MD80 Systems question

[chperplt]

My systems book is lacking an adequate explination of the ART and ATR systems.

Can someone post a brief narrative on these two systems.. The book I have isn't clear on when either system is armed/active or what conditions have to be met for them to work.

Thanks

 

[enigma]

ART is a fuel control unit function that adds fuel after one on the engines drops rotation speed at takeoff/flex power. The ART system doesn't move the throttles, it is a solenoid on the FCU. ATR is an auto throttle function that increases the throttles if the DFGS senses either a level off or sink rate under 1500 feet AGL after takeoff.

In other words, ART adds power to the remaining engine after one engine fails, where ATR adds throttle to both engines if you sink after takeoff.

I'm sure that this isn't the most technically correct answer, (and certainly doesn't include all of the nuances) but it gets to the gist of it.

regards,
enigma

 

[flx757]

enigma is in the basic ballpark, but not exactly right on a couple of the points he made.

ART (Automatic Reserve Thrust) is a fuel control function that keeps 850 lbs of thrust in reserve for use after an engine failure on takeoff, provided you are making a NORMAL power takeoff (TO selected on TRI; ART switch in AUTO). For a max power or flex power takeoff, the ART switch is off, therefore this reserve thrust is not available, since you are already making a max power takeoff. (A flex power takeoff is a max power takeoff at a given assumed temperature, which provides for a lower EPR setting than a normal power takeoff at the current ambient temp.)

For the ART to be "ready" (green ready light illuminated):
1) The system must be operational (self-test satisfactory)
2) The ART switch must be in AUTO
3) Slats not retracted
4) A valid N1 signal from both engines indicating the engines are operating.

The ART system then is ARMED when both engines are above 64% N1.

The ART activates (amber ART light illuminated) when:
1) A 30% N1 differential in sensed (indicating an engine failure).
or
2) Windshear is detected by the WAGS
or
3) The DFGC is switched or loses power


The ATR (Automatic Thrust Restoration) is a function of the Autothrottle system. It also provides for an increase in power following an engine failure on takeoff (and if the ART is also armed, will only increase the power up to a point that will allow for the additional 850 lbs of thrust that the ART provides to prevent overboosting the engines).

For the ATR to activate, the Autothrottles must be on, the Flight Directors have to be in the Takeoff mode, and engine power at less than G/A thrust. If the system detects an engine failure ABOVE 350 ft RA (and this system defines an engine failure as BOTH a 7% N1 and .25 EPR differential in the same direction OR a vertical speed of zero or less for 5 secs on takeoff), the autothrottles will drive to G/A thrust.


**Disclaimer** I am at home with no reference material. So I may not have this completely correct...but I think I got most of it. I'll double-check it tomorrow to be sure.

 

[justApilot]

enigma is in the basic ballpark, but not exactly right on a couple of the points he made.

ART (Automatic Reserve Thrust) is a fuel control function that keeps 850 lbs of thrust in reserve for use after an engine failure on takeoff, provided you are making a NORMAL power takeoff (TO selected on TRI; ART switch in AUTO). Actually you have just described a MAX POWER takeoff (T.O. on the TRI, ART switch in AUTO and Zero assumed temp) If the ART fires you will get reserve power.For a max power or flex power takeoff, the ART switch is off, therefore this reserve thrust is not available, since you are already making a max power takeoff. (A flex power takeoff is a max power takeoff at a given assumed temperature, which provides for a lower EPR setting than a normal power takeoff at the current ambient temp.) T.O. FLEX is actually a reduced power takeoff (standard power takeoff) T.O. FLEX on the TRI, assumed temp something other than zero and the ART switch off is how you get the standard power takeoff. If you loose an engine during a standard power takeoff ART does not fire, you are supposed to have enough thrust to get the job done.

Reserve Trust is called for if the TRI window has zero selected, ART switch is on and the T.O button on the TRI is selected.

 

[flx757]

Nope. You are most definitely wrong about both the MAX power and FLEX power takeoff references above.

For a MAX power takeoff, the ART switch is OFF. If the ART is in AUTO, you have the 850 lbs of thrust in reserve and therefore is NOT a MAX power takeoff. The same applies for a FLEX takeoff. Sure, the power is "reduced", but it is "reduced" to a lesser EPR than what you would get by making a NORMAL power takeoff at the current ambient temp. By selecting FLX on the TRI, an assumed temp greater than ambient and the ART switch off, you are making a MAX power takeoff for THAT ASSUMED TEMP. Again, yes it will be "reduced" if compared to the normal power EPR for ambient. But the system is looking at it as a MAX power takeoff. No thrust in reserve, hence the ART is off.

I would be happy to give you the word-for-word description from our systems manual when I get to work. But of this part of my answer, I am sure. I may have left a few details out of the working description of the ART vs. ATR, but the definitions...from a systems standpoint, of NORMAL, MAX and FLEX takeoff power, and how to set the system up for each, I am certain.

 

[Jeff Helgeson]

The SAT Test answer...

ART is to T/O as,

ATR is to FLEX.

