Nose dive at takeoff when enabling AP

[Andiehuk 7]

Hi,

I've been doing some test flights tonight and have noticed perhaps (well I can't see it mentioned anywhere) a missing point in the step by step docs which could be what's catching certain people out with regard to the aircraft diving after takeoff when enabling the AP. It's probably really obvious to most but it caught me out doh

- As per the docs I set my initial altitude to a value greater than the THR RED altitude.

- I run through all the checks (everything is dash dot etc as expected), I'm ready to take off.

- At VR I rotate to approximately 15 degrees, gear up. flaps up > than s speed, reduce throttle at correct stage etc

- I now turn on the AP and the plane immediately drops the nose and starts diving. A common theme after reading a number of posts on the subject.

What I have noticed is unless you actually left click the ALT knob after setting your intial altitude the system doesn't seem to pick it up i.e. it doesn't show on the PFD above the ALT ticker. There is however a really low value below the ALT ticker on the PFD just after takeoff which I believe is what the aircrafts AP thinks is the correct level to be at, hence the dive. It varied on my display but was around 100 most times. Now when I set my initial altitude I always left click the ALT knob afterwards and hey presto on enabling the AP after takeoff no dive, just a lovely continuing climb to the correct level. The initial ALT I set can also be seen above the ALT ticker on the PFD before I even takeoff which of course is where it should show for a climb.

Now I'm sure you hardended airbus fans already know the above or can correct me if this is the wrong procedure etc but it's sorted out the nose dive on takeoff for me and wasn't obvious in the step by step guide.

Oh and another thing. I've also found that even though you have a dash dot on the hdg display and are supposedly in managed mode sometimes the AP does not follow your planned route when turned on after TO. I have to left click the HDG knob to wake it up/confirm it. This doesn't happen all the time but I'd say it was 50/50 in my case. I just do that also before TO

Hope this helps someone else.

All the best

Andy

[vali 31]

I had first problem indicated by you also, several times, I could not find the reason why but yes, if left click on ALT is used again it works.

The plane did not crash but if this would happen in real life I think passengers will be really "happy" and will say their prayers

But it happen also that the plane climb over the ALT set initially.

I mentioned here but no feedback at the moment: http://www.forum.aerosoft.com/index.php?showtopic=39274

So it seems that at the moment this CLB mode is not 100% robust.

[Finn 873]

Whenever You change any setting on the FCU, You must either push or pull the knobs.

Any change must be confirmed looking on the PFD readouts / FMA.

Right after take off the aircarft will fly runway heading until 400 ft AGL whereafter it will start follow Your flightplan.

The FMA must show NAV when flightplan following is active.

Finn

[vali 31]

For me Airbus approach is very clear.

Example: I set the initial ALT, push the button. After takeoff there is sometimes the dive or climb over set ALT, if I push ALT again is going back to normal. It was

not always happening. In my screen can be seen ALT CRZ with green on FMA but plane was still climbing.

Also related to FMA, it is displayed with blue RWY TRK instead of NAV before going to TO FLEX or TO/GA.

[SimPilot767 157]

Confirm.

On the original airbus, you just engage the A/P after takeoff in about 400 ft (after having selected and "pushed" speed, hdg and alt prior to takeoff).

Until there is a fix, it´s a simple workaround to immediately push ALT again after engaging the A/P.

Timo

[Maxloading 48]

Now I do all mya take off on manual.Speed 250, runway heading, altitude Fl120 and +1800 fpm.I follow the FP 25° bank angle,release the stick an I have the time to my checks and then I put everything on managed mode and it's 'fine., no mre problems.

AlainV

[SimPilot767 157]

...I think you mean pitch, not bank, but anyway: 25° are too much.

Normally you rotate to 15-18° with a rotation-rate of 3°-5°/sec.

That´s slow! But if you do so, the aircraft is above 100 ft AGL when

you finished your rotation and hence it is in direct law and keeps the pitch.

Timo

[Maxloading 48]

Sorry, maybe be I did not make myself clear .On take off I follow the FD manually wich gives me appx 15° pitch with 2500 FPM. I then follow the SID ( programmed manually) with a bank angle of 25° when I turn.The FBW maintain that position when I release the stick and I do my checks. I now put the AP on and engage the a/c managed mode an fly normally.It works everytime.

AlainV