Respected Turkish business newspaper Dünya reports that the second metro line to the airport will be "Halkalı - Airport" line and 28 kilometers long and 8 kilometers is tunnel. Total tunnel two way is 15.9 kilometer.

Boring will be done by Turkish tunnel specialist E-Berk. E-Berk already refurbıshed the TBM which bored Dudullu-Bostancı tunnel to use in this project. TBM diameters is 6,56m.

"New İstanbul Airport" (called "New Atatürk Airport" by public) is one of the biggest airports in world but commuting to airport is nightmare. Taxis charge fortune and busses late in heavy traffic. Metro tunnels hope to finish misery.

Boring of new metro line tunnel start in 1 month and finishes in 2,5 years says E-Berk company.

Read (Turkish) https://www.dunya.com/ekonomi/havalimanina-bir-metro-hatti-daha-haberi-453141