FLEX757 has the best answer and explaination of ATR. The ATR system restores normal or maximum T/O Power according to the criteria already listed in his post.

Engine failure: ATR uses the auto throttles to advance the power of the good engine to the amount of thrust that would have been used if T/O had been selected on the TRI. It may even advance the power to the same value as if the ART had fired. I am not sure on that one?

Lack of VSI climb: ATR boosts the power of both engines to the value of thrust that would have been available if T/O had been selected on the TRI. I believe Automatic Thrust Restoration is a good name for this system, as it bests describes it's function. It restores the thrust from reduced or FLEX to maximum or normal T/O values.

Jeff

 

[chperplt]

Thanks for the info guys!!!

 

[justApilot]

Play around with it at the gate, it won’t lie.



Max Power T/O:

Art switch ON
TRI zero
T.O. Button on
(the RAT temp is used to compute MAX power)


Standard (reduced) power

ART switch OFF
TRI selected to a temp less than ambient (if the current temp is in the window than yes that would give you MAX for the current conditions)
T.O. FLX button on


Reserve Power

ART switch OFF
TRI zero
T.O. Button on

 

[justApilot]

Let me correct something......

the TRI during a Standard (reduced) power takeoff is going to be a value more than ambient temp (outside temp 28c TRI 50) if the outside temp was the same as the TRI temp then you would be getting MAX power

FLX I know what you are saying. Semantics...

 

[bafanguy]

I think there may be some terminology/procedural differences here as well as maybe some minor functional differences in one company's TRI/ATS versus another.


What you guys are calling "automatic thrust restoration", we called "autothrottle advance". It worked as you've described but we apparently didn't have the negative VSI trigger ( or we weren't told about it if was there ). Our books also contained the following caveat concerning this system: "Advancing thrust levers on a surging engine will hinder surge recovery and may result in eventual engine faliure". The system may not be doing you a favor in SOME situations.

Our ARTS would also fire when a increasing/decreasing windshear was detected.

And, ARTS is disarmed when:

Slats are retracted, or,
both N1's below 49%, or,
ARTS switch OFF.

I suppose it's possible to come up with some FLX setting & assumed temp to produce something other than a FLX epr. For example, FLX with an assumed temp of "00" is the equivalent of "NORM" power. And I have tried that one on the airplane because it was mentioned in some of our stuff and tried it to satisfy myself it was true. Maybe there are others too.

 

[enigma]

enigma is in the basic ballpark, but not exactly right on a couple of the points he made.

ART (Automatic Reserve Thrust) is a fuel control function that keeps 850 lbs of thrust in reserve for use after an engine failure on takeoff, provided you are making a NORMAL power takeoff (TO selected on TRI; ART switch in AUTO). For a max power or flex power takeoff, the ART switch is off, therefore this reserve thrust is not available, since you are already making a max power takeoff. (A flex power takeoff is a max power takeoff at a given assumed temperature, which provides for a lower EPR setting than a normal power takeoff at the current ambient temp.)

For the ART to be "ready" (green ready light illuminated):
1) The system must be operational (self-test satisfactory)
2) The ART switch must be in AUTO
3) Slats not retracted
4) A valid N1 signal from both engines indicating the engines are operating.

The ART system then is ARMED when both engines are above 64% N1.

The ART activates (amber ART light illuminated) when:
1) A 30% N1 differential in sensed (indicating an engine failure).
or
2) Windshear is detected by the WAGS
or
3) The DFGC is switched or loses power


The ATR (Automatic Thrust Restoration) is a function of the Autothrottle system. It also provides for an increase in power following an engine failure on takeoff (and if the ART is also armed, will only increase the power up to a point that will allow for the additional 850 lbs of thrust that the ART provides to prevent overboosting the engines).

For the ATR to activate, the Autothrottles must be on, the Flight Directors have to be in the Takeoff mode, and engine power at less than G/A thrust. If the system detects an engine failure ABOVE 350 ft RA (and this system defines an engine failure as BOTH a 7% N1 and .25 EPR differential in the same direction OR a vertical speed of zero or less for 5 secs on takeoff), the autothrottles will drive to G/A thrust.


**Disclaimer** I am at home with no reference material. So I may not have this completely correct...but I think I got most of it. I'll double-check it tomorrow to be sure.

what he said

 

[Swede]

{shiver} Thank you Boeing for transport aircraft with a real FMC and a throttle quadrant/ECU combination which won't overboost the engine(s). ART and ATR are probably still one of the favorite systems questions designed to terrorize MD-80 guys. One of a dozen or more hideous laundry lists of "what is needed to arm/actuate 'X' "

Need more power? Push the throttle to the stop and get full rated power without blowing up the engine. What a bizarre concept!

And yes I know Boeing owns McD-D, but they didn't design the beast.

 

[Yank McCobb]

I don't think any 70's era designed Boeings had the capablility of which you speak, either. I know the 727s and 737s that I flew from that era didn't.

Boeing didn't design the 717 either, but it can do exactly what you speak of with it's FMC/ECU combination.

No one has a monopoly on old technology or new. Surely you are not so clueless or naive to believe otherwise now are you?

What a concept.