difference between saaru adiru 777

[mothergoose1]

whats the difference between both,im confused,are the systems independant,also turning the button off will also turn off saaru or is it different.in terms of flying how will it affect me,

[LME (GOD)]

Two independent systems...think of the SAARU as the standby gyro instrument and the ADIRU as the normal ops. As long as there is power on the aircraft the SAARU is powered, the ADIRU switch doesnt affect it.

[mothergoose1]

excellently explained!thanks buddy,

[STBYRUD]

More importantly though the SAARU is incapable of inertial navigation, it can only provide attitude and air data (as the name implies).

[ACMS]

Yes and when you turn the ADIRU off the SAARU takes over on the PFD’s. As it’s supposed to do with
a failure.
On one flight after I switched off the ADIRU the PFD’s lost their attitude information. There was a failure in a component and no automatic switch over to the SAARU occurred, this was a No Go in the MEL.

[tcasblue]

We had two dispatches with an inoperative SAARU. One of the actions required was to select the EEC's in ALTN and do a full thrust takeoff. Pretty short takeoff on a 80 minute flight with not too many pax and a 30 knot headwind. The return flight was interesting because we got a overtemp on the EGT around Vr. Obviously that was a separate issue but it was interesting to discover that concerns about the condition of a very expensive engine(after having the EGT circle turn red) turned out to not be a big deal. The plane was flying again quite quickly and because the overtemp was quite small and fairly brief(because the thrust lever was moved aft fairly quickly), the maintenance center guy said that they would have to do a borescope check some time in the next few days.

Anyways, it is 34-21-07-02. A bunch of other stuff has to be operable. The MEL is a bit tricky because it says "NOTE 1: For ENG EEC MODE L or R status or advisory messages displayed, the airplane must also be dispatched using MEL item 73-21-02-02". But this message was not displayed either time at the gate. But it does display after engine start, so best to go to the other MEL before engine start and that is where the EEC's are set to ALTN for the full thrust takeoff. Best to just plan for the full thrust takeoff with both MEL's completed before pushback. Otherwise, you have to go to the second MEL after engine start and then take the time to go through the set-up for max thrust with the engines running.

[KrazyKraut]

The ADIRU supplies primary flight data, inertial reference, and air data. The ADIRU is fault–tolerant and fully redundant.

The SAARU is a secondary source of critical flight data for displays, flight control systems, and other systems. If the ADIRU fails, the SAARU automatically supplies attitude, heading, and air data. SAARU heading must be manually set to the standby compass magnetic heading periodically.

The SAARU also supplied data for the standby instrument.

Most autopilot/FD modes become unavailable is the IRS part of the ADIRU fails, as the SAARU cannot supply the required data, including LNAV, VNAV, TOGA, LOC and GS (!) - you need to fly the ILS raw data! - TRK and HDG.

So, with a complete ADIRU failure, you are looking at flying mostly manually.