Why does my "Auto Pilot" disengage on its own?? :(

[i_hate_toms]

I am flying a Boeing-777 from heathrow to san francisco international.
This problem occurs when I'm configuring my aircraft for landing/ touchdown..
This is what i do:-
Remember, the Auto Pilot, and the Auto throttle are in control of the aircraft at this point.
I start reducing speed. Say i dial in 200kts in IAS mode. Next I start reducing altitude -- I dial in, say FL100, set vertical speed to say -800, and press the "VS/FPA" button.
The green light for "altitude hold" turns off, another green indicator under VS/FPA lights up, and the aircraft begins a slow descent.

When I reach 200kts IAS, i start applying FLAPS and dial a lower speed, say 180 kts. I next get the ILS Frequency and Heading of the runway i am to land on, and dial them in for NAV1.
I apply some more flaps and dial in say 170kts for IAS.
The A/P and A/T are still in control of my aircraft and everything appears to be going nice and easy.
When I reach FL100, I apply some more FLAPS and dial in an even lower speed, say 160kts. When I'm in range of the ILS, I disengage the LNAV and dial in a HDG that will take me on a flight path in which i can intercept "Glide Slope" of the runway. The aircraft banks a little and starts changing course towards the glide slope. I now apply some more flaps, say flaps are now at 15. The A/T and A/P are still in control of the aircraft.
This goes on for like 30 seconds and then a "Master Caution" indicator lights up, a loud audio alarm fills the cockpit, and one of the cockpit displays show "Auto Pilot Disengaged".
It's not catastrophic, i don't crash, I take manual control of the aircraft and proceed to land visually. But why does the autopilot disengage on its own? That too, in an awkward situation-- I am close to the ground, the airspeed is pretty low, the flaps are set, and the aircraft is banked (remember, we started changing course to intercept the glide slope). The room for error is very low, one single miscalculation will stall the aircraft and make me lose control, with altitude so low, a loss of control will most likely result in a crash -- i would definitely not want the autopilot to kick out in such a critical stage of the flight. Surely the auto pilot should be able to auto-land the aircraft, switch to retard flare mode and control it even after touchdown-- all i would do is set autobrakes to say 2 or 3, arm the speedbrakes, arm thrust reversers, and apply throttle to slow down the aircraft after touchdown, everything else should be handled by the AutoPilot. Ideally i would take manual controls at about altitude 500 ft, but i am forced to take manual control from about 3,000 ft. Pretty scary. What am I doing wrong? I have tried every little thing i can think of. I even turned on the "Seat-belt" sign for the passenger cabin thinking that might be the problem. but no matter what i do, the A/P would still disengage. (FGFS/ Boeing-777). Any idea??

 

[Turbo10]

You should be using the approach button for ILS approaches which will align your plane with the runway heading through the localiser and take you down the glideslope. The HDG button just flies the plane in a selected heading, it has nothing to do with ILS localisers.

 

[i_hate_toms]

u probably didn't read it right.
i will do the LOC and the APP once i am close enough to the ILS glide slope.
i cannot just start the final approach 300 nm away from the glide slope!
But when i'm 38,000 ft up and .84mach fast, it's a good idea to start losing some altitude and speed..
the HDG has got nothing to do with the landing, i know how to fly sims
i use the hdg to point the plane towards the glode slope, the "fly base" part of the approach, i generally try to intercept at 90 degrees, when i'm about to be there, close to the glide slope, i'll start the localizer and approach!

 

[Turbo10]

oh sorry i got lost, of course you can't do an ILS approach 300nm from it, there is a distance limit on VOR's, NDB's and such. You should only start the ILS approach after ATC tells you to, and when you're close to the approach itself.

 

[i_hate_toms]

right! so then why does the autopilot disconnect in such a vital moment?? any idea?? thnks for writing

 

[Turbo10]

Well for staters you should not be going down to 160knots at 10,000 feet. The speed limit is 250 under 10,000 so stay at that until you get close to the approach. Starts slowing down and putting flaps up when you are doing the approach. If you dial the frequency and the Course of the ILS into Nav1 and hit approach when you are about 2000feet when you are ready for the actual ILS approach. The approach will then keep you on that heading usiong the localiser and then take you down the glideslope.

