Congress spokesperson Randeep Singh Surjewala on Wednesday attacked Defence Ministry for not upgrading the Indian Air Force's An 32 aircrafts, one of which went missing over Arunachal airspace on Monday.

The An-32 aircraft, with 13 onboard, had taken off from Jorhat in Assam and was destined to the Mechuka Air Landing Ground in Arunachal Pradesh. The plane stopped communicating with ground staff 35 minutes after takeoff.

Quoting a report in a defence news portal, Randeep Singh Surjewala said that he was sad to learn "that missing AN-32 had SOS Signal Unit that’s OBSOLETE" and questioned the government on why were the aircrafts were not upgraded despite an agreement.

"Pray for safety & well-being of IAF personnel & crew of missing Aircraft AN-32. Sad to know that missing AN-32 had SOS Signal Unit that’s OBSOLETE. Govt must tell- Why was upgradation of AN-32 not completed despite India & Ukraine agreement of 2009?" Surjewala's tweet said.

The story shared by Randeep Singh Surjewala says the missing aircraft was equipped with a single Emergency Locator Transmitter (ELT) called the SARBE 8, manufactured by the British Firm Signature Industries. According to the report in Indian Defence News, the SARBE 8 has been out of production since and 2005 and the company said that they went effectively obsolete by 2009. The SARBE 8 Emergency Locator Transmitter was replaced by a unit called the SARBE G2R-ELT, now sold by Orolia, a US and France based company set up in 2006.

While the ELT installed in the missing IAF An-32 jet may still have been operational, no signal from the unit has been detected by rescuers trying to home in on the wreckage of the aircraft.

Referring to a 2016 case, when another IAF An-32 vanished over Bay of Bengal, Surjewala questioned the government why it did not take mitigating measures to prevent any future incident.

"Despite a similar accident earlier of losing an AN-32 aircraft en route to Andaman and Nicobar islands & which was not tracked, why have mitigating measures not been taken by Defence Ministry?" Congress spokesperson said.

In a series of tweets, Randeep Singh Surjewala also raised queries on as to why An-32 was being used the treacherous terrain when the IAF has aircrafts better equipped for the route.

Search for missing IAF plane underway

The defence officials on Tuesday said that a massive search operation involving a large fleet of planes, choppers and ground force was underway and satellite imagery being used to trace an AN-32 transport plane of the IAF.

Aircraft equipped with advanced sensors including C-130J, AN-32 and Indian Navy's long-range maritime reconnaissance aircraft P8I were deployed besides Mi-17 and ALH helicopters of the Army to locate the missing plane, officials said.

ISRO's Cartosat and RISAT satellites are taking images of the area around Menchuka to help the rescuers find the plane.

Officials said the area has thick vegetation and difficult terrain which are making the rescue operation challenging.

The IAF on Monday said the aircraft took off from Jorhat at 12.27 pm for the Menchuka advance landing ground in Shi-Yomi district in Arunachal Pradesh, and its last contact with the ground control was at 1 pm.

A total of eight aircrew and five passengers were on board the aircraft.