C172 Flight Instructor reported a tail strike occurred due to a loss of lift during the landing flare; most likely due to the wind conditions. The Flight Instructor took control of the aircraft from the student and after getting all three wheels on the ground; inspected the aircraft and notified Tower.

Narrative

Upon return from a cross-country instruction flight; the aircraft sustained a tail strike. The winds were reported as variable and had been a strong crosswind throughout the day. On final approach I instructed the student to be prepared for a go-around due to the strong variable wind conditions. Upon landing flare; the aircraft incurred a substantial loss in lift and I instructed the student to add power; but it was too late. Almost immediately; the aircraft sank and touched down as I quickly gave back pressure on the yoke to allow the mains to hit first and subsequently the tail strike occurred. The student then added the power I called for earlier; only for me to instruct the student to reduce power to idle; as all three wheels were already on the ground. Upon inspecting the aircraft; the tie down hook was missing; and I immediately called the Tower to let them know. The main contributing factor was the strong variable wind conditions along with a lack of power input when the sudden loss of lift occurred. Another possible contributing factor was that the nose strut appeared to be recently serviced as it was fully extended allowing for a more than normal tail low attitude.