Hello all, 

Thank you all for your answers.

Headley : I always cut the APU when taxiing, when the 4 engines are on.

wsmeier :  Yes, I have the latest version of the plane : 3.00.8605 . 

berts : Thank you for your advice, I note and I would do this if ever I have this problem again.

DrJ1 : I first start the engine 4 and 3 first, once this starts, I start the 2 and 1 .

I again made a flight today, with the same procedures of starting up which I usually made. This time I made the flight on P3 DV4 and not V3, I had no problem.

Once again thank you for your answers. In spite of my bad English, because I use a site of translation, you all understood me.

 

 

Alexis,. Glad you got it sorted out.   Blue skies 

18 hours ago, DrJ1 said:

If I remember correctly if both buses switch from APU to engine generators at about the same time this momentary period without power from any source was enough to lose the center IRS.

I recall that Atlas starts 1 & 4 at the same time, so it shouldn't cause any problems.

Switching power sources from APU to engine should not cause power breaks. The two power sources are synchronised prior to switching...  and for a very brief moment (less than 120 milliseconds), both APU and Eng power are put online at the same time (on the same side/half of the split system bus). It's known as a NBPT (no break power transfer). I believe the 744 was the first aircraft to have this system.