Project Tupolev Team :: View topic - AFCS

arrow12 · Êóðñàíò

The Tu-154b2 is descending swiftly on the ILS: speed is about 300 km/h,
the AP & AT are working fine and the LOC & "Glissade" are engaged.
Everything is perfect until the warning of the OM rings: at about 400-450m
ground a double AFCS bank & pitch failure occurs (with red signal lamps)
and the AP disconnects.
The AT keeps on working.
Any explanation??
Understand that the automatic ILS-Approach schould work until approx.
120m ground. Is this correct??
Very grateful for any good advice.
arrow12 Óëûáêà

WalterLeo · ÊÂÑ

arrow12

There are more than one explanations:

Ãðóñòü

a) ILS out
b) Gyro failure
c) hydraulics failure
d) automatic go around mode activated (without intention e.g. by moving throttles).
e) navigation computer still on?
f) flying procedure: did you try to establish on ILS-GP from above (a NONO not only in russian planes)?
g) too fast ? AoA should be 6,5 deg up (154 b2 154 m 6 deg), 300km/h seems fast.
h) flaps set for landing?

Did it occure once or often? If it reappears can you make a screenshot of captains panel?

Regards

Walter

arrow12 · Êóðñàíò

Hallo Walter,
Thank you for your speedy reply.
Your assumptions: a, b, c, d, e, f are all negative, as far as I know.
Flaps are set for landing (full down);
It did occur each time up to now (say 10-12x)
Will have to try it with the proper AoA as you suggest. Probably that might
do it. Will keep you posted.
Best regards,
arrow12

WalterLeo · ÊÂÑ

arrow12

Another trap I have forgotten: In the Tu-154 the HSI doesnt move automatically to the choosen track as in western airplanes, you have to choose the radial on the navigation subpanel and turn the HSI to the correct value of the landing track on the HSI.

The AP can fly the plane on ILS onto the runway (the landing will be solid!)

Good luck

Walter

arrow12 · Êóðñàíò

PROBLEM RESOLVED!! The Tu-154b2 did a perfect fully automatic
landing. None of the causes envisaged was the problem: simply too much
fuel in the tanks on approach (e.g. Max. Landing Weight exceeded!)
The reason: for training I used to take off, fly downwind, position the a/c
for the ILS-intercept... approach and land. All in all no more than 15-20 min.
airborne. BUT on the flowmeter I inserted between 25-30 (000) of fuel.
Obviously far too heavy: like a check of the load manager would have shown.
With a reduced fuel quantity of around 10 everything went perfect.
AoA was around 8, Speed 260-270 Km/h and this gave a firm but nice and
correct landing.
So when the AFCS checked the weight of the a/c on final and found
it too heavy it just disconnected (like it should be). That's it!

Thank you Walter.

WalterLeo · ÊÂÑ

Overweight landings only in an emergency (and by hand!) and did you check the COG/ position of stabliizer? Shourley it was out of limits for a landing also!
With 260-270 km/h on glideslope AoA should be 6,5 deg, seems you where still too heavy.
I doubt, that ABSU (an old but trusty AP) can check the aircrafts weight, seems it disconnects if its flightcontrols are passing a certain limit

P.S.: Pardon: I stumbled over your expression "I put the flowmeter": The fuel in the tanks is not changed by changing the flowmeter´s needle, you have to go to the FS menu. If you do not do this the tanks will contain by chance fuel defined in an other airplane before choosing ANTK-Tupolev...

Ñë¸çû

Best regrads

Walter

arrow12 · Êóðñàíò

Hello Walter,
Finally I did everything according to the book:
- Load sheet for correct weight and balance, e.g. well in the limits for MLW
and CoG;
- Speed on the ILS-Approach 260-265 kmh,
- AoA between 0,6-0,65 sometimes up to 0,7 =
- Perfect ILS-automatic landing.

So, problem resolved?? Yes, definetly.
But one question remains.
As you say, the good old AP handles all weights and does not recognize
therefore a possible Over-weight (flies approaches with AoA up to 0,9!)
So, why after all the AFCS-failure on long-final??
I might have found the answer:
I realized that on the AFCS-failure flights for some reason I forgot to set the switches 214 to on (after alignment of the gyros).
Since I switch them on, everything has worked fine.
Can that - after all - be the reason??

Many thanks - as always - for your valuable help.
arrow 12

WalterLeo · ÊÂÑ