Just wondering if the hydraulic Power Transfer Unit is an option on 767's? (There doesn't seem to be one in PIC).A pilot was asking on the PPRuNe website why there was no Right A/P operation on the real 767 when the L & C hydraulic systems were both inop. The response was that the Stab Trim system needs the L/C hydraulic systems...and the Autopilot needs the trim system to operate properly.However, according to my notes, Manual Trim (using the control column trim switches) can be achieved in the air with the L & C Hydraulic systems switched off because of a device known as a "PTU" (Power Transfer Unit) located in the tail of the 767. This uses the Right Hydraulic system to power a hydraulic pump which provides hydraulic power to the Stab Trim system.However, I don't seem to be able to control the stab trim in PIC in this situation. Is the PTU an option on the 767?Thanks.Cheers.Ian.

Just wondering Ian, what systems do the non-electric Stab trim levers on the left side of the throttle quadrant use? I thought these levers were the normal backup to electric trim but perhaps not integrated with the autopilot or something? I am a licensed novice prone to confusion.

Hi Ian!Interesting topic. According to my CBT software, there is no PTU available. (Could therefore be an airline option). I thought that this was one of the biggest differences (apart from the size) between he 757 and 767. (No ADP on the 57)

Hi, Mark.The PTU might not be the sort of thing mentioned in a pilots manual. It may be referred to as the "PES" (Pitch Enhancement System).... Not to be confused with the Passenger Entertainment System ;-)Pls refer to my other message.Cheers.Ian.

>Just wondering Ian, what systems do the non-electric Stab >trim levers on the left side of the throttle quadrant use? >I thought these levers were the normal backup to electric >trim but perhaps not integrated with the autopilot or >something? >>I am a licensed novice prone to confusion.Hi, Jonas (I know the feeling) ;-) The controls on the left hand side of the throttles are for "Alternate Trim". These levers (or switches, depending on the installation) bypass the trim computers (aka the "Stabilizer Trim & Aileron Lockout Modules" or "SAM's" for short) in the Electronics Bay....and act directly on the Stab Trim Control Unit in the tail of the aircraft. The Stab Trim Control Unit controls the flow of hydraulic fluid to the jackscrew motors (which move the stabilizer).Where there are the lever type "Alternate" trim controls on the throttle quadrant (as in PIC), these operate mechanical cables which operate hydraulic valves on the Stab Trim Control Unit which allow hydraulic fluid to power the stabilizer trim motors in the tail. The mechanical cables run all the way from the cockpit to the tail.If there are electric Alternate trim switches on the throttle quadrant (our later aircraft have these), electrical signals are sent from the switches to solenoids on the Stab Trim Control Unit in the tail, which then operate the hydraulic valves which allow hydraulic fluid to power the stabilizer trim motors. This electric version is like the 747-400 system (although the electric switches are on the rear right hand side of the throttle quadrant).It sounds complicated (and is!). You probably need a diagram to properly understand the signal flow. I'm hoping someone has a picture of this handy?The Pitch Enhancement System (of which the PTU is a part) is only operative when the pilots use their control column trim switches. If I haven't mentioned it already, the stab trim runs at only a quarter of the normal rate in this mode. Seems like a strange setup.Cheers.Ian.P.S. BTW, sorry for the tardy response... I couldn't get onto the AVSIM site yesterday.

...only vaguely related to this topic and guaranteed to add more confusion to the mix... :-)I was checking out the A/P system on a 767 last night and tried engaging the right A/P with only the right hydraulic system operative (using HDG HOLD and V/S as FD modes). The R A/P engaged without any problems at all... and I was able to set various V/S's on the MCP and watch the elevator move up and down. There were no EICAS messages related to the A/P or to the Stab Trim. I must point out here that the operation of the A/P in the air can (and sometimes does) differ from the operation of the A/P on the ground (in real life).Interestingly, I was able to set a zero v/s and set an MCP altitude at the current altitude (around 0000 @ Sydney) and switch back and forth between V/S and ALT HOLD (with the MCP pushbuttons illuminating). I'm wondering if this is possible on the real aircraft in the air? More manual reading required, I guess :-)Cheers.Ian.

Well Ian, we have PTU's on our 757's. I thought they were standard.Of course, switching between V/S and ALT HOLD has nothing to do with the altitude you dialed into the MCP altitude window. ALT HOLD is simply holding the current exact altitude. In flight you can indeed switch in level flight to a 0 fpm V/S and select V/S, we use it on non-precision approaches (NDB/VOR). Should be no problem switching to ALT HOLD at any time. Once the airplane has captured an altitude and it is not in a VNAV mode, it will automatically go to ALT HOLD so you dial in anything in the altitude window without anything happening because the ALT HOLD mode is detached from the altitude window.Back on the subject of the PTU. On the 757, it only supplements the left hyd sys electric motor-driven pump to operate the flaps/slats, landing gear, nose wheel steering and hydraulic driven generator. Since the 757 trim system uses C and R hydraulic sys, it's different since use of PTU (R hyd operating) automatically means the trim works as well. Without the C or R sys pressure, there is no trimming however.Iz

This is from a 767 AOM:Pitch Enhancement System (PES)The Pitch Enhancement System (PES) consists of a hydraulic motor in the rightsystem driving a pump which uses trapped left trim system fluid to operate thestabilizer. It will automatically activate if both the left and center hydraulicsystems are lost in flight. Only electric trim is available at approximately 1/4 thenormal rate. Alternate and automatic trim will be inoperative.Hope it help a little Ian :-hah

>Of course, switching between V/S and ALT HOLD has nothing to >do with the altitude you dialed into the MCP altitude >window. I'm still a little confused about this, Iz...In PIC, say you are flying straight and level at 3000' and are in ALT HOLD: If your MCP altitude is set at 3000', and you push the V/S switch, nothing happens (no mode change). However, if you select 2000' on the MCP and select V/S, the V/S button illuminates and the V/S window shows 0000 (synching to the current V/S). The same happens in Aerowinx's PS1 (although the V/S button illuminates momentarily, then the A/P switches back to ALT HOLD).During your non-precision approaches, is your MCP altitude set at the current altitude when you push the V/S button?My notes really don't give me a clear picture of what would happen in this particular situation (an un-annuciated Alt Hold or an annuciated one). Something which doesn't help is the fact that there are differences between Boeing aircraft with respect to A/P mode transitions and annunciations.Anyway, thanks for the feedback :-)Cheers.Ian.

Sorry, Cold Bear... no help.... I was already aware of this.The pilots at PPRuNe say that they have confirmed my findings on the ground (No A/P trip off), but tell me that the A/P will trip off in the air, but.... I'm wondering if they only know this from simulator experience... It's probably not very likely that they've experienced a dual hydraulic failure in the air.Thanks anyway.Cheers.Ian.

>I'm wondering if they only know this from simulator experience... It's probably not very likely that they've experienced a dual >hydraulic failure in the air. Hmm... these "pilots" who think they know everything when they're in fact just playing with their flight sims! Makes me sick. :-erks:-lolMartin767 fetishistIt's a lot like life and that's what's appealing