hours: 4,602 total, 5,655 in this make and model, 4,403 as pilot in command, 45 in the last 90 days, 30 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Instrument (IMC), Day - Wind: 360° at 11 knots, gusting 20 - Visibility: 6 statute miles - Lowest ceiling: 1,300 ft overcast - Temperature: 36 °F, dew point 34 °F - Altimeter: 30.45 inHg - Observed at: IEN, 25 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20180424004259A](https://openairdocs.org/incident/20180424004259A), Apr 24, 2018: Cessna T303, Batesland, SD, Substantial damage. On April 24, 2018 at 9:59AM- MDT, a Cessna 303 owned by aberdeen flying service inc. was involved in an accident while en-route from aberdeen, south dakota to… ## Docket (6 files) The files NTSB released with the investigation on November 6, 2018, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=97102. 3.3 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 585 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40468031&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Record of Conversation (item 2, .PDF, 58 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40471886&FileExtension=.PDF&FileName=Record%20of%20Conversation-Master.PDF - Pilot Statement (item 3, .PDF, 170 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40468032&FileExtension=.PDF&FileName=Pilot%20Statement-Master.PDF - Weather Information (item 4, .PDF, 928 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40468033&FileExtension=.PDF&FileName=Weather%20Information-Master.PDF - Pilot Weather Briefing Information (item 5, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40468034&FileExtension=.PDF&FileName=Pilot%20Weather%20Briefing%20Information-Master.PDF - Photo (item 6, .PDF, 1 photo, 216 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40468035&FileExtension=.PDF&FileName=Photo-Master.PDF From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.