Sunday, March 12, 2017

Piper PA-28-151, N43503: Accident occurred July 01, 2015 near Twin County Airport (KHLX), Galax Hillsville, Virginia

Aviation Accident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf

Docket And Docket Items - National Transportation Safety Board: https://dms.ntsb.gov/pubdms

Aviation Accident Data Summary - National Transportation Safety Board:  https://app.ntsb.gov/pdf

The National Transportation Safety Board did not travel to the scene of this accident. 

Additional Participating Entity:

Federal Aviation Administration / Flight Standards District Office; Charleston, West Virginia 

http://registry.faa.gov/N43503

NTSB Identification: ERA15LA257
14 CFR Part 91: General Aviation
Accident occurred Wednesday, July 01, 2015 in Galax Hillsville, VA
Probable Cause Approval Date: 02/13/2017
Aircraft: PIPER PA28, registration: N43503
Injuries: 1 Minor, 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The commercial pilot was conducting a cross-country personal flight and reported that the airplane was on the final approach leg of the traffic pattern when it impacted terrain short of the runway. The pilot stated that there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation; however, he could not recall what occurred just before or during the accident sequence. The pilot-rated passenger noted that the airplane was low during the final approach and that he put his hand on the pilot’s hand to add power but that the airplane impacted the ground about that time. 

Although the pilot indicated that he believed that the airplane might have descended due to a microburst, he noted that it was not raining at the time of the accident. Further, there was no evidence of any microburst activity within 10 miles of the accident site about the time of the accident and no indications of any outflow boundary or gust front.

An airplane performance study using GPS and reported wind data revealed that the pilot was slowing the airplane while on the downwind leg of the traffic pattern, and that, while turning onto the final approach leg of the traffic pattern, he continued slowing it while turning onto the base and final legs of the traffic pattern. While on the final approach leg of the traffic pattern, he allowed the airplane to slow to near the stall speed. It is likely that the airplane exceeded its critical angle-of-attack during the turn at low airspeed, which resulted in an aerodynamic stall and the airplane’s subsequent impact with terrain short of the runway.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot's failure to maintain adequate airspeed while turning onto the final approach leg of the traffic pattern, which led to the airplane exceeding its critical angle-of-attack and experiencing an aerodynamic stall.

HISTORY OF FLIGHT

On July 1, 2015, about 1704 eastern daylight time, a Piper PA-28-151, N43503, was substantially damaged when it impacted terrain while on approach to Twin Country Airport (HLX), Galax Hillsville, Virginia. The commercial pilot sustained a minor injury and the pilot-rated passenger was not injured. The airplane was privately owned and operated under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The flight originated from New River Valley Airport, Dublin, Virginia, about 1643, and was destined for HLX.

The pilot stated that after takeoff he flew towards HLX, and the wind direction favored landing on runway 19. He entered a midfield left downwind leg of the traffic pattern for runway 19, and when the airplane was "abeam the numbers," he lowered the flaps to the first notch (10 degrees), went full rich on the mixture control, and descended 300 feet, but did not turn on carburetor heat. He turned onto the base leg and then onto a short final approach leg for landing. The airplane was 500 feet above ground level (agl) at an airspeed of 80 mph, and the next thing he knew they were on the ground. He indicated the engine was "running OK," and that it did not sputter or experience any type of power loss. He believed the airplane may have descended due to a microburst, and when asked if there was a rain shower nearby, he reported "no." He also indicated that when the airplane was low to the ground, the passenger put his hand on top of his, which was on the throttle control and added full power, but it was too late. He was asked if he stalled the airplane and reported that he did not. On the NTSB Pilot/Operator Aircraft Accident/Incident Report form submitted by the pilot, he indicated there was no mechanical failure or malfunction with the airplane.

The pilot-rated passenger indicated that the pilot listened to the automated weather observing system (AWOS) prior to entering the traffic pattern and the winds were variable across the runway at 7 to10 mph. He indicated that the pilot entered the traffic pattern for runway 01 at 3,400 feet mean sea level (msl) at an airspeed of 100 mph. The pilot then decided to fly across midfield to look at the windsock and elected to land on runway 19. The passenger indicated all seemed normal except for being lower than the traffic pattern altitude, but later reported that was typical for the pilot since he was a bush pilot in Alaska. The passenger became preoccupied with an I-pad as the flight continued, and noticed a drop in engine rpm as the pilot was turning onto the final approach leg of the traffic pattern. He looked up and saw terrain but did not see the runway. He looked quickly at the gauges and saw no irregularity and instantly grabbed the pilot's hand and pushed the throttle. He indicated that at almost the same time he felt a tremendous impact force. He and the pilot then exited the airplane after it came to rest.

