52-year-old Bal, who one of the key officers handling the AgustaWestland scam case, had gone for a morning walk when he suffered the heart attack, Defence Ministry officials said here.
His body has been sent for post-mortem, they said.
A 1986-batch West Bengal cadre officer, Bal was holding the important charge of Joint Secretary and Acquisition Manager (Air) in the Ministry where he was looking after all the acquisition projects of the IAF.
The officer is survived by his wife, son, who is an engineering student in Vellore, and a daughter.