A Mountain Locator Unit or MLU is a radio transmitter designed to be used by mountain climbers as an emergency locator beacon when the wearer needs rescue.
Unique to Mount Hood[1], these devices can be rented for $5 at Portland-area outdoor shops[2] and the Mount Hood Inn at Government Camp, which is open 24 hours a day. The MLUs are simple radio beacons, and thus require search and rescuers to use traditional radio direction finding (RDF) equipment that provides a bearing, but not a precise location, to the beacon.
Groups scaling the mountain are recommended to carry an MLU and all climbers must register before climbing and sign out upon return.
The MLU was designed after a school group with two adults and seven children perished on Mount Hood in 1986. (See Mount Hood climbing accidents.) The bodies of some of the group were found in a snow cave a day after the searchers had passed within fifteen feet of their shelter without noticing them.[3]
According to Steve Rollins of Portland Mountain Rescue, the units are worn on a sash across the chest and are relatively light.[4] This is less expensive than either purchasing or renting a personal locator beacon, which typically cost significantly more than $500 or rent for $50 per week, but include a GPS receiver and a transmitter designed for reception by a satellite network, for increased coverage and decreased response time.[5]
The Mount Hood MLU system is controlled and maintained by the U.S. Forest Service and Clackamas County Sheriff. Transmitters broadcast at 168.54 MHz and provide good signals when buried in snow. It can be received at up to 20 miles (32 km), though the signal travels in line of sight, so it can't be received from behind a ridge or deep in a canyon.[6] The technology is very similar to wildlife tracking systems.[7]
A Mountain Locator Unit only transmits a signal. It cannot be used by the lost to gain any information, not even to find others with such a unit. Signal reception is by searchers cooperating with the Clackamas County Sheriff, and they listen for signals only when a rescue search is activated. A search is activated when a registered climber is overdue, or when specifically requested.[8]
Oregon State Representative John Lim (R) introduced House Bill 2509, which would require climbers to use an electronic signaling device when climbing above 10,000 feet between November and March.[9] The Oregon House of Representatives passed an amended version[10] of the bill 33 to 22 on March 28, 2007 after a lengthy floor debate[11] and passed it onto the Oregon State Senate where it died in committee.[12] The bill was widely opposed by mountain rescue organizations for its unintended consequences which would increase climbing accidents.[13]