The FAA plans to decommission the remaining 29 direction finders (DF) in Alaska unless the aviation industry raises specific objections. DF, first used before World War II, performs one simple function: telling its operator which direction a transmitted radio signal is strongest. A skilled DF operator could pinpoint the location of a lost aircraft. DF steers, as they’re called, have saved thousands of lives over the past 80 years. But now, replaced by more accurate technologies such as GPS and ADS-B, DF is seldom used.