Call async_write from outside connect handler in asio

I use the asio library to make TCP connections. The async read/write operation is made from the handler function of async_accept.

        mAcceptor.async_accept(*(mConnection->Socket()),
                boost::bind(&TCPConnection::HandleAcceptForWrite, this, 
                pI8Msg, 
                boost::asio::placeholders::error));

void TCPConnection::HandleAcceptForWrite(
        INT8* pI8Msg, 
        const boost::system::error_code& err)
{
    if (!err) {
        TransmitData(pI8Msg);//--> Want to call this fn from outside the handler
    }
    SocketAcceptConnection(pI8Msg);
}

I want to avoid the call to TransmitData (async_write) from within the handler.

I intend to call write from anywhere outside the handler of accept. When I do this I get the error - 'Bad file descriptor'

Is it always necessary to do an async write from within the handler? Please share any code sample if it can be called from elsewhere.