A helicopter of the Indian Air Force crashed near Arunachal Pradesh’s Tawang town early on Friday, killing seven military personnel. The Mi-17 V5 helicopter crashed at Yangchi, 130 km from Tawang, during a training sortie, The Indian Express reported.

Among those who died were five Indian Air Force officers and two from the Indian Army. Their bodies have been recovered.

The helicopter was on an air maintenance mission when it crashed at 6 am, the Indian Air Force in a statement. A court of inquiry has been ordered to ascertain what caused the crash.

The mishap took place a day before Air Force Day celebrations.

The Russia-made Mi-17 V5 is considered one of the world’s most advanced military transport helicopters. India has more than 150 such choppers in service and has ordered for 48 more, according to NDTV.