Amir Ali, who worked on the Bakerloo line, allegedly planned to travel to Pakistan or Afghanistan to join the Taliban.
When his home was raided, police found recordings of lectures by a radical Islamic preacher convicted of soliciting murder, the jury was told.
They also discovered the note to his wife, daughter, four, and three-year-old son.
‘He asked for his wife’s forgiveness and that he would see her soon in this life or the thereafter,’ said prosecutor Duncan Penny.
Ali is accused of booking a flight to Pakistan with the aim of joining the holy war there or across the border in Afghanistan.
The 28-year-old, a Tube driver for five years, paid £555 for the flight from Heathrow to Islamabad, it was alleged.
He was also said to have bought supplies, including a self-inflating pillow, a sleeping bag and a pair of waterproof trousers.
Photos of Ali posing with AK-47 rifles and a pistol were found at his Ilford home, Snaresbrook crown court heard.
Police also found documents advocating religious violence and tapes of lectures by Sheikh Abdullah el-Faisal, who was found guilty of soliciting murder in 2003. In his note, Ali told his wife not to be upset with him for not being there.
Mr Penny added: ‘He told her to tell the children that he loved them very much but that he had to go for the sake of Allah because Allah and his prophet Mohammed came first.’ Ali denies one charge of preparation for acts of terrorism. The case continues.
How comfortable must Londoners be with the fact that people like this are allowed access to the strategic transport infrastructure of one of the world’s pre-eminent cities?
Are Transport For London carrying out background checks for applicants for (highly sought-after and very well-rewarded) London Underground train driver postions?
If not, the next time one of them gets that Sudden Jihad feeling, it might not be Afghanistan that’s on the destination board.