I wanted to fly today from EGLL Heathrow to OMAA Abu Dhabi. But when I reached FL270 the plane started slowing down from 485kts ground speed. When I reached and levelled off at FL390 which was my cruise altitude, it kept on getting slower and the nose began to raise up causing the aircraft to stall and drop.
The aircraft was the A380.
I also wanted to fly earlier today in the morning with an a330 from EGLL to KJFK John F Kennedy and the same thing was happening.
I am a frequent infinite flight user and I am now on grade 3 and had more than 290 flights and most of them are long haul ones and never experienced something like this until today.
Any ideas on how to resolve this issue?