Eagleville, CA, USA
N327PC
Cessna TR182
The aircraft collided with mountainous terrain on an instrument flight rules (IFR) flight plan and in instrument flight conditions after encountering what a Safety Board weather analysis later established was rime icing conditions, a mountain wave induced downdraft greater than 5,000 feet per minute, and severe turbulence. Over the last 2 hours of the flight, the pilot had experienced difficulty maintaining his assigned altitude and had reported to controllers that he was in moderate turbulence. On one occasion the flight descended below the minimum en route altitude and had difficulty in climbing back to the assigned cruise altitude; however, the pilot continued flying toward his flight planned destination. Just before the accident, the flight's clearance was to maintain 14,000 feet. Recorded radar data indicates that at 1711:28 the airplane had descended to 13,800 feet, and 12 seconds later at the time of the last radar hit, the airplane had descended to 13,200 feet, which was an average descent rate of approximately 3,000 feet/minute. During the uncontrolled descent, the airplane impacted upsloping 5,770-foot mean sea level (msl) terrain in a nose down pitch attitude, about 2 miles from its last recorded radar location. The accident occurred about 53 nautical miles from the pilot's destination airport, and after the pilot had been en route nearly 5 hours. Prior to departure, the pilot called FSS for a weather briefing and told the specialist that he "had been on DUATS" and just needed an overview. FSS personnel informed the pilot that thunderstorms and snow showers were forecast over portions of his planned route including the general area encompassing his destination. No specific mention of turbulence or any mention of mountain wave conditions was provided to the pilot. The NWS's AIRMET that was in effect had not been upgraded to mention the possibility of severe turbulence or the mountain wave condition, despite pilot reports of these types of adverse weather conditions over a wide geographic area. Within a few minutes of the accident, an airport located 23 nautical miles from the crash site reported its surface wind was 19 knots with 32-knot gusts. The visibility was between 0.5 and 1.0 miles in moderate snow and freezing fog; the vertical visibility was between 100 and 900 feet; the temperature was 30 degrees Fahrenheit; and the altimeter setting was 29.78 inches of Mercury. A witness who was located 1 mile from the accident site reported a mixture of snow and rain (sleet) was present and was blowing nearly horizontally at the time, which precluded her from seeing the accident. The pilot's turbocharged and supplemental oxygen-equipped airplane had the capability of cruising at 20,000 feet msl. Flight into known icing conditions was prohibited, and the airplane was neither anti-ice nor deice equipped. Four days prior to the accident, according to the pilot's personal flight record logbook, he indicated having flown the accident airplane into moderate icing conditions.
HISTORY OF FLIGHT On April 25, 2003, about 1712 Pacific daylight time, a Cessna TR182, N327PC, collided with mountainous terrain while cruising in instrument meteorological conditions (IMC), on an instrument flight rules (IFR) flight plan. The airplane descended from 14,000 feet in mountain wave and icing conditions until it impacted upsloping 5,770-foot mean sea level (msl) terrain. The airplane was destroyed, and the instrument rated private pilot and passenger were fatally injured. The pilot co-owned and operated the airplane. The accident occurred about 1.5 miles south of Eagleville, California. The business flight was performed under the provisions of 14 CFR Part 91, and it originated from Scottsdale, Arizona, about 1214 mountain standard time (mst). The pilot's flight planned destination was the Lake County Airport, Lakeview, Oregon. The accident occurred about 53 nautical miles (nm) south-southeast of Lakeview after the pilot had been flying almost 5 hours. While en route, the pilot had communicated with a series of Federal Aviation Administration (FAA) facilities. According to the FAA, at no time did he report experiencing any problems with his airplane. At 1241, the pilot received an IFR clearance to climb to 14,000 feet. The pilot acknowledged the clearance and climbed as directed, as evidenced by data transmitted from the airplane's Mode C (altitude reporting) transponder. At 1532, the pilot advised the controller that he was unable to hold altitude, and he had descended to 13,000 feet. The controller informed the pilot that the minimum vectoring altitude was 13,300 feet. The pilot advised the controller that he would climb back to 14,000 as soon as possible. At 1539, the pilot reported he was back at 14,000 feet and asked if there were any reports of smoother air