EAGLEVILLE, CA, USA
N900RA
Aero Commander 500S
The airplane collided with mountainous terrain during cruise after encountering turbulence and downdrafts associated with mountain wave conditions. According to Federal Aviation Administration (FAA) records, the pilot called the Reno Automated Flight Service Station at 0941 and filed an IFR flight plan, then asked for the winds aloft forecast, which was provided. The pilot did not request any additional weather briefing information for the flight. No other record was found that the pilot obtained additional weather forecast information from any official source associated with the FAA or the National Weather Service. At the time of the pilot's call to the Reno AFSS, several AIRMET weather advisories had been issued hours prior detailing warnings for turbulence and clear icing along the route of flight. The advisories warned of occasional moderate turbulence below 18,000 feet in moderately strong westerly winds especially in the vicinity of mountainous terrain. Clear Air Turbulence (CAT) between 18,000 and 40,000 feet was forecast over the area of the accident site due to jet stream wind shear and mountain wave activity. The pilot departed under visual flight rules (VFR) and picked up his instrument flight rules (IFR) clearance en route and climbed to 14,000 feet. The pilot later asked if he could maintain 12,500 feet. The controller advised him that the minimum IFR altitude on this segment of his route was 14,000 feet, and the pilot cancelled his IFR flight plan. The controller advised the pilot that he had lost radar contact, and instructed the pilot to squawk VFR and the pilot acknowledged the transmission. The last radar target was about 1/2 mile east of Eagle Peak (elevation 9,920 feet) in the Warner Mountains. Rescuers discovered the wreckage near the crest of Eagle Peak on November 23. Investigators found no anomalies with the airframe, engines, or propellers that would have precluded normal operation. The NWS had a full series of AIRMETs current over the proposed route of flight, which included mountain obscuration, turbulence, and icing. Analysis of the weather conditions disclosed a layer between 9,500 and 11,000 feet over the accident site area as having a high likelihood of severe or greater turbulence. A pilot on the same route of flight reported at 1127 that he was in instrument conditions at 11,000 feet, and experiencing light turbulence and light clear icing conditions. He also reported encountering updrafts of 2,000 feet per minute, which was indicative of mountain wave activity. A company pilot was in a second Aero Commander trailing the accident airplane and he reported that at 1147, at a position near the accident site, he encountered a severe downdraft. He applied full climb power, but as the airplane passed over the accident site position, the airplane continued to lose altitude even at maximum power. At 1159, he was able to gain altitude, and return to his assigned cruising altitude of 14,000 feet. The second Aero Commander was turbocharged, the accident airplane was not. Analysis showed that the topography of the area was critical in this case, given that the accident site was at an elevation of 9,240 feet on the eastern slope of Eagle Peak. The accident airplane's flight track was normal along the airway until immediately downwind of the higher terrain. As the flight approached the lee side of the mountain, it came under the influence of the mountain wave and first encountered an updraft and then a downdraft, which increased in amplitude as the flight progressed towards Eagle Peak. Eagle Peak was the tallest point along the Warner Mountain range and the steep slope of this terrain was significant when the mountain wave action was encountered. Such terrain features have been known to enhance the vertical downdrafts and updrafts associated with the most intense mountain wave turbulence.
