Translation
Perhaps even us Brazilians here will disagree and this is OK. But from my perspective, if one of us tell the other to "desacelerar" this has only one meaning: "reduce thrust". If one wanted to tell the other to brake he would have said: "freiar". And if one tell the other "não consigo" he means that he tried and discovered that he could not complete the action.
Mind you the "desacelerar" in the transcript came from an english translation of what was said, as done at the NTSB. One would have to listen to the tape and the voices to learn what the pilots really said in
portuguese. Anyone has done this?
But "desacelerar" in usual portuguese will never mean "slow down". It could mean "slown down in the contect of reducing thrust".
Do you know how it is called the thrust pedal in a car: "acelerador".