After four days of overflights rangers in Denali National Park and Preserve are scaling back their search for two Japanese climbers missing on Mount McKinley.

Park officials announced today that search managers have determined that further air operations were unlikely to locate the men. However, mountaineering rangers will continue to try and determine the whereabouts of the climbers through extensive digital imagery collected during the past week.

Tatsuro Yamada, age 27, and Yuto Inoue, age 24, were expected to return from a climb of the Cassin Ridge on May 22. With no sign of the men, the National Park Service began planning the search on May 23, although cloudy and windy weather initially kept all aircraft on standby.

From May 24 to May 27, skilled observers flew a total of 33 hours of helicopter and fixed-wing flight time in the aerial search effort. More than 3,000 high-resolution photos of the search zone were captured during these flights. Analysis of the enlarged and enhanced images enables a concentrated and effective search effort to continue at ground level.

Through today, there has been no sighting of the climbers or gear on or near the route, nor any evidence of a fall or related disturbance on the snow surface.

Clues found throughout the week suggest that Yamada and Inoue reached the upper elevations of the route, including multiple sets of footprints and a campsite at 17,000-feet. Tracks followed by a subsequent climbing party reportedly reached upwards of 19,000 feet. Additionally, during a low-level flight on Wednesday, May 28, mountaineering rangers aboard the NPS Lama helicopter discovered tracks traversing the 5-mile length of the Kahiltna Peaks.

According to the journals left in camp, the team had intended to approach their route via this knife-edge ridge, which reaches a peak elevation of 13,440 feet. The tracks follow the dramatic ridgeline and connect with the Cassin Ridge, indicating the team accomplished an arduous and highly technical new variation on the traditional approach.

In a discussion with Denali rangers a month prior to their climb, Yamada and Inoue said they planned to take five to six days of food and fuel on the Cassin Ridge portion of their climb. Furthermore, as is typical of a quick, technical ascent of the route, the team likely took minimal, lightweight gear. Based on the dated journal entries, the men probably left their camp at 7,800 feet as early as May 10, and as such, have been without food and water for as long as 10 to 14 days.

In light of their limited supplies and the subzero temperatures, search managers consider that survival is outside the window of possibility. Observers have thoroughly searched the route and surrounding areas to the degree that if the climbers were visible on the surface, there is a high probability they would have been discovered.