at either 16,000 or 18,000 feet. The controller cleared the pilot to maintain 16,000 feet. The pilot reported level at 16,000 feet at 1541. He informed the controller that he had experienced light to moderate turbulence at 14,000 feet. Then, at 1603, the pilot advised the controller that he had descended below 15,000 feet but was climbing back to 16,000 feet. The controller instructed the pilot to maintain a block altitude of 15,000 to 16,000 feet. The pilot did not indicate that he was experiencing any problems. At 1651, the pilot requested a lower altitude. The controller instructed the pilot to maintain 14,000 feet. At 1706, the pilot was still cruising at 14,000 feet, and he asked the controller whether he had "received any pilot reports for icing." The pilot also stated "I'm about to go in the soup here in a minute." The controller responded "no reports in your area there's been reports north of Klamath Falls, and the Lake County altimeter two niner seven six." The pilot acknowledged the controller's information at 1706:51. There were no further transmissions recorded from the accident airplane pilot. FAA recorded radar data indicates that about 1711:16, the airplane was cruising in a northerly direction near the centerline of Victor Airway 165, which has a minimum en route altitude of 14,000 feet msl, and a minimum obstruction clearance altitude of 11,900 feet msl. Without receiving an air traffic control clearance, the airplane descended and turned right. By 1711:28, the airplane had descended to 13,800 feet. Recorded radar data indicates that 12 seconds later, at 1711:40, the airplane had descended to 13,200 feet. At this time, the airplane's position was 41 degrees 15.767 minutes north latitude by 120 degrees, 08.533 minutes west longitude. This was the airplane's last recorded position on radar. The airplane impacted terrain about 2 miles north of this location. A witness, who resides near Eagleville, reported hearing the sound of a low flying airplane's engine about 1715. The noise abruptly terminated with the sound of a "boom." The witness additionally reported that she did not observe the airplane because the sleet was blowing nearly horizontally, and her visibility was reduced between 1.0 and 1.5 miles. About noon the following day, wreckage from the airplane was located approximately 1.0 mile west of where the witness had been located. PERSONNEL INFORMATION The pilot held a private pilot certificate with airplane single engine land and instrument airplane ratings. The pilot received the instrument rating on September 20, 2001. The pilot's flight record logbook indicated that as of April 22, 2003, his total flight time was approximately 600.1 hours. His total actual and simulated instrument flight time was about 39.8 and 37.8 hours, respectively. The pilot's last flight review and instrument proficiency check were successfully completed on February 13, 2003. Both examinations were performed in the accident airplane. During the examinations the pilot logged 1.5 hours of simulated instrument flight time. Since May 2001, all of the pilot's logged single engine flight time was acquired flying the accident airplane, and the pilot had logged about 167 hours in the airplane. The pilot's logbook indicated that between April 17 and 22, 2003, he had logged 6.3 hours of actual instrument flight time. In pertinent part, the following notations were written in the pilot's flight record logbook: Date Notation (1) 9/25/2001 "First REAL IFR" (2) 1/16/2001 "ICE in Valley..." (3) 5/16/2002 "IFR into Decreasing weather" (4) 4/21/2003 "IFR to Min GPS 34 Approach LOST GPS. MOD ICE" (5) 4/22/2003 "IFR @ 15,000 NO ICE" (6) 4/22/2003 "15,000 Auto Pilot Failed and came Back." AIRCRAFT INFORMATION Operating Limitations and equipment. The airplane's engine was both turbocharged and carbureted. The maximum certificated operating altitude was 20,000 feet msl. The airplane was equipped with supplemental passenger and crew oxygen. The airplane was not equipped with weather radar, anti-icing, or deicing equipment. Flight into known icing conditions was prohibited. Maintenance Records. The FAA reported that its review of the airplane's maintenance records revealed the airplane received its last annual inspection on January 17, 2003, at a total (airframe log) time of about 2,745 hours. The last maintenance performed on the airplane involved an oil change and landing light replacement, and it was accomplished on April 19, 2003, at a total time of 2,797 hours. Since accomplishment of the last annual inspection, no evidence of maintenance squawks or repairs was found relating to the flight control, pitot-static, or navigation systems. METEOROLOGICAL INFORMATION Weather Conditions, Surface and Constant Pressure Charts. A staff meteorologist with the National Transportation Safety Board's Operational Factors