Piedmont-Triad International Airport
Aircraft Accident/Incident Report

Greensboro, North Carolina 27401
Wednesday, March 30, 2011 17:46 EDT

The pilot was flying the third of four scheduled flights for the day and was returning with a passenger to the passenger’s originating airport. The flight was operating in instrument meteorological conditions on an instrument flight rules flight plan. About 45 minutes into the flight, as the airplane neared the destination airport, the pilot advised air traffic control that she would need to enter a holding pattern and wait for the weather conditions at the destination airport to improve. The controller advised the pilot of several other airports with better weather conditions that were between 25 and 40 miles from her destination. The pilot declined the alternatives, and, about 9 minutes after entering the holding pattern, advised the controller that she would like to divert to an airport not far from her original destination, if the weather conditions there were "good." The controller immediately provided the pilot with radar vectors toward the requested diversion airport. The original destination and diversion airports were located about 13 nautical miles (nm) apart, and similar weather conditions prevailed at both airports, including low ceilings and visibilities in mist and fog. After vectoring the flight toward the diversion airport, the controller advised the pilot of the weather conditions. After a brief discussion regarding other flights that recently completed instrument approaches and successfully landed at the diversion airport, the pilot elected to continue to that airport despite the reported weather conditions. The controller provided vectors to the pilot for an instrument landing system approach and informed her that the runway visual range was 4,000 feet, which was above the 1,800-foot required landing minimum for the approach. Radar data indicated that the flight subsequently intercepted, briefly passed through, and then re-intercepted the final approach course before descending and crossing the final approach fix about 200 feet below the published intercept altitude. The flight continued its descent below the glideslope until reaching a point about 3 nm from the runway and 400 feet above the ground, at which time the pilot initiated a missed approach. The airplane climbed to about 700 feet above the ground and then again began to descend. The last radar return showed the airplane about 600 feet above the ground. The airplane impacted the ground about 1,800 feet beyond the last radar return indicating that, during the final seconds of the flight, the airplane entered a steep descent with an average angle of about 18 degrees. The wreckage was located about 2 nm from the runway. The debris path, which was about 600 feet in length and oriented with the runway heading, and the fragmentation of the wreckage indicated that the airplane was traveling at a relatively high airspeed when it impacted the ground. Examination of the wreckage revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation, and there was no indication that the airplane struck any objects before it impacted the trees identified as the initial point of the debris path. Analysis of the radar data for the approach portion of the flight showed that the accident airplane trailed another airplane on the instrument landing system approach by an average of 1.5 minutes and about 5 nautical miles. A wake vortex analysis based on the radar-observed positions of both airplanes showed that the accident airplane remained below the calculated wake vortices generated by the airplane ahead until that airplane landed. Additionally, analysis of the accident airplane’s calculated pitch, roll, and heading did not indicate that the airplane encountered a wake vortex. The airplane’s calculated bank angle remained below 10 degrees for at least the final 3 minutes of the flight, and the largest calculated bank angle observed was 6 degrees left after the pilot advised air traffic control that she was initiating a missed approach. The published missed approach procedure included a climbing left turn. Analysis of the last 9 seconds of radar data indicated that the airplane’s groundspeed increased from 109 to 129 knots, while its altitude remained within a 100-foot range. This abrupt increase in speed likely resulted from increased thrust as the pilot initiated the missed approach and increased engine power. During this time, the pilot was vulnerable to a vestibular illusion associated with forward acceleration known as a somatogravic illusion, which causes a false sensation of increased pitch, particularly when flying in low visibility conditions. Further analysis of the airplane’s radar data-based performance showed that the maximum pitch attitude attained during the missed approach was about 13 degrees nose up; however, calculations indicated that the pilot’s maximum vestibular/kinesthetic perception of the airplane’s nose-up pitch may initially have been closer to 19 degrees, which would have prompted her to lower the airplane’s nose. If the pilot lowered the nose in response to a perceived increase in pitch, the airplane would have accelerated even more rapidly, exacerbating the somatogravic illusion and causing the pilot to lower the nose even further. (Analysis showed that the pilot’s perception of the airplane’s pitch likely remained above actual pitch for the remainder of the flight, as perceived pitch decreased from about 19 to 6 degrees nose up.) As a result, the airplane’s final flight path would have approximated a parabolic trajectory. This is consistent with the accident airplane’s transition from a climb to a steep descent.Furthermore, the pilot had only about 13 seconds between the start of the airplane’s final descent and terrain impact; this would have reduced the likelihood of a successful recovery, given that studies have shown that pilots can require 21 to 36 seconds to transition to stable instrument flight after spatial orientation is lost. Therefore, it is likely that the pilot experienced spatial disorientation due to a somatogravic illusion and placed the airplane in a nose-low attitude as a result. A review of company records revealed that, in the 6 months before the accident, the pilot performed six instrument approaches, two of which were performed on the morning of the accident flight. In addition, the pilot had conducted a total of seven instrument approaches in the accident airplane type. These numbers suggest that the pilot had only minimal instrument flying proficiency. However, it is difficult to determine the pilot’s level of instrument flying proficiency based solely on recency of experience and the number of instrument approaches conducted in the accident airplane type. Furthermore, even highly experienced, proficient pilots occasionally experience brief episodes of spatial disorientation. The influence of the pilot’s instrument flying proficiency on the pilot’s spatial disorientation could not be determined. Available information indicated that the pilot had a rest opportunity of 7 hours 44 minutes the night before the accident, which was close to her reported sleep need of 8 hours per night. In addition, although the pilot had been on duty for 13 hours by the time of the accident, she received a 5-hour break at an intermediate stop before she began preparing for the accident flight. It is possible she used some of this time to obtain additional rest. Furthermore, the accident occurred at a time of day that is normally associated with high levels of alertness. Thus, the available evidence does not support a conclusion that the pilot’s performance was degraded by fatigue. No blood sample was available for toxicological testing, but tissue specimens were used for ethanol and drug assays. No ethanol was found in any tissue. Sertraline was detected in the liver. Since blood levels for butalbital (detected in the liver and kidney) and promethazine (detected in the kidney) (both of which can cause sedation and impair mental and/or physical ability) were not available, it was not possible to assess the pilot’s level of impairment at the time of the accident. Based on the tissue levels of butalbital, promethazine and sertraline, it was likely that, at some point the day before, or the day of, the accident flight, the pilot ingested these medications. Whether actual blood levels of butalbital and/or promethazine were great enough to interfere with the pilot’s aeronautical decision-making or flying skills at the time of the accident could not be determined.

The pilot’s spatial disorientation due to a somatogravic illusion while conducting a missed approach in instrument meteorological conditions, which resulted in the airplane’s descent into objects and terrain.