The private jet cruised at 30,000 feet, headed from Miami to Green Bay, Wis. Joe Philbin, his wife, Diane, and their five children had settled into cushy seats for what should have been the flight of a lifetime. They had every amenity at their fingertips, and a monumental career move to celebrate.

It was the evening of Jan. 23, 2012, two days after Philbin was introduced as head coach of the Miami Dolphins, a dream job for a forever assistant who spent nearly three decades behind the scenes. All the family members had put on their fancy clothes and happy faces for the news conference. They were excited about relocating from frigid Wisconsin to balmy Florida, and thrilled to share in the pinnacle of the coach’s professional life.

But up there in that plane, alone at last, away from the cameras, reality hit them like a 250-pound linebacker barreling in at full speed. The mood turned somber. And they cried. One thing was keeping the night from being perfect. Michael wasn’t there.

Ten days earlier, Joe and Diane Philbin had buried their 21-year-old son, Michael, following his accidental drowning in the icy Fox River in Oshkosh, Wis. The college junior, their second-oldest child, had been partying with friends and gone missing around 2:30 a.m. on Jan. 8, the night after Philbin interviewed for the Miami job. A security guard heard someone yelling for help, and called police. The body was recovered the following afternoon. Investigators believe he stumbled into the river and couldn’t get out.

Seven months have passed, and still, it’s difficult for Philbin and his wife to discuss their loss. Diane Philbin broke down a few times during a phone interview. The coach has rarely addressed it publicly since taking over the team, but he opened up in an interview on Tuesday.

“At one point, everything went quiet and everybody on the plane was crying,’’ Philbin recalled. “The kids were crying because their brother wasn’t with them. It’s been really tough, on all of us. But you realize when you have that kind of love in the family, that kind of support for each other, you can make it. You can survive and get through anything.’’

Last month, the Philbins moved Michael’s body from Wisconsin to a Fort Lauderdale cemetery. They wanted the whole family together in South Florida. “We had a little ceremony when he came down, short, just us,’’ Philbin said, choking up. “Diane’s been over five or six times.

“We were just over there last Saturday morning. The team got back from Carolina at 4 o’clock. They had a Mass at 9 a.m. for all the people that had been buried there in July. We went over there, it was great. Our son Matt was there Tuesday, before heading back to Texas. It was big-time important for us to have Michael here with us.’’

INFANT LOST

Michael was not the first child the Philbins lost. Thirteen years earlier, infant daughter Katherine died at childbirth in Boston, right about the time the coach was leaving a job at Harvard for the University of Iowa, his final college job before joining the Green Bay Packers nine years ago.

The family heartaches have given Philbin a greater perspective on life and the NFL. It is evident in his mild-mannered demeanor and ability to make decisions without being rattled. Choosing a starting quarterback? Small potatoes. This is a man who took on a high-profile, high-pressure job in the midst of a horrible tragedy, when other people would have crumpled and wanted to hide. At the same time he was helping his wounded family adjust to a new life, he was in the throes of the NFL draft and the start of training camp.