Why DOES the AP disco alarm ring out on liftoff ?

[JSACKS 0]

Why does the AP disco warning alarm go off sometimes when lifting off in the 744? I cannot find a consistent reason for this. Or it a glitch? I wondered if it was an alarm for lifting off prior to attaining V2 when heavy; or whether the angle of climbout is too steep; or....something.Is this bad piloting or is this an unintended alarm?Jonathan

[Guest]

did you flip on the AP switch before takeoff?

[JSACKS 0]

No, no way! Never would do that.Jonathan

[Guest squidie]

You set the altitude hold before take off?

[JSACKS 0]

No, I don't set anything like ALT HLD before t/o. I set LNAV and VNAV to "armed" status and engage TO/GA power as I always do. The MCP is fine and the FMC is running the show. At rotation, all seems well and then a moment or two or three later, the AP disco alarm goes off. This is a fairly recent development. It happens seemingly at random. I cannot fathom it. Is the AP alarm disco SUPPOSED to go off at any time during rotation or climbout--if something is out of whack? Baffling....??Jonathan

[Guest Hawkeyeted]

I'm confused because you should have the AP on before 400ft AGL. You should only be LNAV/VNAV ARMED at best.Perhaps you're hearing the A/T alarm?

[Guest matsuman]

JS,I had this problem before and made some adjustment on my take-off.Make sure you have a good positive rate of climb, establishing the the speed/alt before hitting the AP button command on MCP.Keep that joystick or yoke pull pressure for couple of seconds after you hit the AP button...just to make sure it is on a good nose up climb.I think when you let go your joystick as soon as you hit the AP, the plane tends to sink a bit and you will hear that warning sound.Thanks,Kin M.(KLAX)

[JSACKS 0]

Kin and everybody else:I am NOT touching the AP on takeoff or on climbout. I do NOT switch the AP on until reaching at least 1000' AGL (when I couple if to LNAV + VNAV) and I usually climb out manually to flaps 5 and CLB N1 kicking in before engaging the AP. The AP is OFF all this time. (The nose does not sink and I do not attempt to turn the AP on EVER unless the yoke and controls generally are centralized.)I arm LNAV and VNAV to provide inputs to the FD for hand fly from liftoff. The FMC is fully programmed and commands TOGA power and everything else. I have done scores of takeoffs in this manner normally and perhaps 10-12 of them have had this random alarm, six of them last night which is exceptional and surprising to me. All I am asking is whether this is a PMDG glitch or I am searching for something in the t/o procedure that could conceivably be wrong. But the AP is OFF during this whole period.Jonathan

[lostmoon 0]

its a glitch. it's happened to me on several occasions. sometimes it happens, sometimes it doesn't. a cold reboot helps solve it.

[JSACKS 0]

Aha! A fellow simmer who has struck the same thing. And it is a glitch. Well, as I've said before, as long as I know some things are glitches--and are relatively minor--I can live with it. Thanks for posting!Jonathan