Wed, May 28, 2003
The NTSB recommends that the FAA:
Issue a flight standards information bulletin
(FSIB) informing operators and pilots of single-engine helicopters
equipped with Rolls-Royce Model 250 series IV engines of the
circumstances of this accident and indicating that a potential
fault with the full authority digital electronic control system may
cause a sudden, uncommanded decrease of engine power without any
identified cockpit indication or warning. The FSIB should also note
that switching to manual mode may correct the engine power problem
but that recovery to full power may take 2 to 6 seconds, thus
possibly precluding a successful recovery to normal flight while
operating in those altitude/airspeed combinations under which a
safe autorotational landing is not probable. (A-03-18)
Require the manufacturer of the full authority digital
electronic control system installed on helicopters equipped with
Rolls-Royce Model 250 series IV engines to modify the system such
that an erroneous or erratic in-range potentiometer throttle
position angle signal will not cause an uncommanded increase or
decrease in fuel flow, which could result in a drastic reduction in
engine power. (A-03-19)
Prohibit the operators of single-engine
helicopters equipped with Rolls-Royce Model 250 series IV engines
from operating in those altitude/airspeed combinations under which
a safe autorotational landing is not probable until it is shown
that the operation of these engines provides an adequate margin of
safety. (A-03-20)
Require, on an expedited basis, that the on-aircraft test
procedure developed by Rolls-Royce to identify faulty
potentiometers be performed, on a repetitive basis at a
conservative interval, on all Bell 407, MD-600, and OH-58
helicopters to determine if the potentiometer contained in the
hydromechanical unit (HMU) is working properly. HMUs with faulty
potentiometers should be replaced. (A-03-21)
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