FADEC
 

"To be a true, 100%, Full Authority Digital Engine Control, there must not be any form of manual override available. This literally places full authority to the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails.":confused:

True or False?

Jack

The answer is?
 

False........i think?

FADEC
 

"To be a true, 100%, Full Authority Digital Engine Control, there must not be any form of manual override available. This literally places full authority to the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails.":confused:

True or False?
True,

The answer is in the question "Full Authority Digital Engine Control" full means it controls everything. However it is not as simple as that, there are many paths for backup.

Tristar 500

While I can't speak definitively for all aircraft types, the ones I know will experience an engine shutdown if there is a total FADEC failure. The redundancy built into FADECs makes this a rare occurrence, but it can and does happen. That said, far more engine failures are attributed to technical faults within the engine (i.e. blade failures etc) than a FADEC failure. In my outfit, the one and only engine shutdown due to a FADEC failure was actually caused by a bleed air line coupling failure, which pumped raw hot air at the FADEC until it overheated and shut down. Not really the FADEC's fault.

FADEC
 

Fadec is a full authority control for an engine measuring and matching aircraft requirements for flight, it normally has 2 independant channels for each engine (A & B channels) with independant power supplies and also independant of the airframe power supplies.

The fadecs normally take their references from the air data computers and flight directors for their calculations and output to the engines, and there is sometimes a switch in the cockpit for a mode selection (take-off, climb & cruise)

The pilot usually has a switch to allow him to select between channels for each engine but that's about all really, the fadecs usually recheck all parameters (flight requirements and engine parameters) about 40 times per second.

It would not be normal to have a pilot over-ride as the pilot's hand on the throttle would not normally be quick enough to control the fuel flow.

The throttle is a request really to the fadec to ask for more or less power than the fadec sees the aircraft telling it it needs, but depending on selection & configuration this isn't a guarrantee of changing parameters and varies between manufacturers, there are other external feeds into the fadec too like WOW sensors, flaps etc.

The fadec is normally at the heart of an aircraft avionic system as most other things feed into it and each engine and each fadec has an independant data source to ensure 100% redundancy so for 2 engines to fail at once is on a par with the big prize in the lottery after 10 months of roll overs.

There are some aircraft particularly turboprops where the engine has an HMU and this can have a complete manual reversion but I don't really know of any full fadec jets to have manual reversion although having said that I am willing to be educated otherwise.

Was contributing to this thread this morning before it was relocated. As Robin1953 points out FADEC is a mixture of many things and only parts of it could fail, not the whole lot. I recall that the manual said the whole system is designed VERY carefully because if it did all fail the engines would go to idle. So the thought of the FADEC system failing is.............hang on a minute NSandI have just called me and I have won a million on the premium bonds!

CF34-8E
FADEC Full Authority Digital Electronic Control

Dual Channel

In line and cross monitored

independent power supply with backup supply from AC electrical system

inputs
Thrust Lever Angle from RVDTs
stop switch signal
weight on wheels
engine id
application id
air data (total air temperature, altitude, mach number)
bleed system configuration discrete
electronic N1 trim
Take Off Data Settings and Thrust Rating System data
discrete inputs (start, ignition, windshear warning, ice detector, fire handle, maintenance requests)
weight on wheels and wheelspeed data
aircraft monitored propulsion system parameters (oil quantity, oil temperature, fuel temperature, oil pressure, N1 vibe, N2 vibe, thrust reverser)
aircraft configuration data (landing gears position, flaps position)
fault status information on aircraft systems
radio altimeter
P0 (Static Px)
P3 (HP Comp outlet Px)
N1
N2
T2 (Inlet temp)
T45 (ITT)
VG position
OBV position
Ignition
Various signals to and from the Fuel Metering Unit


The signals from the AC are transmitted to each FADEC via an ARINC data bus.
The FADEC can use cross engine inputs in case of data failure.

Channel failures will result in automatic channel swap

Dual channel failures (FADEC critical Fault) will shut down the engine with an ENG FAIL message

The pilot or autothrottle move the thrust levers. The position is sensed and sent to the FADEC. This signal along with all the other inputs is used to set an N1 target.

