19991028032079A

(.19) On October 28, 1999, at 1841 eastern daylight time, the goodyear airship "spirit of akron", N4A, was substantially damaged during a collision with trees following an uncontrolled descent near Mogadore, Ohio. The certificated commercial pilot received minor injuries. The night sign technician was not injured. Visual meteorological conditions prevailed for the demonstration flight that originated at the wingfoot lake airport (wfl), akron, Ohio, approximately 1725. No flight plan was filed for the flight conducted under 14 CFR part 91. In a written statement, the pilot said the purpose of the flight was to test the night sign and film the flights from the ground. The pilot reported that the airship was fueled prior to takeoff and that he performed weight and balance and performance calculations. He said this was discussed with the airship's crew chief and the appropriate ballast adjustments were made prior to takeoff. In a telephone interview, the manager of airship operations stated N4A was a "one-of-a-kind, turbine-powered, fly-by-wire airship." He said the engine power and thrust vectoring controls were completely independent of the flight controls. The pilot reported that after takeoff, he flew several approaches at the videographer's request following both left and right-hand traffic patterns. He said that control authority was switched back and forth between the pilot control positions and "both control authority transfers were normal." The pilot said the filmed portion of the flight was completed and that he was released to turn the night sign on. He said: "once released, I began a climb on a westerly heading to an altitude of 600 feet AGL (above ground level). Coinciding with my level off, I noticed N4A was being blown slightly to the northeast so I placed in a little left correction to get back into the wind. The airship began a left turn. When I felt the airship was close to being into the wind, I placed into the controls right ruddervator input. At this time, the airship continued in a left-hand turn and the nose lowered as the ship went downwind. I immediately checked the master warning panel to see if I had ...[a] malfunction indication. There was no indication." The pilot reported that the airship continued in an uncontrolled, left-hand descent as he attempted several emergency and troubleshooting procedures. He said: "I as ked [the technician] to go into the aft compartment and see if both sets of fins were moving. He returned with a response that only one actuator was operating and he said he heard 'a loud grinding noise.' Following this observation, I engaged the emergency flight control backup system and obtained no response from the controls. [The technician] went back again and reported the loud noise was still present." The pilot reported that only after repeated attempts to troubleshoot the system and regain control did malfunction indications appear on the warning panel. The airship continued its descent and came to rest in some trees. The airship gondola was removed from the site and examined at the goodyear facility on November 1 and 2, 1999, under the supervision of federal aviation administration aviation safety inspectors. According to material provided by the flight control system manufacturer, the system "is a triple redundant primary flight control system (fcs) that provides full authority control of the airship's ruddervator control surfaces." The system sends a signal from the control stick through a series of mixing, processing, and amplifying electronics to a pair of triplex s yrvo actuators. These actuators convert the electronic control signal to a mechanical output shaft "which will interface directly with the existing drive capstan assembly." Examination of the starboard triplex servo actuator revealed the final drive gear and the output shaft splines were stripped. Testing of the fcs revealed that all three systems performed as designed through the starboard actuator and provided output to the final drive gear. However, the stripped gear moved inside the stripped shaft and provided no output to the capstan assembly. The starboard actuator controlled the upper port and lower starboard control surfaces. In a telephone interview, the FAA operations inspector said, "with the shaft stripped out, the pilot lost approximately 50 percent of his control authority." The final drive gear and the output shaft were sent to the NTSB materials laboratory in Washington, DC for further examination. The pilot reported 1,468 hours of flight experience, 374 hours of which were in this model airship. Winds reported at akron, Ohio at the time of the accident were from 190 degrees at 8 knots. (-23)eir pending final outcome of investigation. On October 28, 1999, at approximately 1715 EST, a goodyear blimp GZ22, N4A, crashed in a wooded area in suffield township, Ohio after experiencing a loss of control with the flight control system. The flight originated at wingfoot lake handar and was operating in VMC weather ocnditions. No flight plan was filed. The blimp sustained substantial damage and the commerical pilot received minor injuries during the evacuation of the aircraft and the passenger was not injured.