A witness reported seeing the airplane fly over the runway at midfield in a steeper than normal left bank; the witness estimated the altitude to be between 200 and 250 feet agl. About 1 minute later, the same witness was notified by an individual that the airplane may have crashed.

METEOROLOGICAL INFORMATION

An AWOS report taken at the accident airport at 1655, indicated the wind was from 240 degrees at 7 knots, the visibility was 10 statute miles and broken clouds existed at 4,800, 5,000, and 11,000 feet agl. The temperature and dew point were 25 and 16 degrees Celsius, respectively, and the altimeter setting was 30.00 inches of mercury. The AWOS observation did not detect any significant precipitation during the period. There was no indication of microburst activity (dry or wet) within 10 miles of the accident site, and no outflow boundaries were identified in the vicinity of the accident site.

The Roanoke/Blacksburg (RNK) morning and afternoon upper air soundings surrounding the period were also reviewed. The 1900 sounding depicted a destabilizing atmosphere with a Lifted Index of -3 and supported scattered thunderstorms and rain shower development during the afternoon period. The estimated cloud base was near 4,000 feet agl. Both soundings showed a light low-level wind shear environment below 800 feet agl with an approximately 15 knots shear.

There were no pilot reports of low-level wind shear, but there was a report of moderate turbulence at 7,000 feet.

ADDITIONAL DATA/INFORMATION

GPS Data

The airplane was equipped with a portable Garmin 396 GPS receiver, and although the pilot indicated he was not using it, the GPS receiver was retained and sent to the NTSB Vehicle Recorder Laboratory for read-out. The unit was downloaded and found to contain data covering the entire flight. Review of a plot of the GPS data points revealed the airplane proceeded to the destination airport and flew across the runway, then turned to the left and flew in a northerly direction east of the runway consistent with a downwind leg. While on the downwind leg of the traffic between 1703:07 and 1703:34, the groundspeed slowed from 80 knots to 65 knots, or approximately 75 mph. The data indicated that the airplane turned onto the base leg of the traffic pattern and climbed slightly to 2,831 feet GPS altitude, or about 190 feet above the runway elevation, then turned onto the final approach leg of the traffic pattern. It then descended to 2,618 feet (near ground level) and slowed to 62 knots groundspeed, or about 71 mph. The last data point with a valid groundspeed of 62 knots was at 1703:53; the airplane at that time was located about 470 feet from the approach end of runway 19.

Weight Information

Weight calculations were performed using the latest empty weight of the airplane provided by the pilot/owner (1477.2 pounds), and the weights of the pilot and pilot-rated passenger per their last medical examination of 174 and 261 pounds, respectively. The calculations also included the estimated fuel burn for the 21 minute flight subtracted from the full usable fuel load at takeoff, which resulted in a useable fuel load of approximately 272 pounds. The calculation indicated that at the time of the accident, the airplane gross weight was about 2,184 pounds.

Stall Speed Information

According to the Pilot's Operating Manual (POM), based on the airplane's calculated weight at the time of the accident, the approximate power-off stall speed with no bank and flaps retracted was approximately 64 mph. The POM did not specify the stall speed at any flap setting other than retracted or fully extended.

Performance Study

According to the NTSB Performance Study which utilized data from the GPS receiver, and winds aloft of 7 knots from 240 degrees, the airplane was slowing on the downwind leg of the approach. At the last point before the airplane's turn onto the final approach leg of the traffic pattern, its equivalent airspeed with the winds was 65 mph. The next two calculated airspeeds showed the airplane continuing to slow through the turn. Based on the radius of turn between the downwind and final legs of the traffic pattern using 65 mph, the necessary bank angle was calculated to be about 27 degrees. Extrapolating stall speed based on a bank angle of 27 degrees resulted in 69 mph for flaps up and 62 mph for flaps down. The study indicated that the accident airplane was lighter than gross weight; therefore, the stall speed was estimated to be 2 to 3 mph slower (67 and 60 mph), respectively.

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