History of Flight
On July 8, 2012, at 2114 eastern daylight time, a Piper PA-42, registration N332SM, sustained substantial damage during a gravity wave encounter near Charleston, West Virginia. The airline transport pilot and two passengers were not injured. Instrument meteorological conditions prevailed, and an instrument flight rules flight plan was filed. The flight departed Yeager Airport (CRW), Charleston, West Virginia at 2052 and was destined for Middle Georgia Regional Airport (MCN), Macon, Georgia. The personal flight was operated under 14 CFR Part 91.
The pilot obtained a preflight weather briefing, which depicted an area of convective activity west of CRW moving east. Conditions at CRW included calm winds, light rain, and good visibility under a layer of overcast clouds at 11,000 feet. The flight was cleared for takeoff and asked to expedite for another airplane on final approach. The pilot complied but stated that the expedited takeoff precluded a final "sweep" of the area ahead on the airplane's onboard radar, and the satellite weather receiver could not obtain a signal prior to takeoff.
The pilot contacted Indianapolis Air Route Traffic Control Center at 2105 while climbing from 5,000 feet after departure. Noting several lightning strikes on the Stormscope, the pilot requested and received a deviation to the left of planned course.
At 2110, after clearing the airplane to climb to 23,000 feet, ATC queried the pilot about conditions. The pilot reported "light bump" at current altitude and stated they entered IMC around 15,000 feet.
Shortly after, the pilot saw a flash of lightning that "appeared close." The airplane entered a rapid ascent, with the vertical speed indicator reflecting a climb of more than 4,000 fpm. The pilot reported a "strong kinesthetic sense of upward acceleration," disconnected the autopilot, and neutralized the controls. Both gyroscopic instruments tumbled, leaving no attitude reference. The pilot made a "mayday" transmission before hearing the stall warning horn, followed by a "falling and twisting" sensation. Suspecting a steep spiraling descent or spin, the pilot reduced engine power. Perceiving ground lighting as the airplane exited clouds, the pilot recovered to level flight at approximately 8,000 feet.
After regaining control, the pilot requested radar vectors back to CRW and landed without incident. Upon disembarking, substantial damage was observed to both the left and right elevators.
Personnel Information
The pilot held an airline transport certificate (multiengine land), commercial certificates (single-engine land and sea, multiengine sea), and a flight instructor certificate (single/multiengine, instrument airplane). He reported 4,080 total hours, with 389 hours in the accident make and model. His most recent FAA first-class medical was issued January 3, 2012.
Aircraft Information
According to FAA records, the airplane was manufactured in 1981 and equipped with two Pratt & Whitney PT6A turboprop engines. The most recent 100-hour inspection was completed June 6, 2012, at a total aircraft time of 6,091 hours.
Meteorological Information
The National Weather Service Surface Analysis Chart for 2000 depicted a stationary front across northern West Virginia, a surface low in southern Virginia, and a high pressure system in eastern Kentucky. Station models showed temperatures 70-80°F, dew-point spreads of 4°F or more, variable winds less than 15 knots, partly cloudy skies, and light rain.
At 1345, the SPC issued a severe thunderstorm watch for West Virginia and Virginia valid through 2200, discussing favorable conditions for severe thunderstorms with 2-inch hail, extreme turbulence, and cumulonimbus tops to 55,000 feet.
The 2054 CRW observation: wind 150° at 3 knots, 10 miles visibility, light rain, few clouds 1,500 feet, broken 4,800 feet, overcast 10,000 feet, temperature 23°C, dew point 21°C, altimeter 29.97 inHg. Remarks noted rain began 2012, ended 2021, began again 2039, cumulonimbus distant all quadrants.
The 2154 observation: wind 210° at 7 knots, 10 miles visibility, light rain, few clouds 1,000 feet, broken cumulonimbus 4,800 feet, overcast 10,000 feet, temperature 23°C, dew point 21°C, altimeter 30.00 inHg. Remarks: rain ended 2100, began 2139, occasional in-cloud and cloud-to-ground lightning distant SW through NW, cumulonimbus all quadrants moving east, valley fog.
SIGMET 1E issued at 2055 warned of severe thunderstorms moving from 280° at 20 knots, tops above 45,000 feet, hail to 2 inches, wind gusts to 60 knots.
The Area Forecast at 2045 forecasted broken 6,000 feet, overcast 10,000 feet, tops to 22,000 feet, scattered light rain showers, widely scattered thunderstorms, cumulonimbus tops to 45,000 feet.
NWS Charleston WSR-88D base reflectivity images showed 30-45 dBZ values along the flight path between 2107 and 2113, indicating "light to very strong" echoes. Base velocity imagery depicted transverse gravity wave bands perpendicular to the flight path, which the airplane would have passed through between 2109 and 2113.
The 2000 upper air sounding for Roanoke, Virginia, 72 nautical miles southeast, depicted a conditionally unstable vertical environment supportive of cloud formation, rain showers, thunderstorms, moderate potential for downbursts and strong wind gusts, low-level wind shear, potential for clear air turbulence in several layers, with highest potential near 20,000 feet. A temperature inversion at 20,000 feet had high potential for updrafts and downdrafts. The area was conducive for gravity wave formation and propagation and strong turbulence.
The pilot's preflight briefing contained valid METARs, TAFs, Area Forecast, SPC outlook, SIGMETs, AIRMETs, CWAs, NWS watches and warnings, PIREPs, forecast winds aloft, and a text radar summary valid at 2045. No record of additional weather information received.
Additional Information
A Garmin GPSMAP 496 was downloaded by the NTSB Vehicle Recorders Laboratory. The accident flight recording began at 2052 as the airplane departed CRW to the southwest, turned south-southeast, and climbed to 23,000 feet at an average groundspeed of 217 mph. Between 2113 and 2115, groundspeed decreased, the airplane entered a rapid ascent followed by rapid descent, with recorded groundspeed fluctuating from 13 to 728 mph (likely inaccurate due to GPS issues during unusual attitudes). After 2115, groundspeed and altitude stabilized around 150 mph and 8,300-9,000 feet as the airplane turned back to CRW, landing at 2138.
A gravity wave is formed when unstable air rises or descends into a stable layer, creating waves that propagate outward, resulting in updrafts, downdrafts, wind shear, and turbulence. Sources include thunderstorms, jet streams, and up- or downdrafts. When a low-level temperature inversion or stable layer exists with a conditionally unstable layer above, a gravity wave duct can trap energy. These conditions were present near the accident location and altitude just prior to the encounter. Current forecasting can predict favorable environments but not specific formation or intensity.