Two small planes collided in midair just north of Phoenix, Arizona on Friday, killing four people.

According to a KSAZ report, the planes were both single-engine, with two people aboard each. The collision occurred on Friday morning, about 15 miles northwest of Deer Valley Airport in Phoenix.

The details of the crash have not yet been determined. Witnesses only reported seeing the two planes crash in midair. One of the planes was reportedly left relatively intact, while the other was, according to KSAZ, “charred wreckage.”

The Phoenix-based TransPac Aviation Academy has revealed that two of those killed were flight instructors for the academy. The organization has stated that it will set up a memorial fund for the families of those who died.

“I was terribly saddened to learn of the loss of two of our members of the TransPac Aviation Academy family,” said Stephen Goddard, CEO of TransPac. “We extend our deepest condolences to the family, friends, and fellow colleagues of the two instructors that were lost today. The individuals involved were deeply connected here at TransPac and their loss is felt by all of us. The entire extended TransPac community, including our Alumni, is in shock and mourning for the loss of both of these two good men. We are not releasing personal information about the individuals at this time out of respect for the families during this time of sadness and grieving.”

Goddard stated that TransPac is cooperating with the Federal Aviation Administration (FAA) and National Transportation Safety Board (NTSB) on the investigation of the accident.