LOCK HAVEN, PA, USA
N760AB
American Blimp Corp. ABC-A-60
The pilot received a weather briefing in person from the Flight Service Station at the departure airport. The predicted headwinds for the planned airship flight over mountainous terrain were 15 knots gusting to 25 knots. An Airmet issued for the proposed route of flight 45 minutes after takeoff called for occasional moderate turbulence over rough terrain due to strong low-level winds. In cruise flight approximately 500-600 feet above ground level, the airship encountered '...a severe sustained downdraft...' that could not be overcome with full power and full up elevator. The airship subsequently collided with trees. An update to the same Airmet one hour after the accident called for occasional moderate and isolated severe turbulence over rough terrain.
On July 1, 1998, at 1105 eastern daylight time, an American Blimp Corporation ABC-A-60, an airship, N760AB, was substantially damaged during collision with trees following an uncontrolled descent near Lock Haven, Pennsylvania. The certificated commercial pilots were not injured. Visual meteorological conditions prevailed for the positioning flight that originated at Williamsport, Pennsylvania (IPT), at 0900, and destined for Youngstown, Ohio (YNG). A visual flight rules flight plan was filed for the flight conducted under 14 CFR Part 91. In a written statement, the pilot reported he obtained a weather briefing in person at the IPT Flight Service Station, at 0800. The airship departed, at 0900, and the pilot reported "normal" operations in cruise flight until 1050. He said: "About 1050 am in level flight at about five to six hundred feet above the highest obstacles, aprox. 3,000 ft MSL (mean sea level), over a tree covered plateau, the ship experienced a severe sustained downdraft. The engines were at full power and elevators were placed in a full up position. "Shortly thereafter the ship made its initial impact with the treetops. The gondola descended below the treetops and both engines were stopped. The location was approx. 8 miles NW of Piper Memorial (LHV). "The ships maneuvering and pressure relief valves were opened to induce further descent. "The ship bounced from treetop to treetop for about 10 minutes before settling in a tree with the gondola about 40 feet in the air. The helium rip cord was pulled but apparently unsuccessfully. The air-to-helium rip was successfully pulled." After he contacted the IPT Flight Service Station by cellular telephone, the pilot stopped the engines, turned off all switches and circuit breakers, and jettisoned equipment. Both pilots then egressed the airship by climbing down the tree. The pilot further stated: "In about 15 minutes the ship blew away, later to be found approximately 300 yards away." In a telephone interview, the pilot stated the predicted winds at IPT were 15 knots gusting to 25 knots, and 10 knots gusting to 20 knots at their destination. Winds at IPT at takeoff were 9 knots gusting to 16 knots. The pilot said the headwind encountered during the flight resulted in the airship achieving a 15 knot ground speed as indicated by the ship's global positioning system receiver. He said a "...consistent, strong, huge downdraft ..." could not be overcome by full elevator and full engine power application. When questioned, the pilot stated the airship had no wind limitations imposed by the manufacturer for flight operation. He added, "Practically speaking, around 35 knots. It's situational, it's the type of wind that's important. Change in direction of gusting conditions are a critical component. It's not wind speed change as much as directional change that's important." An Airman's Meteorological Advisory (AIRMET) released by the National Weather Service, at 0945, called for occasional moderate turbulence below 10,000 feet due to strong northwesterly low level winds over rough terrain. An update to the same AIRMET released, at 1215, called for occasional moderate and isolated severe turbulence below 10,000 feet due to strong northwesterly low level winds over rough terrain. The pilot reported there were no mechanical deficiencies with the airship. He added, "Control, engine response, everything was perfect. There was no degradation at all."
the pilot's encounter with unforecasted downdrafts.
Source: NTSB Aviation Accident Database
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