Sometimes when flying the 737 pmdg the a/t switch wont engage, it comes on and then it flips off, the little annunciator light comes on and says "check fms", but i am not flying with the fms in the vnav mode , ? why wont the a/t engage , thankspeter

ck this out No autothrottles after installing the PMDG 737NG 800/900 or autothrottle switch will not latchThis is caused failure to follow the Normal Checklist. Engine generators on the overhead panel are not selected ON after engine start, which causes the autothrottle switch to disarm. Turn ON the generator by cycling the GEN switch to ON momentarily and ensuring the Blue Gen off Bus light is out and the problem should be corrected.Dennis OKTPA

thank you very much , I will try that. regards Peter