Bell Helicopter announced last month a supplemental type certificate (STC)–free to operators–that increases the maximum takeoff weight of its 206B-series JetRanger to 3,350 pounds from 3,200 pounds. It was initially unclear whether the 150-pound increase also applied to Bell’s earlier Rolls-Royce 250-C20-powered 206Bs and B2s, or only the follow-on B3s with their 250-C20B and J engines (the current -C20J version involves only a minor gearing change from the -C20B to reduce the noise level). A Bell spokesman answered, “The STC is intended to apply to the entire commercial 206B fleet. No specific 206B structural minimum configuration is necessary for the STC.” In addition, Bell said, “The STC would also apply to any Model 206A modified by SI 206-80, which installed the 250-C20 engine [replacing the 250-C18], upgrading the 206A to a 206B.”
According to Ron Bower, of Bower Helicopter, Austin, Texas, the JetRanger series has had a total production run of some 4,560 helicopters; 2,358 of them are B3s, which first appeared in mid-1977. (Bell still builds JetRangers and sold 10 last year, as well as a number of trainers for the U.S. Army.)
STC SR09397RC consists of a flight-manual supplement and a revised placard for the airspeed indicator. The STC stipulates a speed restriction of 78 knots (from 115 knots) until the first 150 pounds of fuel are burned, which Bell estimates to take an average of about 45 minutes, depending on temperature and altitude.
A Bell spokesman said it is too early to tell how much of an effect the new STC
will have on the market value of used JetRangers. Shannon Bower, who, with his father, Ron, operates Bower Helicopter, said the weight increase is good news for all JetRanger operators, current and future. He said the engineering for the upgrade dates back to his father’s round-the-world flight in a JetRanger in 1994. The younger Bower said, “The Bell Helicopter product-support team did the engineering study proving that the helicopter and the engine could handle the extra 150 pounds. Dad needed the extra fuel for his flight, and the FAA approved the Bell team’s engineering study, specific to that aircraft– Serial Number 4300. It’s really good news that that increase is now available to other JetRanger operators.”
The younger Bower told AIN that the speed restriction at the heavier weight is intended to guard against so-called “two per” vibrations–two vibrations per revolution of the rotor. “When a two-blade rotor goes too fast, too heavy, it induces two-per vibrations that are uncomfortable for the passengers and not good for the airframe,” said Bower. As part of regular maintenance, rotor systems are routinely checked for track and balance to eliminate one-per and two-per vibrations.