December 1, 2000
Buying
with Bower: FADEC And Your Helicopter, Part 1
by Ron Bower
A EUROPEAN PILOT RECENTLY asked me to describe the
benefits of Full Authority Digital Electronic Controls (FADEC) and how it
compares to the traditional engine controls from an operator’s point of view.
FADEC is probably the most radical technological change in turbine engines
since the Korean War. Like it or not, FADEC is here to stay. FADECs are now standard equipment on nearly all new turbine
helicopter engines, such as those that power the Bell 407, 427, and 430; the MD
600N and MD Explorer; the Agusta A119 Koala; Sikorsky
S-76C+; and the Eurocopter AS-350B-3 and EC-135.
Because of the benefits of this new technology, aftermarket FADECs and Health Utilization Monitoring Systems (HUMS) are
being applied to older engines such as the Rolls-Royce Model 250 series.
Lycoming even has FADECs running on piston engines in
a number of light airplanes.
Since most pilots have not yet flown with a FADEC, this column is intended
to be just an introductory primer to familiarize you with its benefits and
differences as compared to earlier fuel control and monitoring systems.
In a nutshell, a FADEC is smarter, faster, more precise, more procedurally
driven, and more honest than human pilots. At the heart of FADEC is a computer
that is connected to a variety of input sensors measuring TOT, torque,
compressor and turbine rpm, rotor rpm, OAT, and battery voltage. These sensors
also may measure airdata, such as airspeed, altitude
and barometric pressure. Pilots monitor these sensors constantly.
The FADEC analyzes the inputs and decides how to control the fuel flow and
governing of the turbine engine to keep the engine within optimal design performance
limits.
FADECs replaced the old hydromechanical
fuel controls and governors that typically use internal differential pressures
for decision making and then communicate with each other through pneumatic
hard-tubing lines.
I suspect much of the ambivalence some pilots feel toward FADEC is the
reluctance that we all feel when moving into unknown territory. Hydromechanical fuel controls have been around for three
decades or more, and many pilots are used to them. In addition, some early FADECs, such as those in the
However, as with any computer, a FADEC’s actions
are determined by a software program, and behind every
program is a fallible human programmer. The programs can be downloaded into the
FADEC computer (usually from a laptop). Similar to Windows 95, 98, and 2000,
the software has different versions—and maybe an occasional bug.
The FADEC monitors and logs selected information from the sensors, including
start counts, events, surges, engine run time, and malfunctions. It also
monitors exceedences, such as overtorques,
over-temps and hot starts.
If the FADEC program detects a "fault" that it can’t deal with, it
alerts the pilot by a panel light and/or alarm that lets
the pilot know that the FADEC needs to be in manual mode. The latest version of
the FADEC in the
Manual mode means the pilot must now make throttle correlation adjustments
to the fuel control (collective up, add throttle; collective down, roll off
throttle—gently!).
These actions are much easier for pilots who "learned" on piston
engine helicopters. New FADEC pilots must learn new emergency procedures
dealing with FADEC failures.
Certainly, one of the most important benefits of FADEC is a controlled
automatic start sequence. With proper procedures, the FADEC auto start will
eliminate hot starts (where TOT goes overtemp beyond
the manufacturer’s limits).
Hot starts can easily be $100,000+ events. Moreover, the FADEC also
optimizes the start by adjusting fuel flow to keep the starting temperature not
just within limits, but also at a preprogrammed optimum temperature for quicker
starts.
Next month, "Buying With Bower" will look at how diagnostic
tools can enhance the benefits of FADEC.