Ratted out?

Gone are the days of ripping down the runway trying to set an N1 engine speed while still looking out the windshield to stay on the centerline. Starting a FADEC engine is now as simple as moving start and run switches. And it’s impossible to overspeed or over-temp an engine with FADEC in control. As engine manufacturers like to say, FADEC protects the engine from us pilots.

Before FADEC, mechanical fuel control units used pneumatics and engine rpm to set engine power in response to throttle movements. The mechanical systems work OK, but very small throttle movement can cause big changes in engine power. And, except for the extreme limits, the duty to set engine power for the variations in temperature, altitude, and airspeed fell on the pilot. Turbine engine management consumed a big chunk of our attention. Now computers handle the job.

The reason the “full authority” is key to FADEC is that for years many engines—notably the 731 family from Honeywell née Garrett—had electronic fuel controls. But those controls, called DEEC for digital electronic engine control, did not have full control. The DEEC is a single channel system that hands control to a mechanical system and the pilot if there is a failure. That’s why a taxi check item with DEEC is to turn it off and move the throttle lever to make sure you have mechanical control.

FADEC is a multi-channel computer system that is granted full engine control from start to shutdown because of its inherent redundancy. FADEC even has its own dedicated engine-driven generator that supplies power even if all normal electrical power on the airplane is lost.

To maintain full control of a turbine engine, FADEC computers must monitor dozens of engine parameters, not just basics like temperature and rpm. And what computers monitor, they can also store in memory. That means FADEC not only operates and controls our engines, it also records every aspect of their operation and performance, including what we pilots do to the engines.

The computerized tracking of all aspects of engine operation is a huge benefit to maintenance. An engine inspection is typically a technician examining the engine closely, but more important, downloading the memory of the FADEC. Many more complex airplanes transmit FADEC and other maintenance data anytime the airplane is within Wi-Fi reception range. Those data are then analyzed looking for any change in engine performance or exceedance of normal parameters. With that information it’s possible to spot a problem long before it becomes serious. FADEC is a key to the very long engine life and overhaul intervals we now all enjoy.

But FADEC can also rat out a pilot. It happened to us in the Cessna Citation CJ4 Gen2 that I fly.

The engines went through a scheduled “minor” inspection, and everything looked great. But when the computers at Williams were finished analyzing the data from the FADECs, they discovered we had left the power in takeoff detent just beyond the five-minute limit for normal two-engine operation. The date and time were also recorded, so we could look back and see it was on departure from a higher elevation airport with a somewhat complicated departure procedure. Both pilots were busy tracking the standard instrument departure and failed to notice the throttles still in takeoff detent.

Guilty. And Williams handed down our sentence. The error cost two engine cycles. That’s not a big penalty, but it means maintenance schedules and the life limit of some parts based on engine cycles is now two counts shorter.

Other pilot errors FADEC can record and report include starting with low battery or ground power unit voltage. That’s particularly worrisome in the CJ4 because it was originally certified with a lithium-ion battery. The Li-ion batteries have a nominal fully charged voltage of a little more than 26 volts, compared to the 24-volt full charge of a conventional lead acid or nicad battery. So, instead of having a more typical 23- or even 22-volt minimum starting voltage, the CJ4 has a 24-volt minimum.

With the lithium battery removed after an overheat during ground power cart operation early in the CJ4 life, we now must fly with a conventional battery. So, if we lose even a fraction of the fully charged 24 volts the limitations say, we can’t start on the battery. FADEC records that voltage, and if you press the start button with 23 volts showing, and the engine hot starts, you’re in trouble. Warranty probably won’t cover the damage, and neither will your engine maintenance payment plan.

I’m not sure how FADEC calculates and stores this information, but it knows the direction and velocity of the wind at engine start. Williams engines have low tailwind and crosswind starting limitations compared to other engines. In the CJ4, the limits are 10 knots of either tailwind or crosswind component for starting. The limitations are silent on gust factor, so I’m not sure what you do if a gust hits after you push the start button, other than to hope and pray.

And the start wind limits are no joke. I talked with the crew of a CJ4 that had a hot start so severe a fire broke out and damaged the tail cone of the airplane. FADEC somehow recorded an exceedance of the wind-start limitation. Not long ago, the Textron Aviation mobile service team technicians were at our hangar and mentioned they had just been working on another CJ4 with engine damaged by a hot start. FADEC recorded an exceedance of start wind limitations, and the warranty was voided.

I’m old enough to remember when cockpit voice recorders (CVR) first made an appearance in business airplanes. Many pilots couldn’t wait to hit that erase button after each flight was complete. Now few, if any of us, give much thought to the CVR dutifully recording our every word.

There is no erase button on a FADEC. While FADEC protects both pilots and engines from operational errors under almost all conditions, it removes all doubt if pilots make a mistake. Should we be paranoid? Probably a little, because as its name implies, FADEC never sleeps.

J. Mac McClellan is a corporate pilot with more than 12,000 hours and is a retired aviation magazine editor living in Grand Haven, Michigan.