 

[Turbo10]

Just saw that you're using flight gear, I would really recommend buying FS9 or FSX, they are far superior

 

[i_hate_toms]

i dont get to the point where i press the APP.. The AP disconnects before that.
flew smaller aircraft, this is the first time i'm trying to fly a huge 777, and screwing up
i'll keep the speed about 250kts and try again. let's see if that's causing in. thnx for writing
At what speed should the plane touch down? surely it cannot touch down at
IAS 250kts, that'd be crazy fast!

 

[Turbo10]

i dont get to the point where i press the APP.. The AP disconnects before that.
flew smaller aircraft, this is the first time i'm trying to fly a huge 777, and screwing up
i'll keep the speed about 250kts and try again. let's see if that's causing in. thnx for writing
At what speed should the plane touch down? surely it cannot touch down at
IAS 250kts, that'd be crazy fast!

nono not at 250 knots, it depends on the plane itself and the weight and such. I don't get why the AP disconnects, it normally only disconnects if you mess around with the yokes

 

[lucasbytegenius]

If you nosedive into the tarmac you can safely land the plane and most/half of its passengers by sacrificing yourself in the nose crush zone.

 

[i_hate_toms]

If you nosedive into the tarmac you can safely land the plane and most/half of its passengers by sacrificing yourself in the nose crush zone.

lol. would you do that if u were flying it? u probably can't nosedive, without complete loss of control. i've tried crazy things too- if u disable all automation, take complete control of the aircraft yourself, and then push the throttle to full while pushing the yoke all the way forward to commit a sudden nosedive, the aircraft violently roles to one side and keeps rolling. once this happens, you're done. it's almost 100% impossible to recover from the roll. there's no controlled nosedive. We're talking about a humble 777, not an F16

 

[i_hate_toms]

nono not at 250 knots, it depends on the plane itself and the weight and such. I don't get why the AP disconnects, it normally only disconnects if you mess around with the yokes

this does the trick. if i don't reduce the speed below IAS 200kts while i'm higher than 5000ft, the AP doesn't disengage. I navigate to the end of the glide slope at a little more than 90 degrees and press the LOC/APP. Two small yellow dots appear on the primary flight display. The one under the artificial horizon shows up first, soon followed by the other on its side. The dots eventually centre themselves, i apply full flaps and reduce IAS to 140 kts, arm the autobrakes. The primary flight display switches from LOC to LAND3. I touch down at about 135kts, nice and smoothe
Thanks for ur help bro, helped a lot. The 777 is so different from the cessna lol

 

[Turbo10]

this does the trick. if i don't reduce the speed below IAS 200kts while i'm higher than 5000ft, the AP doesn't disengage. I navigate to the end of the glide slope at a little more than 90 degrees and press the LOC/APP. Two small yellow dots appear on the primary flight display. The one under the artificial horizon shows up first, soon followed by the other on its side. The dots eventually centre themselves, i apply full flaps and reduce IAS to 140 kts, arm the autobrakes. The primary flight display switches from LOC to LAND3. I touch down at about 135kts, nice and smoothe
Thanks for ur help bro, helped a lot. The 777 is so different from the cessna lol

No problem mate

 

[Darren]

If you nosedive into the tarmac you can safely land the plane and most/half of its passengers by sacrificing yourself in the nose crush zone.

This guy.


Whenever I play flight sims I just turn off damage, fly in a 747, and do barrel rolls and crash into the ground at 1000mph then bounce in to the sky. Sometimes I question myself.

 

[Turbo10]

This guy.


Whenever I play flight sims I just turn off damage, fly in a 747, and do barrel rolls and crash into the ground at 1000mph then bounce in to the sky. Sometimes I question myself.

Yeah but that gets boring very fast. Doing it properly is much more fun and rewarding

 

[i_hate_toms]

Yeah but that gets boring very fast. Doing it properly is much more fun and rewarding

wait a minute, are u saying u can intentionally start a nosedive with AP and AT off, let the aircraft enter that violent roll and spiral towards the ground at IAS approaching Vne, yet somehow manage to recover from it unharmed?? Must be a real good pilot
if i do this on the 777 i have got installed here, i invariably fail to regain control of the aircraft. Try as i may, i cannot bring the aircraft out of the roll. By the time i begin to regain some control, it's already too late. That ominous 'Terrain Terrain Pull up Pull up' warning goes off and i slam into the tree-tops before i can 'pull up'. ..

EDIT: there i go. I just tried it again, and as usual, crashed again