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On March 26, 1999, at 1241 central standard time, a Robinson R22 Beta helicopter, N2323V, was destroyed when it impacted terrain during an uncontrolled descent while maneuvering near Houston, Texas. The commercial pilot and his passenger were fatally injured. The helicopter was registered to a private individual and operated by Helicopter Services, Inc., of Spring, Texas. Visual meteorological conditions prevailed and a company VFR flight plan was filed for the local photo flight operated under 14 Code of Federal Regulations Part 91. The flight originated from the David Wayne Hooks Airport, Houston, Texas, at 1010, and made a stop at the CBD Heliport, Houston, Texas, between 1150 and 1220.
The operator reported that a photo flight was planned to loop the city of Houston in a clockwise direction, originating from the David Wayne Hooks Airport. Radar data obtained from Houston Terminal Radar Approach Control facility and photo logs found at the accident site indicated that the helicopter flew over Houston's downtown area then flew southwest to the accident area where the passenger was to photograph a six story parking garage. One minute and 45 seconds before radar contact with the helicopter was lost, the helicopter was tracked turning to the right at 600 feet msl. The last altitude return recorded the helicopter at 400 feet. See the enclosed radar data for more information.
Numerous witnesses in the accident area observed the helicopter maneuvering at approximately 500 feet above the ground. Three witnesses stated that the helicopter came in from the west and made a slow, tight turn to the left (when viewed from below). During the turn, they witnessed the helicopter spin "out of control" about its vertical axis. The helicopter's initial turns about its vertical axis were described by some as being "jerky, not smooth." Various other witnesses stated that they watched the helicopter spinning about its vertical axis with its nose pitched down between 10 to 45 degrees. Four witnesses stated that they observed the helicopter in the inverted position at one time during the incident. Three witnesses stated that they saw the tail boom break or fold in two just prior to the helicopter impacting the ground. All of the witnesses stated that the main rotor blades stopped rotating, and the blades were described as bending upward in a "gull-wing shape." The helicopter was then described as "falling out of the sky" and impacting the ground. Many of the witnesses stated that they heard the engine operating prior to the main rotor blades stopping.
Witness statements reported conflicting directions of rotation of the helicopter about its vertical axis (clockwise vs. counterclockwise). Investigators were able to ascertain, from the statements and follow-up telephone interviews, that the direction of helicopter rotation reported depended on the witness' position relative to the helicopter (witnessing the incident from above or below the helicopter). The witnesses positioned below the helicopter at the time of the incident saw the helicopter rotate counterclockwise (or to the left). The witnesses positioned above the helicopter in the nearby office buildings reported the helicopter as rotating clockwise (or to the right) about its vertical axis.
At 1253, the weather reporting facility at the William P. Hobby Airport, Houston, Texas (located 9.5 miles southeast of the accident site), reported the wind from 100 degrees at 10 knots, visibility 10 miles, a few clouds at 4,500 feet agl, temperature 68 degrees Fahrenheit, dew point 50 degrees Fahrenheit, and an altimeter setting of 30.16 inches of mercury.
The commercial helicopter pilot obtained his helicopter flight instructor rating on February 26, 1999. The pilot also held private pilot privileges in single-engine land airplanes. According to the pilot's logbook and the operator's records, the pilot had accumulated a total of approximately 215 flight hours, of which 113 were in helicopters, and 97 hours were in the same make and model as the accident aircraft. The pilot was issued a second class medical certificate on October 20, 1998, with the following limitation: must wear corrective lenses.
The two-bladed, two-seat, blue Robinson helicopter was manufactured on March 13, 1992. The helicopter was powered by a Lycoming O-320-B2C engine (serial number L-17312-39A). A rotor rpm governor was installed on the accident helicopter. According to the pilot operating handbook, the governor was designed to assist the pilot in "controlling the rotor RPM in the normal operating range." The governor "will not 'prevent' over- or under-speed conditions generated by aggressive flight maneuvers." The helicopter was certified with dual removable flight controls. The passenger's foot pedal controls and the cyclic control bar were removed prior to the accident flight. The helicopter's last annual inspection was completed on February 25, 1999, at which time the airframe and engine had accumulated a total of 1,756.2 hours. The helicopter had accumulated approximately 1,832.0 hours at the time of the accident. A "squawk sheet," found beneath the helicopter's right seat at the accident site, did not list any discrepancies following the last annual inspection.
WRECKAGE AND IMPACT INFORMATION
The helicopter impacted the ground in an upright position and came to rest on a measured magnetic heading of 153 degrees in the middle of Mercer street on the west side of Houston, Texas. All of the helicopter components were located in the city street within a 50-foot area.