There are flat spots in the Thrust lever range that act like switch positions. e.g.
Idle flat- The FADEC sets the appropriate idle thrust based on all the other inputs. (there are 4 idles)

CON flat- FADEC sets continuous thrust.

TOGA Flat - the FADEC sets Take Off thrust based on the inputs from the Take off data set and other inputs, or Go Around thrust.

MAX- FADEC sets Reserve Thrust and signal other AC systems to configure. i.e. Bleed air off.

Input from the Automatic Take Off Thrust control system will modify the TOGA flat to give reserve thrust in case of engine failure or windshear based on other AC inputs.


This is just a summary. The tech description is over 100 pages long. The AOM has about 2 pages dedicated to the FADEC.

I presume this thread was started to help understand what may have happened to the 777. Without an full understanding of it's FADEC it's folly to guess what happened.

Actually the FADEC can override the pilot if it decides a command is wrong in a given set of circumstances.

Could you give an example please?

Fadec Lag
 

B777 CRASHLANDING DUE TO FADEC LAG ???
During the early years of the A320, there were two significant crashes in France and Bangalore , India. They were semi attributed to non responsive auto-throttles and the infamous low approach of the A320 during an airshow where the aircraft continued in ground effect and crashed.

http://youtube.com/watch?v=-kHa3WNerjU

It's been a long time, but I think the early French A320 airshow crash was a pilot vs. automation mode selection issue. The engines did not spool up because they never received the command - ie not an engine controls issue at all. The aircraft automation was in landing mode.

i.e. GIGO

:eek: Where did you get that from?

The investigation found that the engines on the A320 at Habshiem did spool up on command, in fact they spooled up faster than manufacturer data predicted.

Correct.

PROBABLE CAUSES: "The Commission believes that the accident resulted from the combination of the following conditions: 1) very low flyover height, lower than surrounding obstacles; 2) speed very slow and reducing to reach maximum possible angle of attack; 3) engine speed at flight idle; 4) late application of go-around power. This combination led to impact of the aircraft with the trees. The Commission believes that if the descent below 100 feet was not deliberate, it may have resulted from failure to take proper account of the visual and aural information intended to give the height of the aircraft."

The autothrottles, and the aircraft, did as they were commanded.

Software - common mode?
 

Is it allowed for the software in both EECs to be modified, or just reloaded, before a flight?

That would seem to be in the same category as checking all MCDs at the same time.

Unfortunatley I believe not i.e both FADEC's can be replaced at once if required.....IIRC Having replaced FADECS in past for software revision they had to be replaced as matched pair. :hmm:

Any revisions might effect such things as EICAS warnings etc...so It would be logical to have both engines running same, otherwise very confusing to the pilot :eek:

I seem to remember all that was required was an Idle run and computer download to check for any generated faults. At least as a flight control they would need duplicate Inspection for fitting so I suppose that is one up on a MCD Installation etc...

I don't think that there would be a software download just before a flight.

There's a lot of work before release in testing the software to ensure that it doesn't do anything bad. I also don't recall a recent roll-over of software for the Trent 800 series, I assume that BA will be flying software from at least a couple of years ago, so plenty of experience.

VnV

Don't critical SW components need to be n-versioned with voting? I know from many years back (I think) the 744 FADEC was designed this way.

Just a quick response, Trent 800 FADECs are two lane systems but both lanes run identical software...


...make of that what you will.

VnV

Edit: so were the RB211 boxes for the 747-400

They are normally dual channel i.e A/B with additional cross checking between each seperate FADEC IIRC


I would hope that all software testing is done before its released from vendor :)

Once you fit the FADEC it should not need much more than an Installation run

Coming back to the original topic, the answer is: depending on type. While most aircraft with FADEC engines do stop if both channels are dead, I know of at least one aircraft, the Avro RJ series, where they have one FADEC and one backup mode.

On the other hand I do not see the a problem with FADEC only controlling an engine. In the old days of cable, rods and wires, you could also have a complete control failure of an engine.

Dani