Taking the stand for a second day as part of a multi-million dollar defamation trial, Ms Heard cast Mr Depp as deeply troubled by jealousy and drugs.
Mr Depp is suing Ms Heard for $50m (£40m) over an article in which she said she was a victim of abuse.
She is countersuing for $100m.
On Thursday, Ms Heard alleged that much of her ex-husband’s anger was caused by his belief that she was seeing James Franco, whom she said Mr Depp “hated”.
..........................................Mr Franco starred alongside Ms Heard in Pineapple Express and The Adderall Diaries.
That jealousy, she claimed, led an angry Mr Depp to repeatedly question her on a flight from Boston to Los Angeles, in which he allegedly kicked her.
“He just kicked me in the back. I fell on the floor,” she said. “No one said anything. No one did anything. It’s like you could hear a pin drop on that plane.”
The court also heard a recording allegedly of Mr Depp on the flight, which Ms Heard said showed him “howling” while suffering from the effects of drug use.
Following the incident, Ms Heard said he met her in New York to apologise and to prove he was sober and committed to change.
Jurors have repeatedly heard about the incident on the flight. In his own testimony, Mr Depp said that he took Oxycodone pills and fell asleep to avoid Ms Heard.
During her testimony, Mr Depp could sometimes be seen closing his eyes. At one point, he shook his head quietly.
Ms Heard alleged she had the fight with Mr Depp after an argument about his daughter Lily-Rose, who was about 14 at the time.
“She was so young,” Ms Heard said. “I felt protective.”
Additionally, Ms Heard also detailed their surprise engagement and a previous discussion over a prenuptial agreement with Mr Depp.
She claims that Mr Depp told her that “the only way out of this is death”.
“I didn’t care either way, but I did feel it [the agreement] would eliminate suspicion or doubt, and it would make things easier,” she added.
Earlier in the trial, Mr Depp claimed he never struck Ms Heard, or any women. Instead, he said she was often abusive herself and had a “a need for conflict”.
At several points in her testimony, Ms Heard claimed that Mr Depp attempted to control her career, becoming angry at her efforts to find new roles.
These arguments, she added, would often end in Mr Depp taking things “too far” by striking her or breaking things in their home before leaving and eventually apologising.
“He would never have to deal with the clean-up. He would never have to deal with the destruction, or see me or the house that he’d destroyed,” she said.
In one apology e-mail shown to jurors, Mr Depp described himself as “savage” who was sorry for the disappointment he caused. She said this was “typical” of his apologies.
“I was encouraged because I thought it meant he could really hurt me,” she added. “Sometimes I didn’t think he understood how much he could hurt me.”
The defamation cases stems from a December 2018 opinion piece in the Washington Post, in which she said she was a victim of abuse but did not name Mr Depp.
His lawyers have said that the piece “incalculably” damaged his career prospects.
