This was Patel's second appearance before the agency in connection with the case. The Nationalist Congress Party (NCP) leader has been called again for questioning on Wednesday.
He was questioned for over eight hours on Monday by the ED. The case follows a criminal complaint registered by the ED over alleged irregularities in fixing air slots for international airlines that purportedly led to losses for Air India.
Patel has denied any wrongdoing. The ED has already questioned several Air India officials and also recorded statements of the then Civil Aviation Secretary and others involved in processing and finalising the agreements.
Patel was the Civil Aviation Minister in the United Progressive Alliance (UPA) government between 2004 and 2011, when the merger of Air India and Indian Airlines took place.
According to senior ED officials, the agency asked Patel about Air India and the ministry officials who favoured foreign airlines by giving up profit-making routes and timings.
The ED officials also sought details of Patel's bank account and details of his properties. Patel's questioning has come over a month after the ED filed its final report in the alleged aviation scam.
In its May 1 chargesheet, the ED named corporate lobbyist Deepak Talwar and alleged that he finalised various communications addressed to Patel on behalf of Emirates and Air Arabia.
Talwar, currently in judicial custody, was extradited to India from the United Arab Emirates (UAE) in January this year.
The ED probe encompasses the Air India-Indian Airlines merger, purchase of 111 aircraft from Boeing and Airbus for Rs 70,000 crore, ceding of profitable routes and schedules to private airlines, and opening of training institutes with foreign investment.
It is also investigating how the money received in Talwar's accounts was transferred to government employees, including those in the civil aviation ministry.
( With inputs from IANS )