A message has been posted on the PPRuNe Tech Log forum asking why the Autothrottle has to be disconnected before selecting the Alt flaps to 5 units (on 767-200's and -300's). I've run out of ideas. Do any of you bright sparks have any suggestions?Thanks.Cheers.Ian.P.S. Is this common to all airlines, or is this airpline-specific?

Ian I've had a look through our QRH for the slat/flap alternate operation, and cant find any reference to having to disconnect autothrottle? I will have a look on Pprune to see what they're saying.The only thing that springs to mind is the hugely increased operating time of the alternate flap system? It strikes me that disconnecting the autothrottle at that stage of flight would be increasing workload at a very critical stage of flight...

Here's a few things I've been toying with, HP....The A/T will disconnect if no position information is available from the FSEU(Flap/Slat Position Module) when in SPD mode, N1 mode in flight, or VNAV SPD mode, but I don't see why there would be an FSPM fault generated by selecting ALT flaps 5. I know that flap position indication is known to be inaccurate when in Alt Mode, but, at the moment, I'm not sure why this would affect the A/T system to the point of causing it to disconnect. This inaccuracy may affect alpha computations within the A/T computer.... but I really don't know enough about the system to be sure.Later 767's do have different flap asymmetry circuits (e.g. our OGV), but I don't see how that would affect the A/T.Cheers.Ian.

Qantas' checklist does not call for the autothrottle to be disconnected, however it has the note Autothrottle may disconnect during alternate flap extension attached to the LEADING EDGE FLAP ASYMMETRY checklist, under trailing edge flap extension.

Ian, I could not find anything regarding the 757/767 but here's some info of what happens on the 777 if alternate flap mode is cycled, it may be of some help, although this occurs going from alt. back to normal. I could not find anything in our flight test procedures on 757/767 autothrottle disconnect although It may be there somewhere. An Autothrottle disconnect is a known and expected response to the switching of the flap system fromalternate back to normal operation.When this switching occurs, both FSEU channels undergo the equivalent of a power up restart, whichinvolves internal self-tests and removal of FSEU data from the -629 buses for approximately 1 second.'The Thrust Management Function (TMF) monitors FSEU data from the -629 buses. If the TMF detects no activityfrom the FSEU (by missing 3 consecutive expected updates - which would take 300 milliseconds) and then sees itcontinually missing for a further 600 milliseconds, then the TMF will assume the FSEU system is failed, and, withoutvalid flap data, will disconnect the Autothrottles.Therefore, the TMF will disconnect if it sees Flap data missing from the FSEU for more than 900 milliseconds,which is very close to the approximately one second data loss time for the FSEU. Because of the asynchronousnessof the FSEU, AIMS/TMF, and the I/O traffic on the -629 buses themselves, it is possible on some occasions to havethe FSEU data detected as valid again before the 900 ms has elapsed, in which case, the Autothrottle would stayengaged, and on other occasions to trip the timer and cause the disconnect

Thanks, Wallace. From what I've heard/seen, those 777's take ages to boot up from a dead ship, for this very reason (internal self tests on power up). I'm surprised that the flap data is only missing for 900ms! Everything on the 777 seems slow: Tests through the MAT seem to take forever. It amazes me that these aircraft go out on time so often.Cheers.Ian.

No problem Ian ,although the 777 doesn't seem to take any longer to power up than the 737NG. It seems the LCD's are always the last thing to come online, maybe thats why it seems the glass cockpit planes are slow to power up because you have no displays for some time. The funny thing is ,we still load the Jep nav datbase from 6 floppy's and it takes about 40 min's to load on our NG's ,so I guess some things are still in the stone age comparing aircraft technology with the home PC industry . Could you imagine seeing a flight control computer in the EE bay with the words powered by microsoft on it.

There may be a clue in there somewhere, Anthony J, but then again.... :-)Not sure how intelligent the asymmetry circuits are, but conceivably, a TE flap position transmitter fault could cause an asymmetry warning.The A/T disconnect circuits are looking for position transmitter "fail" logic. The diagrams I have with me at the moment suggest that the A/T is receiving TE flap position data directly from the Left Flap/Slat Position Module (FSPM). Loss of TE position transmitter signal(s) from the FSPM disconnect the A/T, but if there are any time delays or other prerequisites concerning the TE flaps, I don't know. The trip circuitry may only look at TE flap position when the flaps, switches or lever are in a specific range. There may be some kind of fault trigger threshold around Flaps 5 (or the threshold may be set lower than this, but there are inbuilt time delays which trip the A/T at around the 5 unit point). Normally, the TE flaps begin to move when you select Flaps 5 (No movement at Flaps 1). Perhaps, between Flap 1 and Flap 5 the TE flap position fault detection system wakes up in the A/T computer(?)There is no apparent Flap Slat Electronics Unit (FSEU) input to the A/T. What the FSEU does is also look at the position transmitters (so that it can generate transmitter failure or asymmetry warnings/messages). I see that Asymmetry warnings are generated when the asymmetry reaches 12% of full TE travel: Where 12% is in relation to Flaps 5, I don't know. If it is before Flap 5 and the flaps are frozen automatically at that 12% point, would you be allowed to select Flaps 5 via the ALT flaps system? Is 5 units the maximum asymmetry tolerable? (Roll correction is possible via trim up to this point, perhaps?). Using Alt control, you may be able to drive the flaps to the A/T computer flap fault detection point/threshold (if there is one).VH-OGV ("new" aircraft) has even more complex/sophisticated Flap Asymmetry circuits, but I can't find/see anything to suggest that the A/T logic is any different (with regard to flap fault detection) from the older aircraft.A question for Boeing, perhaps.Thanks.Cheers.Ian.

Could you imagine seeing a flight control computer in the EE bay with the words powered by microsoft on it."It's a nightmare just knowing that the IFE systems on some 777's are Windows-driven :-hah I may have mentioned this before, but, on some aircraft if you powered up the IFE and depowered it before it had properly initialized, the IFE system would sometimes fall over (and reloading all the software is a solid 24 hour job). I think this has been corrected, however (but I'm not going to tempt fate by doing so). ;-)"It seems the LCD's are always the last thing to come online, maybe that's why it seems the glass cockpit planes are slow to power up because you have no displays for some time."Not sure about this. The 747-400ER also has LCD screens, but I don't think it takes any longer to boot up the aircraft. I think it's more a case of the sophistication level of the 777 data bus system. All the computers have to talk to each other before they come on line, unlike the earlier generation aircaft (767's, 747's, etc)Anyway, I'm waffling again.... 'nuff said for one day. :-)Cheers.Ian.

I hear you there Ian, I used to spend alot of time troubleshooting IFE systems, they are getting better, but they still give us more trouble than any other aircraft system, second only to galley equip such as ovens and coffee makers ect.... It seems Every airline has a completley different vendor. Just a quick note , for anyone interested. We delivered the first 737NG to with the re-designed rudder PCU's today. It now has tripple redundancy like all other Boeing aircraft. Seperate input rods for A&B hyd, and standby PCU. There is also force fight overide capability between each system now, with cockpit warning indications. The FAA has given the airlines 6 years to comply with this design change, so all 737's will have essentially the exact same sytem.