Division performed a study of the forecast and observed meteorological conditions pertinent to the accident flight. The study findings are included in the docket for this accident report. In summary, the study indicated the following: According to the Surface Analysis Chart produced by the National Weather Service (NWS), a low pressure center existed off the Oregon coast with an occluded front extending from the low pressure center southeastward into southwestern Oregon and into northern California. Another low pressure system was located in central Nevada, and it was associated with a stationary front that was oriented in a northeast to southwest direction. The accident site occurred ahead of the occluded front and northwest of the stationary front. NWS radar summary charts depicted numerous echoes over Oregon and northern California, with scattered echoes over Nevada. Echoes in the range of very light to light intensity were identified west of the accident site and moving to the northeast at 20 to 23 knots. No echoes were identified over the accident site. Constant pressure chart data depicted an upper level low pressure system off the Oregon coast with a trough of low pressure extending south off the northern California coast. The station models surrounding the accident site all indicated temperature-dew point spreads consistent with near saturated conditions at the 700 millibars level (about 10,000 feet). The station model for Reno, Nevada, indicated at the 500 millibars level (about 18,000 feet) a wind from the west-southwest at 90 knots, and a temperature of -18 degrees Celsius. The wind flow was depicted from the west-southwest about 50 knots over the accident site, with an approximately 40-knot horizontal wind shear per 100 miles. The advisory circular "Aviation Weather" (AC 00-45) identifies wind shears of 18 knots per 150 miles associated with moderate turbulence, and shears of 40 knots per 150 miles (similar to those found over the accident site) with severe turbulence. Topography. The accident site was located on the eastern upward slope of the Warner Mountain Range, which is oriented in a north-to-south direction. North-to-south oriented mountain ranges, especially those with steep slopes on the lee side like those found in the vicinity of the accident site, have been involved in previous accidents that were found related to mountain wave activity and downslope winds. Upper Air Data. The NWS's Reno Forecast Office assessed the atmospheric stability from soundings. In brief, at the accident airplane's reported cruising altitude of 14,000 feet, the wind was identified from 230 degrees at 57 knots. The temperature was identified as -17 degrees Celsius. The sounding had a lifted condensation level (LCL) or estimated base layer of the clouds and level of free convection (LFC) at 9,229 feet. The sounding had a relative humidity greater than 75 percent from this level to about 13,000 feet, which supports airframe icing from the freezing level (7,255 feet) to this level. This layer was identified as stable and supported rime type airframe icing. The sounding also indicated that between 12,600 and 17,400 feet there was a greater than 87 percent chance for moderate to severe turbulence. Mountain Wave Algorithm. Algorithms were used in the examination of sounding data obtained from the NWS's Reno Forecast Office and predicted the existence of mountain waves and turbulence. Specifically, the sounding indicated that the predominate wave was identified at 23,500 feet, with a wavelength of 7.5 miles from crest to crest. The wave's maximum vertical velocity was 5,242 feet per minute, based upon a half width of 1.8 miles between Eagles Peak and the Sunrise Valley (near the accident site area). Satellite Data. Both infrared and visible images were obtained from satellite data. Infrared images indicated that the closest cumulonimbus cloud was about 85 miles west-northwest of the accident location. A layer of mid-level clouds over a lower stratiform layer were indicated in the accident site area. Animating the images and measuring the distance the clouds traveled with time revealed the clouds' motion was from 230 degrees at 56 knots. Pilot Reports. Multiple pilot reports (PIREPs) were recorded over northeast California and northwest Nevada surrounding the time of the accident. The reports indicated, at various altitudes, the existence of moderate to occasional severe turbulence, light rime ice, and mountain wave conditions. Area Forecast, AIRMETS and SIGMETS issuance criteria. The forecast for northeastern California was for an overcast sky condition at 8,000 feet msl with tops to 25,000 feet; visibilities 3 to 5 miles; light showers of snow and rain; and southerly winds gusting to 25 knots. The NWS had issued an Airman Meteorological Information advisory (AIRMET) for the geographic area, which