enigma
good ol boy
- Joined
- Nov 26, 2001
- Posts
- 2,279
flx757 said: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