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Saturday, July 1, 2006

Safety Watch

Tim McAdams

Underestimating Weight

According to the NTSB, the pilot of a Bell 206L departing on a sightseeing flight lifted the helicopter to a hover and turned west. When he realized the wind was from the northeast, he turned right about 270 deg. and initiated a southeasterly takeoff run. During the approximate 275-ft. takeoff run, the skids may have contacted the surface once.

The pilot felt like the helicopter did not have full power. However, he verified the torque at 96 percent and the temperature was OK. Additionally, the pilot stated he did not hear or see any cockpit warnings. He then thought that the helicopter may need more forward speed, and attempted to increase the speed.

The helicopter did not gain altitude as it neared the end of the heliport, so the pilot executed a right turn in an attempt to clear the tail rotor from the pier, but the tail rotor struck the edge of the pier as the helicopter descended. The helicopter then impacted the water, the pilot deployed the floats and the helicopter rolled inverted.

When asked about the lack of engine power, the pilot stated that normal full power for the helicopter was 100-percent torque, but the manufacturer allowed 105 percent for 5 sec. The pilot normally obtained 90-98 percent torque during takeoffs, depending on temperature and wind. Although there were no cockpit warnings, the pilot thought that the rotor rpm might have been low as the helicopter descended into the water. When asked about the reason for the lack of engine power, the pilot added that sometimes dirt or dust could lodge in the fuel system (N1 governor) and then dislodge from the impact.

When asked if the helicopter was overweight, the pilot stated no, because he was able to hover with an indicated turbine outlet temperature (TOT) of 720C and 92-percent torque.

According to his written statement and telephone interview, the pilot reported that the helicopter was fueled the previous night, and had approximately 220 lb. of fuel on board at the time of the accident. However, the director of operations for the company estimated about 275 lb. of fuel.

When asked about the helicopter's weight and balance for the accident flight, the pilot stated that he did not ask passengers their weight, and did not have a scale at the heliport. Rather, he estimated the weight and balance. For the accident flight, he estimated 150 lb. per person, as there were three male passengers and three female passengers.

After the accident, an FAA inspector questioned the passengers about their weights. The passengers reported their weights as 132 lb., 176 lb., 187 lb., 207 lb., 210 lb., and 213 lb. In addition, the pilot weighed about 190 lb. Although the pilot estimated 150 lb. per passenger, the average weight of the passengers was approximately 188 lb.

Basic empty weight of the helicopter was 2,687.40 lb. The maximum gross weight of the helicopter was 4,000 lb., which yielded a useful load of 1312.60 lb. The weight of the fuel was 220 lb., as reported by the pilot. The total weight of the occupants was approximately 1,315 lb. Those weights revealed that the helicopter was about 222 lb. overweight at the time of the accident, not including the weight of clothing, personal effects, and baggage.

Review of a flight manual for the make and model revealed that the maximum takeoff (5-min. limit) TOT was 810C. Review of the Power Check Chart, contained in the flight manual, revealed that at 88F (the temperature the day of the accident), at sea level, with a TOT of 810C, the available torque was approximately 92 percent.

Review of the Hovering Ceiling In Ground Effect Maximum Continuous Power chart, contained in the flight manual, showed that at 88F, at sea level, the maximum hover weight of the helicopter was approximately 3,800 lb.

Review of the Hovering Ceiling In Ground Effect Takeoff Power chart, contained in the flight manual, revealed that at 88F, at sea level, the helicopter could hover at 4,000 lb. However, the chart did not provide data beyond the helicopter's maximum gross takeoff weight.

The U.S. National Transportation Safety Board determined the probable cause of this accident was the pilot's inadequate preflight planning, which resulted in an attempted takeoff with an overweight helicopter, and subsequent impact with a pier and water. Factors were a high ambient temperature and unfavorable winds.

The FAA has recently raised the standard average weight for operators with a no-carry-on bag program to 184 lb. in the summer and 189 lb. in the winter. Had this pilot used these numbers he would have discover that the aircraft was over gross weight. Even at, or slightly below, maximum gross weight, little or no power margin may exist. When unsure about passenger weights, it's better to overestimate.

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