encompassed the pilot's route of flight. The AIRMET advisory was issued for IFR conditions and mountain obscuration, clouds, precipitation, fog, and mist. The AIRMET warned of occasional ceilings below 1,000 feet above ground level and visibilities below 3 miles in mist and fog. The AIRMET was updated several times during the pilot's flight, and the updates indicated occasional moderate turbulence below 18,000 feet due to gusty low-level winds over rough terrain, moderate rime to mixed icing-in-clouds and in-precipitation, between the freezing level and 16,000 feet. Significant Meteorological Information advisories (SIGMETs) are issued by the NWS Aviation Weather Center for severe icing, severe or extreme turbulence, duststorms/sandstorms that lowers visibility to less than 3 miles, and volcanic ash. These SIGMET items are considered to be widespread because they must be affecting or be forecast to affect an area of at least 3,000 square miles at any one time. However, if the total area to be affected during the forecast period is very large, it could be that only a small portion of this total area would be affected at any one time. There were no severe weather forecast alerts, convective SIGMETs, SIGMETs, or center weather advisories current for the route. No NWS weather advisory warned of the possibility of encountering severe turbulence, severe icing, or mountain wave activity. Turbulence and Mountain Wave Guidance. The NWS and FAA have jointly issued several publications relating to weather for pilot training and certification knowledge requirements. For example, in Advisory Circular 00-45E some of the locations for turbulence associated with mountain waves are identified as follows: Moderate Turbulence - In mountainous areas with a wind component of 25 to 50 knots perpendicular to and near the level of the ridge, within 5,000 feet of the ridge, or at the base of relatively stable layers. Severe Turbulence - In mountainous areas with a wind component exceeding 50 knots perpendicular to and near the level of the ridge, or at the base of other stable layers below the tropopause. Pilot Briefing and Witness Reports. Prior to the pilot initiating his flight from Scottsdale, he received an abbreviated weather briefing from a FAA Flight Service Station (FSS) briefer. At 1041 mst, the pilot advised the FSS briefer that he had been "on DUATS" (Direct User Access Terminal Service) and just desired to obtain an overview of the forecast weather conditions. The pilot informed the briefer that he could fly up to 20,000 feet. He also stated, in part, that "I'm going to be above the icing other than on descent." The briefer advised the pilot that the forecast for Klamath Falls (about 60 nm west of the pilot's Lakeview destination, and about 89 nm northwest of the accident site) indicated light snow showers and "some thunderstorm development" in northern California and northwestern Nevada by 1500. The pilot inquired if the conditions were "isolated or does it look like it could be significant?" In part, the FSS briefer responded "it could be significant." The briefer elaborated and made the following statement: "Well, I see they even have em in northeastern Nevada too in their forecast so basically the whole northern half of the state of Nevada is calling for thunderstorms." The pilot responded by stating "wow...you're just full of good news aren't you." The FSS briefer then stated "if you went through there in the morning hours it wouldn't be such a big deal but by late afternoon it's kind of the peak period for that stuff to develop." The briefer also advised the pilot that the forecast tops of the thunderstorms were 33,000 feet msl. Weather Reports, 1704 and 1713, Alturas ASOS. At 1704, an automated surface observing system (ASOS) located at the Alturas Municipal Airport reported its local weather conditions. Alturas is located about 23 miles west-northwest of the accident site, at an elevation of 4,374 feet msl, and was the closest aviation weather reporting facility to the accident site. In pertinent part, Alturas reported that its surface wind was from 250 degrees at 19 knots, with gusts to 32 knots. The horizontal visibility was 1 mile, and the sky was obscured with a vertical visibility of 100 feet in the light snow. The temperature was 32 degrees Fahrenheit. At 1713, the Alturas special weather observation indic
the pilot's encounter with mountain wave activity with downdrafts and severe turbulence, which resulted in a loss of airplane control and impact with terrain. Contributing to the accident was the pilot's improper decision to continue flight into an area of adverse weather, and the failure of the National Weather Service to issue an adequate weather advisory of possible severe turbulence.
Source: NTSB Aviation Accident Database
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