Manchester, MA, USA
N614LG
American Blimp Corp. A-60+
Prior to departure, the operator's maintenance personnel performed engine starts, runups, and pressure checks. While a mechanic was performing the engine runups, a gust of wind kited the blimp and then forced it down, fully collapsing the wheel strut which was mounted to a truss assembly in the bottom of the control car in close proximity to the rudder control system's idler shaft assembly drive sprockets. The pilot of the blimp who witnessed the incident, discussed the incident with a mechanic, then entered the control car and moved the rudder pedals and control wheel each way to insure that there were no flight control restrictions; however, prior to departure, the pilot did not perform a pre-unmasting flight control check with the aid of the crew chief, which was required by the aircraft flight manual. After applying power and lifting off, the nose of the blimp began to move left. The pilot could not arrest the turn with the application of right rudder. There was no response or feedback from the rudder and the blimp began to drift to the east. The pilot tried to steer using differential power but, when he added power on either engine, it only increased the rate of turn to the left. As the blimp continued to drift eastward while simultaneously turning left, the blimp approached a metropolitan area and the Atlantic Ocean. The pilot then descended so that if the blimp drifted towards an "open" area, a rapid descent could be initiated to the ground. The descent was then continued by venting helium from the blimp's envelope. As the blimp continued to descend the pilot realized that there were no open areas in which to land, and as the blimp was headed into the wind, he brought both engines to idle and held both helium valves full open until the blimp settled into trees. Post incident examination of the blimps rudder control system revealed that the pedal cable/chain assembly had slipped off of the idler shaft assembly outboard drive sprocket. Further examination revealed that the sprocket was partially surrounded by two metallic tabs, one located above the sprocket, and one located below the sprocket, which acted as a chain keeper guard; however, the front and left side of the sprocket was unguarded.
HISTORY OF FLIGHT On September 26, 2006, at 1215 eastern daylight time, an American Blimp Corporation A-60+, N614LG, received minor damage when it impacted trees in Manchester, Massachusetts, following a loss of control during the initial climb from Beverly Municipal Airport (BVY), Beverly, Massachusetts. The certificated airline transport pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local aerial advertising flight conducted under 14 CFR Part 91. According to the pilot, prior to departure, the operator's maintenance personnel had performed engine starts, engine runups, and pressure checks of the blimp. While a mechanic was performing the engine runups, a gust of wind "kited" the blimp and then "forced it down," fully collapsing the wheel strut. After discussing the incident with the mechanic, the pilot moved the rudder pedals and control wheel through full deflections each way to ensure that there were no flight control restrictions. The pilot stated that during the flight control check "there was no unusual feel to the controls." However; he did not perform a pre-unmasting flight control check with the aid of the crew chief. At approximately 1205, the pilot requested pushback from the mast. When the blimp began moving to the left, the pilot noted that the blimp did not seem to move off of the wind as much as normal. He also noted that the ground crew on the right rope was pulling on the rope. After receiving clearance for takeoff, at approximately 1210 the pilot applied power and lifted off. After reaching approximately 100 feet in altitude, the nose of the blimp began to move to the left, and the pilot applied right rudder to try to arrest the turn. The blimp did not respond, and the pilot then "pumped" the rudder pedals, and noted that there was no response or feedback from the rudder. The pilot radioed his ground crew and the air traffic control tower and declared an emergency. He advised them that he was having rudder problems and did not have directional control. As the blimp began to drift eastward, the pilot attempted to steer the blimp using differential power; however, when he added power on either engine, it only increased the rate of turn to the left. The blimp continued to drift towards the east while simultaneously turning to the left, and the pilot became concerned that the blimp was approaching a metropolitan area and the Atlantic Ocean. The pilot descended to an altitude of 300 feet so that if the blimp drifted towards an "open" area, a rapid descent and emergency landing could be initiated. The descent was continued by venting helium from the blimp's envelope. The pilot realized that there were no open areas that he could safely land in. and when the blimp was once again headed into the wind, he brought both engines to idle and held both "helium valves" full open. The blimp then settled into the trees, approximately 40-feet above the ground. The blimp came to rest at 42 degrees, 33.62 minutes north latitude, 70 degrees, 54.63 minutes west longitude, after drifting 5.2 nautical miles since its departure from BVY. PERSONNEL INFORMATION According to Federal Aviation Administration (FAA) records, the pilot held an airline transport pilot certificate, with multiple ratings including commercial pilot, lighter-than-air airship. His most recent FAA first-class medical certificate was issued September 19, 2005. He reported a total flight time of 11,931.2 hours, with 6,210.8 hours in make and model of blimp. AIRCRAFT INFORMATION The blimp was a twin-engine 128-foot long, non-rigid airship of conventional design with an envelope capacity of 68,000 cubic feet. According to maintenance and FAA records, the blimp was manufactured in 1997. The blimp received a 100-hour inspection on September 23, 2006 and at the time of the incident, had accumulated 9823.7 total hours of operation. METEOROLOGICAL INFORMATION A weather observation taken at BVY about 22 minutes before the incident included winds from 280 degrees at 11 knots, visibility 10 miles, sky clear, temperature 64 degrees Fahrenheit, dew