HISTORY OF FLIGHT On November 21, 2001, at 1126 Pacific standard time (PST), an Aero Commander 500S, N900RA, collided with terrain near Eagleville, California. Commander Northwest Limited was operating the airplane under the provisions of 14 CFR Part 91. The airline transport pilot licensed pilot, a commercial rated pilot passenger, and three passengers sustained fatal injuries; the airplane was destroyed. The personal cross-country flight departed Reno, Nevada, at 1037, en route to Wenatchee, Washington. Visual meteorological conditions prevailed at the nearest reporting station, which was 24 miles away. An instrument flight rules (IFR) flight plan had been filed. The approximate global positioning system (GPS) coordinates of the primary wreckage were 41 degrees 17.69 minutes north latitude and 120 degrees 11.936 minutes west longitude. According to Federal Aviation Administration (FAA) records, the pilot called the Reno Automated Flight Service Station at 0941. The records show that the pilot filed an IFR flight plan, then asked for the winds aloft forecast. The specialist provided the winds aloft information. The pilot did not request any additional weather briefing information for the flight. No other record was found that the pilot obtained additional weather forecast information from any official source associated with the FAA or the National Weather Service. At the time of the pilot's call to the Reno AFSS, several AIRMET weather advisories had been issued hours prior detailing warnings for turbulence along the route of flight. The advisories warned of occasional moderate turbulence below 18,000 feet in moderately strong westerly winds especially in the vicinity of mountainous terrain. Clear Air Turbulence (CAT) between 18,000 and 40,000 feet was forecast over the area of the accident site due to jet stream wind shear and mountain wave activity. Complete details of the weather forecasts and conditions can be found in the Meteorological Information Section of this report. A transcript of recorded radio transmission indicated that the pilot informed clearance delivery that he would depart under visual flight rules (VFR) and pickup his IFR clearance en route. At 1044, the pilot requested his IFR clearance from Reno Departure Control. Departure control cleared him to his destination via radar vectors Lakeview (LKV) VORTAC (very high frequency omni-directional radio range, tactical air navigation) as filed. They then cleared him via the V165 airway as filed, and the pilot acknowledged the clearance. At 1051, the pilot checked in with Oakland Air Route Traffic Control Center (ARTCC) climbing through 12,000 feet to 14,000 feet. The controller instructed the pilot to fly a heading of 350 degrees to intercept V165. At 1054, the pilot asked if he could maintain 12,500 feet. The controller advised him that the minimum IFR altitude on V165 was 14,000 feet, and the pilot cancelled his IFR flight. The controller said that he could provide flight following, but would lose radar contact in 20 miles. At 1059, the controller advised the pilot that he had lost radar contact, and instructed the pilot to squawk VFR and approved a frequency change; the pilot acknowledged the transmission. Recorded radar data depicted a target operating along V165 at a mode C reported altitude of 10,500 feet. Between 1112 and 1126, the data indicated a series of up and down oscillations of 100 to 200 feet, which increased in frequency as the target approached the Warner Mountain Range. At 1124:58, the target made a slight change in course to the northwest and began descending. The last target occurred at 1126:22, at 41 degrees 17 minutes 09 seconds north latitude and 120 degrees 11 minutes 41 seconds west longitude. This was about 1/2 mile east of Eagle Peak (elevation 9,920 feet). Rescuers discovered the wreckage near the crest of Eagle Peak on November 23. A team recovered the wreckage on July 23, 2002. PERSONNEL INFORMATION A review of FAA airman records revealed that the pilot held an airline transport pilot certificate with an airplane multiengine land rating. He held a commercial pilot certificate with ratings for single engine land, single engine sea, and glider aero tow. He held a certified flight instructor certificate with ratings for airplane single engine and multiengine land, instrument airplane, and glider. The operator estimated that the pilot's total flight time was 20,000 hours. The pilot held a ground instructor certificate with ratings for advanced and instrument. He held an airframe and powerplant mechanic certificate. The pilot held a second-class medical certificate issued on February 23, 2001. It had the limitations that the pilot must wear corrective lenses and possess glasses for near and interim vision. AIRCRAFT INFORMATION The airplane was an Aero Commander 500S, serial number 3070. The operator reported a total airframe time of 8,101 hours. The last annual inspection occurred on September 30, 2001. The airplane had a Textron Lycoming IO-540-E1B5 engine, serial number L-8632-48, installed on the left side. Time since overhaul on the engine at the annual inspection was 1,197 hours. The airplane had a Textron Lycoming IO-540-E1B5 engine, serial number L-6421-48, installed on the right side. Time since overhaul on the engine at the annual inspection was 1,197 hours. METEOROLOGICAL INFORMATION A National Transporation Safety Board staff meteorologist prepared a factual report, and a summary of the report follows. All directions are referenced to true north and