Tommy Lee forced himself on a woman in a helicopter cockpit ... groping her, kissing her and penetrating her against her consent ... according to a new lawsuit.
The Motley Crüe rocker is being sued by a woman who says the alleged sexual assault happened way back in February 2003 when she was riding in a chopper with Tommy and another man.
In the lawsuit, obtained by TMZ, the woman says she was friends with the helicopter pilot, and he invited her on a tour of San Diego County ... but when she got to the airfield, Tommy was there, and she was told the plans changed and they would all three be riding up to Los Angeles.
The woman claims she felt pressured to go, and once airborne she says Tommy and the pilot started drinking alcohol, smoking weed and snorting cocaine.
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In the docs, the woman says the men pressured her to come up to the cockpit and sit on Tommy's lap ... and as soon as she obliged, she says Tommy forced himself on her.
The woman claims Tommy began groping and kissing her, but when she tried to pull away he became more forceful. She claims he penetrated her with his fingers while fondling her breasts.
In the suit, the woman claims Tommy also pulled down his pants and attempted to force her head down towards his genitals.
She says, when they got to Los Angeles, Tommy hugged her and bounced and then the pilot flew her back to San Diego in silence.
In the docs, she says the alleged incident left her feeling shock, distress, humiliation, shame and guilt ... claiming she didn't go to the cops because she didn't think she would be taken seriously.
Since the alleged incident, the woman says she's suffered from anxiety, depression, PTSD and other physical and psychological harms ... and she's going after Tommy for damages.
We reached out to Tommy's camp ... so far no word back.