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Altitude hold failure?

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Well Guys,Installed, performed the pre flight, and got my IFR clr from Seattle. And, as I get airborne, on climb out about 3000 MSL, i engage the A/P. Select LNAV to follow the SUMMA5 departure, and I select the 'Hold' ALT button. . . well, nothing happens, oh, I had my A/T on and SPD set to 250 knots. Well, I had to climb the plane by hand, all the way from SEA - LAX. Thats a problem, and I cant seem to figure out why the ALT Hold would not engage.blah, help plz?

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Guest Ian_Riddell

"I select the 'Hold' ALT button. . . well, nothing happens, oh, I had my A/T on and SPD set to 250 knots. Well, I had to climb the plane by hand, all the way from SEA - LAX."Why would you want to select ALT HOLD if you wanted to climb, Josh? :-hmmm (Or is this a two-part problem?).Cheers.Ian.

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*shurg* maybe Im just use to the generic DF panel. Ill go RTFM lolregards

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Josh,Assuming you had given the FMC a cruise altitude, just hit the VNAV button (under LNAV). It will climb at 250 kts under 10000 then accelerate above it.If you wish to control altitude / climb manually, then one frequent use is to use FL CH (Flight Level CHange if I re-call). This will climb / descend at the most suitable rate in order to keep your chosen speed.If you wish to go the other way around (fixed rate), then click the button under the VS wheel, this will allow you to set the climb / descent rate and will adjust throttle accordingly to meet the required speed (if set).This panel is very flexible in the ways you can control speed and climb, tho I've yet to discover how to turn off the altitude hold without turning off the AP altogether, in order to manually fly the plane down a GS for example, but still have the AP control the heading and speed. Oh well. ......Hope the above helpsKing Hoyle - ZNY

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Guest ielchitz

Hi Josh!Nice to see you popping on to the forum!First of all .. my apologies that I could not help you out this evening.. I was having my own issues trying to get things sorted out with asrc... I feel like an S1 again .The vertical modes in the 767 are a little tricky until you get the hang of them.My underdstanding of them is as follows:V/S - Vertical Mode... Flip the VERT SPD wheel to get the desired vertical speed. One thing to note.. If you are currently BELOW the altitude you have dialed into the ALT on the MCP and you put in a positive v/s - then your acft will climb to that altitude and level off. If you are AT or ABOVE the altitude set on the MCP and you dial in a POSITIVE vertical speed... then your aircraft will climb into outer space.. In other words vertical speed will allow you to fly AWAY from the desired altitude... for that reason I believe when using v/s you should always set the desired altitude in the MCP first and THEN engage v/s.FLCH is airspeed dependant. The aircraft will change its pitch to maintain the desired airspeed based on the calculated thrust you have programmed using the thrust computer. For example.. if you are at FL250 and wanted to go to FL290, you would dial in 29000 on the MCP altitude window.. and then engage the FLCH. You can then set the desired airspeed using the airspeed wheel. If you set it to say.. 280 IAS.. the aircraft would maintain constant thrust (as set by the thrust computer) and change the pitch so that you would climb at 280 IAS.. regardless of the vertical speed it needs.. This also works GREAT when you are a little lower down and speed becomes an issue for sequencing.. you are at 12,000 and are told "Reduce speed to 230 knots or less.. descend and maintain 8,000" You would change your airspeed to 230 on the speed dial.. then once you reach 230 you turn the dial to 8000 and hit FLCH.. now you will descend to 8000 at a speed of 230 ias.The altitude HOLD function will level out the aircraft immediately.Let's say you are in a climb using either VNAV, FLCH, or vertical speed to FL290 and are passing FL210 when ATC tells you "AAL301, traffic just popped up at your 12, 2 miles FL220 opposite direction suggest you stop your climb without delay" You can hit the ALT HOLD button and your aircraft will level out immediately. I can not recall 100% if it changes the target altitude on the MCP or not.VNAV is an entirely different beast whicn I am not going to get into at this time.. you need to really read and play around with it.. just remember to use VNAV I believe you need to have yoru FMC set up correctly while on the ground (people always forget the flap settings and as a result they never get the complete message on the take off screen).I am pretty sure that covered the basics... there are many others on this forum who no LOADS more than I do about this aircraft.. and have vast amounts of sim adn r/w experience as compared to my 1000 hours in the PIC... keep pluggin away and keep reading.. and whatever you do.. do not stop reading this forum .See ya in the skies Josh,Ian Elchitz CYWGPIC Addict (even though recently I have been branded a plastic lover)

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LOL, Yea thanks IE . . . ASRC can be a challenge thats for sure. Youll get a hang of it :)Ill take what I just read from your post and try to remember it.Thanks,JH

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I have a quick question about altitude hold. Have you ever been in a situation where the AP won't take control of the VS climb rate? I am set up for take off... FD on, Power set, Auto Throttle set, Trim on 4, LNAV on, flaps set. Rolling with 70%, then select N1 selected, rotate at correct speed, gear up, select CLMB 1, select CMD. VS light comes on and VS showing 2500fpm, but I still have total control over VS using the yoke, autopilot is doing nothing. This continues for about a minute and it eventually then take over the climb. LNAV is working fine. (Note I prefer not to use VNAV and have found VS is great in the past) I can see no pattern to this and just wondered if you had ever had this happen to you or had any ideas what could cause this behaviour? Thanks for any advice to solve this one!Graham.

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Guest Ian_Riddell

"FLCH is airspeed dependant. The aircraft will change its pitch to maintain the desired airspeed based on the calculated thrust you have programmed using the thrust computer. For example.. if you are at FL250 and wanted to go to FL290, you would dial in 29000 on the MCP altitude window.. and then engage the FLCH. You can then set the desired airspeed using the airspeed wheel. If you set it to say.. 280 IAS.. the aircraft would maintain constant thrust (as set by the thrust computer) and change the pitch so that you would climb at 280 IAS.. regardless of the vertical speed it needs."Your last sentence may have to be modified slightly, to be 100% correct, Ian. FLCH is a little more compex than this. According to the Boeing Maintenance Manual, in FLCH mode, "the Thrust Management Computer controls the thrust to attain a vertical speed so that the transition to a new altitude takes about 2 minutes (subject to the EPR/N1 REF.....(value)". For example, if you request a small altitude change of 1000', the elevators will control the airspeed to a fixed value and the throttles will move to give you a thrust value which will give you a climb rate (V/S) of 1000'/per 2 minutes (i.e. 500fpm). This V/S would be achievable in most phases of flight without the throttles going up to the THR REF limit, so a 500fpm V/S would be seen on your instruments.For large altitude changes (increases), FLCH still aims for a particular vertical speed, but it will be limited by the thrust available from engines. If a 20,000' FLCH is requested, the throttles move forward to try to get you to 20,000' in 2 minutes. This means a V/S of 10,000fpm is the target. However, these sort of V/S's are not possible in a 767.In descent, a similar logic applies, but the thrust limit in this case is the throttle lever aft stop.Try some small altitude changes in PIC and you will see that FLCH is not an "all or nothing" type of mode (You may find the V/S's not to be spot on in PIC, but, as I understand it, FLCH in real life can give you higher than expected/predicted V/S values, depending on "wind & weather").Hope this helps.Cheers.Ian.

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Guest ielchitz

Ian,If I could give you another "STAR" on your rating - I would do it in a second. It's posts like that which make this forum what it is. I had no idea about this "two minute" thing before.. can not wait to try it out.Thanks Ian,Ian Elchitz CYWG

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