LennyWith respect to SOPs I'm not sure you're allowed to just make you're own...airlines operatre a strict set of published procedures, in some cases everything down to what to say on an approach etc. That is in the real world of course and you may treat realism as you like.yes, my personal sop on taxi in is1) start APU2) turn either left or right pack OFF just prior to shutdown3) turn on the L and R isol valves just prior to shutdown...Why the dilly are messing about with packs before engine shutdown? What's the use? I think you may have picked some bad habits up from dreamfleet 737?After all the videos and jumpseats I've been through the procedures is...Vacate runway....APU start (and other things et al).Gate arrival....-confirm APU running-fuel control switces cutoffcaptain runs through overhead completing the following:-Seat belts off-IRS's off or align (depending on drift/turnaround time)-Electric HYD pumps OFF-Demand pump selectors OFF-Fuel pumps off-ISOL valves open-Beacon off below 20% N2EVERYTIME!!!

ok, i'll take it from you then, thanks for informing me, i will ammend my procedures.Cheers

"Why the dilly are messing about with packs before engine shutdown? What's the use? I think you may have picked some bad habits up from dreamfleet 737?"...and in my case, I must have picked up some bad habits fixing airplanes/reading the Boeing Maintenance Manual ;-)Cheers.Ian.

Hi IanIf there's a collective reason why turning the packs off before shutting down servs a purpose please tell me as you are more in the know about this stuff than me. I just know the standard procedures are [d]deffinatley[/b] (I checked tonight about 3 times at work) shutdown the engines first.

"If there's a collective reason why turning the packs off before shutting down serves a purpose please tell me as you are more in the know about this stuff than me."I'm not sure I'm suggesting that the packs be shut down, Harrison, but rather that the bleed isolation valves be opened before engine shutdown. The temporary pack shutdown/spooldown is a result of the pilots' method.I had to have a good think about this one. I may be a little over my head when it comes to 767 bleed systems. It has some subtleties that not all Boeings have.The APU bleed control system is pretty smart on a 767. It looks at ECS load, bleed valve positions, bleed pressures, bleed user switch positions and a host of other parameters... and adjusts the air output accordingly. One of the things that the APU Controller (Computer) is trying to do is to prevent compressor stall. Like any engine stall, it can put an enormous strain on engine components. It adjusts air coming into the compressor to do this, but there is a also a diverter valve which allows excess pressure to be dumped rapidly if the inlet air cannot be controlled fast enough (I believe like a Turbo engine wastegate). However, sometimes its response is not always as quick as we'd like it to be. Our, as did many airlines', 747-400's used to have problems with certain bleed components which did put a big strain on the bleed system/APU, especially during start. As a temporary fix, we had to ensure that one pack was running during start, to reduce "shock-to-the-system". However, even with the bits and pieces operating normally, as engineers, we try to reduce the possibility of this shock happening where possible. The pilot procedures seem to be centered around speed and efficiency. The maintenance procedures seem to be centered around system longevity. As an example, on most aircraft when we want to put the aircon on on an aircraft, we put one pack on first, let the bleed pressure stabilize, then put on the next one, and so on. We try not to assault the APU with as many loads as possible at the one time.The 767 APU bleed valve, with the main engines running (N2 50% or more), is closed by system logic (even though the APU bleed switch may be selected ON). I had overlooked this, as not all Boeing APU valves do this: On a 747-400, the APU Bleed Valve opens if the back pressure from the engines is not too high. When the engines are shut down the APU slowly takes over if the Isolation Valves are open (no slam dunking of bleed pressure here). The 747-400 doesn't have the one way Isolation Valves like the 767 has, either. This is something else I had temporarily overlooked, but... I'll continue my story.On engine shutdown on a 767, as per the pilots' way, the engine are shut down with the Isolation Valves closed, allowing APU air into the centre duct. However, pressure is lost from the L & R ducts and the packs begin spooling down. As I understand it (I may have overlooked something!), the APU knows the packs are still selected on, but I think it also knows that the Isolation Valves are still closed, so it remains in a low flow mode (someone may have to confirm this). Depending on how fast the two Isolation Valves are opened by the pilots, the APU suddenly sees that two packs are on-line and has to immediately provide pressure for two pack turbines that have started to slow... or have slowed down (depending on the "procedural" flow in the cockpit). From an engineers point of view, it may be better to open the isolation valves first (No big drop in Centre duct pressure because of the one-way Isolation Valves) and as the engines drop below 50%N2 (only a small drop from idle), the APU bleed slowly takes over the job of pressurizing the ducts and keeping the packs running at a fairly constant speed.I don't know if the following diagram helps (or is totally correct), but....http://members.ozemail.com.au/~b744er/767/...ownSequence.gifBeing outside the aircraft, you get to hear a lot of the noises that the pilots may not hear... Such as the air racing down ducts after valves have been opened... or the APU diverter valve blowing off steam, so to speak, when the pilots reduce bleed loads (such as turning off packs quickly (or other bleed user systems) prior to engine start. Some of these sounds you never quite get used to... especially if you're not expecting them. Sudden loud compressed air noises generally make you flinch.... as I'm sure it makes the bleed air systems also ;-)Of course, all this depends on the timing of switch selections and various other things. I'm not quite ready to propose a change to the AOM :-), because I'm sure Boeing have already thought of these things. I just wonder why they chose to go the way they did.Hope this helps.Cheers.Ian.

Well for the umptyith time a simple question ends up with another incredible graphic depiction of a Boeing aircraft system. I said in a post a few weeks ago that we are never able to leave Ian without a plausible answer to a complex question. We can chalk up one more score for the engineer from Down Under. Once again he comes through. Very nice explanation of what happens when we flip a couple of switches.Actually, I open the isolation valves while the APU is in the start-up mode and leave them open till after engine start on the next hop. But the bad thing is that I am often so busy figuring out where I am on field after landing, and where those taxiways ATC is telling me to follow to the ramp are, that the APU might not get turned on before find my parking spot. This is one of the hazards of a one man show in the cockpit and flying to so many different and new locations.Great job everyone with the replies to this post. It is most informative.Regards,Mike

Thanks Ian for the explanation, I find them very interesting and useful at a time when I'm doing my ATPL training. You never know, it could pay dividends in a debate later on in life :)Anyway, to conclude the discussion I managed to get hold of some 757/767 sops, and here we have the procedures for shutdown:http://forums.avsim.net/user_files/39707.jpg