The search for a missing American couple, last seen on June 20 before their small plane took off from Wolf Lake, Alaska, has been called off.

For nearly three weeks, Canadian and U.S. forces' aircraft scoured the mountainous terrain between Wolf Lake and Whitehorse after pilot Gary Patigler, 70, and wife Ingrid, 68, failed to turn up at Erik Nielsen Whitehorse International Airport.

The Iowa couple were on a camping trip in the Yukon and Alaska, using their Beechcraft Bonanza six-seater plane as transportation to remote locales.

Upwards of 70 people - military and civilian - were involved in the search on the Canadian side of the border.

In addition to several civilian aircraft, two air force Hercules out of Winnipeg and two Buffalo planes from the Canadian Forces base in Comox, B.C. were rotated into the mission.

During more than 400 flying hours, searchers covered 21,000 square kilometres of terrain in a failed bid to find the Patiglers.

While the couple's plane was outfitted with a standard emergency transmitter, no signal was detected, leaving searchers to comb the region and go on leads from possible eyewitnesses.

As Patigler was an experienced pilot and the couple was prepared for camping with shelter and food, if they survived the crash, there was hope they were alive and waiting to be rescued. What caused the plane to go missing remains a mystery.

The file has since been turned over to the RCMP as a missing persons case.

The public is asked to contact Whitehorse RCMP if they have any information related to the missing aircraft or the whereabouts of Gary and Ingrid Patigler.