The NCP leader is being questioned for his alleged involvement in awarding favourable air traffic rights to foreign airlines that caused losses to national carrier Air India.
On Monday, Patel was questioned for nearly eight hours by the ED. He refused to answer media queries on what transpired at the probe office.
The name of Patel, who was the civil aviation minister between 2004 and 2011, surfaced in a charge sheet filed by the ED against corporate lobbyist Deepak Talwar on March 30.
The agency had in its charge sheet said that Talwar, who is currently in judicial custody, allegedly acted as a middleman to favour foreign private airlines. It also said that Talwar was in regular touch with the former Aviation Minister.
"Talwar finalised various communications on behalf of Emirates and Air Arabia to be addressed to the then Minister of Civil Aviation Praful Patel," Special Public Prosecutor (SPP) DP Singh, appearing for the agency, had told Special CBI Judge Anuradha Shukla Bhardwaj on May 1.
Talwar, who was extradited from Dubai on January 30, allegedly received payments to the tune of Rs 272 crore during 2008-09 from these international airlines in lieu of securing favourable traffic rights.