EDIT: RAF Lakenheath reported that the pilot was finally located and is unfortunately deceased. “We are deeply saddened by the loss of Lt. Allen, and mourn with his family and fellow Reapers of the 493rd FS. The tremendous outpouring of love and support from our communities has been a ray of light in this time of darkness," said the organization.
EDIT: The Coastguard has located wreckage from the fighter jet and recovery efforts are underway, according to RAF Lakenheath. Search and rescue efforts continue for the pilot.
The F-15C Eagle dropped into the sea at 9.40 AM local time. At the time of the accident, it was carrying out a routine training mission. The cause of the crash remains unknown. More importantly, the pilot is still yet to be found. The RAF Lakenheath statement said:
"The aircraft was from the 48th Fighter Wing, RAF Lakenheath, United Kingdom. At the time of the accident, the aircraft was on a routine training mission with one pilot on board. The cause of the crash as well as the status of the pilot are unknown at this time, and U.K. Search and Rescue have been called to support."
According to him, there were four military jets in the air at the time of the crash.
Sky News also reported that the Coastguard was coordinating a response after receiving reports of the accident, sending a helicopter along with Bridlington and Scarborough RNLI lifeboats.
Other vessels may also be heading to the scene after the Coastguard issued a Mayday broadcast.