point 46 degrees Fahrenheit, and an altimeter setting of 29.89 inches of mercury. WRECKAGE AND IMPACT INFORMATION A post incident examination of the blimp by an FAA inspector revealed multiple punctures in the envelope, and minor damage to the fins, gondola, and the right engine. The examination of the rudder control system revealed that the pedal cable/chain assembly had slipped off of the idler shaft assembly outboard drive sprocket. TESTS AND RESEARCH In a previous incident in October 2002, a sister ship to the incident aircraft (Serial No.15) also experienced a loss of rudder control when the rudder control chain came off the inboard sprocket of the idler shaft. A post incident inspection by the operator found that the chain guard was bent and misshapen, which allowed the rudder control chain to come off the sprocket and jam the rudder control system. This resulted in issuance of a maintenance memorandum (MM 0220) by the operator. MM 0220 required inspection of the chain guards on both the rudder and elevator systems for bending or damage, and a measurement of the gap between the top of the control chain and the chain guard. MM0220 was followed four months later by a manufacturer's service letter (SL 64-1) that required the addition of a 365-day inspection of the flight control system chain keeper guards to assure that the gap between the chain keeper guard and the top of the chain did not exceed a specified value. Review of the Flight Control System A review of the blimp's flight control system by the National Transportation Safety Board revealed that the primary flight controls for the rudder were installed for operation from the front left seat and utilized a chain and sprocket to provide mechanical advantage to a series of control cables. These control cables crossed each other about 22-inches aft of the idler shaft assembly drive sprocket and passed through a set of fairleads to the control horns on the rudder. Examination of manufacturer's data revealed that five sprockets existed under the floor of the gondola. Each sprocket had a series of metallic tabs that partially surrounded the sprocket. These tabs functioned as a chain keeper. However, closer examination revealed that the idler shaft assembly outboard drive sprocket's chain keeper guard consisted of only two of these tabs, one located above the sprocket and one located below the sprocket. The front and left sides of the sprocket were unguarded. The idler shaft assembly inboard drive sprocket was of similar design, and was also unguarded on its aft and left sides. Review of the Landing Gear Design The blimp's landing gear consisted of a single strut equipped with dual 6 by 15 inch tires mounted on a pivoting fork that was damped by a piston assembly. During a review of the blimp's technical data it was discovered that the landing gear was mounted to a truss assembly in the bottom of the control car, in close proximity to the idler shaft assembly drive sprockets, which were also mounted, to the truss assembly. ADDITIONAL INFORMATION On November 5, 2006, the Safety Board received an email from the pilot providing additional information. In the email, the pilot stated that while the ground crew was fueling and preparing the blimp for flight, the pilot and the mechanics did their preflight walk-around inspection. The pilot advised that the normal practice was for one of the mechanics to do the engine starts, run ups, control checks and pressure checks of the aircraft. The pilot also advised that he observed the checks and run ups on the day of the incident, and that a full visual check of the controls was performed prior to the full power runups. After he sat in the pilot's seat he did move the rudder pedals and wheel full deflection each way to insure that nothing was restricting the movement. The pilot then preformed a check of all switches and instruments, listened to the ATIS and collected data need for flight calculations. The pilot experienced problems with the on/off/volume knob of one of the radios, and discussed this with the senior mechanic. The distraction of the radio problem caused the pilot to skip his normal "personal" procedure of putting his head out the window and watching the movement of the lower rudder and left elevator. According to the pilot, the procedure of who did the preflight, engine starts, checks and runups varied with each pilot and operation. These ranged from the pilot doing the full walk around preflight, engine starts, checks and runups by themselves, to the mechanic doing everything and the pilot boarding just prior to coming off the mast. Company and Flight Manual Guidance Six years prior to the incident, the operator issued an operations notice (NOTOPS 17/00) which described the pilot in command's action for checking flight control function as required by the FAA approved flight manual, Pre-Unmasting Check, Page 4-29, requiring that flight control function be checked with the assistance of the crew chief prior to unmasting, and required that the pilot in command; "Check that elevators and rudders are working correctly over their full travel, free movement and in the correct sense." This was to be "implemented immediately by all pilots in command before any unmasting." Corrective Actions On September 26, 2006 the operator initiated a fleet wide flight control system inspection and safety check and verification of proper flight control movement as prescribed in the AFM Pre Un-masting Check. On September 27, 2006 the manufacturer contacted other operators, advised them of the subject incident, provided them with the flight control system inspection and safety check guidance, and reiterated the need to verify proper flight control movement as prescribed in the AFM Pre Un-masting Check. On October 2, 2006, the operator reissued NOTOPS 17/00 which described the PIC's action for checking flight control function as required by the AFM. On October 11, 2006, the manufacturer released service bulletin SB-137-01, which required the installation of secondary chain keepers on all their blimp models.
A malfunction of the rudder control system, and the pilot's inadequate preflight inspection. Contributing to the incident was the inadequate design of the chain keeper guards.
Source: NTSB Aviation Accident Database
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