MIA99FA125

The pilot transmitted that he was encountering 'pretty bad' clear air turbulence at his assigned altitude and requested a lower altitude from the military approach radar controller. The controller gave the pilot a turn because of conflicting traffic, and while in the turn the pilot transmitted that turbulence was now 'severe'. He made another garbled transmission that sounded as if he was saying, 'headed down' or 'going down'. He disappeared from the radar scope and the wreckage was found later, having impacted the ground on a tree preserve about 13 miles northeast of the Savannah VOR. No evidence of any precrash failure or malfunction could be found with the airplane's engine or airframe, or their components.

History of flight

On April 12, 1999, about 1410 eastern daylight time, a Piper PA-16, N5796H, registered to a private individual, operating as a 14 CFR Part 91 personal flight, crashed while descending to a lower altitude attempting to avoid the pilot's reported clear air turbulence near Hardeeville, South Carolina. Visual meteorological conditions prevailed and no flight plan was filed. The airplane was destroyed and the private-rated pilot and a passenger sustained fatal injuries. The flight originated from St. Simon's Island, Georgia, about 1 hour before the accident.

The flight had just completed transiting Savannah's Class C airspace under radar control and had been handed off to Beaufort Marine Corps Air Station Approach Control Radar for the transit through their military operating area when the accident occurred. The pilot reported that turbulence was "pretty bad" at his assigned altitude of 5,500 feet msl, and he requested a lower altitude. The controller had to give the pilot a left turn because of conflicting traffic at 12 o'clock and 4 miles, opposite direction, at 4,000 feet msl. N5796H was observed to start the left turn, the pilot transmitted conditions were now severe turbulence, and the radar ceased showing a return at 1409. The sequence of events was confirmed during the radar facility's playback of the audio/video tapes of the radar controller's scope picture and communications with N5796H. Jasper County Sheriff's Department personnel found the wreckage about 0210 the next morning.

Personnel information

Information on the pilot is contained in this report on page 3, under First Pilot Information and in copies of the pilot's logbook pages, under Other Pertinent Forms and Reports.

Aircraft information

The original engine logbooks were reported lost. The engine, serial no. L-8552-15, reported as having an estimated 1,500 hours on it, received an inspection and major maintenance and was installed on the airplane on January 7, 1991, at a tachometer time of 4,859.6 hours. The airframe had been rebuilt and completed by the pilot and his father on January 7, 1991 at a tachometer time of 4,859.6 hours and a total airframe time of 2,246 hours. The last annual inspection was accomplished on June 6, 1998, at a tachometer time of 5,795.2 hours. The tachometer time read at the wreckage was 5,891.6 hours. The maintenance records revealed the airplane sustained taxi damage in June, 1995, and the left landing gear, as well as the two left wing lift struts were replaced on August 1, 1995. The airplane sustained right wing damage in September, 1997, and the front spar, leading edge cover, and outboard drag wires were replaced on October 4, 1997. The airplane had been modified per STC for use with automotive fuel, installation of Univair stamped aluminum wing ribs, installation of Stits poly-fiber covering, and installation of the Jensen Aircraft lift strut forks. Additionally, the original fuel system had been removed and replaced with the Piper PA-22 fuel system, (removal of the fuselage tank and addition of a right wing tank).

The normal category maximum gross weight for of the airplane is 1,650 pounds. The gross weight of the airplane at the time of the accident was about 1,565 pounds. The baggage compartment is limited to 50 pounds, total weight. The airplane had been fuelled with 20.2 gallons of automotive fuel charged to and signed by the pilot at 1216. Weight and balance calculations for the accident flight were performed using known pilot, passenger, fuel, and baggage weights. Exact locations of the passenger and baggage prior to the accident could not be determined. The calculations showed that an out-of-balance condition would have existed with the passenger and excess baggage located in the rear seats.

Meteorological information

The Beaufort 1356 and the Savannah 1355 hourly weather observations reported no cloud cover or restrictions to visibility at the time of the accident. The surface winds at Savannah at 1355 were reported as, from 320 degrees at 13 knots, gusting to 22 knots. Surface winds at Beaufort at 1356 were reported as, from 290 degrees at 12 knots, gusting to 16 knots. The Charleston NOAA Doppler 88D radar depiction of the winds at 5,500 feet msl at 1411, taken from a station 24 miles north of the accident site shows that winds were from 320 degrees at 30 knots. Although surface winds were reported as gusting, the wind profile chart showed no large variances in direction or velocity for winds from 1,000 agl to 6,000 agl, within the accident site area, (see NOAA chart #1). The same NOAA station shows only ground clutter and no convective activity in the accident area at 1405, (see NOAA chart #2). Additional meteorological information is included in this report on page 3 under Weather Information.

Communications

The Beaufort Approach Control Radar facility's copy of the audio/visual tape of N5796's radar returns and communications revealed a background noise toward the end of the airplane's last transmission. The noise distorted the readability, but the words, "headed down" or "going down" could be discerned. The tape was sent to the National Transportation Safety Board Vehicle Recorder's Laboratory, Washington, DC, for analysis.

Wreckage and impact information

The airplane impacted a dense forest grove of 2-inch to 12-inch diameter pine and sweet gum trees within the Union Camp Corporation's Argent Circle reforestation project at coordinates N 32.19.48 degrees by W 81.01.27 degrees, or about 13 miles northeast of the Savannah VOR. The airplane's attitude at impact between rows of trees was, wings nearly vertical, (left wing low) at about 60 degrees nose down, according to tree and ground marks. The wreckage path was oriented about 045 degrees, magnetic, and heavy automotive fuel spewage was detected in the foliage from about 360 degrees, magnetic, to about 135 degrees, magnetic, and extended beyond the wreckage in a circular pattern about 40 feet in radius. The propeller and spinner had separated and were found at the bottom of an 18-inch deep by 6-foot radius crater in the hard packed dirt. The propeller attaching bolts, with the crankshaft flange bushings still attached, had pulled out of the crankshaft flange. The flange was slightly bent, but intact on the crankshaft. The spinner revealed evidence of extreme impact crushing. One propeller blade was bent rearward from the hub at about 40 degrees. The other blade was similarly bent rearward about 35 degrees in an "S" shape. Both blades showed chordwise striations and leading edge burnishing. The main wreckage was located about 8 feet beyond the crater. The airspeed indicator needle was stuck at 185 mph, (Vne speed is 140 mph). About 130 pounds of luggage and personal effects were strewn around the wreckage from about 9 o'clock to about 2 o'clock relative to the longitudinal axis. Windshield and side window glass damage was too extensive to permit reconstruction. The seatbelts showed evidence that the pilot was safety belted to his seat and that the passenger was not.

All airframe components were found at the wreckage site. Flight control surfaces and airframe components, including the wings, wing lift struts and fittings, and empennage revealed no evidence of precrash failure or malfunction. Flight control continuity was established for all three axes. The engine had received severe impact damage. Six of the eight spark plugs were bent or broken, but their electrodes revealed deposit coloration consistent with normal engine operation. The accessory housing assembly was impact damaged and hand rotation of the crankshaft and oil pump was not possible until the housing was removed. Once the housing was removed, rotation of the crankshaft, accessory drives including the oil pump, and valve action checked normal. The carburetor broke loose at the throttle body, and the fuel inlet line separated from its inl