distances are in nautical miles. Heights are above mean sea level (msl) unless otherwise noted. Visibility is in statute miles and fractions of statute miles. The IIC converted all time to PST. The report included a topographical map, which showed the accident site on the eastern slope of the Warner Mountain Range. Surface Observations Alturas (KAAT), California, which was the nearest reporting station, was 24 miles west-northwest of the accident site at an elevation of 4,374 feet. It had an Automated Surface Observation System (ASOS). An aviation routine weather report (METAR) for Alturus was issued at 1055. It stated: auto; skies 3,400 feet overcast; visibility 10 miles; winds from 190 degrees at 12 knots; temperature 8 degrees Celsius (C); dew point 4 degrees C; altimeter 29.90 inches of mercury. The remarks section noted that the thunderstorm sensor was inoperative. A METAR for Alturus at 1155 stated: auto; skies 3,400 feet overcast; visibility 10 miles in light rain; winds from 220 degrees at 6 knots; temperature 7 degrees Celsius (C); dew point 5 degrees C; altimeter 29.88 inches of mercury. The remarks section noted less than 0.01 inch of precipitation since the last observation, and that the thunderstorm sensor was inoperative. Surface Analysis Chart The National Weather Service (NWS) Surface Analysis Chart issued for 1000 on November 21, 2001, depicted a low pressure system over Idaho with a dissipating cold front to the south of the accident site. This system turned into a warm front and connected with an occluded frontal system with a low pressure system with a central pressure of 988 millibars (mb) off the Pacific coast. Across central and northern California, two high pressure systems with central pressures of 1019 mb and 1020 mb were on either side of the dissipating cold front, with one high pressure system located immediately to the south-southwest of the accident site. The isobars depicted an increasing gradient off the Pacific Northwest coast, but no significant pressure gradient over northern California at the surface. Weather Depiction Chart The NWS Weather Depiction Chart issued for 1100 depicted the dissipating cold front to the south of the accident site. It depicted a large area, which included the accident site, of marginal visual flight rule (MVFR) conditions over central and northern California, and southern Oregon. Station models in northern California closest to the accident site depicted the MVFR conditions with continuous light to moderate rain with overcast ceilings from 1,600 to 3,000 feet. Two isolated areas of IFR conditions were also depicted across western and central California, to the west and south of the accident site. Radar Summary Chart The NWS Radar Summary Chart for 1115 depicted a large area of echoes over central and northern California, western Nevada, Oregon, and western Washington. It depicted echo intensity in the vicinity of the accident site as very light to light rain, with echo tops to the west ranging from 22,000 to 24,000 feet. One of the closest radar sites used in northern California, however, was not available. The closest cell motion was over Oregon and indicated movement to the east-southeast at 51 knots. Constant Pressure Charts The NWS constant pressure charts for 700 mb depicted a low pressure system off the Washington and Oregon coast with an associated trough of low pressure extending eastward and southward from the low. A high pressure system was also depicted further to the south of the low in the Pacific Ocean approximately 28 degrees north latitude and 132 degrees west longitude. Between these two systems, the compressed contour lines over northern California and Oregon indicated a steep pressure gradient, with the strongest gradients off the Pacific Northwest coast. The orientation of the contour lines indicated westerly winds over Oregon, northern California, and Nevada. The zero degree isotherm was out of phase with the contour lines and was to the west of the accident site. The 700 mb best approximated the conditions of the last known altitude of the accident airplane at 10,500 feet, and indicated a westerly wind with temperatures below freezing. The station model for Reno on the 700 mb chart indicated a height of 3,032 meters (9,948 feet), with a west-southwest wind at 40 knots, a temperature of -1 degree C, and a temperature-dew point spread of 0 degrees C, indicating saturated conditions or clouds at that level. The pressure tendency indicated a height fall of 40 meters (120 feet) during the last 12 hours. The station model for Medford, Oregon, indicated a west wind at 70 knots, a temperature of 0 degrees C, and a temperature-dew point spread of 2 degrees C. The height of the 700 mb surface was at 2,944 meters (9,659 feet), with a height fall of 60 meters (200 feet) over the last 12 hours. The conditions at Medford were directly upwind from the accident site and an indication of the wind flow over the Warner Mountain Range. The 500 mb Constant Pressure chart for 1800 on November 22, 2001, depicted conditions of the mean atmosphere at approximately 18,000 feet. The trough of low pressure off the western United States continued to be depicted, and it depicted a double high pressure system over the approximate 700 mb positions. The contour lines continued to indicate a tight gradient over the northwestern United States. The station model over Reno indicated a 500 mb height at 5,574 meters (18,287 feet), with a west wind at 65 knots, temperature of -13 degrees C, and a temperature-dew