The landing skids and rear crossover tube were deformed, shattered, and separated from the fuselage. The forward crossover tube was deformed and remained attached to the fuselage. The tail cone was found separated into three pieces. The horizontal and vertical stabilizers were intact, but were found separated from the tail cone. The upper stabilizer was bent to the left. A section of separated tail boom displayed a deep narrow dent on its left side, which deformed the DANGER sign painted on its surface. The dent displayed smudges of light blue paint transfer. The tail rotor gear box remained attached to the stabilizer area of the tail cone. Both of the tail rotor blades separated where the blade starts to taper into the hub, and were found laying within 3 feet of the tail rotor gear box. Both tail rotor blades exhibited no leading edge damage. The tail rotor blade pitch change links remained attached to the tail rotor hub and to the blades. The tail rotor hub was manually rotated and found to rotate freely with no binding of the tail rotor gear box.
The main rotor shaft was intact and exhibited no signs of bending deformation. The main rotor control tubes were secured to the lower (non-rotating) swashplate. The main rotor hub was intact; however, the droop stops were found fractured. The main rotor pitch change links were attached to the blades, but were fractured at their attachment to the upper (rotating) swashplate. The elastomeric teeter stops were in place, but split horizontally through the middle. Both main rotor blades were bent upward. The underside of both main rotor blades exhibited dents and short scratches, but no long chordwise scrapes. The outboard ends of the main rotor blades exhibited a light blue paint transfer similar to the smudges located on the separated section of tail cone. The main rotor gear box was fractured into several pieces.
The main and auxiliary fuel tanks were found ruptured. Police department personnel and numerous witnesses stated that they smelled a "strong fuel odor" immediately following the accident. Fire department personnel stated that there was a small stream of fluid resembling fuel and oil leading to a nearby street drain.
Cockpit caution/waning light bulbs were examined under a magnifying glass at the accident site. Two of the bulbs, the low rotor RPM warning light and the low oil pressure caution light, had filaments that were stretched and deformed.
The helicopter was rotated on its side by investigators to allow an examination of the engine. The carburetor was shattered into numerous pieces. The engine accessory crankcase was fractured and the magnetos were separated from the accessory section. Damage to the helicopter around the engine area prevented any further examination of the engine at the accident site.
Flight control continuity could not be established as a result of impact damage.
MEDICAL AND PATHOLOGICAL INFORMATION
An autopsy on the pilot was performed by the Harris County Medical Examiner's Office on March 26, 1999. Toxicology tests performed on the pilot revealed that 0.117 ug/mL of Propoxyphene (a prescription narcotic painkiller), 0.589 ug/mL of Norpropoxyphene (a metabolite of propoxyphene), and 8 ug/mL of Acetaminophen (a painkiller/fever reducer/over-the-counter medication) were detected in the blood. The above mentioned drugs were also detected in the urine. An unquantified amount of Cimetidine (trade name Tagamet, commonly used to combat heartburn and/or acid indigestion) was detected in the blood and urine. The use of Propoxyphene during flight is not approved by the FAA. Telephone interviews with a friend of the pilot revealed that the pilot used the painkillers on "rare occasions when his back pain would flare up." The back pain was reportedly caused by an automobile accident, which occurred a few years prior to the helicopter accident. According to the friend, the pilot did not indicate that he was in pain prior to the flight.
RESEARCH AND TESTING INFORMATION
On April 6, 1999, an examination of the engine, main rotor gear box, tail rotor gear box, sprag clutch, and flight controls was performed under the supervision of the NTSB IIC at Air Salvage of Dallas near Lancaster, Texas.
The engine's accessory case was removed and the accessory gears were inspected. The oil pump in the accessory case would not rotate due to the impact damage to the case. When the oil pump internal case was removed, the gears rotated freely with no indication of pre-impact problems. There was no rotational scarring evident on either side of the oil pump housing. The remote oil filter was removed, cut open and examined. The filter was found to be clean and free from any foreign material. The ignition leads were all impact damaged. The ignition leads were cut and the magnetos' drives were rotated by hand, producing a spark on all distributer cap towers.
The engine cooling fan was manually rotated to check continuity of the internal engine components. All four cylinders produced thumb compression when the crankshaft was rotated, and all their respective valves operated during crackshaft rotation. Crankshaft continuity was verified from the fan to the accessory gear box.
The spark plugs were removed from the cylinders and examined. The #2,3,4 top and the #3 bottom spark plugs were bent from impact resulting in the center electrode being off-set. The #1 bottom spark plug was fractured at the hexed section. The remaining spark plugs were unremarkable.
The main rotor gear box was removed and disassembled. The transmission box was fractured at the upper transmission cap. The oil sump was shattered into multiple small pieces. The oil had drained from the gear box and tiny brittle particles from the sump and case were found inside. The bearings displayed even wear on all surfaces with no discoloration present. The beveled gear and flat gear indicated even wear on the teeth. All bearings and their respective races indicated signs of non-rotational impact damage.
The sprag clutch was removed and hand rotated. It exhibited normal operation when rotated manually, with the clutch rotating freely in one direction and engaging in the other. The clutch was disassembled. The bearings and the individual sprags were intact with no anomalies noted.
See the enclosed airframe and engine manufacturer's reports for additional information.
The helicopter was released to the owner's representative on April 15, 1999.