One of the pilots on board the Jet Airways flight 9W 118 that went incommunicado last week was sleeping while the other pilot had chosen a wrong frequency to communicate. The flight had to be intercepted and escorted to London by German Air Force planes. Neither of the pilots could be contacted on the universal emergency frequency of 121.5 MHz because the second pilot had kept his headset at a very low volume, reported The Times of India.

The pilot who was asleep was reportedly taking “controlled rest”, which is allowed by regulatory agencies. The incident is still being investigated. “This issue is being probed by the airline and the Directorate General of Civil Aviation. At this stage we will not be able to say anything else,” a Jet Airways spokesperson told The Times of India. The airline had earlier said the crew of the flight had been grounded till the DGCA investigates the episode.

German air traffic control had contacted the crew of another Delhi-London Jet Airways flight that was flying ahead of 9W 118. They then got in touch with Jet Airways’ flight operations in India who used a satellite phone to contact the pilots of 9W 118.

The Mumbai-London Jet Airways aircraft had more than 300 passengers and 15 crew members on board when it went off the radar for about 33 minutes. The incident, which took place on February 16, happened when the air traffic control in Slovakia was handing over charge to Prague.