point spread of 0, and a height falls of 20 meters (120 feet) over 12-hour period was also depicted. Medford displayed no wind data. The 250 mb chart for 1800 depicted conditions at 34,000 feet. Based on the isotachs, the chart depicted a jet stream core of 170 knots off the northern Californian and Oregon coast with westerly winds in excess of 70 knots over the accident site. Upper Air Data The model sounding, located approximately 50 miles south of the accident site, for 1000 depicted saturated conditions with below freezing temperatures from approximately 800 mb to 630 mb or from approximately 6,500 feet to 13,000 feet. The freezing level was near 850 mb or approximately 5,000 feet. The wind profile indicated winds from the south-southwest at 10 knots at the surface and veering to the west-northwest with height with increasing wind speeds. The maximum wind was from the west-northwest at 95 knots about 250 mb or 34,000 feet and just below the tropopause. At 700 mb or approximately 10,000 feet, the sounding indicated saturated conditions with the wind from the west at 45 knots and a temperature of -3 degrees C. The closest standard upper air station was Reno (KREV), located approximately 104 miles south-southeast. The 1600 sounding from KREV indicated a stable, saturated environment from approximately 9,500 feet to 19,000 feet, with the freezing level at 9,000 feet. The wind profile indicated a wind from the southwest at 8 knots at the surface with winds veering to the west through a deep layer with little variation in direction with height through 500 mb or approximately 18,000 feet. The mean wind was from 268 degrees at 52 knots. The observed wind at 10,000 feet or 700 mb, the closest to the last reported altitude of the accident airplane, was from 245 degrees at 45 knots, with a temperature of -0.7 degrees C. The sounding from Medford, Oregon, immediately upwind from the accident site, indicated westerly winds at 72 knots at 10,000 feet with a temperature of -0.3 degrees C. Weather Radar Information The nearest Weather Surveillance Radar 1988, Doppler (WSR-88D) from Washoe County (Reno) located 99 miles south-southeast detected echoes in the 5 to 20 dBZ range or weak to moderate echoes along the route of flight and over the accident site. At this range the radar beam had a width near 10,000 feet. The National Radar Mosaics at 1100 and 1200 also confirmed a large band of weak to moderate echoes over northern California and western Oregon. Pilot Reports A pilot in a light multiengine airplane operating along the same route of flight as the accident airplane reported at 1127 that he was in IMC conditions at 11,000 feet, and experiencing light turbulence and light clear icing conditions. He also reported encountering updrafts of 2,000 feet per minute along the route of flight. Two other pilot reports were significant. One urgent report indicted severe turbulence at 11,000 feet near Redding (RDD), California, at 1524. This was approximately 150 miles west of the accident site and at the same approximate altitude. The other significant pilot report was over Bishop (BIH), California, at 1532. This pilot reported only light to occasional moderate chop, but observed stratiform cap clouds obscuring the mountain tops and stretching on the western side and dissipating on the east side. He also reported altocumulus standing lenticular (ASCL) cloud formations. This was also in the vicinity where the GOES-10 water vapor imagery indicated moisture channel darkening. The majority of other pilot reports over northern California, to the southwest and south of the accident location, reported multiple layers of clouds and instrument meteorological conditions. Turbulence reports varied from none to continuous light to moderate turbulence, and appeared to get more intense with time. Icing reports also varied over the area with several pilots reporting light to moderate icing between 12,000 feet and 16,500 feet. The type of icing varied from rime, mixed, to clear ice. Over the Reno area, several air carrier pilots reported low level wind shear and turbulence from the surface to approximately 13,000 feet, and higher clear air turbulence reports after 1100. One of the pilots in an Airbus jet reported moderate turbulence from 5,000 feet to 10,500 feet, with a severe jolt of turbulence at 10,500 feet. Satellite Data The Geostationary Operations Environmental Satellite number 10 (GOES-10) from 1030 through 1130 indicated multiple layers of clouds extending over the area. The infrared image at 1130 indicated a large band of clouds obscuring the accident site, which was on the northern edge of a band of cirrus type clouds. A radiative temperature of 233.20 degrees Kelvin or -39.96 degrees C was over the accident site, which corresponded with cloud tops in the range of 30,000 feet. Area Forecast The Area Forecast (FA) issued at 0345 was valid until 1600. The forecast began with a warning in the header to see the AIRMET Sierra series for IFR conditions and mountain
the pilot's encounter with forecast mountain wave conditions, moderate or greater turbulence, and icing, with downdrafts that likely exceeded the climb capability of the airplane, which was encountered at an altitude that precluded recovery. Also causal in the accident was the failure of the pilot to obtain an adequate preflight weather briefing which would have included a series of Airmets that were in effect at the time.
Source: NTSB Aviation Accident Database
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