An interesting development occurred tonight during my climb-out of KLAX on the VTU4 bound for San Franciskey (And, in this case: "Did you drive or did you flew?" , I flew (kind of)).Seems my fingers - before I could engage my brain - inadvertantly turned the CENTRE SELECTOR KNOB to ATT, thereby losing the IRU alignmnet on the centre, which then disengaged my A/P... which is fatal - cause I can't hand-fly the beast in the dark! Now, no matter how hard I tried, I was at a loss to maintain altitude, airspeed, all the while trying to restore attitude and heading. I was hopeless, and needed a co-pilot. MY one-year-old daughter was asleep at the time, and Rob Hall is 3000 km to the east...My question (now that you've had a good laugh): Does this happen in the real world? If so, what is the best method to cope with this situation?Daryl ShuttleworthDS 3339http://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

Hi Daryl,Well, first of all, remember that you have three IRU's. So if the CTR is dead, you still have the Left and Right IRU. Therefore you could have activated the left/right autopilot. As long as nothing else failed, your only consequence would have been that you would have been limited to LAND2 (autoland with only 2 AP's - raised minima)I believe there is a delay built into the IRU in case you inadvertantly switch any IRS off in flight, it will wait a couple of seconds before actually losing the alignment. However, I'm not 100% sure about this, maybe Qavion or someone else can ellaborate on this.In case you lose full alignment on all three IRU's, you'll have to request vectors and do the best you can.Regards,Mark

A rather complex question with lots of if's and's or but's, guys.... ;-)Loss of a single IRS has varying effects depending on flight phase, airline options, etc, etc.On our 767's ....Normally, at least two (any two) IRS's must be operating for any A/P to engage. However, when the aircraft is on the ground, the A/P in command must be fed by its respective IRU. "On the ground" in this case is defined to be when the airspeed is less than 60kts. Therefore, in cruise, ALL Autopilots should operate normally with the remaining two IRS's still OK.I have been told that the IRS's on a 767 can be turned OFF for a few moments without causing any problems, but I'm not 100% sure if this is the case for selecting ATT briefly, then going back to NAV.Incidentally, I noticed recently on one of our aircraft, that if you select ATTitude after being in NAV, you are locked into ATTitude until you cycle the IRU selector knob to OFF. That is, if you select ATT (from NAV), then NAV or ALIGN, the IRU will remain in ATTitude mode (I assume indefinitely). I don't know if this is true for all 767's?Hope this helps.Cheers.Ian.

"Normally, at least two (any two) IRS's must be operating for any A/P to engage. However, when the aircraft is on the ground, the A/P in command must be fed by its respective IRU. "On the ground" in this case is defined to be when the airspeed is less than 60kts. "Darn, forgot about that again! I remember discussing this with you last summer, after making this observation in the real sim.So no AP will engage (in the air) with only 1 IRS in NAV mode?Regards,Mark

"So no AP will engage (in the air) with only 1 IRS in NAV mode?"This is how I understand it, Mark ;-)However, according to my training notes, IRS's provide the following critical "inner loop" data (necessary for keeping the A/P's engaged):"Pitch angle and pitch rate,Roll angle and roll rateStabilizer positionAcceleration during approach...."...and one airline's Boeing Maintenance Manuals says..."ATT mode outputs are attitude/heading, rate, acceleration and vertical velocity".Apart from "Stabilizer position", it appears the two sets of parameters are the same! i.e. almost everything required by the A/P's in terms of outer loop sensors is available in ATT mode.Confusing to say the least. I may have to look at the requirements for Outer Loop data also, and/or, if I get the opportunity, simulate this scenario on a real aircraft (on the ground, of course). i.e. Two IRS's in NAV (including the critical one), engage an A/P and then switch one of the IRS's to ATT.Cheers.I.

That would be great!Do you know if the FD works with the IRU's in ATT?In PS1.3 they do, in 767PIC they don't :-)Its great that Boeing does everything to keep everyone in the loop ;-)I'm sure 99 out of 100 rated pilots wouldn't know the answer either.Also, pretty sure there are pins you can set on the FCC that will make it work differently... :-)Regards,Mark

I see you have sparked another thread of technical subtleties.I think the simple answer was to switch CMD from CTR (the IRU that got pooched) to L or R CMD and Bob's your uncle....not to mention you 'should' be able to fly it back down with A/P off at night ya mook!You are still my hero.Rob.

D'oh - of course I could have used the LEFT or RIGHT A/P - quel dork I am!Lord, brain lock.Thanks guys.BTW, Mike Murphy informs me that there are invisible click spots on the panel? ;)Daryl ShuttleworthDS 3339http://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

Thanks for chirping in Rob - you want me to Bertuzzi you?JOKING! Bertuzzi deserves everything he got and more! I am not condoning hitting anyone from behind... only Rob.Daryl ShuttleworthDS 3339http://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

arent there such on any woman? :-xxrotflmao

Only you would enjoy hitting on men from behind ya wankah.Now shuddap and go fly the PIC767...will be hunting you down Friday night...and Murf has his cop light out with your name on it.------------------------This forum has gone to hell in a handbasket :-)------------------------Who is Bob anyhow (a la "Bob's your uncle")??

Bob Loblaw...say it very quicklyBob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob Loblaw Bob LoblawDaryl ShuttleworthDS 3339http://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

"Do you know if the FD works with the IRU's in ATT?"I believe the FD can operate with only the one IRU valid (as long as it's the local/respective one). However, things are becoming less clear the more I read....I have just read in my 744 training notes that there was a modification carried out which allowed only one IRS (the "local"/respective one) to satisfy autopilot arming conditions in cruise. These notes don't specify if two non-local ones are also allowed in cruise.I think we have to be very careful to stick to specific aircraft types here (and modification status of particular aircraft).Re Inner and Outer Loop (sensors):Outer Loop sensors provide data to the FCC's(A/P computers) appropriate to the current A/P mode. The loss of these sensors may cause mode reversion rather than autopilot disengagement (i.e. the autopilot may revert to attitude hold rather than disconnect completely...resulting in A/P Cautions, rather than Warnings). Outer loop data is provided by Air Data Computers, FMC's, ILS's and Rad Alts. Only one (of each) Outer Loop sensor (the local one) is required in cruise (according to one airline's Boeing 767 manual). This same manual also mentions that only the local one is required for FD ops.Inner Loop sensors are concerned with attitude (autopilot stability).The catch here is that IRS's provide both Inner and Outer Loop data. In cruise, only one Outer Loop sensor (where there are redundant sensors) is required for A/P engagement. However, with the IRS's in ATT, they may not be able to provide appropriate data for the mode required (e.g. LNAV mode requires airplane position data. Without the IRS position info, the FMC will not be able to compute LNAV guidance, so the A/P will not engage in LNAV).At times, one has to be thankful that the aircraft usually tells you (with flags/aural warnings) that something is not working properly and can often pinpoint (through built-in tests) the airplane computer/sensor which is causing the problem :-) Pilots and maintenance engineers would rarely be faced with the in-depth problem of figuring out whether or not an A/P should or should not engage in certain circumstances. They just try it to see if it does ;-)Cheers.Ian.

"Pilots and maintenance engineers would rarely be faced with the in-depth problem of figuring out whether or not an A/P should or should not engage in certain circumstances. They just try it to see if it does ;-)"Yes, well, how do you program this? :-)Unfortunately, this seems like a situation where you have to guess :-(Thanks,Mark

What Follows is a quote from another website, about a situation that occured for real. Daryl, you better learn to hand fly in the dark.At the KTM ground, before depature for Hongkong, the B757/200 Flight NO: RA 409 had an IRS problem where by one of the IRS was not working. The Commander had asked the Engineers to fix the problem before the flight as they thought they would need it during an approach to Hongkong Airport. God knows what the Engineers did, all the 3 IRS were gone. BTW I agree 100% with middle path regarding the maintenance not being too good on the RA Jets. (The engineers seem to be more interested in flying allowances than keeping the Aircraft Airworthy. That is the reason why the RA B757 Jet Engineers have more flight hours than the RA B757 Captains and co-pilots. So, you can guess the qualifications of the Engineers youself). Later, after fiddling with the problem (I wouldn't call it fixing the problem) for 30 minutes the Engineers were able to recover 2 out of the 3 IRS. At that ,point the Commander asked them to replace the unserviceable IRS. Although the company had a brand new IRS in their stuck, the Engineers told the Commander that the couldn't do it (Your guess is as good as mine) because they didn't have the qualification to do it !?! So, what the Engineers did was release the flight under MEL.Right after the T/O on IGRIS 1A departure while the aircraft was turing right to intercept the 4 DME ARC, The aircraft lost both the remaining IRS. Followed by all the navigation equipments failure, Ex. all auto pilots gone, HSI gone, ADI gone, Auto Throttle Gone, No vor, No dme no RMI as well as Yaw Damper failure.Condition was marginal VFR at the time of departure. The crew had with them the magnetic (Ball) compass, standby Artificial Horizon to control the Aircraft and all manual flying. For about 45-50 minutes the Aircraft was trying to fly VFR under cloudy condition and the Aircraft was headed towards New Delhi. But Later as the WX at KTM Airport improved the crew decided to Land back at KTM Airport.The factor that contributed to the safe Landing of B757 was crew's knowledge about the local terrain and that KTM is their home base. Had this happended (I hope and pray that it doesn't happen again to anyone else) to some other Foreign Airline, I feel it would have been Very Very Difficult (but not impossible) to come out of the Kathmandu valley which is sorrounded by mountains.